***Useful Information For The Working Sparky***

[Doomed]

Thank you, more good reference material.

By the way, your spell checker seems to of thought you meant the french resistance....

and I thought that testing a test meter on a known live circuit was frowned on now?

 

[amberleaf]

Sorry about my Spell Checker , it was Made in Scotland
Broken my Glass , wearing my Wife’s Glasses , PS I like the word Résistance from Halo Halo
British Version ↔ Resistance )
When you mention about the Test Meter you open a can of Worms !!!!! do you take a Proving Unit Every time you use you Test Meter on Mains ?
Ps you never Know HSE may come up with that yet ???? Thank you Amberleaf
Doomed keep up the good work Mate ,

Why Inspect & Test

Inspection & Testing of Electrical Installations

The Electricity at Work Regulations 1989 is a Statutory Document :
It is a Legal Requirement that Statutory Regulations are Complied with ,
Not to Comply is a Criminal Offence and Could Result in a Heavy Fine and Evan Imprisonment to Extreme Cases ,

These Regulations to Ensure that Places of Work Provide a Safe , Well-Maintained Electrical Systems ,
A Simple way to Provide this is to Ensure that Newly Installed Circuits & Existing Installations are Tested on a Regular Basis ,
Electrical Test Certificates are Used to Record what has been Done and Confirm that the Installation Meets the Required Standard ,

British Standard for Electrical Installations is BS-7671
The Requirement for Electrical Installations , within this Standard , Regulation 610.1 States that “ Every Installation “ shall ,
During Erection and on Completion before being put into Service be Inspected & Tested to Verify , so far as Reasonably Practicable ,
That the Requirements of the Regulations have been Met “

Regulation 610.1 States that “ where Required , Periodic Inspection & Testing of Every Electrical Installation shall be Carried out in
Accordance with Regulations ( 621.2 to 621.5 ) in Order to Determine as far as is Reasonably Practicable, whether the Installation
Is in a Satisfactory Condition for Continued Service “ ,

Document P of the Building Regulations 2000 for Electrical Safety came into Effect on 1 Jan : 2005 And was Amended in April 2006 ,

The Purpose of this Document is to Ensure Electrical Safety in Domestic Electrical Installations ,

General ,
This States that Electrical work must Comply with The Electricity at Work Regulations 1989 and that any Installation or
Alteration to the Main Supply must be Agreed with the Electricity Distributor ,

Protection Against Flooding
The Distributor must Install the Supply the Supply Cut-Out in a Safe Place and Take into Account the Risk of Flooding ,
Compliance with The Electricity Safety , Quality and Continuity Regulations 2002 is Required , its Law

For the Apprentice
This is all got to do with Testing ( this is a Start , all you need to know, ive broke it down )

“ Useful Piece of Equipment “

( R1 = R2 ) Socket Adapter
Socket -Tester ( Measure the Effectiveness of the Earth ) the Earth Fault Loop Impedance ,
This will Not Only be Useful for the Safe Isolation of Socket-Outlets ,
It can also be Used for Ring-Circuit Testing and the ( R1 = R2 )
Testing of Ring-Circuit / Radial-Circuit , Without having to Remove them from the Wall ,

Test-Socket-Adaptor ( R1 / Phase-Live ( R2 / Earth ( Rn Neutral

HSE “ GS-38 Leads “ should be :
Flexile and Long Enough , but Not to Long ,
Isolated to Suit the Voltage at which they are to be Used ,
Coloured where it is Necessary to Identify One Lead from the Other ,
Undamaged and Sheathed to Protect them Against Mechanical Damage ,

Measurement Equipment Used by Electricians when Working on or Investigating Power Circuits with a Rated Voltage Not Exceeding 650Volts ,
Heath & Safety ( GS-38 ) Approval Mains Voltage Indictor , ( Maintain Output Voltage for Extended Testing )
GS-38 Test Lamp Fused ( Range 80 / 500 Volts ( 230v / 15watt Pygmy Lamp )

“ The Probes should “
Have a Maximum of 4mm Exposed Tip ( Preferably 2mm )
Be HRC Fused at 500mA or have Current Limiting Resistors ,
Have Finger Guards ( to Stop Finger Slipping on Live Terminals )
Be Colour Identified ,

“ Locking Devices “ Padlock / and other Locking off Devices for MCBs ,

( Warning Notices )
( Live Circuit Warning )
( Danger Do Not Switch On )

Proving Units
Battery Powered Proving Unit , Essential for Safe Use of Voltage Indicators & Test Lamps ,
● Proving Unit Check : all Neon Lamps Located within the Testing Device illuminate for Duration of ( PROOF TEST )

Regulation 4(3) of the Electricity at Work Regulations 1989 Recommends that the Following Procedure be Adopted so that the Device Itself is ( Proved ) –

● Connect the Test Device to the Supply Which is to be Isolated ; this should Indicate Mains Voltage ,
● Isolated the Supply and Observe that the Test Device Now read ( 0V )
● Connect the Test Device to Another Source of Supply to “ Prove that the Device is Still Working Correctly ,
● Lock-Off the Supply and Place Warning Notices “ Only then should Work Commence on the Dead Supply ,

( EAWR ) Regulation 12
Means for Cutting off the Supply and for Isolation :
( EAWR ) Regulation 13
Precautions for Work on Equipment Made Dead :

You must make Absolutely Certain that you and you Alone are in Control of the Circuit to be Worked on
Proving the Circuit is Live you can Proceed as Follows ,

Step 1 , Ensure Voltage Indicator / Test Lamp is Working Correctly , ( Voltage Lights Lit )
Step 2 , Test Between “ All “ Live Conductors and Live Conductors and Earth ,
Using Test-Socket-Adaptor ( R1 / Phase-Live ( R2 / Earth ( Voltage Lights Lit )

Step 3 , Locate the Point of Isolate , Isolate and Lock Off , ( Warning Notices )

Step 4 , Test Circuit to Prove that it is the Correct Circuit that you have Isolated , ( No Voltage Lights Lit )
Using Test-Socket-Adaptor ( Test Between “ All “ Live Conductors and Live Conductors and Earth ) L/N/E ,

Step 5 , Check that the Voltage Indicator is Working by Testing it on a Proving Unit or Know Live Supply , ( Voltage Lights Lit )

Most GS-38 Test Lamps will Trip an RCD when Testing Between Live & Earth ,
Better to Use an Approved Voltage Indicator to GS-38 as most of these do Not Trip RCDs ,

 

[iceman]

thats very helpfull amberleaf but how does one remember all that for the 2391 holy grail exam? lol wot areas do you think i should mainly concentrate on regarding regs and gn3? i knw all the test equitment scales and voltages, certificates for periodic and miner works eic etc testing ring final ciruits insulation resistence polarity ze zs rcd pfc functional testing any help would be great cheers



Please posts your question in the main forums. Thanks.

 

[amberleaf]

Supplementary Protective Bonding Conductors ( Where Required )

Supplementary Bonding is Required where Circuit Disconnection Times Cannot be Met ( Regulation 411.3.2.6 ) or
Where there is an Increased Risk of Electric Shock ,
Those Areas would be in Bathrooms , Swimming Pools & Other Special Locations ,

Where Disconnection Times Cannot be Met and the Effectiveness of Supplementary Bonding is Required to be Checked
( Regulation 415.2.2 ) a Simple Test is Required ,

Automatic Disconnection is by a Protective Device , Regulations give a Formulae -
( R ≤ 50V / Ia ) if the Circuit is Protected by an RCD , the Formulae Becomes ( R ≤ 50V / I∆n )

When this Formulae is Used , it will Ensure that Any Touch Voltage in the Bonded Area will Not Rise above ( 50 Volts a.c. )
Before the Protective Device Operates ,

The Formulae where a Protective Device is in Place for Automatic Disconnection of Supply ( ADS )
Step 1 , find ( Ia ) for a 5 seconds Disconnection Time ,
Device 32Amp BS- 88 fuse

Appendix 3 / BS-7671 fig 3.3A
32A Device a Current of 125 Amp is Required to Operate the Fuse ,
This Value Can also be Found by Using the Maximum ( Zs ) Value Found Table 41.4 ( 1.84Ω )

Calculation : Ia = Uo ÷ Zs ( Ia = 230 ÷ 1.84 = Ia = 125A
This Method Can be Used for all Protective Devices :

Now the Values Can be Used to Verify that the Area does or does Not Require Supplementary bonding to be Installed ,
( R ≤ 50V ÷ Ia ( 50 ÷ 125A = 0.4Ω ) is the Maximum Value Permitted between Exposed or Extraneous Conductive Parts ,
If when Measured it is found that the Résistance is Higher than 0.4Ω then Supplementary bonding will be Required
The Values of Résistance will Not be the Same for Different Ratings or Type of Protective Devices ,

Where an RCD is Installed to Protect the Circuit the Calculation to find out if Supplementary bonding is Required ,
R = 50v ÷ I∆n ( R = 50v ÷ 0.03 R = 1666Ω , ( 50v ÷ 30mA = 1.666Ω

Bonding is Not well-Understood by Joe Public ,
You have Travelled 20/30 Miles to Fit Kitchen / Completed Everything to Comply with Required Regulations ,
A few days later, however, and before you have been paid for the Work ,
You Receive Phone Call from your Customer Informing you that his Next door Neighbour has Spotted that you
Have Not Bonded the Sink , of Course your Customer will Believe that his Neighbour is Right and you have Forgotten Something ,

The Choice is your / Do you Try and Convince your Customer that his Neighbour is Wrong ,
Do You Travel back to the Job to Carry Out the Bonding to Ensure Big Bucks ,

Just Put a Couple of Earth Clamp and a Short Length of 4mm2 Earthing Round the Pipes ,
( Cheaper just to Use the Supplementary Protective Bonding in the First Place )

For the Apprentice :

2.5mm2 / 1.5mm2 / Twin & Earth Cable 22meters long ,
OSG 9A ( Résistance of Copper ) 2.5mm2 / Copper : 7.41

The Résistance / Phase Conductor , ( R1 )
R1 - 7.41 x 22m ÷ 1000 = 0.163Ω *

Divide the Largest Conductor by the Smallest to find the Ratio of Conductors ,
( how much Bigger is the Largest Conductor , ( 2.5 ÷ 1.5 = 1.67

2.5mm2 Conductor is 1.67 x Larger than 1.5mm2 Conductor , therefore , it must have 1.67 x less Résistance than 1.5mm2 Conductor ,
0.163Ω * x 1.67 = 0.27Ω ( this is the Resistance of 1.5mm2 Conductor ,

OSG 9A ( Résistance of 1.5mm2 Copper : 12.10mΩ ( 22meters of 1.5mm2 Copper ,
22 x 12.10 ÷ 1000 = 0.266Ω

Final Check : OSG 9A
Résistance 2.5mm2 / 1.5mm2 Cable , we will See that it has a Résistance ( 19 51mΩ ) per meter
22 meters of it will have a Résistance of ( 22 x 19.51 ÷ 1000 = 0.429Ω

The Résistance Value of 2.5mm2 ( 0.163Ω ) and the Résistance Value of the 1.5mm2 is ( 0.266Ω )

Add them Together : ( 0.163Ω + 0.266Ω = 0.429Ω ( Finally , 0.429Ω is the Résistance of our 2.5mm2 / 1.5mm2 -
Measured as One Cable ,

This beats tons of paper work ,

“ Insulation Résistance “

This is a Test that can be Carried Out on a Complete Installation , or Single Circuit
For This Case ,
Domestic , ( Single Circuit or Ring ) New Installation ,
The Test is Necessary to find Out if there is Likely to be any Leakage of Current Through the Insulated Parts of the Installation ,
A Leakage could Occur for Various Reasons ,

Good Way to Think of this Test is to Relate it to a Pressure -Test
We Know that Voltage is the Pressure where the Current is Located in a Cable ,
On a Low Voltage Circuit , the Expected Voltage would be around 230v a.c the Voltage Used in an Installation Test on a 230V -
Circuit is 500v d.c , Which is More than Double the Normal Circuit Voltage , therefore , it can be Seen as a Pressure Test Similar
To a Plumber Pressure Testing the Central Heating Pipes ,

Circuits between 0V – 50v a.c
Required Test Voltage , ( 250v d.c. )
17th Edition : ( 0.5MΩ )

Circuits between 50V a.c – 500v a.c
Required Test Voltage , ( 500V d.c. )
17th Edition : ( 1MΩ )

Circuits between 500V & 1000V a.c.
Required Test Voltage , ( 1000V d.c. )
17th Edition : ( 1MΩ )

Domestic Installations ,
Remember that Testing should be Carried Out from the Day the Installation Commences ( Regulation 610.1 )

“ Insulation Résistance “
If for Some Reason , there is a Piece of Equipment Connected to the System that Cannot be Isolated from the Circuit Under Test ,
Do Not Carry Out the Test Between Line Conductors – Only Test Between live Conductor & Earth
This is to Avoid Poor Readings and Possible Damage to Equipment , this Test should Only be Carried Out on Individual Circuits ,
Not the Whole Installations , as it is Important to Test as Much of the Installation as Possible ,

Three Phase Sub-Mains is Tested the Results are :

L1 to Earth is 130MΩ
L2 to Earth is 80MΩ
L3 to Earth is 50MΩ
N to Earth is 100MΩ

If these Conductors were now Joined and Tested to Earth the Value would be as Given ,
Calculation ,
1 1 1 1 1
--- + --- + --- + --- + ---
R1 R2 R3 R4 Rt / N

( 1 1 1 1 1 )
--- + --- + --- + --- + --- = 19.92MΩ
130 80 50 100 0.05

Enter it this way into a Calculator : ( Remember the Button 1/X )

130X-1 + 80X-1 + 50X-1 + 100X-1 = X-1 = 19.92MΩ

This Value is Still Acceptable but Lower because the Conductors are in Parallel ,

Iceman , this is what you can face ,
Swindon Massive , send email to Kev , 20 pounds C/D It’s a Must

A Ring Circuit is Protected by a 30A BS-3036 Semi-Enclosed Rewirable Fuse
Measured ( Zs ) 0.96Ω

( Final Circuits Not Exceeding 32A )

This is a Ring Final Circuit , Disconnection time has to be 0.4sec ( table 41.2 BS-7671
Maximum ( Zs ) / 30A Rewirable Fuse – 1.04Ω

Eighty per Cent of this Value must Now be Calculated , this can be Achieved by Multiplying it by ( 0.80. )
1.04 x 0.80 = 0.83Ω

The Measured Value for the Circuit must now be Lower than the Corrected Value if it is to Comply : BS-7671
Measured Value 0.96Ω
Corrected Value 0.83Ω

The Measured Value of ( Zs ) is Higher , therefore , the Circuit will Not Comply ,

Option one is the Preferred Method because it will give an Accurate Value whereas the Test in -
Option two will Include Parallel Paths and because of this will Often give Lower Readings ,

Option one should Always be Used for an Initial Verification as the First Reading will be Used as a Benchmark -
To be Compared with Results taken in Future Periodic Tests ,

On a Periodic Inspection Using Option two , a Higher Test Results is Obtained than on the Initial Verification ,
This would Indicate that the Circuit is Deteriorating and that Further Investigation would be Required ,

The Methods Described here must be Fully Understood by Anyone who is Intending to sit the ---- & ------
---- Exam on Inspection & Testing of Electrical Installations ,

For the Apprentice
BS 7671 lists Five Types of Earthing System :

TN-S, TN-C-S, TT, TN-C, and IT.

T = Earth (from the French word Terre)
N = Neutral
S = Separate
C = Combined

I = Isolated ( The source of an IT system is either )

Connected to Earth through a Deliberately Introduced Earthing Impedance or is Isolated from Earth. All Exposed-Conductive-Parts of an Installation are Connected to an Earth Electrode. )

When Designing an Electrical Installation, One of the First things to Determine is the Type of Earthing system.
The Distributor will be Able to Provide this Information.

The System will Either be TN-S, TN-C-S (PME) or TT for a Low Voltage Supply given in Accordance with the
Electricity Safety, Quality and Continuity Regulations2002. Appendix 2 This is because TN-C Requires an Exemption
from the Electricity Safety, Quality and Continuity Regulations, and an IT system is Not Permitted for a
Low Voltage Public Supply in the UK because the Source is Not Directly Earthed. Therefore TN-C and IT
Systems are both Very Uncommon in the UK.

 

[amberleaf]

Regs : 4E4A :

3 - Core Swa ( 3 x 95 Csa = 285mm2 Clipped Direct 289 Amp ( 300mm2 )
3 - Core Swa ( 3 x 70 Csa = 210mm2 Clipped Direct 238 Amp ( 300mm2 )
4 - Core Swa ( 4 x 70 Csa = 280mm2 Clipped Direct 238 Amp

2391 / 2392-10 my advice is to look through most of the Notes ive Downloaded / 1 / 5 pages ,
This may help you to Jog your Memory , Ps – Put them all together and you have most of the Answers, like this ,
2391 will do a Lot off writing ,
BS 7671 Electrical forms

● Electrical Installation Certificate ( 3 Signatures )
Approved Contractor Issuing the Certificate has Not been Responsible for the Design – or the Inspection & Testing Off the Electrical Work ,
Certification of the three Persons must be Carried Out Separately Using ,
(1) Designer , (2) Constructor , (3) Inspector ,

● Electrical Installation Certificate ( 1 Signature ) 2392-10
( One Person is Responsible for the Design )

The Electrical Installation Certificates is to be used only for the Initial Certification of New
Installation or For an Addition or Alteration to an Existing Installation “
where NEW circuits have been Introduced “

The "Original" Certificate is to be given to the person ordering the work ( Regulation 632.1 ) A duplicate should be retained by the Contractor.

● Electrical Installation Certificate 2382-10 ( New Work Only

This Certificate is only Valid if accompanied by the Schedule of Inspections and the Schedule(s) of Test Results.

● EIC Schedule of Inspections ( Schedule of Circuit Details Continuation Sheet )
● EIC Schedule of Test Results ( Continuation Sheet )

● Minor Electrical Installation works Certificate

Twenty Short Questions , 2391 old Questions
Your working to this Principle , somewhere along the Line ,

(1) three Single Sockets have been added to a Ring Final Circuit : State
(a) Inspection & Testing Certificate that will need to be Completed ,
(b) Title in Law Given to the Inspection
(c) Legal Status of the Inspection
(2) an Engineering Works 18 years Old and is Due for Inspection and Test : State the
(a) Type of Inspection and Test Required ,
(b) Documents that must Accompany the Completed Certificate ,
(c) Circumstances under which the Type of Inspection and Test in (a) above may Not be Required ,
(3) State the Legal Status of the following
(a) BS-7671 : 2008
(b) Guidance Note 3
(c) HSE , GS-38
(4) Give One Example of Each of the Following
(a) an Exposed Conductive Part
(b) an Extraneous Conductive Part
(c) Direct Contact
(5) State Three Methods of Protection Against Indirect Contact
(6) State the Earthing Systems that Use the Following as Return Path
(a) Pen Conductor
(b) Cable Sheath
(c) General Mass of Earth

612.9
Methods of Calculation of Earth Fault Loop Impedance from Given Data and Measurement of Conductor Résistance

The External Earth Fault Loop Impedance ( Ze ) can be Calculated Using the Supply Voltage & the Prospective Earth Fault
Current Value Measured at the Supply ,
( Ze ) = Supply Voltage ( Prospective Earth Fault Current )
Final Circuit Earth Loop Impedance ( Ze ) can be Calculated by Adding the External Earth Fault Loop Impedance ( Ze )
( to the R1 + R2 Value of the Circuit ,

General Rule of Thumb is to Multiply Tabulated Values by 0.8 before Comparing the Test Values Obtained During Test ,
Requirements of Regulation 411.4.5 or 411.5.4 ,

411.4.5 ( Zs x Ia ≤ Uo ) 230 ÷ 0.57Ω = 403A Earth Fault Conditions
( Zs ) Should Not Exceed 0.8 Times , Appendix 14
( Zs = Uo ÷ Ia , 230 ÷ 403 = 0.5 Ω

Earth Fault Loop Impedance Exceeds 0.8 / Uo / Ia ,
A More Precise Assessment of Compliance with Regulation 411.4.5 or 411.5.4 as Appropriate , may be Made (i) (ii) (iii) (iv) (v)
Note : Other Methods are Not Precluded ,

p-249 fig 3.4 Type B, MCB to BS-EN 60898 / RCBOs BS-EN 61009-1 , Overcurrent , 32Amp / 160A ( Zs ) 41.3
Ief / Zs ≤ Uo ÷ Ia ( Zs ≤ 230 ÷ 160A = ( Zs ≤ 1.437Ω
Max Loop Impedance , 32A – I 160A required ( 41.3 ( 32 / Zs 1.44Ω

RCBO , BS-EN 61009-1 Appendix 3 p-243
Zs = Uo ÷ Ia ( 230 ÷ 160 = 7.18
411.3.2 Specifies Max Disconnection Times for Circuits ,
Conditions for Automatic Disconnections Cannot be Fulfilled by Overcurrent Device ,

“ Fault Protection ”
Fault Protection can be Met by Meeting the Disconnection times Regs , 411.3.2
This is Achieved by Limiting Earth Fault Loop Impedance ( 41.2 41.3 41.4 )
411.3 Requirements for Fault Protection :
(1) 411.3.1.1
(2) 411.3.1.2
(3) 411.3.2
BS-88-22 80A ÷ 740A = 0.1sec ( PSSC ) Fig , 3.3a 80A 740A / 0.4sec ;
BS-88-22 - BS-88-6 : 41.4 - 40A / Zs / 1.35Ω ( Uo ÷ Zs = 170A / 230 ÷ 1.35 Ω = 170A ) 170A – 5sec Fig , 3.3b
40 ÷ 170A = 0.2 sec ( PSSC )

PS off to the Mother Land , 5 Days ,
Jason you have 5 Days Holiday , hit the 24-Pack ? , Amberleaf

 

[amberleaf]

Old Notes some Revision : 2391 “ Iceman “
9A / OSG ( R1+R2 )
10mm2 / 4mm2 ( 6.44mΩ/M
( R1+R2 ) : 6.44 x 14.75 = 0.095Ω
( Zs ) Circuit - 0.095Ω + 0.7 = 0.795 ( 0.8 ) Ω
Max : ( Zs ) 45A BS-3036 : 3.2B ( 41.4 ) 5sec – 1.59Ω
C/f ( t ) 1.59 x 0.8 = 1.27Ω
As the Actual ( Zs ) is Lower
9A / OSG : 4mm2 Cooper Conductors ,
Résistance / 4.61mΩ / M
( R1+R2 ) Phase & CPC / 4mm2 – 9.22mΩ / M
( R1+R2 ) : 9.22 x 67 ÷ 1000 = 0.061Ω ( 0.61Ω ),
As it is a Ring ( 0.61 ÷ 4 = 0.15Ω ,
( R1+R2 ) Value 0.15Ω ,
( Zs = Ze+ R1+R2 ) 0.63 + 0.15 = 0.78Ω
As Max : permissible ( Zs ) is given 0.9 from OSG , “ No ( t ) ( Ci )
Sub / ( Ze ) from the actual ( Zs ) to find Max : permissible ( R1+R2 ) Value ,
( R1+R2 ) = 0.9 – 0.63 = 0.27Ω
Now Sub : actual ( R1+R2 ) Value from Max : permissible Value , ( 0.27 -0.15 = 0.12Ω )
Max : Résistance that our Spur could have ( 0.12Ω )
Length / transpose / Calculation :
( mV x Length ÷ 1000 = R )
Find Length transpose to : ( R x 1000 ÷ mV / Length )
Therefore : ( Length = 0.12 x 1000 ÷ 9.22 = 13meters ) :

2.5mm2 / 1.5mm2 ( Résistance 19.51m/Ω per meter .
( 5.8 meters of the Cable have ( Résistance 5.8 x 19.51 ÷ 1000 = 0.113
0.113 is ( Résistance of the Additional Cable , ( R1+R2 ) for this Circuit will now be ( 0.2 + 0.1133 = 0.313Ω )

9A / OSG ( 10mm2 Copper / Résistance 1.83mΩ x 22 ÷ 1000 = 0.4Ω ) *
By Calculation ↔ ( Zs = Ze+ R1+R2 ) or Use a Low Current Test Instrument , *

1/50 + 1/80 + 1/60 + 1/50 = 0.069 ( R = 1 / 0.069 = 14.45Ω ) *

Determining Touch Voltage : ( Ze ) x Rated mA - I∆n / RCD
TT / ( Ze ) = 200Ω ( Main RCD is Rated at 100mA
200Ω x 100mA ÷ 1000 = ( 20V )

For Circuit(s) having Conductors of up to 25mm2 Operating at Normal Frequency ( 50Hz ) Inductance may be Ignored
And it is Acceptable to Determine ( Zs ) Using the Formula
Rather than by Measurement Using an Earth Fault Loop Impedance Test Instrument , Zs = Ze+ R1+R2

Popular Question is “ When can ( Zs ) “ be Less than ( Ze ) given that ( Zs = Ze+ R1+R2 ) ( 239- ) ←

Testing and Measuring it ( Ze ) at Origin and ( Zs ) at the Furthest Point ( 239- ) ←
( Zs ) Test : Check the Continuity of the Earth

Earth Loop Impendence Test ,

( Ze ) is Part of the Earth Fault Loop Impendence External to the Installation ( the Impendence of the Supply )
( R1 ) is the Résistance of the Consumers Phase Conductor from the Origin of the Circuit to the Most Distant Part of the Circuit ,
( R2 ) is the Résistance of the Consumers Protective Conductor from the Origin of the Circuit to the Most Distant Part of the Circuit ,

( Zs = Ze+ R1+R2 )
( R1 ) is the Résistance of the Live Conductor :
( R2 ) is the Résistance of CPC

( Zs = Ze ) will give you ( R1+R2 ) approx ,

Therefore to find ( R2 ) in Isolation you need to know the Value of ( R1 ) and Subtract this from the Above or just Measure it Directly with a Meter ,
> ( Ze ) is the External Impedance Measured at the
> Incoming Point of the Supply at the Premises , it is
> the Résistance of the Phase Cable and the Return to
> the Transformer ,
( Zs = Ze+ R1+R2 ) is Measurable Via Method ( 2 ) Long Lead : ( Zs = Ze+ R1+R2 ) : ( R2 ) is a Measure of Résistance of CPC only Via Long-Lead ( Method ( 2 ) ( Ra ) is the Résistance of the Earthing Conductor :

( Ze ) on a TT Systems as this would be the Compete Earth Loop Path which would include ( Ra ) plus the Résistance
Of the Suppliers Electrode ,
The Impedance of the Transformer Winding and the Impedance of the Suppliers Phase Conductor

V = I x R so ( Ix R ) should be Less than 50V Touch Voltage :
Maximum ( I ) will be the Tripcurrent of the RCD Used being that it is a TT System
The ( R ) should be the Résistance from Earth to the Appliance etc . Including the Earth Rod ,
But as ( Zs ) would Include the Full Circuit , it will Obviously be Higher than half the Circuit Therefore if the Calculation Still
Remains Lower than 50V it will Obviously Remain below 50V if the Résistance Value is Used and Recorded
So yes ( Zs ) is not Strictly Relevant but it can be Used which is Good as it is an Easy Reading to Obtain ,
e.g. 100mA x 20Ω = 2Volts ( 100 x 20 ÷ 1000 = 2V = Touch Voltage )

TT System use the Touch Voltage System ( Described as the Alternative Method ) so the Résistance of the Live Conductor is Irrelevant ,

( Ze ) on a TT Systems as this would be the Compete Earth Loop Path which would include ( Ra ) plus the Résistance
Of the Suppliers Electrode ,
The Impedance of the Transformer Winding and the Impedance of the Suppliers Phase Conductor

V = I x R so ( Ix R ) should be Less than 50V Touch Voltage :
Maximum ( I ) will be the Tripcurrent of the RCD Used being that it is a TT System
The ( R ) should be the Résistance from Earth to the Appliance etc . Including the Earth Rod ,
But as ( Zs ) would Include the Full Circuit , it will Obviously be Higher than half the Circuit Therefore if the Calculation Still
Remains Lower than 50V it will Obviously Remain below 50V if the Résistance Value is Used and Recorded
So yes ( Zs ) is not Strictly Relevant but it can be Used which is Good as it is an Easy Reading to Obtain ,
e.g. 100mA x 20Ω = 2Volts ( 100 x 20 ÷ 1000 = 2V = Touch Voltage )

TT System use the Touch Voltage System ( Described as the Alternative Method ) so the Résistance of the Live Conductor is Irrelevant ,

( R1+R2 ) is the Résistance of the Circuit Phase Conductor & the Résistance or the Circuit Protective Conductor ,
One of the Dead Test i.e. Pre-Energization
Connect the Circuit Phase Conductor to Earth Rail , Either by Removing it from the MCB or by Using a Short-Linking Wire ,

At the Furthest Most Point of the Circuit Measure the Résistance between Phase & Earth ( CPC )
Using a Low Resistance Ohms Meter , this is your ( R1+R2 ) Value
The ( R1+R2 ) for Ring Final Circuit is Done Slightly Differently ,

( Ze ) is the External Earth Fault Loop Impedance to the Installation ( it is Measured in Isolation ) i.e. You need to Isolate the Supply ,
Disconnect the Earthing Conductor from the ( MET ) and Measure the Impedance between Phase and the Earthing Conductor using -
An Earth Fault Loop Impedance Tester ,
Once you have Completed the Test , Remember to Reconnect the Earthing Conductor before you Re-Energize !!1
( Zs ) is the Total Loop Impedance of the Circuit , it can be Done by Measurement at the Furthest Most Point of the Circuit or by -
( Zs = Ze+ R1+R2 )

( PFC ) is Basically the Maximum Current which can Flow in the System,
It needs to be Conducted at the Origin , for this you need to Conduct a ( PSSC ) Prospective Short Circuit Current Test :
Which is between Each Phase & Neutral / or Phase – Phase if 3 Phase )
( PEFC ) is between Each Phase & Earth -
The Highest Value is the Prospective Fault Current ( PFC ) ( Ze ) is the ( Z ) at the External Part of the Installation , that is Immediately after the Meters as Far as Practicable
( Ze ) Power Off , at your Mains ( or Only ) Isolator with all Bonds Disconnected ( also Check the Prospective current here ,
With Bonds Connected then Check Prospective Current Again ( it is Usually Higher Due to ( Parallel Paths ) -
This Highest Reading is the ( PFC )
Check ( R1+R2 ) on each Circuit Add to ( Ze ) then this gives the Calculated ( Zs )
When Energised ( With Bonds Reconnected of Course ) then Recheck that ( Zs = Ze+ R1+R2 ) or Less than Due to ( Parallel Paths ) -
This Confirms ( Zs ) Actually Does Exist ,

Also PH-PH in 3-Phase for a ( PFC ) or Double the Single Phase Readings ,

( Zs = Zdb+ R1+R2 )
Where the Distribution Board is at the Origin of the Installation , ( 239- )

2391 / this is a Written Exam , Use some off the Wording ,

 

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239x “ Wording “ Iceman

The Insulation Resistance should be above 2MΩ
If it is Less than Further Investigation must be Carried Out as ( a Latent Defect may Exist ) *

In any Exam it is Vital that the Question is Read Carefully , Often it is better to Read a Question Several Times
To try and Understand what is being Asked

If the Question asks for a Fully Labelled Diagram , then Marks are Awarded for the Diagram and the Labelling ,
Where the Question Asks “ Explain with the Aid of a Diagram “ then a Diagram and a Written Explanation is Required ,

When the Question ask for a List then you will be Expected to List a Sequence of Events in the Correct Order , -
( Just a List with No Explanation ) if you are Required to State Something then a Statement is Required in No Particular Order ,

List the Sequence of Dead Tests :
(a) Continuity of Protective Conductors’ ( Including Main & Supplementary Equipotential Bonding : Test
(b) Continuity of Ring Final Circuit Conductors : Test
(c) Insulation Résistance : Test ( Remember the Wording , Use in the Right Contents )

State Three Statutory Documents Relating the Inspecting & Testing ( of Electrical Installations )
(a) The Electricity at Work Regulations 1989 ( No more No Less )
(b) The Health & Safety at Work Act 1974
(c)

Always try to Answer the Questions in “ FULL “ using the Correct Terminology :
For Example : if Asked “ Which is the Type of Inspection to be Carried Out on a New Installation”
The Answer must be : An Initial Verification ,
For the Document Required for Moving a Switch or Adding a Socket the Answer must be :
An Electrical Installation Minor Works Certificate , ( Not Just Minor Works )

The Initial Verification of an Installation or Circuit is Very Important and it must be Carried Out Correctly :
The Documentation for this Serves two Purposes ,
Firstly , it is a Certificate which should be Provided to Show that the Installation has been Installed Correctly and that it is Safe to Use
This Certification should Not be Issued Until the Installation has been Tested & the Results have been Verified as being Satisfactory ,

It would be a Pointless Exercise to just Inspect & Test an Electrical Installation when it is Completed – it is Vital that the
Installation is Inspected Regularly During the Installation and Before any Cables are Finally Covered Up ,

Remember ↔ that , When you Sign the Electrical Installation Certificate ,
You are Taking Responsibility for Every Part of the Installation that you Sign for
This should Not be Taken Lightly because , if an Accident Occurs Due too an Unsafe Installation ;
The Person who has Carried Out the Inspection & Test May Well be Held Responsible ,
( Remember Your Arse is on the Firing Line )

In Many Ways , Initial Verification Should be Easier than Carrying Out a Periodic Inspection on an Existing Installation
As the Person Carrying Out the Test should know their Way around it ,
Because they would have seen it as it was being Installed ,

PS : Use the Correct Terminology ←←←←
Insulation Résistance Test Instrument : ( NOT Megger )

Low Reading Ohms Meter ( Not Continuity Tester or millli Ohms Meter )

Electrical Installation Certificate / or ( EIC ) NOT Electrical Installation Report
Schedule of Test Results – ( NOT Schedule of Test or Schedule of Results )

Testing ( 3-Phase Induction Motor )

There are Many Types of 3-Phase Motors but far the Most Common is the Induction Motor ,
It is Quite Useful to be Able to Test them for Serviceability

Before Carrying Out Electrical Tests it is Good Idea to Ensure that the Rotor Turns Freely
This may Involve Disconnecting any Mechanical Loads . The Rotor should Rotate Easily and you should Not be Able to hear any Rumbling from the Motor Bearings , if the Motor has a Fan on the Outside of it , Check that it is Clear of any Debris which may
Have been Sucked in to it , Also Check that any Air Vents into the Motor are Not Blocked ,

Generally : if the Motor Windings are Burnt Out there will be an Unmistakable Smell of Burnt Varnish
It is still a Good Idea to Test the Windings as the Smell could be from the Motor being Overloaded
Three Phase Motors are Made up of Three Separate Windings / in the Terminal box there will be ( Six Terminals ) as Each Motor Winding will have Two Ends , The Ends of the Motor Windings will Usually be Indentified as -
( W1 , W2 ; U1 , U2 ; or V1 , V2 ) The First Part of the Test is Carried Out Using a Low-Résistance Ohms Meter ,
Test Each Windings End – End ( W1 to W2 , U1 to U2 , and V1 to V2 ) The Résistance of Each Winding should be Approximately
The Same and the Résistance Value Will Depend on the Size of the Motor ,
If the Résistance Values are Different then the Motor will Not be Electrically Balanced and it should be Sent for Rewinding , if
Résistance Values are the Same , then the Next Test is Carried Out Using an ( Insulation Résistance Tester ) MΩ
Join W1 and W2 Together , U1 and U2 Together , and V1 and V2 Together ,
Carry Out an Insulation Résistance Test between the Joined Ends , i.e. W to U then W to V and then between U and V , -
Repeat the Test between Joined Ends and the Case , or the Earthing Terminal of the Motor ↔
( these Tests can be in any Order to Suit you )
Providing the Insulation Résistance is ( 2MΩ ) or Greater then the Motor is Fine , if the Insulation Résistance is above ( 0.5MΩ )
This Could be Due to Dampness and it is Often a Good Idea to run the Motor for a While before Carrying Out the Insulation Test -
Again as the Motor may Dry Out with Use :

To Reconnect the Motor Windings in Star : Join W2 , U2 and V2 Together and Connect the 3-Phase Motor Supply to -
W1 , U1 and V1 , if the Motor Rotates in the Wrong Direction , Swap Two of the Phase of the Motor Supply

To Reconnect the Motor Windings in Delta , Join W1 to U2 , U1 to V2 and V1 to W2 and then Connect the 3-Phase Motor -
Supply One to Each of the Joined Ends ,
If the Motor Rotates in the Wrong Direction , Swap Two-Phases of the Motor Supply ,

Test Instruments’

Guidance Note GS-38
GS-38 is for Electrical Test Equipment Used by Electricians and Gives Guidance to Electrically Competent Persons Involved in
Electrical Testing , Diagnosis and Repair , Electrically Competent Persons :
Electricians , Electrical Contractors , Technicians , Mangers or Appliance Repairers

Voltage Indicating Devices
Instruments Used Solely for Detecting a Voltage Fall into Two Categories :
Detectors that Rely on an Illuminated Lamp :

Lamps are Fitted with a 15Watt Lamp , and Should Not give Rise to Danger if the Lamp is Broken , a Guard should also Protect it ,

Detectors that Use Two or more Independent Indicating Systems / One of Which May be Audible /
And Limit Energy input to the Detector by the Circuitry Used , Two-Pole Voltage Detector
i.e. a Detector Unit with an Integral Probe , an Interconnecting Lead and a Second Probe

These Detectors are Designed and Constructed to Limit the Current and Energy that can Flow into the Detector
This Limitation is Usually Provided by Combination of the Circuit Design Using the Concept of Protective Impedance , and
Current- Limiting Resistors built into the Probe , the Detectors are also Provided with in Features to Check the Functioning
Of the Detector before and After Use , The Interconnecting Lead and Second Probes are Not Detachable Components ,
These Type of Detectors’ do Not Require Additional-Limiting Resistors or Fuses to be Fitted Provided that are Made
To an Acceptable Standard and the Contact Electrodes are Shrouded

Voltage Indicating Devices :

Guidance Note GS-38
Lamps and Voltage Indicators are Recommended to be Clearly Marked with the Maximum Voltage which may be Tested by the
Device and any Short Time Rating for the Device if Applicable ,
This Rating is Recommended Maximum Current that should Pass-Through the Device for a Few Seconds
As these Devices are Generally Not Designed to be Connected for more than a Few Seconds ,

 

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239- Calculation of the Maximum ( Zs ) of the Circuit Breakers’
It is Often Useful to be able to Calculate the Maximum ( Zs ) Value for Circuit Breakers without the Use of Tables ,
BS-EN 60898 Devices : ( 20A / BS-EN 60898 Device )
Type B / MCB Must Operate within 3 to 5 Times its Rating ,
( Worst Case Scenario Therefore ) we must Assume that the Device will Not Operate until a Current Equal to ( 5 ) times -
Its Rating Flows Through it ( Ia ) for a 20A Type B / MCB this will be ( 5 x 20A = 100A )

If we Use a Supply Voltage of 230volts – which is the Assumed Open Circuit Voltage ( Uo ) of the Supply -
Ohm’s Law can be Used to Calculate the Maximum ( Zs )
( Zs ) = Uo ÷ 100 = ( Zs ) = 230 ÷ 100 = 2.3Ω

To Check this look : BS-7671 / 41.3 ( the Value ( Zs ) 20A Type B / MCB = 2.3Ω

( 20A / BS-EN 60898 Device ) Type C / MCB Must Operate at a Maximum of 10 times its Rating ( In )
( 10 x 20 = 200A ( 230 ÷ 200 = 1.15Ω )
To Check this look : BS-7671 / 41.3 ( the Value ( Zs ) 20A Type C / MCB = 1.15Ω
Type D / MCB with a Nominal Operating Current ( In ) Must Operate at a Maximum of 20 times its Rating : -
( 20 x 20 = 400A ( 230 ÷ 400 = 0.57Ω )
To Check this look : BS-7671 / 41.3 ( the Value ( Zs ) 20A Type D / MCB = 0.57Ω
The Maximum ( Zs ) Values for a Type C are 50% of the ( Zs ) Value :
The Maximum ( Zs ) Values for a Type D are 50% of the ( Zs ) Value : of a Type C MCB ,

Maximum Earth Loop Impedance ( Zs ) for Fuses :
Fuses have to Operate at 0.4 or 5 sec Depending on the Type of Circuit which they are Protecting ,
To find the Maximum Permissible ( Zs ) Value for a Fuse , the Current Curves in Appendix 3 / Fig : 3.1

Find the Maximum Permissible ( Zs ) for a BS-1361 Fuse with a Rating of 20Amp with a Required Disconnection Time of 0.4 sec
( Look in Appendix 3 / Fig : 3.1 , the Left-Hand side of the Grid Represents the Disconnection Time )

From the Bottom Left-Hand Corner , follow the Line Upwards Until the Horizontal Line Representing 0.4 sec is Found
Follow the Horizontal Line across to the Right Until the Bold Line for a 20Amp Fuse is Found ,
From where the Horizontal Line Touches the Bold Line move Vertically Down the Page Until you meet the Bottom Line of the Grid ,
The Bottom Line Represents the Automatic Operating Current for the Fuse , it can be Seen that the Current Required is Around 130Amps
( The Table in the Right-Hand top Corner of the Page will Show this Value to be 135Amps )

( Zs ) = Uo ÷ Ia / ( Zs ) = 230 ÷ 135 = 1.7Ω
To Check this look : BS-7671 / 41.2 / ( Zs ) BS-1361 / 20A = 1.7Ω

( Do not Forget to Correct this Value for the Conductor Operating Temperature & Ambient Temperature : if Required ,

This Calculation can be Used for any Type of Protective Device :
Remember that the Disconnection Time for a Circuit Breaker will always need to be 0.1 sec

Comparing Maximum ( Zs ) & Measured ( Zs )
Unfortunately we Cannot Compare this Value Directly to any Measured ( Zs ) Values that we have :
This is because the Values given in BS-7671 for ( Zs ) are for when the Circuit Conductors’ are at their Operating Temperature -
( Generally 70ºC )

Assume that we have a Circuit Protected by 32A BS-EN 60898 Type B :
Measured ( Zs ) is 0.98Ω
5 x 32 = 160A ( 230 ÷ 160 = 1.44Ω )

The Measured ( Zs ) at 70ºC for the Circuit is 1.44Ω )
To find ¾ of 1.5 we can Multiply it by 0.8 ( 1.5 x 0.8 = 1.2Ω )

1.2Ω now becomes our Maximum Value : and we Compare our Measured Value Directly to it without having to Consider the Ambient Temperature or the Conductor Value :
In this Case it is , and the 32Amp Type B Device would be Safe to Use ,

 

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RCBO : Double Pole ,
“ Earth Leakage “
“ Overload Protection “
“ Short Circuit Protection “
“ Over Voltage & Surge Voltage Protection “
“ Switch Line & Neutral for Increased Safety “
“ Will Replace Existing Earth Leakage Devices “

239-

Why do we Need to Confirm Correct Polarity ?

Incorrect Polarity can Give rise to Danger in a Number of Ways :

(i) Parts of the Installation May Remain Connected to the Line Conductor when Switched off by a Single-Pole Device but , for all Intents and Purposes , will Appear to be Dead :
(ii) in the Event of an Overload , the Circuit-Breaker or Fuse Protecting that Part of the Installation would Disconnect the Neutral of the Circuit , Leaving the Load at Full Line Voltage ,
(iii) An Earth Fault Current Might Remain Undetected by Overcurrent Protective Devices

Re-Cap :

Electrical Installation Certificate -
Intended for New Installation Work ; including Alterations and Additions to Existing Installations ,
Domestic Electrical Installation Certificate -
Intended for New Installation Work ; including Alterations and Additions Existing Installations , in a Single Dwelling ( House or Individual Flat )
Minor Electrical Installation Works Certificate -
Intended for Minor Installation Work that Does Not Include the Provision of a New Circuit ,
Periodic Inspection Report : for an Electrical Installation -
Intended for Reporting on the Condition of an Existing Installation ,

Nature of Supply Parameters :

Provision is Made to Record the Supply Parameters which Comprise ,
Normal Voltage(s) U ( Line to Line ) : Uo ( Line to Earth ) ( in Volts )
This Parameter can Generally be Determined Only by Enquiry ,
For Public Supplies in the UK , U / 400V and Uo 230V – Two Phase / Three-Phase Supplies ,
And U – Uo are 230V – Single-Phase Supplies

Nominal Frequency , ( f ) / Hz
This Parameter can Generally be Determined Only by Enquire , ( in UK Nominal Frequency ; Invariably ( 50 Hz )

For the Apprentice What is GS-38 "IEE Guidance Note 3: Inspection and Testing ,
Guidance Note GS38, published by the Health and Safety Executive ( HSE ), sets out in clear and concise terms the features that any instruments and meters should have if they are to be used to carry out electrical tests in accordance with BS 7671. In order to comply with the Electricity at Work Regulations 1989 it is critical that any competent person carries out electrical testing safely, and this guidance note draws attention to the risks of using test instruments that do not meet the GS38 standard. In brief, some of the requirements for test instruments include:
• The test probes should have finger guards, ideally 2mm or 4mm of exposed conductive tip (to prevent the user accidentally making contact with either the probes or live conductors under test) and should be fitted with a High Breaking Capacity inline fuse or fuse-and-resistor combination with a low current rating (to prevent the probes rupturing under high short-circuit currents and/or damaging the test instrument if incorrect range settings are used, typically drawing more than 500mA ).

• The test leads should be adequately insulated to suit the environment in which they’re being used, are coloured differently from each other so as to be distinguishable, are flexible, are capable of handling the maximum current range of the test instrument and are shrouded or sheathed to protect against mechanical damage, securely connect the leads to the test instrument and safeguard against the possibility of direct contact with live parts.
GS38 also Identifies Three Categories of Test Instruments, namely those that:
• Test for the presence of a voltage ( voltage detection )
• Measure Voltages
• Measure current and resistance ( as well as, in some cases, Inductance and Capacitance )

• Look at the test instrument, probes, leads and connectors for any obvious signs of physical damage. Have you stored the test instrument properly? Did you lend it out to someone that didn’t look after it ? Are there knots, kinks or cuts in the leads ? Is the case cracked ? Are the connections loose ?
• Look at the ratings on the test instruments, probes, leads and connectors to make sure they’re suitable for the job you’re asking them to do. Do you know what range you need to be using ?
• Does the test instrument have a calibration date on it? If you don’t know when the instrument was last calibrated, how can you be sure you’re getting the right readings ?
Before carrying out any actual tests, make sure you know all the procedures involved in carrying out safe isolation on the circuit(s) you intend to work on.
To sum up, GS38 has been designed both to keep both you and others safe and to try and define a clear standard that manufacturers can work towards to make sure electrical testing is carried out sensibly and safely. Although high-quality test instruments can be costly one-off purchases, keep in mind the cost of your own safety ! As with any tools, good quality instruments and meters pay for themselves many times over and being skilled in their use is a true measure of a Qualified and Competent Electrician .

For the Apprentice : some Revision ,
A 6A BS-EN-61009-1 RCBO with a Maximum Value of Earth Fault Loop Impedance of ( 1.92Ω is Type D )
( Part 4 : Protection for Safety , Regulation 411.4.7 ( 41.3 )

The Maximum Disconnection Time for a Circuit Supplied by a Reduce Low Voltage System Using a 110V Midpoint Earthed
Transformer is ( 5sec ) Part 4 : Protection for Safety , Regulation 411.8.3

Where Basic Protection and / or Fault Protection is Provided , Certain External Influences may Required Additional Protection
Provided by ( Use of 30mA RCDs ) Part 4 : Protection for Safety , Regulation 415.1.1

The Horizontal Top Surface of a Barrier or Enclose which is Readily Accessible shall Provide a Degree of Protection of at Least
( IPXXD or IP4X ) Top of CU : Part 4 : Protection for Safety , Regulation 416.2.2

The Symbol Used to Show that a BS-88 Device has a Motor Circuit Application is ( gM ) Symbols Used in the Regulations p-35 - 411.4.6

The Effectiveness of Protective Measures should be Considered with Regard to ( Maintainability ) -
Party 3 : Assessment of General Characteristics , Regulation 341.1

The Measure of Automatic Disconnection of Supply is Employed for a Circuit Supplying 13A Socket-Outlet Intended
For General Use by Ordinary Persons , which of the Following does “ NOT “ Contribute to the Provision of Fault Protection ,
( Reinforced Insulation ) Part 4 : Protection for Safety , Regulation 411.1 (ii)
(a) Protective Earthing (b) Main Protective Bonding Conductor (c) Additional Protection by RCD ( d) Reinforced Insulation ) ←←

Basic Protection may be Provided by : Basic and Enclosures to IPXXB or IP2X (Part 4 : Protection for Safety , Regulation 416.2.1 ,

Which of the Following need “ Not “ be Tested Under Fire Conditions to Ensure Compliance with Non-Flame Propagating Requirements :
( a) Cables : ( b) Protective Devices ←←← : (c) Conduit Systems : (d) Trunking Systems : Part 4 : Protection for Safety , Regulation 422.2.1

In the Event of an Earth Fault on the HV side of a Substation the LV Installation may be Affected by :
( Uf ) Part 4 : Protection for Safety , Regulation 442.2

A Cable Concealed in a Wall Outside the Prescribed Zone at a Depth of Less than 50mm Must :
( be Enclosed in Earthed Metallic Conduit ) Part 5 : Section & Erection of Equipment , Regulation 522.6.6

239- this may come up in the Future ,

“ Client Demand for a Continuous Supply “

Where the Client Does Not want Any Interruption in the Supply and it is Not Possible to Work on Effected Area during Normal Working Hours ;
Arrangements should be Made for a Planned Maintenance or Shut Down in Order for the Repair to be Carried Out Safely

 

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2392 - Measurement of Prospective Fault Current Using a Two-Lead Instrument : ( Set , Loop – 20kA )

Take Particular Care During the Test Process ;as Fault Conditions are Most Severe at the Origin of an Installation ,
Where this Test is being Preformed ,

The Prospective Short-Circuit and Prospective Earth Fault Current are to be Measured ( or Determined by an Alternative Method )
At the Origin and at Other Relevant Points in the Installation ,
Note that a Measurement made at a Point in the Installation such as an Item of Switchgear fed by a Distribution Circuit would not be the Maximum for the Installation
The Earthing Conductor , Main Equipotential Bonding Conductors and Circuit Protective Conductors should all be Connected
During these Tests , because the Presence of these and any Other Parallel-Paths to Earth May Reduce the Impedance of the Fault Loop and so Increase the Prospective Fault Current , ( PFC )

The Instrument to be Used is an Earth Fault Loop Impedance Test Instrument , with or Without a Prospective Fault Current Range ,
A Set of Test Leads is Required , having Two or Three Probes to Suit the Requirements of the Particular Test Instrument ,

A Two-Lead Test Instrument Connected Across the ( Line and Neutral ) of an Incoming Supply ,Not that for Measuring a Line to Earth Value ,
The Instrument Must be Connected Across the Line and Main Earthing Terminal

Measurement of Prospective Fault Current Using a Three-Lead Instrument : ( Set , Loop – 20kA )
Three-Lead Instrument Connected Across the Line, Neutral and Earth of an Incoming Supply ,
Procedure :
Check that the Test Instrument , Leads , Probes and Crocodile Clips ; are Suitable for the Purpose ,
Select the Appropriate Range and Scale ( Prospective Fault Current 20 kA )
Observing all Precautions for Safety , Connect the Instrument to the Incoming Energised Supply to Measure a ( Line to Neutral Value )
Check the Polarity Indictor “ if Any “ on the Instrument for Correct Connection ,
Press the Button :
Record the Reading :
Repeat the above Steps ; as Appropriate , with the Instrument Connected for Measurement of the ( Line to Earth Value )

If the Test Instrument does Not have a ( Prospective Fault Current Range ) the Readings given by the above Procedure are
( Fault Loop Impedance in Ohms )
To Convert each of these Readings into a Prospective Fault Current ,
( Divide them into the Measured Value of Line to Neutral Voltage )
Measured Voltage : 230V / Measured Value of Fault Loop Impedance between ( Line & Neutral ) at the Origin = 0.05Ω
Maximum Prospective Short-Circuit Current ( Line to Neutral ) 230 ÷ 0.05 = 4600A / or 4.6kA

( This Value would have been Given Directly if the Instrument had a ( Prospective Fault Current Range )
The Same Procedure is Now Repeated , Taking Readings between ( Line and Earth ) to Determine the Maximum Prospective Earth Fault Current ,

The Higher of the Two Prospective Fault Current ( Line to Neutral or Line to Earth ) should be Recorded on the Certificate or Report ;
“ Warning “ Do-Not Test Between Lines with 230V Instrument :

Three Phase Supplies
Unless a Test Instrument Designed to Operate at 400V :
It will be Necessary to Calculate the Prospective Fault Current between ( Lines )
Where an Installation is Supplied by Two or More Phases , the Maximum Prospective Fault Current is Likely to be between ( Line Conductors )

The Prospective Fault Current Between Line can be Determined by Using the Measured Value of the Line to Neutral ( PFC )
Complex Relationship between the Line to Neutral and the Line / Line Values of Prospective Fault Current,
( tends to err on the Safe Side )
The Prospective Fault Current ( Line to Neutral )
( Line to Neutral Prospective Fault Current Multiplied by Two :
4.6kA x 2 = 9.2 kA

A Circuit-Breaker to BS-3871 will have an ( M ) Number Marked on it :
This Indicates its Short-Circuit Capacity in kA
M4 Denotes 4000A ( 4 kA ) M9 Denotes 9000A ( 9 kA )
Fuses are Not so Straightforward :
BS-3036 - 1 kA to 4 kA ( Depending on Duty Rating )
BS-1361 – 16.5 kA
BS- 88 – 40 kA to 80 kA ( Depending on Duty )

Overcurrent Protective Devices having a Rated Current up to 50A Incorporated in a Consumer Unit Conforming to part 3 of
BS-EN60439 : 1991 ( Annex ZA of Corrigendum June 2006 )
Are Considered Adequate for a Prospective Fault Current of up to 16 kA ,
Provided the Consumer Unit is Fed by a Service Cut-Out having an ( HBC Fuse ) to BS-1361 Type II ,
Rated at Not More than 100A , on a Single-Phase Supply of Nominal Voltage up to 250V

Schedule of Works Required for “ FIRE PROTECTION in a 2-Storey Semi-Detached / Terraced House

“ To Provide Adequate Means of Escape in Case of Fire “

Provide and Fix a Half-Hour Door ( FD ) FD-30S to any Room Other than a Bathroom or Water Closet ( WC ) which Opens onto the Ground Floor
Hallway or First floor Landing , Conforming to British Standards ( BS ) BS 476: Parts 22,23 / 31.1 Installation to BS-8214:1990
This will Normally Include the Ground , Floor Kitchen , Ground Floor / Lounge / Dining Room & the Fist Floor Bedrooms ,
These should be Hung on Three Hinges , which Comply with BS-EN 1935 ( European Notation ) to Leave Gaps Not Greater than 4mm ( Millimetres )
To the Head and Stiles and Not More than 8mm at the Bottom ,
If a Production Size Fire Door will Not Provide a Minimum Overall Gap of 4mm & 8mm Respectively the Either :-
(a) a Single Strip of Hardwood Lipping may be Glued and Pinned to the Door Edges :
(b) a BS-476 Fire Door Blank May be Cut to Size and the Vertical Edges Finished with Hardwood Lipping as Above :

1.2 insert a Combined Intumescent Strip / Smoke Seal to Routed Edges of the Stiles and Top Rail of the Door ,
Alternatively the Strip can be Fitted to the Jambs and Head of the Frame or Lining ,

1.3 Door Stops Do Not Need to be Changed Providing they are Sufficient to Retain the Door , if New-Planted Stops are Fitted they Must be
Fixed by 38mm No 10 Screw at 230mm Centres

1.4 Provide and Fix the Following Ironmongery :
1 . Self Closing Device of an Approved Type ( Perko , Briton , Dorma or Similar )

Garden Gate Type Springs and Rising Butt Hinges are NOT Acceptable :
2 . Latch – Mortice Latch , Tubular Mortice Latch , Mortice Sash Lock , all Complete with Suitable Knob or Lever Furniture ,
Or Cylinder Rim Night latch , we Would Recommend the Fitting of a Combined and Latch Unit , This is Lockable from the Outside
With the Use of a Key , and on the Room Side bt Means of a Thumb Turn ,

Note : Locks Do Not have to be Provided on Internal Doors , However if they are Fitted they Must Meet the Above Specification :

1.5 Exit Doors which are Required to be Fastened During Occupation of the Premises must be Made to Open Easily and
Immediately from the Inside , without the Use of a Key ,

( Fire Signs )
2.1 Provide and Fix to all Doors, a Sign Stating ” FIRE DOOR KEEP SHUT “ in Minimum Lettering of 5mm
2.2 Provide and Fix to any Understairs Cupboard Door , or Cupboard Door Situated off the Ground Floor Hallway or Fist Floor Landing ,
A Sign Stating “ FIRE DOOR KEEP LOCKED “ In Minimum Lettering of 5mm

2.3 All Fire Safety Signs should Comply with BS-5499 : Part 1:1990
2.4 Fire Safety Check List Notices ( as Enclosed ) should be Provided and Sited on the Inner Faces of all the Doors ,

 

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Other Considerations

There are Additional Regulations and Codes of Practice that Need to be considered during the design of an
be considered during the design of an installation. These will affect the choice of consumer unit.
Division of Installation : Section 314.1 Calls for the Installation to be so Divided to:
( a ) Avoid Hazards and Minimize Inconvenience in the Event of a Fault
( b ) Reduce the Possibility of Unwanted Tripping of the RCD due to Excessive Protective Conductor Currents.

To Comply with these Requirements the Circuits of an Installation should Not be Connected to a Single RCD, as this could Lead to Loss of Supply to the Entire Installation in the Event of a Fault on One Circuit,
clearly Inconvenient for the User of the Building

All Circuits of an Installation should Not be Connected to a Single RCD :

● BS 5839-6:2004 Fire detection and Fire alarm systems for buildings
This Code of Practice has particular requirements for dwellings. This document makes reference to the power supply to such systems
and mentions RCD’s. The circuit supplying these systems should preferably not be protected by an RCD. This however is going to be
difficult to achieve if the circuit supplying these systems is buried in the walls and standard domestic wiring systems are used. Indeed the supply cables would need to be specially protected in earthed metal conduit etc. for RCD protection not to be used.

According to BS 5839, circuits supplying fire or smoke alarms in dwellings can be protected by an RCD provided that either:
(i) The RCD serves only that circuit. For example with the use of an RCBO ,
(ii) The RCD should operate independently of any RCD feeding socket outlets or portable equipment ,

Where RCD Protection is Needed for Smoke Detector Circuits it should Preferably be Supplying that Circuit ,

● The following options, each with their own benefits, can be considered by the installation designer. ( Electrician )

Consumer Unit Arrangements “ Not Permitted “
A consumer unit with a 30mA RCD main switch would not meet the requirements of the regulations for 3 main reasons:
Consumer Unit Arrangements “ Not Permitted “
A consumer unit with a 30mA RCD main switch would not meet the requirements of the regulations for 3 main reasons:
• The Fire detection circuit and the socket outlet circuits share a common RCD. This would be against the requirements of BS 5839.
• The cumulative effects of electronic equipment in the modern home, is such that some current is likely to flow in the protective conductor.
A 30mA RCD will trip between 15-30mA. This could cause unwanted tripping, regulation 314.1 (iv) refers.
• Any fault would result in the loss of all the lighting, this could in itself cause a hazard and the lack of power to the fridge / freezer
circuit for example would be very inconvenient. Regulation 314.1 (i)

A Consumer Unit with a 30mA RCD Main Switch would Not meet the Requirements of the Regulations

● Consumer Unit Arrangements Option 1
Main Switch with RCBO’s On All Circuits

A standard main switch disconnector controlled consumer unit could
be used with every circuit having individual RCD protection at 30mA.
This could be achieved by selecting RCBO’s for every outgoing
circuit instead of the usual MCB’s. A fault on any circuit would not
affect other circuits and hence all relevant regulations would be met by such a design.

Selecting RCBO’s for every outgoing circuit meets all relevant regulations

● Consumer Unit Arrangements Option 2
Split Load Twin RCCB plus Dedicated RCBO
This arrangement provides a dedicated 30mA RCBO for the smoke
detector circuit, but combines the rest of the circuits across two
further 30mA RCCB’s. Careful arrangements of the circuits can
reduce the likelihood of nuisance tripping, thereby limiting the
inconvenience or potential hazards that a loss of supply can cause by limiting the number of circuits affected.

This arrangement provides a dedicated RCBO for the smoke detector circuit

● Consumer Unit Arrangements Option 3

Split Load 3 RCCB Board
This arrangement provides a 30mA RCCB for the smoke detector
circuit which could also supply other circuits e.g. lighting, and
combines the rest of the circuits across two further 30mA
RCCB’s. Careful arrangements of the circuits can reduce the
likelihood of nuisance tripping, thereby limiting the inconvenience
or potential hazards that a loss of supply can cause by reducing the number of circuits affected.

This arrangement provides a RCD for the smoke detector circuit which could also supply other circuits e.g. lighting

● Consumer Unit Arrangements Option 4
Split Load Twin RCCB
This arrangement provides two separate 30mA RCCBs with the
circuits spread across both. The design of the circuit arrangements
must ensure the smoke detector is not fed from the same RCD as
socket outlets. Careful arrangement of the other circuits can reduce
the likelihood of nuisance tripping, thereby limiting the inconvenience
or potential hazards that a loss of supply can cause. However with
all circuits now over just two devices certain compromise must be accepted

The smoke detector must not be fed from the same RCD as socket outlets

● Consumer Unit Arrangements Option 5

Split Load Twin RCCB plus unprotected circuit
Under the 17th Edition requirements it is still possible to install some
circuits in domestic premises that are not fed via an RCD. Different
wiring systems would need to be used. The cost of installation could
rise considerably if most circuits were installed using armoured cable or earthed metal conduits.

The smoke alarm circuit could be installed in such a way to negate
the need for RCD protection, this may be possible by using one
of the other wiring methods described in 522.6.6 for the length of
run that the cable is in the wall (use of earthed metal conduit for
example). Or depending on the layout of the property there maybe an
attached garage for example where surface wiring might be possible.
The requirements of that regulation are therefore not applicable.

The smoke detector must not be fed from the same RCD as socket outlets

The level of compliance with the Regulations would therefore be the
same as option 2 Split Load Twin RCCB plus Dedicated RCBO.

If the smoke alarm circuit is not to be protected by an RCD it must be installed using

a method from (i) to (iv) of regulation 522.6.6

239- : Guidance for Recipients on the Recommendation Codes

Only One Recommendation Code should have been Given for Each Recorded Observation ,
Recommendation Code (1)
Where an Observation has been Given a Recommendation Code (1) ( Requires Urgent Attention )
The Safety of those Using the Installation may be at Risk ,
The Person Responsible for the Maintenance of the Installation is Advised to take Action without Delay to Remedy the Observed Deficiency
In the Installation , or Take Other Appropriate Action ( Such as Switching Off and Isolating the Affected Part(s) of the Installation )
To Remove the Potential Danger ,
The N----- Approved Contractor Issuing this Report will be Able to Provide Further Advice :

It is Important to Note that the Recommendation Given at Section 1 Next Inspection of this Report for the Maximum Interval until
The Next Inspection , is Conditional Upon all Items which have been Given a Recommendation Code 1 being Remedied without Delay ,

Recommendation Code (2)
Recommendation Code 2 ( Requires Improvement ) indicates that , Whilst the Safety of those Using the Installation may Not be at Immediate Risk ; Remedial Action should be Taken as Soon as Possible to Improve the Safety of the Installation to the Level Provided by the National Standard for the Safety of Electrical Installations BS - 7671

The N----- Approved Contractor Issuing this Report will be Able to Provide Further Advice :
Items which have been Attributed Recommendation Code 2 should be Remedied as Soon as Possible

Recommendation Code (3)
Where an Observation has been Given a Recommendation Code 3 ( Requires Further Investigation ) the Inspection has Revealed an Apparent Deficiency which could Not , Due to the Extent or Limitations of this Inspection , be Fully Identified , Items which have been Attributed Recommendation Code 3 should be Investigated as soon as Possible
The Person Responsible for the Maintenance of the Installation is Advised to Arrange for the N----- Approved Contractor Issuing
This Report ( or Other Competent Person ) to Undertake Further Examination of the Installation to Determine the Nature and Extent of the Apparent Deficiency

Recommendation Code (4)
Recommendation Code 4 ( Does Not Comply with BS-7671 ( as Amended ) will have been Given to Observed Non-Compliance(s)
With the Current Safety Standard which Do Not Warrant One of the Other Recommendation Codes ,
It is Not Intended to Imply that the Electrical Installation is Unsafe , but Careful Consideration should be Given to the Benefits of Improving these Aspects of the Installation ,
The N----- Approved Contractor Issuing this Report will be Able to Provide Further Advice ,

 

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Frequency of Inspections
The frequency of the periodic inspection and testing must be determined taking into account:
1. the type of installation
2. its use and operation
3. the frequency and quality of maintenance
4. the external influences to which it is subjected.
It is recommended that periodic inspection and testing is carried out at least every:
1. 10 years for a domestic installation
2. 5 years for a commercial installation
3. 1 year for swimming pools
Other instances when a periodic inspection should be carried out are:
1. When a property is being prepared to be let
2. Prior to selling a property or when buying a previously occupied property
Scope
The requirement of BS-7671 IEE Wiring Regulations, for periodic Inspection and Testing is for INSPECTION comprising careful scrutiny of the installation without dismantling, or with partial dismantling as required, together with a sequence of tests considered appropriate by the person carrying out the inspection and testing.

Electrical Testing - Legal Requirements 239-

Letting
You must maintain the electrical installation and any equipment provided by you, in a safe condition.
The Landlord and Tenant Act 1985 requires landlords to ensure the electrical installation is safe when the tenancy begins, and that it is maintained in a safe condition throughout that tenancy.
One way of ensuring safety is to undertake a regular visual inspection of the installation, looking for any obvious signs of damage such as damaged cables, socket-outlets showing scorch marks, etc.
In addition, the Institution of Electrical Engineers recommends that electrical installations are formally inspected and tested by a competent person on change of occupancy, and at least once every ten years.
Businesses
Any business premises from Guest houses, Shops, Offices or Hotels, are required under the Electricity at Work Regulations, that the electrical installation be checked. to satisfy this requirement.
Building Regulations
Part P of the Building Regulations (England and Wales) was introduced by the Government on January 1st 2005. It is designed to reduce accidents caused by faulty electrical installations and to prevent incompetent installers from leaving electrical installations in an unsafe condition.
Part P applies to the following situations:
• Dwelling houses and flats
• Dwellings and business premises that have a common supply eg shops that have a flat above
• Common access areas in blocks of flats such as corridors or staircases
• Shared amenities in blocks of flats such as laundries or gyms
• In or on land associated with dwellings – such as fixed lighting or pond pumps in gardens
• Outbuildings such as sheds, detached garages and greenhouses
Approved Document P is called ‘Electrical Safety’ and will be complied with if the standard of electrical work meets the ‘Fundamental Requirements of Chapter 13 of BS7671'.
Section P1 of Part P states: ‘Reasonable provision shall be made in the design, installation, inspection and testing of electrical installations in order to protect persons from fire and injury’
Section P2 of Part P states: ‘Sufficient information shall be provided so that persons wishing to operate, maintain or alter an electrical installation can do so with reasonable safety’
Part P applies only to fixed electrical installations that are intended to operate at low voltage or extra-low voltage which are not controlled by the Electricity Supply Regulations 1988 as amended, or the Electricity at Work Regulations 1989 as amended.
Note 1: The Workplace (Health, Safety & Welfare) Regulations (1992) apply in common parts of flats and similar buildings if people such as cleaners and caretakers are employed to work in them.
Note 2: The Electricity at Work Regulations (1989) cover all electrical work carried out professionally and the competence of the individuals carrying out that work
Note 3: Part P is concerned with safety and does not directly cover system functionality
Note 4: Part P does not specifically cover dwellings in places of work normally covered by the Electricity at Work Regulations (1989), such as caretakers flats in schools, MOD barracks etc.

The Periodic Inspection Report form is intended for reporting on the condition of an existing electrical installation.
You should have received an original Report and the contractor should have retained a duplicate. If you were the person ordering this Report, but not the owner of the installation, you should pass this Report, or a full copy of it, immediately to the owner.
The original Report is to be retained in a safe place and be shown to any person inspecting or undertaking work on the electrical installation in the future. If you later vacate the property, this Report will provide the new owner with details of the condition of the electrical installation at the time the Report.
The 'Extent and Limitations' box should fully identify the extent of the installation covered by this Report and any limitations on the inspection and tests. The contractor should have agreed these aspects with you and any other interested parties (Licensing Authority, Insurance Company, Building Society etc) before the inspection was carried out.
The Report will usually contain a list of recommended actions necessary to bring the installation up to the current standard. For items classified as 'required urgent attention', the safety of those using the installation may be at risk, and it is recommended that a competent person undertakes the necessary remedial work without delay.
For safety reasons, the electrical installation will need to be re-inspected at appropriate intervals by a competent person. The maximum time interval recommended before the next inspection is stated in the Report under 'Next Inspection.'
Accessories and Switchgear
It is recommended that a random sample of a minimum of 10 per cent of all switching devices is given a thorough internal visual inspection of accessible parts to assess their electrical and mechanical condition.
Protection against Thermal Effects
The presence of fire barriers, seals and means of protection against thermal effects will be verified.
Protective Devices
The presence, accessibility, marking and condition of devices for electrical protection, isolation and switching will be verified. It should be established that each circuit is adequately protected with the correct type, size and rating of fuse or circuit-breaker. The suitability of each protective and monitoring device and its overload setting will be checked.
Visual Inspections
Joints and Connections
It is not practicable to inspect every joint and termination in an electrical installation, nevertheless a sample inspection is made. An inspection is made of all accessible part of the electrical installation e.g. switchgear, distribution boards, and a sample of luminaire points and socket-outlets to ensure that all terminal connections of the conductors are properly installed and secured. Any signs of overheating and conductors, terminations or equipment will be thoroughly investigated and included in the Report.

239- Regs : page – 340 ( PS this will come up along the Line )
✔’
indicates that an inspection or a” test “ was carried out and that the result was satisfactory
‘✗’
indicates that an inspection or a” test “was carried out and that the result was Not satisfactory( Applicable for a Periodic Inspection Only )

N/A’ indicates that an inspection or a” test “was not applicable to the particular installation

LIM’ indicates that, that exceptionally, a limitation agreed with the person ordering the work prevented the Inspection being Carried Out ( Applicable for a Periodic Inspection Only )

prevented the inspection or test being carried out

 

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239- Test !! It is Big Exam , Good Luck for your examination , Amberleaf
Please have a Look at what am down Loading it will Help you Somewhere along the Line
PS some Old Notes

● Give THREE reasons for carrying out a polarity test on an installation, as required by BS-7671
● The resistance of an earth electrode is to measured. If a mains supply is unavailable, state the
(a) instrument to be used
(b) terms used to describe the TWO other test electrodes.

● State (a) why it may not be possible to obtain a measured value of loop impedance for a circuit protected by an RCD (b) how this value may be determined without the use of a special instrument
● A loop impedance test is to be conducted on a radial socket outlet circuit. State
(a) where in the circuit the test should be made
(b) TWO conditions that may affect the validity of the measured value as a comparison to the maximum value
● State THREE reasons for the use of a 20mA RCD
● In the formula IΔ n = 50/Zs (a) state what is represented by ‘50’ (b) the maximum residual current rating of the RCD required, when the value of Zs is 500Ω
● The PFC at the origin of an installation is to be measured. State the
(a) instrument to be used
(b) measurement units
(c) importance of the breaking capacity of the protective devices at the origin
● Section B – Answer ALL SIX questions Questions 21 to 26 all refer to the following scenario and Fig. 1 (attached).
Fig.1 shows the main intake and circuit arrangements for the new electrical installation in a refurbished dentist’s surgery. The heating, ventilating and air-conditioning unit (HVAC), located outside the building is supplied using p.c.v./p.c.v./s.w.a. multicore cable. All other circuits are wired using p.v.c. single-core cables enclosed in concealed p.v.c. conduit and surface trunking (c.p.c’s are the same size as the phase conductors). The lighting is a mixture of tungsten filament, fluorescent and PIR-controlled exterior security lights. The installation has been completed and is ready for inspection and testing.
● State the
(a) type of inspection and test to be completed (b) certificate that will need to be completed (c) signatures that are required on the certificate in b) (d) status of the signatories (e) documents that must accompany the certificate in b) (f) information regarding the incoming supply that should be recorded on ONE of the documents in e) (g) person who should keep the original completed documents

“ What types of electrical work DOES Part P cover “

Part P applies to electrical installations in buildings or parts of buildings comprising:
> dwelling houses and flats;
> dwellings and business premises that have a common supply – for example shops
and public houses with a flat above;
> common access areas in blocks of flats such as corridors and staircases;
> shared amenities of blocks of flats such as laundries and gymnasiums.

Part P applies also to parts of the above electrical installations:
> in or on land associated with the buildings – for example Part P applies to
fixed lighting and pond pumps in gardens;
> in outbuildings such as sheds, detached garages and greenhouses.

“ How will compliance with Part P be enforced ”

Electrical installations within dwellings are now covered by Part P (and others) of
the building regulations. As such, failure to comply with the building regulations is a
criminal offence and Local Authorities have the power to require the removal or
alteration of work that does not comply with the requirements.

As with other building regulations, they must be followed. This ensures compliance,
as well as regulated enforcement of standards and ultimately quality of workmanship

“ What benefits is Part P aiming to provide “

it is expected that bringing electrical work in dwellings under building regulations
control will reduce the number of deaths, injuries and fires caused by faults in
electrical installations. It is also expected that nationally, Part P will lead to an overall
improvement in the competence of electrical contractors and to an improvement in the quality of electrical work.

Insurance companies are not yet offering cheaper home insurance if your electrical
installation is checked compliant to latest regulations and Part P.

We are seeing 'required' demands from insurance companies that are let through
landlords - safety and Part P compliant against any recent updates / changes.

Longer term (2007 onwards) we expect additional movement through the government
and through insurance companies to begin to 'drive' Part P, requiring electrical
certification to be confirmed against building works since 2005 and creating a
framework for confirmation of safety upon change of ownership (conveyance).

Electrician : 2392-10 ←

As Part P is now a regulatory requirement for electrical installations within homes,
insurance companies will challenge claims when faced with related electrical issues,
with possible failure ( invalidation ) of the claim, if Part P was not followed.

Building Regulations

The Requirements of this Part Apply Only to Electrical Installations That are Intended to Operate at Low or Extra-Low Voltage – are :-
(a) in Dwellings
(b) in the Common parts of the Buildings Serving one or more Dwellings , but Excluding power Supplies to Lifts ,
(c) in a Building that Receives its Electricity from a Source Located within or Shared with a Dwelling , and
(d ) in garden or in or on Land Associated with a Building where the Electricity is from a Source Located within or Shared with a Dwelling

** Extra Low Voltage = 50v ac or 120v ripple free dc
** Low Voltage = not exceed 1000 V ac or 1500 V dc between conductors,
or 600 V ac or 900 V dc between conductors and earth.

Standard domestic 'mains' electricity = Low Voltage (as defined above)

Simply, Part P aims to tighten and enforce electrical regulations as defined by the
Institute of Electrical Engineers (IEE). These regulations now mean *most* electrical
changes, additions and updates within dwellings fall under Part P, and must comply
with the IEE, the BS-7671 wiring regulations

What is Periodic Inspection & Testing
The 'Electricity at Work Regulations 1989' in Regulations 4(1) and 4(2) lay down the requirement to ensure that an electrical installation should be designed, installed, constructed and maintained in a safe manner at all times. The basis for periodic inspection and testing is derived from Guidance Note 3 of the 'IEE Wiring Regulations BS7671:2008'.
Inspection & Testing of an electrical installation generates a Periodic Inspection Report which is a condition report supplemented by testing results. The Periodic Inspection Report will normally consist of:
• Client information and details of the installation
• Supply characteristics and Earthing arrangements
• Observation & Recommendations
• Extent & Limitations of Testing
• Summary of the Inspection
• Inspection & Test Schedules
'IEE Inspection and Testing Guidance Note 3' “ GN-3 “
The Testing of an electrical installation follows BS-7671:2008 and comprises of:
• C.P.C Continuity
• Ring Circuit Continuity
• Insulation Resistance
• Polarity
• Earth Fault Loop Impedance
• Prospective Fault Current
• Operation of Residual Current Devices
• Functional Testing
Testing is carried out as far as is reasonably practicable as defined in EAWR 1989.

 

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The Electricity at Work Regulations

Regulation 3: Persons on Whom Duties are Imposed by these Regulations
Regulation 4: Systems, work activities & protective equipment
Regulation 5: Strength and capability of electrical equipment
Regulation 6: Adverse or hazardous environments
Regulation 7: Insulation, protection and placing of conductors
Regulation 8: Earthing or other suitable precautions
Regulation 9: Integrity of Referenced Conductors
Regulation 10: Connections
Regulation 11: Means for Protecting from Excess of Current
Regulation 12: Means of cutting off the supply and for isolation ( Isolation from sources of energy )
Regulation 13: Precautions for work on equipment made dead
Regulation 14: Work on or near live conductors
Regulation 15: Working space, access and lighting
Regulation 16: Persons to be competent to prevent danger and injury :

The On-site Guide is intended to enable the competent electrician to deal with small installations (up to 100 A, 3-phase )

“ Inspection & Testing before into Service “ 2392-10 Electrical Installations should be Inspected and Tested as Necessary and Appropriate During and the End of Installation , Before they are taken into Service , to Verify that they are Safe to Use ,Maintain and Alter and Comply with Part P of the
Building Regulations and with any Other Relevant Parts of the Building Regulations

An HSE Inspector , whilst visiting a high-volume manufacturing plant , spots a serious problem with a complex machine –whilst it is running through a long “ cycle “ The machine IS under human supervision , which one of the following actions , available to him/her , is most appropriate in this case ,
( Issue a Deferred prohibition notice )

this will allow the machine to complete its “ cycle ( with safeguards’ in place ) after which time , it MUST NOT
Be used until the fault is repaired this option is available to Inspectors in this cases where shutting down in “ mid-cycle “
Can itself – cause danger / expensive damage

“ Apprentice “ Domestic Electrical Installation Condition Report :
A Visual Condition Report , which includes Inspection but Not Testing :

A Periodic Inspection Report ( Including Inspection & Testing )

Residual Current Devices ( RCDs ) are used Extensively in Installation to Provide Fault Protection and / or Additional
Protection Against Electric Shocks ,17th Edition of the IEE Wiring Regulations most if not all , Final Circuits in new or rewired
Installation in Domestic Premises need to be Provided with Additional Protection by an RCD having a Rated
Residual Operating Current ( I∆n ) – 30mA and an Operating Time Not Exceeding 40mS at ( 5 I∆n )

While RCDs Provide an Enhanced Level of Shock Protection , Precautions should be Taken to Avoid Unwanted Tripping of the Devices on Healthy Circuits , ( Repeated Unwanted Tripping is Likely to Damage User Confidence in RCDs , )

Unwanted Tripping of RCDs can be Caused by the Currents that may flow in the Protective Conductors of Circuits Supplying
Certain Items of Class 1 ( Earthed ) Equipment During their Normal Operation , Such Items Include Equipment Incorporating :

● Electrical Noise ( Radio Frequency )
Suppression Filters , such as Personal Computers , Hi-fi Equipment , TVs , DVDs
● Heating Elements , such as Cookers , Water Heaters or Radiant Heaters ,
● Motors , such as Fridges & Freezers ,

To avoid Unwanted Tripping , RCDs Should be so Selected and Circuits so Subdivided , that any Protective Conductors Current
Expected to Occur During Normal Operation of the ( Load(s) will be Unlikely to Cause Tripping of the Device ,
It is worth Noting that Product Standards Permit Certain Equipment such as Personal Computers , to Create up to ( 3 mA )
Of Leakage Current in the Protective Conductor ,
Tripping of RCDs the Number of Items of Protective Conductor Current-Generating Equipment per Circuit ,
And the Number of Circuits Served by each RCD , needs to be Sufficiently Small ,

As a Rule of Thumb , Tripping of an RCD may Result if the Total Protective Conductor Current in the Circuit(s)
It Serves Exceeds 50% of its Rated Residual Operating Current that is 15 mA for a 30 mA Device ,

“ Routine Inspection & Maintenance of Fire Safety Installations “

Once Fire Safety Installations , such as Fire Detection and Fire Alarms Systems and Emergency and Escape Lighting Systems ,
Are in Use , they should be Subject to Regular Checks and Maintenance , these Checks are Split into Daily , Weekly , Monthly ,
Three-Monthly , Six-Monthly , and Yearly Checks :
● the Indication of Normal Operation of the Control Panel of a Fire Detection and Alarm Systems or Emergency and Escape Lighting Systems ,

● Weekly Checks includes , Amongst other things , Standby Batteries are in good Condition and the Control Equipment is Able to Receive a Fire Signal and Initiate the Evacuation Procedure :

● Amongst other things , the Operation of Standby Generator Sets should be Checked Monthly , involving the Simulation of Power Failure and Allowing the Systems to be Energised for One Hour , Additionally , the Failure of the Supply to the Normal Lighting should be Simulated Monthly , and all Signs and Luminaires Inspected to Determine that they are Functioning Correctly ,

● Annual Checks by Competent Person(s)
Should be made amongst other things ,of the Fire Detection and Alarm Systems , Self-Contained Luminaires over Three-Years old and Sprinkler Systems ,

 

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City & Guilds Unit Breakdown

Unit 201
This unit is the first to complete and comprises of the following sections:
● Identify the legal requirements
● Identify occupational specialism’s
● Identify sources of technical information
This is a general Health and Safety unit that also covers some of the fundamentals of the industry, such as the use of drawings.
Unit 202
The second unit and the first one that involves the student thinking more and using their Math’s and Physics skills.
● Describe the application of basic units used in electro technology
● Describe basic scientific concepts related to electro technology
● Describe basic electrical circuitry and applications
● Identify tools, plant, equipment and materials
This unit introduces standard units as well as the theory and calculation behind resistance and resistivity and other technical concepts. Ohms Law is introduced at this point.
Unit 203
The third unit is an amalgamation of the first two. It splits Health and Safety and Electrical Principles into two but also requires both parts to be passed independently to achieve the certificate.
● Safe systems of working
● Using technical information
● Electrical machines and a.c. theory
● Polyphase systems
● Over current, short circuit and earth fault protection
Some of the more useful fundamentals of electrical installation are covered, such as protective devices and the purpose of earthing. Motors and a.c. theory also come into play.
This unit also contains Unit 204 which is a practical assessment involving the measurement of 3 phase supplies, both voltage and current and on and off load and the measurement of the different voltages and currents found in a standard fluorescent circuit. This is assessed internally but is needed to claim for your final certificate.
Unit 205
The unit that concludes the level 2 focuses on installation design and Regulations and covers the following subjects.
● Regulations and related information
● Purpose of specifications and data
● Types of installations
● Undertaking electrical installation
As part of unit 205 you have to complete Unit 206, you are expected to complete a large practical task (which can vary centre to centre) that consists of different wiring system such as steel conduit, trunking, swa and lighting and socket outlet circuits.
Unit 301
The start of the level 3 takes all the aspects of level 2 and increases the depth of content. It works in the same way as Unit 203 in that it is split into 2 parts, Health and Safety and Science and Principles and you must achieve a pass in both sections. Expect to cover the following:
● Comply with Statutory Regulations and organisationaI requirements
● Apply safe working practices and follow accident and emergency procedures
● Work effectively and develop competences
and for the second part
● Understand the functions of electrical components
● Understand electrical supply systems, protection and earthing
Unit 302
This unit concentrates on Inspection, Testing and Commissioning and takes the theory up to level 3 where you are expected to test live installations. It is made up of a practical assessment and a 2 hour written examination covering all aspects of Inspection and Testing.
Unit 303
Almost identical to unit 302, this unit concentrates on Fault Diagnosis and Rectification and finishes in a practical assessment and a 2 hour written exam.
Electrical Qualifications 2007

The actual AM2 is split into 4 sections:
• Section A involves a composite installation. It is a partially completed installation which you must finish. You need to know how to terminate SWA (armoured) cable, MIMS (Mineral Insulated Metal Sheathed or simply Pyro to many) and be comfortable with simple motor circuits, although you are given a wiring diagram. Once complete a visual and a functional test needs to be carried out.
• Section B involves an inspection and test of the installation
• Section C involves safe isolation procedures and a risk assessment
• Section D is fault diagnosis and rectification
AM2 Hints and Tips
Below are some ideas to help you pass the AM2 practical exam.
• Practice reading from a circuit diagram before you start
• Be especially comfortable with motor circuits and following the wiring diagram given to you beforehand
Be comfortable with lighting circuits in singles, make sure you know how to wire a landlords override switch and a Two-Way and Intermediate Lighting Circuit
•
• Take a padlock with you just in case and keep your tools locked
• Take a sharp knife such as an electricians knife sold by RS, Stanley knives or craft knives will not be permitted
• Fully understand the correct safe isolation procedure, make sure you keep the key in your pocket or locked away
• Know how to fault find, remember, continuity and insulation resistance tests are your friends
• Practice MIMS cable but leave it until the last task on the installation
• Practice doing back to back bends in steel conduit

Water heaters
As a general rule, any water heater over 15 litres should be fed by an independent circuit. Again, calculations should be made regarding the power consumption of the heating element although in most instances, it will be fed by a 16A protective device and 2.5mm2 cable.
OTHER CIRCUITS
Fire alarm
Introduced into the Building Regulations, specifically, Part B: Fire Safety, was the provision of a separate circuit for a fire alarm. It is thought that a separate circuit will not be isolated for any period of time hence the need to remove it from circuits such as lighting or socket outlet circuits.

 

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239- Inspection Testing & Certification of Electrical Installations Exam ( Old Notes )

The student must be aware of the correct use of terminology when answering questions, marks will be lost for incorrect use, some common examples include:
Using the term 'live' instead of 'phase'. Remember a live conductor includes the neutral also
Using the term 'completion certificate' instead of Electrical Installation Certificate
Using the term 'electrical inspection certificate' instead of Electrical Installation Certificate
Using the term 'initial' inspection certificate' instead of Electrical Installation Certificate
Using the term 'minor works certificate' instead of Minor Electrical Installation Works Certificate
Using the term 'Periodic Inspection Certificate' instead of 'Periodic Inspection Report for an Electrical Installation'
Incorrect use of the terms used to describe the 'Earthing Conductor' and Main Equipotential Bonding Conductors' For example using the incorrect term 'Main Bonding Conductor' instead of 'Earthing Conductor' and using the incorrect term 'Earth Bonding Conductor or even Bonding Conductor' instead of Main Equipotential Bonding Conductor
Incorrectly describing the 'Continuity of protective conductors' or 'Continuity of Ring Final Conductors' test as 'Open Loop' test when describing how to obtain R1 + R2
Incorrectly referring to 'Inspection Schedule' instead of 'Schedule of Inspections'
Incorrectly referring to 'Schedule of Tests' or Test Results Schedule instead of ' Schedule of Test Results'
It may sound petty, but you must learn to use the correct terms or you will lose marks - All the available past exam papers and the periodic inspection report check-list describe the correct terms to use
Naming documentation
When requested the documentation to complete during an initial or periodic inspection, many candidates will mention the Electrical Installation Certificate or the Periodic Inspection Report but forget to mention the 'Schedule of Inspections' and Schedule of Test Results'
Completing documentation
Many of the latest written exam papers include the requirement to complete an Electrical Installation Certificate or Periodic Inspection Report along with the accompanied 'Schedule of Inspections' and Schedule of Test Results' Often the question only asks the candidate to complete the schedule of test results for say a new ring final circuit. Many candidates waste valuable time and lose marks by completing the schedule of test results for every circuit given in the specification in part B of the question paper.
BIG TIP: READ THE QUESTION CAREFULLY:
Many candidates continue to get the value of Zs wrong for the circuit in question in part B of the exam. Check out my
A common error when completing questions involving schedule of test results is to forget to indicate functional tests have been performed and found satisfactory/unsatisfactory. To tick the tick box when completing details of ring final circuits, ensuring to indicate continuity of ring final conductors have been performed.
Failure to record the type of earthing system, i.e. TN-S, TN-C-S, TT,
Failure to record the value of Ze, PFC, Nominal voltage, Nominal frequency, are common errors.


Test procedures
A very common question is to explain in detail how to perform an insulation resistance test, often on a lighting circuit. Candidates regularly fail to state the instrument used which is an 'Insulation Resistance Ohm-meter' (Not a Megger! You will not gain any marks if you answer a Megger) Many candidates fail to identify the test voltage required for typical 230/240 volt installation which is 500 volts and the acceptable test value which is 0.5 Meg-ohm or greater (again due to change under 17th edition to a minimum acceptable value of 1.0 Meg-ohm) City and Guilds usually deliberately pick a lighting circuit that is stipulated as having two way switching, just to see if the candidate mentions to test the strappers in BOTH positions.
Failure to mention testing the insulation resistance of both strappers will lose you marks. Be warned!
Candidates regularly make mistakes when answering RCD questions. Often the question or specifications usually given in part B will make reference to a specific type of RCD for example a 30 mA RCD. Candidates are then asked to state the actual test current applicable to test this type of RCD. Candidates regularly incorrectly state the answer as x1/2 x1 and x5 instead of x1/2 = 15mA x1 = 30mA and x5 = 150mA
A frequent question which often occurs requires the candidate to explain how to perform a continuity test on a ring final circuit and to explain how R1 + R2 for the circuit is obtained. Many candidates regularly continue to get this procedure wrong check out my past exam papers and the Periodic Inspection Report check-list for a thorough explanation on how to perform these tests.
In the March 2007 paper -&- point out many exam candidates still cannot list the correct sequence of tests for a given scenario. One such scenario involves the testing of a lighting circuit, many candidates just listed the typical sequence including continuity or ring final circuit conductors, clearly they received 'Nil Pwa' for their effort
Many candidates could not correctly perform calculations involving the 'rule of thumb' or incorrectly applied the rule to the 'Measured' values instead of the 'Tabulated' values
On questions regarding insulation resistance, some candidates thought 0.00 Meg-ohms was an open circuit. Many candidates could not correctly describe the procedure for performing an external phase-earth fault loop impedance test. C&G are now requesting much more detail to such questions as well as RCD testing, requesting not only details of how to perform an RCD test but circuit preparation before hand as well as reasons why circuit preparation is required. See my March 2007 specimen paper for answers to all these questions including full colour diagram of how to perform the Ze test
October 2007 exam, part B scenario gave many candidates a difficult time. Here you were presented with a TN-C-S system installed in a domestic property, and an underground supply cable is being used to supply an external outhouse. However the electricity supply company will not allow you to use their means of earthing for the outhouse. So how do you provide a means of earthing for the outhouse? Where do you earth the supply cable? What checks must you make on the underground supply cable? Why can't you use the main house TN-C-S system as a means of earthing the outhouse? Many candidates have written to me seeking clarification on the part B scenario questions.
October 2007 Part B scenario
Solution to terminating the underground SWA supply cable
The above diagram is how the -&-'s question may lead you to terminate the SWA of the underground supply cable, since the question informs you. "You are NOT allowed to use the supply companies earthing system as a means of earthing the outhouse" However -&-'s mention nothing about earthing the supply cable itself. It is difficult to decide whether -&-'s are just testing the candidates knowledge of this situation VERY thoroughly or alternatively offering a red-herring to mislead the unwary candidate. Whichever is the reason for this question, it caused many exam candidates a great deal of difficulty and lost time trying to decide what the solution was.
The actual solution stems from BS 7671 regulation 542-01-09 part of this reg states
"If the protective conductor (i.e. the swa) forms part of a cable, the protective conductor shall be earthed only in the installation containing the associated protective device" This therefore has to be the main house end. See the only possible solution below

 

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But where manufactures recommend a method regulation 134.1.1 comes into play with:- Electrical equipment shall be installed in accordance with the instructions provided by the manufacturer of the equipment.

As if this should over ride regulations like 531.2.8 Where an RCD is used for fault protection with, but separately from, an overcurrent protective device, it shall be verified that the residual current operated device is capable of withstanding, without damage, the thermal and mechanical stresses to which it is likely to be subjected in the case of a fault occurring on the load side of the point at which it is installed. Is of debate but I can see anyone forcing you to change to all RCBO after a multi RCD board it fitted and in any case if going through building control direct you have to submit plans first so any objection would be before the work started.

Multi-RCD are required to comply with:-
314.1 Every installation shall be divided into circuits etc. ( only showing part of reg )
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation.
531.2.4 An RCD shall be so selected and the electrical circuits so subdivided that any protective conductor current which may he expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary tripping of the device.

As I read it unless emergency lighting is used then lights should have there own RCD and not shared with any other circuit. The same would apply to fire alarm systems. Items like cookers which could cause other circuits to trip due to high earth leakage and sockets, likely used outside, should not really be on the same RCD as other items in the house. This could also apply to computer supplies.


“ Instructed person “
A person adequately advised or supervised by skilled persons to enable him/her to avoid dangers which electricity may create.:
“ Ordinary person “
A person who is neither a skilled person nor an instructed person.:

“ Wiring Systems “
To conform with the requirements of BS 7671, wiring systems must utilise cables complying with the relevant requirements of
the applicable British Standard or Harmonised Standard.
Alternatively, if equipment complying with Alternatively, if equipment complying with based on an IEC Standard is
to be used, the designer or other person responsible for specifying the installation must verify that any differences between that
standard and the corresponding British Standard or Harmonised Standard will not result in a lesser degree of safety than
that afforded by compliance :
A new series of Regulations ( 522.6.6 - 522.6.8 ) have been introduced in the 17th Edition of the IEE Wiring Regulations
concerning cables concealed in a wall or partition. These new Regulations introduce the concept of skilled person, instructed
person and ordinary person :
“ RCD Protection “
It is now a requirement to protect cables concealed in a wall or partition (at a depth of less than 50 mm) by a 30mA RCD where the
installation is not intended to be under the supervision of a skilled or instructed person where other methods of protection, including the
use of cables with an earthed metallic covering, earthed conduit/trunking or mechanical protection, can not be employed.
Irrespective of the depth, a cable in a partition where the construction includes metallic parts other than fixings shall be protected by
a 30 mA RCD. For example, this means that in a domestic installation, where insulated and sheathed cables are concealed in a
wall at a depth of less than 50 mm and have no mechanical protection, they need to be installed within the safe zones and protected
by a 30 mA RCD.
“ Skilled person “
A person with technical knowledge or sufficient experience to enable him/her to avoid dangers which electricity may create :

 

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Permitted cable routes :

with the British Standard. The effect of environmental conditions and general characteristics around various parts of the installation must be assessed to enable suitable electrical equipment, including the wiring system, to be specified.
For example, cables and equipment used in agricultural and horticultural premises should be installed away from areas or routes used by
animals or be of a type to withstand such attack. Any part of the fixed installation which may be exposed to a severe impact
must be able to survive it. In workshops, for example, where heavy objects are moved, installation of wiring systems in traffic
routes should be avoided or localised protection must be provided. Therefore, when designing a concealed installation, the designer
must select a suitable wiring system. Under the 17th Edition, depending on the type of wiring selected, the method of installation
and whether the installation will be under the control of a skilled person, or instructed person or ordinary person will depend
whether the concealed wiring will require RCD protection or not. For example, in a domestic installation, where insulated and sheathed
cables are concealed in a wall at a depth of less than 50 mm and have no mechanical protection, they need to be installed within
the safe zones and need to be protected by a 30 mA RCD. Regulations 522.6.6 and 522.6.8 are reproduced here for information.
522.6.6 A cable concealed in a wall or partition at a depth of less than 50 mm from a surface of the wall or partition shall:
(i) incorporate an earthed metallic covering which complies with the requirements of these Regulations for a protective
conductor of the circuit concerned, the cable complying with BS 5467, BS 6346, BS 6724, BS 7846, BS EN 60702-1 or BS 8436, or
(ii) be enclosed in earthed conduit complying with BS EN 61386 and satisfying the requirements of these Regulations for a
protective conductor, or (iii) be enclosed in earthed trunking or ducting complying with BS EN 50085 and satisfying the
requirements of these Regulations for a protective conductor, or (iv) be mechanically protected against damage sufficient to prevent
penetration of the cable by nails, screws and the like, or (v) be installed in a zone within 150 mm from the top of the wall or partition or
within 150 mm of an angle formed by two adjoining walls or partitions. Where the cable is connected to a point,
accessory or switchgear on any surface of the wall or partition, the cable may be installed in a zone either horizontally or vertically, to
the point, accessory or switchgear. Where the location of the accessory, point or switchgear can be determined from the reverse
side, a zone formed on one side of a wall of 100 mm thickness or less or partition of 100 mm thickness or less extends to the reverse side.
522.6.7 Where Regulation 522.6.6 applies and the installation is not intended to be under the supervision of a skilled or instructed
person, a cable installed in accordance with Regulation 522.6.6 (v), and not complying with Regulation 522.6.6 (i), (ii), (iii) or (iv),
shall be provided with additional protection by means of an RCD having the characteristics specified in Regulation 415.1.1.
522.6.8 Irrespective of the depth of the cable from a surface of the wall or partition, in an installation not intended to be under the
supervision of a skilled or instructed person, a cable concealed in a wall or partition the internal construction of which includes metallic parts, other than metallic fixings such as nails, screws and the like, shall:
(i) incorporate an earthed metallic covering which complies with the requirements of these Regulations for a protective
conductor of the circuit concerned, the cable complying with BS 5467, BS 6346, BS 6724, BS 7846,
BS EN 60702-1 or BS 8436, or (ii) be enclosed in earthed conduit complying with BS EN 61386 and satisfying the requirements of
these Regulations for a protective conductor, or (iii) be enclosed in earthed trunking or ducting complying with BS EN 50085
and satisfying the requirements of these Regulations for a protective conductor, or (iv) be mechanically protected sufficiently to
avoid damage to the cable during construction of the wall or partition and during installation of the cable, or (v) be provided with
additional protection by means of an RCD having the characteristics specified in Regulation 415.1.1.
NOTE: If the cable is installed at a depth of 50 mm or less from the surface of a wall or partition the requirements of Regulation
522.6.6 also apply. RCD Protection ,An RCD is a protective device used to automatically disconnect the electrical supply when an imbalance is detected between live conductors. In the case of a single-phase circuit, the device monitors the difference in currents
between the line and neutral conductors. If a line to earth fault develops, a portion of the line conductor current
will not return through the neutral conductor. The device monitors this difference, operates and disconnects the circuit when the residual current reaches a preset limit, the residual operating current (IΔn). An RCD on its own does not provide protection against overcurrents. Overcurrent protection is provided by a fuse or a circuit-breaker. However, combined RCD and circuit-breakers are available and are designated RCBOs. Unwanted tripping Unwanted tripping of RCDs can occur when a protective conductor current or leakage
current causes unnecessary operation of the RCD. An RCD must be so selected and the electrical circuits so subdivided that any
protective conductor current that may be expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary tripping of the device. Discrimination Where two, or more, RCDs are connected in series, discrimination must be
provided, if necessary, to prevent danger. During a fault, discrimination will be achieved when the device electrically nearest to the
fault operates and does not affect other upstream devices. Discrimination will be achieved when ‘S’ (Selective) types are used in conjunction with downstream general type RCDs. The ‘S’ type has a built-in time delay and provides discrimination by simply ignoring the fault for a set period of time allowing more sensitive downstream devices to operate and remove the fault. For example, when
two RCDs are connected in series, to provide discrimination, the first RCD should be an ‘S’ type. RCDs with built in time
delays should not be used to provide personal protection. Labelling Regulation 514.12.2 requires that where an installation incorporates an RCD a notice shall be fixed in a prominent position at or near the origin of the installation. The Regulation requires that the notice
shall be in indelible characters not smaller than illustrated in BS 7671, see fig. 4. Testing Refer to Regulations 612.8.1,
612.13.1 and 415.1.1 for requirements in terms of verification of installed RCDs.
“ Conclusion “ 1
Under the 17th Edition designers will now have to determine from the client whether the installation is going to be under the
supervision of a skilled person, instructed person or ordinary person.

Labelling requirement of 514.12.2

 

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Recognised devices ( Remember that BS- is Old / but still in Use )
RCDs are manufactured to harmonised standards and can be identified by their BS EN numbers. An RCD found in an
older installation may not provide protection in accordance with current standards. The following list identifies the applicable current standards:
BS 4293 : 1983 (1993) Specification for residual current operated circuit-breakers. (Replaced by BS EN 61008-1: 1995,
BS EN 61008-2-1: 1995 and BS IEC 61008-2-2: 1990). This Standard remains current :
BS 7071 : 1992 (1998)
Specification for portable residual current devices :
BS 7288 : 1990 (1998)
Specification for socket-outlets incorporating residual current devices. (SRCDs)
BS EN 61008-1 : 1995 (2001)
Residual current operated circuit-breakers without integral overcurrent protection for household and similar uses (RCCBs)
BS EN 61009-1 : 2004
Residual current operated circuit-breakers with integral overcurrent protection for household and similar uses (RCBOs)
Characteristics of RCDs
RCDs are defined by a series of electrical characteristics, three main characteristics are:
1. The rating of the device in amperes, ( I ) :
2. The rated residual operating current of the protective device in amperes, I∆n:
3. Whether the device operates instantaneously or incorporates an intentional time delay to permit discrimination. Such devices are called ‘S’ or Selective :
Devices are manufactured with different values of rated current and rated residual operating current but we will just consider the rated residual operating current of the protective device in amperes, I∆n:
Discrimination
Where two, or more, RCDs are connected in series, discrimination must be provided, if necessary, to prevent danger (Regulation 531-2-9 refers). During a fault, discrimination will be achieved when the device electrically nearest to the fault operates and does not affect
other upstream devices. Discrimination will be achieved when ‘S’ (Selective) types are used in conjunction with downstream general
type RCDs. The ‘S’ type has a built-in time delay and provides discrimination by simply ignoring the fault for a set period of time allowing more sensitive downstream devices to operate and remove the fault. For example, when two RCDs are connected in series, to provide discrimination, the first RCD should be an ‘S’ type. RCDs with built in time delays should not be used to provide personal protection.
Testing
RCDs must be tested. The requirements are stated in the following Regulations:
The effectiveness of the RCD must be verified by a test simulating an appropriate fault condition and independent of any test facility, or
test button, incorporated in the device (Regulation 613-13-1)
Tests are made on the load side of the RCD between the phase conductor of the protected circuit and the associated cpc. Any load or appliances should be disconnected prior to testing. RCD test instruments require a few milliamperes to operate; this is
normally obtained from the phase and neutral of the circuit under test. When testing a three-phase RCD protecting a three-wire circuit, the instrument’s neutral is required to be connected to earth. This means that the test current will be increased by the instrument supply current and will cause some devices to operate during the 50% test, possibly indicating an incorrect operating time. Under this circumstance it is necessary to check the operating parameters of the RCD with the manufacturer before failing the RCD.
Integral Test Device ( Functional Testing ) 612.13
An integral test device is incorporated in each RCD. This device enables the mechanical parts of the RCD to be
verified by pressing the button marked ‘ T’ or ‘Test’ :
Test Instrument
The test instrument used to test RCDs should be capable of applying the full range of test current to an in-service
accuracy, as given in BS EN 61557-6. This in-service reading accuracy will include the effects of voltage
variations around the nominal voltage of the tester. To check RCD operation and to minimise danger during the test, the test current
should be applied for no longer than 2s. Instruments conforming to BS EN 61557-6 will fulfil the above requirements.
● “ OLD RCDs “
General Purpose RCDs to BS-4293 & Protected Sockets-Outlets BS-7288 :
( 240V – 50Hz – 80A – Load BS-4293 RCD ) ↔ ( BS-Number : Only = 200mS ) 50% of operating current : Device should Not Operate ;
100% of Operating current : Device should Operate in Less than 200mS :
Where the RCD incorporates an intentional time delay it should trip within a time range from 50% of the rated time delay plus 200ms’
to 100 % of the rated time delay plus 200ms
● “ NEW RCDs “
General Purpose RCBOs BS-EN 61009-1 ↔ ( BS-EN = Only 300mS )
General Purpose RCCBs BS-EN 61008-1 ( BS-EN 61008-1 : 230V ( 80A – 30mA – 230V )
50% of operating current Device should Not operate :
100% of operating current Device should operate in less than 300mS :
unless it is of ‘Type S’ (or selective) which incorporates an intentional time delay. In this case, it should trip within a time range from 130ms to 500ms ( Appendix 3 , page - 243 )
Additional Protection : Test current at 5 I∆n : I∆n ≤ 30mA / Device should Operate in Less than ( 40mS )

What is an RCD and what does it do? “ Definitions “ p / 29
An RCD is defined, in BS 7671, as: ‘A mechanical switching device or association of devices intended to cause the opening of the contacts when the residual current attains a given value under specified conditions’.

 

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“ 2392-10 “ 17th Edition of the IEE Wiring
Regulations on the 1st January 2008 has major implications for all electrical contractors, designers
and consultants. From 1st July 2008 all new electrical installations will have to be designed to comply with the new regulations : The biggest area of concern at present is the effect on an individual’s home being wired or re-wired.
there are five aspects that the 17th Edition identifies as requiring consideration for installations that are not under the supervision of skilled people (e.g. qualified electricians) or instructed people (e.g. facilities managers) – i.e. most domestic
installations,
● Socket outlets for general use in domestic installations must have the additional protection of an RCD Not exceeding 30mA (regulation 411.3.3 )
● All circuits in locations containing a bath or shower must be protected by an RCD not exceeding 30mA ( Regulation 701.411.3.3 )
● Cables buried in a wall or partition at a depth of less than 50mm, and not mechanically protected by appropriate earthed metal, must be protected by an RCD not exceeding 30mA ( Regulations 522.6.6–8 )
● To prevent nuisance tripping, unnecessary hazards, and minimise inconvenience, circuits should not be connected to a single upstream RCD ( Regulation 314.1 )
● Separate circuits shall not be affected by the failure of other circuits ( Regulation 314.2 )
When designing the installation and selecting the correct assembly, the electrician will need to consider the above
five aspects, in accordance with the regulations. It is not solely the function of a particular consumer unit that has
one, two or three RCDs with an incomer isolator to solve the problem of meeting the 17th Edition regulations.
assembly to ensure that the installation complies with the 17th Edition regulations.
Everything starts ;
When designing an installation in a new build project, there are various options to consider, in order to satisfy
the requirements of the 17th Edition. For example, consider burying the cables more than 50mm into the
walls, or protect the cable with earthed metal, to remove the need for RCD protection. Once the wiring scheme has been finalised, the process of selecting how best to protect the circuits and the people can begin.
The regulations are open to interpretation, particularly regarding the division of installations, where acceptable levels of inconvenience resulting from a fault can be somewhat subjective. ( See page 11 for Regulations 314.1 and 314.2. )
● ( FCA ) Fully Compliant Assembly : ←
● ( PCA ) Partially Compliant Assembly : ←
● ( NCA ) Non-Compliant Assembly : potentially dangerous ; ←
to satisfy all aspects where an RCD has to be used for safety reasons but does not comply with all parts of regulation 314; a Non-Compliant Assembly is judged to satisfy neither safety aspects nor regulation 314. :
Customers are looking for a competitive offering, balanced with potential safety aspects and avoiding the
hazards and nuisance that a short circuit trip, overload condition or earth leakage may cause.
For “ example “ a consumer unit with an isolator and double RCD (see page 3 Example A) is often promoted as a way of meeting the 17th Edition regulations on the basis that every circuit is protected by an RCD, and the circuits split evenly between two RCDs. However, in the event of a fault on either set of MCBs, the RCD may trip as well. This creates an unwanted disconnection of the MCBs where no fault exists (contrary to section 314.1) and also causes unwanted disconnection of other circuits ( contrary to section 314.2 ).
A dual RCD split load board will meet the 17th Edition requirements for the following: :
● Socket outlets for general use in domestic installations must have the additional protection of an RCD not
exceeding 30mA.
● All circuits in locations containing a bath or shower must be protected by an RCD not exceeding 30mA.
● Cables buried in a wall or partition at a depth of less than 50mm, and not mechanically protected by appropriate earthed metal, must be protected by an RCD not exceeding 30mA :
However, depending on the installation design, it is unlikely to satisfy the regulations on:
*To prevent nuisance tripping, unnecessary hazards, and minimise inconvenience, circuits should not be connected to a single upstream RCD. )
* Separate circuits shall not be affected by the failure of other circuits. In the event of a fault on either set of MCBs, the RCD may trip as well. This creates an unwanted disconnection of the MCBs where no fault exists (contrary to section
314.1) and also causes unwanted disconnection of other circuits (contrary to section 314.2 ).
Prior to the 17th Edition, lights have not been part of the RCD circuit as they tend to trip the RCD whenever an incandescent bulb fails, for example, causing unacceptable nuisance. Having the lights in the same circuit may cause nuisance disconnection to any other circuit supplied on the RCD. In addition there is a smoke alarm and a light circuit
on the same RCD, so every time the light circuit trips (when a bulb fails) the house and the alarm circuit could be disabled, putting the occupants at risk of a fire not being detected. The safety implications of this configuration by not
addressing the requirements of section 314 make this a Non-Compliant Assembly :

● ( PCA ) Partially Compliant Assembly : ←
A split load board with independent RCBOs will meet the17th Edition requirements for the following:
● Socket outlets for general use in domestic installations must have the additional protection of an RCD not exceeding 30mA.
● All circuits in locations containing a bath or shower must be protected by an RCD not exceeding 30mA.
● Cables buried in a wall or partition at a depth of less than 50mm, and not mechanically protected by
appropriate earthed metal, must be protected by an RCD not exceeding 30mA :

However, depending on the installation design, whilst this layout takes into account the danger arising from the
failure of a single circuit (such as lighting) it does not fully comply with :
* To prevent nuisance tripping, unnecessary hazards, and minimise inconvenience, circuits should not be connected to a single upstream RCD.
* Separate circuits shall not be affected by the failure of other circuits :
It may be advisable to have a socket circuit on a separate circuit. In larger residential properties it would be advisable to separate the downstairs circuit or the kitchen circuit from the other circuits supplied by a sole RCD to ensure that in the event of a fault there would be at least one power circuit available. Prior to the 17th Edition, it was common to have all
socket power circuits supplied from one RCD with no account of the implications for safety or significant inconvenience being apparent. However, the increasing number of electronic devices now found in a home results in a greater amount of earth leakage current that may lead to a tripping of the RCD and fall foul of 531.2.4.
( Note Also depending on the wiring scheme the smoke detector may not need to be an RCBO. )

Main switch with RCBOs on all circuits : ● ( FCA ) Fully Compliant Assembly : ←


A standard main switch disconnector controlled consumer unit with RCBOs for every outgoing circuit instead of the usual MCBs, will fully comply with the 17th Edition regulations. A fault on any circuit will not impact on other circuits, and so all aspects of the regulations are satisfied.:
● Socket outlets for general use in domestic installations must have the additional protection of an RCD not exceeding 30mA.
● All circuits in locations containing a bath or shower must be protected by an RCD not exceeding 30mA.
● Cables buried in a wall or partition at a depth of less than 50mm, and not mechanically protected by appropriate earthed metal, must be protected by an RCD not exceeding 30mA.
● To prevent nuisance tripping, unnecessary hazards, and minimise inconvenience, circuits should not be connected to a single upstream RCD.
● Separate circuits shall not be affected by the failure of other circuits.

Main switch with RCBOs on critical circuits : ● ( FCA ) Fully Compliant Assembly : ←

By looking closely at the wiring scheme in an installation, the assembly can be made more cost effective by using MCBs to protect some circuits rather than RCBOs, without compromising compliance with the 17th Edition.
For example, at the point of cable entry to the consumer unit, incoming and outgoing cable runs are all encased in suitable ‘metal trunking’ or buried deeper than 50mm, so do not require RCD protection. As none of the cables are in the walls, the smoke alarms similarly do not require RCD protection. The burglar alarm system may have its own trunking or metal covering for the supply to the main control
console. If it does, and all the other devices are low voltage or cable runs in the ceiling, then this too could be MCB protected. This will depend on the wiring scheme employed for this ancillary piece of equipment. You could also decide that the immersion heater cable and cooker point (without socket) are in areas where they can be surface mounted and shrouded inside a short length of conduit, or buried deeper than 50mm in the wall.
This example illustrates that by analysing the wiring scheme, RCBOs can be replaced with MCBs, reducing the
costs whilst still providing a Fully Compliant Assembly ( FCA ).

 

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Split load board with RCBOs on critical circuits : ● ( PCA ) Partially Compliant Assembly : ←

By reviewing the wiring scheme employed with the split load assembly proposed the cost of the finished assembly can be reduced, and partial compliance with the regulations achieved. The split load board laid out here will meet the17th Edition requirements for the following:
● Socket outlets for general use in domestic installations must have the additional protection of an RCD not exceeding 30mA.
● All circuits in locations containing a bath or shower must be protected by an RCD not exceeding 30mA.
● Cables buried in a wall or partition at a depth of less than 50mm, and not mechanically protected by appropriate earthed metal, must be protected by an RCD not exceeding 30mA.:
However, depending on the installation design, it is unlikely to satisfy the regulations on:
* To prevent nuisance tripping, unnecessary hazards, and minimise inconvenience, circuits should not be connected to a single upstream RCD.
* Separate circuits shall not be affected by the failure of other circuits. :
there is still the risk of one circuit failure impacting on another (regulation 314.2); however the level of inconvenience could be considered to be acceptable (only the sockets and showers are affected ), and no hazard or safety issues are inherent. Again, the installer will need to consider the amount of leakage in the installation, due to electronic devices in the house, and it may be a consideration to split the power sockets and have one of them on an RCBO.
The end result is that no base consumer unit exists that complies with the 17th Edition. The choice of
consumer unit and the configuration of devices within it can only be made after the wiring scheme has been finalised. :

Key extracts from 17th Edition of the IEE Wiring Regulations BS 7671 : 2008

314 Division of Installation
314.1 Every installation shall be divided into circuits, as necessary, to (i) avoid hazards and minimize inconvenience in the event of a fault(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit.314.2 Separate circuits shall be provided for parts of the installation which need to be separately controlled, in such a way that those circuits are not affected by the failure of other circuits, and due account shall be taken of the consequences of the operation of any single protective device.
411.3.3 Additional protection
In a.c. systems, additional protection by means of an RCD in accordance with Regulation 415.1 shall be provided fori) socket-outlets with a rated current not exceeding 20A that are for use by ordinary persons and are intended for general use.
531.2.4 An RCD shall be so selected and the electrical circuits so sub divided that any protective conductor current which may be expected to occur during normal operation of the connected load(s) will be unlikely to cause unnecessary tripping of the device.
Section 701 Locations containing a bath or shower
701.411.3.3 Additional protection by RCDs
Additional protection shall be provided for all circuits of the location, by the use of one or more RCDs having the characteristics specified in Regulation 415.1.1 (30mA RCD)
( Note: see regulations 314.1 and 531.2.4. )

Note: There are exceptions when the socket outlets are used by skilled or instructed persons, but not relevant in residential property. For example 411.3.3 relates to socket outlets located anywhere in a home, including the socket in the cooker outlet. However RCD protection for the cooker outlet is required if any of the cables are buried in the wall and not deeper than 50mm, as indicated in 522.6

Fire Alarms :

The entire system should be tested to ensure that it operates satisfactorily and that, in particular,
automatic fire detectors and any manual call points function correctly when tested. Smoke detectors should
be smoke tested with a simulated smoke aerosol that will not damage the detector. Heat detectors should be
tested by means of a suitable heat source unless detector damage would otherwise result. The heat
source should not have the ability to cause a fire. A live flame should not be used.
It should be established that any interlinking works and that sounders operate correctly.
Manufacturer’s tests should be carried out.

Certification :
A certificate should have been issued to the user and this should be available for inspection. For Grade F
systems a certificate should be issued if installed by a professional installer.

User instructions :
The supplier of the fire alarm system should provide the user with operating instructions, which should be
sufficient to enable a lay person to understand, operate and maintain the system. Silencing and disablement facilities should be explained but it should be stressed that system readiness must not be compromised. Recommended action in the event of a
fire must stress the importance of all occupants leaving the building as quickly as possible and that
the fire service is summoned immediately regardless

Routine testing and maintenance :
instructions to users must stress the importance of routine testing. The system should be tested weekly by
pushing the test button. If the dwelling has been unoccupied for a period during which the supply (yes)
could have failed, the occupier should check that the system has not suffered total power failure and is still operable.

Maintenance :
Smoke alarms in Grade D, E and F systems should be cleaned periodically in accordance with the
manufacturer’s instructions. Where experience shows that undue deposits of dust and dirt are likely to
accumulate, so affecting the performance of the system before detectors are cleaned or changed, more frequent
cleaning or changing should be carried out.

Commissioning :

The system should be inspected. Electrical tests made to the mains supply circuit
should include earth continuity, polarity, and earth fault loop impedance. Insulation tests should be made
of all installed cables as required by BS 7671. Electronic equipment should be disconnected to avoid damage.

Supply to a Grade E system where the installation forms part of a TT system.
The 100 mA time-delayed RCD provides protection for the fire alarm system ( and other circuits )
and operates independently of the RCD protection for the socket-outlets


main switch
( 100 mA time delayed RCD )
S-type, double pole to BS EN 61008 :

interconnected by wiring should be connected on a single final circuit. Note that certain alarms are radio linked and such alarms
need not be on the same final circuit ,
Wiring systems :
All cables should be selected and installed in accordance with the requirements of BS 7671 and the recommendations of BS 5839-6.

“ RCCB “

Residual Current Circuit Breaker (RCCB). This is a term that does not appear in the current wiring regs, and does not have a consistent definition or usage. Some manufacturers use it to differentiate RCDs without overcurrent protection from those with it ( i.e. RCBOs ).
Nuisance trips :
A Nuisance trip is an unexpected operation of a RCD that does not appear to be related to an immediately obvious fault. There can be many reasons that these trips occur, some indicate that there is a latent problem with the electrical installation, some may indicate the presence of a serious but as yet unobserved fault, and others may be the result of a minor fault that in itself poses little or no risk ,
Tracing the cause of nuisance tripping can prove to be very difficult and time consuming.

What causes nuisance trips :
Using the wrong busbar
If you have a new circuit that trips the moment you attempt to draw power from it, the most likely cause is common wiring mistake in the CU. Split load CUs will have two or more sections, with a dedicated neutral bus bar for each. If you connect the live of a circuit to a MCB on a section of the CU protected by an RCD, but return the neutral to a bus bar not associated with that RCD, you will get an immediate trip sine the RCD can only "see" one half of the current flow. The same logic applies if using a RCBO, then the neutral for the circuit must be returned to the neutral connection on the RCBO ( and the RCBO's flying neutral wire in turn connected to the appropriate neutral bus bar in the CU).
Excess earth leakage
The RCDs operating principle is to measure the current imbalance between that flowing into and out of a circuit down live and neutral wires. In an ideal world the current difference would be zero, however in the real world there are a various different types of equipment that will legitimately have a small amount of leakage to earth, even operating normally. If the RCD is protecting too many such devices then it is possible that the cumulative result of all these small leakages will be enough to either
● trip the RCD
● or by passing most of the RCD's trip threshold current, make the RCD excessively sensitive to any additional leakage currents

 

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“ Domestic RCD “
This is a deprecated way of installing an RCD such that a single low trip threshold device ( typically 30mA ) protects all the circuits in a property. While counter to the advice given in the present wiring regulations. installations of this type are still commonly found. Whole house RCDs are very vulnerable to nuisance trips, and any such trips remove all power to the property
Wiring faults :
Fault : Neutral to Earth shorts ,
Mechanism :
A particularly problematic fault is a short between neutral and earth on a circuit. Since Neutral and earth are nominally going to be at a similar potential (especially in buildings with TN-C-S / PME . earthing
You can arrive at a situation where the current flow between neutral and earth is lower than the trip threshold of the RCD some of the time, however once the neutral current reaches a high enough level, its potential will be "pulled" away from that of the earth, and you get increased leakage current flow which may cause a trip. Needless to say this threshold will often be reached during transient current peaks caused by equipment being switched on or off.

Insulation breakdown or damage :
As cables and wires age, their Insulation can become less effective .

Faulty RCD :
One obvious possibility (and often overlooked) is that the RCD itself is actually faulty and not tripping at the correct current. A RCD that refuses to reset even when all output connections are removed is an obvious candidate for landfill. Swapping the device with a known good one, or using a RCD test facility , are other ways of finding faulty RCDs. Many RCDs include a "test" button that verifies the unit functions. This simulates a imbalance current internally, which causes the device to operate. Note however that because the test current may be several times the trip threshold, it does not test if the trip threshold has drifted too low or the mechanism has become slow - only that the trip detection and basic mechanics still work.
How to locate the cause of nuisance trips :
There are a number of empirical tests or experiments that you can try to narrow down the source of the problem. We cover some here. The first job is to identify which circuits the RCD is protecting. There is no need to concentrate efforts on examining circuits that are not connected and hence can not be affecting the outcome!
“ Techniques to try “
Do what : Turn off circuits in turn ,
Why : You may be able to identify which circuit is causing the problem by isolating circuits in turn, and seeing which prevents the trip from reoccurring ,

“ Remove appliances from suspect circuits “

Disconnecting appliances from suspect circuits can let you identify if the fault is in an appliance (the most common situation) or the circuits fixed wiring. If you still get trips with everything disconnected then you may have a wiring fault.
If it looks like appliances are to blame, you can apply the "binary chop" principle to narrow down the field quickly - i.e. unplug half of them and see what happens. If it still trips you know in which half the dodgy appliance probably is. The carry on in the same way - halving the list of remaining suspects, until you get close to the answer. (This method isn't bulletproof with RCDs.)
“ Check the likely culprits “
Identifying which appliances you have from the "high risk" categories listed above can help to take you to the cause of the trouble faster :

“ Check the likely culprits “
Identifying which appliances you have from the "high risk" categories listed above can help to take you to the cause of the trouble faster :

“ Identify coincidental factors “
Check for any patterns and relationships between trips and other events. Do they occur only in Damp
weather, or only at certain times of day, or only when the Freezer switches on, or the Central Heating
Pay particular attention to automated systems ( timers, thermostats etc ) that can be controlling significant bits of electrical equipment in your home without your manual intervention .

Notes on Schedule of Test Results ( 2392-10 ) Nice Wording for 2391 ←←

* (1) Type of Supply : is Ascertained from the Distributor or by Inspection ,
* (2) (Ze) at Origin : when the Maximum Value Declared by the Distributor is Used , the Effectiveness of the Earth must be Confirmed by Test , if Measured the Main Bonding will need to be Disconnected for the Duration of the Test ,

* (3) Prospective Fault Current ( PFC ) the Value Recorded is the Greater of Either the Short-Circuit Current or the Earth Fault Current
Preferably Determined by Enquiry of the Distributor ,

* (4) Short-Circuit Capacity : of the Device is Noted , see table 7.2 - OSG – table 2.4 – GN3
The Following Tests , where Relevant , shall be Carried Out in the following Sequence :
Continuity of Protective Conductors , including Main & Supplementary Bonding .
Every Protective Conductor , including Main & Supplementary Bonding Conductors , should be Tested to Verify that it is Continuous and Correctly Connected
* (6) Continuity :
Where Test Method (1) is Used , Enter the Measured Résistance of the Line Conductor Plus the Circuit Protective Conductor ( R1 + R2 )
See 10.3.1 – OSG – 2.7.5. – GN3 : During the Continuity Testing ( Test Method 1 ) the following Checks are to be Carried Out :
(a) Every Fuse and Single-Pole Control and Protective Device is Connected in the Line Conductor Only
(b) Centre- Contact Bayonet & Edison Screw Lampholders have Outer Contact Connected to Neutral Conductor
(c) Wiring is Correctly Connected to Socket-Outlet & Similar Accessories , Compliance is to be Indicated by a Tick in Polarity Colum ( 11 ) ,
( R1 + R2 ) need Not be Recorded if ( R2 ) in Column ( 7 )
* (7) Where Test Method (2) is Used , the Maximum Value of ( R2 ) is Recorded in Column ( 7)
See 10.3.1 – OSG – 2.7.5 – GN3
* (8) Continuity of the Ring-Final Circuit Conductors
A Test shall be Made to Verify the Continuity of Each Conductor Including the Protective Conductor of Every Ring-Final Circuit
See 10.3.2 – OSG – 2.7.6.- GN3
* (9) * (10) Insulation Résistance :
All Voltage Sensitive Devices to be Disconnected or Test Between Live Conductors’ ( Line & Neutral ) Connected together & Earth , The Insulation Résistance between Live Conductors’ is to be Inserted in Column ( 9)
The Minimum Insulation Résistance Values are Given tables : 10.1 – OSG – 2.2 – GN3 :
( All the Preceding Tests should be Carried Out before the Installation is Energised )
* (11) Polarity :
A Satisfactory Polarity Test may be Indicated by a Tick in Column ( 11 )
Only in a Schedule of Test Results Associated with a Periodic Inspection Report is it Acceptable to Record Incorrect Polarity ,
* (12) Earth Fault Loop Impedance ( Zs )
This may be Determined Either by direct Measurement at the Further Point of a Live Circuit or by Adding ( R1 + R2 ) of Column
6 to ( Ze . Zs ) is Determined by Measurement at the Origin of the Installation or Preferably the Value Declared by the Supply Company Used , ( Zs = Ze + ( R1 + R2 ) – Zs should be Less than the Values given in Appendix 2 – OSG or Appx 2 – GN3
* (13) Functional Testing :
The Operation of RCDs ( including RCBOs ) shall be Tested by Simulating a Fault Condition , Independent of any Test Facility in the Device . Record Operating time Column (13) Effectiveness of the Test button must be Confirmed ,
See : Section (11) – OSG or 2.7.15 / 2.7.18 – GN3 ,
* (14) All Switchgear & Controlgear Assemblies , Drivers , Control & Interlocks, etc must be Operated to ensure that they are Properly Mounted , Adjusted , and Installed : Satisfactory Operation is Indicated by a tick in Column (14) ,
( Earth Electrode Resistance )
The Earth Electrode Resistance of ( TT ) Installations must be Measured , and Normally an RCD is Required ,
For Reliability in Service the Resistance of any Earth Electrode should be below ( 200Ω ) Record the Value on form 1- 2 - 6 ,
As Appropriate , see 10.3.5 – OSG or 2.7.12 – GN3

 

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“ Isolation of individual circuits”

Where it is not practical to isolate a distribution board, individual circuits supplied from it can be isolated
by one of the methods described below, depending on the type of protective device used. However, bear
in mind the overriding advice to avoid energising any outgoing electrical distribution services, preferably
until the distribution switchgear and all connected circuits are complete and have been inspected and the
relevant tests carried out.
If any items required to carry out the procedures recommended below are not manufactured for the DB in
question or cannot be obtained through retail/trade outlets, it is acceptable to disconnect the circuit from
the DB as long as the disconnected tails are made safe by being coiled or insulated. Suitable labelling of the
disconnected conductors is important to prevent the supply being re-instated, particularly if other
electricians are present.
It should be remembered that work carried out inside a live DB is regarded as live working when there is
access to exposed live conductors. In this case the appropriate precautions should be taken as described in
HSG85 with respect to Regulation 14 of the Electricity at Work Regulations.
i. Isolation of individual circuits protected by circuit breakers
Where circuit breakers are used the relevant device should be locked-off using an appropriate locking-off
clip with a padlock which can only be opened by a unique key or combination. The key or combination
should be retained by the person carrying out the work.
Note
Some DBs are manufactured with ‘Slider Switches’ to disconnect the circuit from the live side of the circuit
breaker. These devices should not be relied upon as the only means of isolation for circuits as the wrong
switch could easily be operated on completion of the work.
ii. Isolation of individual circuits protected by fuses
Where fuses are used, the simple removal of the fuse is an acceptable means of disconnection. Where
removal of the fuse exposes live terminals that can be touched, the incoming supply to the fuse will need to
be isolated. To prevent the fuse being replaced by others, the fuse should be retained by the person carrying
out the work, and a lockable fuse insert with a padlock should be fitted as above. A caution notice should
also be used to deter inadvertent replacement of a spare fuse. In addition, it is recommended that the
enclosure is locked to prevent access as stated above under ‘Isolation using a main switch or distribution
board (DB) switch-disconnector’.
Note
In TT systems, the incoming neutral conductor cannot reliably be regarded as being at earth potential.
This means that for TT supplies, a multi-pole switching device which disconnects the phase and neutral
conductors must be used as the means of isolation. For similar reasons, in IT systems all poles of the
supply must be disconnected. Single pole isolation in these circumstances is not acceptable.

“ Electrical Permits-to-Work “
An electrical permit-to-work must be used for work on HV systems that have been made dead, and can
be useful in certain situations for LV work. These permits are primarily a statement that a circuit or item
of equipment is isolated and safe to work on. They must not be used for live working as this can cause confusion..

“ Caution Notices “
In all instances where there is a foreseeable risk that the supply could be reinstated as above, an
appropriate “caution” notice should be placed at the point of isolation. For DBs with ‘multiple
isolations’ a single suitably worded notice on each DB, such as the example shown below, would suffice:

* CAUTION: THIS DISTRIBUTION BOARD HAS A NUMBER OF CIRCUITS THAT ARE
SEPARATELY ISOLATED. CARE SHOULD BE TAKEN WHEN REINSTATING THE
SUPPLY TO AN INDIVIDUAL CIRCUIT THAT IT HAS BEEN CORRECTLY IDENTIFIED.

Question 1 :
State the necessary action that should be taken by an inspector on discovering a damaged socket outlet with exposed live parts during a periodic inspection and test :
GN-3 ( Required Competence )
Make an immediate recommendation to the client to isolate the defective part :
Question 2 :
State the documentation that should accompany an Installation Certificate or Periodic Inspection Report :
GN-3 ( Certificates & Reports )
1. Schedule of items inspected :
2. Schedule of test results :
Question 3 :
Why is it necessary to undertake an initial verification ?
GN-3 ( Initial Verification ) G
1. Confirm that installation complies with designers intentions :
2. Constructed, inspected and tested to BS- 7671:2008 :
Question 4 :
State the requirements of Part 6 of BS- 7671 with regard to initial verification :
GN-3 ( Initial Verification )
1. All equipment and material complies with applicable British Standards or acceptable equivalents :
2. All parts of the installation are correctly selected and erected :
3. Not visibly damaged or defective :
Question 5 :
Identify FIVE non-statutory documents that a person undertaking an inspection and test need to refer to
General Knowledge
1. BS -7671:2008 :
2. IEE On-Site Guide :
3. GS 38 :
4. Guidance Note 3 :
5. Memorandum of Guidance to The Electricity at Work Regulations :
Question 6 :
Which non-statutory document recommends records of all maintenance including test results be kept throughout the life of an installation ?
GN-3 ( Initial Verification )
Memorandum of Guidance to The Electricity at Work Regulations (Regulation 4(2) :
Question 7 :
Appendix 6 of BS 7671 allows the use of three forms for the initial certification of a new installation or for an alteration or an addition to an existing installation. State the title given each of these certificates :
GN-3 ( Initial Verification )
1. Multiple signature Electrical Installation Cert :
2. Single signature Electrical Installation Cert :
3. Minor Electrical Installation Works Certificate :
Question 8 :
Under what circumstances would it be appropriate to issue a single signature Electrical Installation Certificate ?
GN-3 ( Certificates )
Where design, construction inspection and testing is the responsibility of one person :
Question 9 :
State the information that should be made available to the inspector:
GN-3 ( Required Information )
1. Maximum demand :
2. Number and type of live conductors at the origin :
3. Type of earthing arrangements :
4. Nominal voltage and supply frequency :
5. Prospective fault current ( PFC ) :
6. External Impedance Ze :
7. Type and rating of overcurrent device at the origin :
Question 9 ( cont,d ) :
The following information should also be made available :
GN-3 ( Required Information )
1 Type and composition of circuits, including points of utilisation, number and size of conductors and type of cable :
2. Methods of compliance for indirect shock protection :
3. Identification and location of devices used for protection, isolation and switching :
4. Circuits or equipment vulnerable to testing :
Question 10 :
Where should the proposed interval between periodic inspections should be noted :
GN-3 ( Frequency )
1. On the Electrical Installation Certificate :
2. On a notice fixed in a prominent position at or near the origin of an installation :
Question 11 :
State in the Correct Sequence the first FIVE tests that would need to be undertaken on an A1 ring circuit during an initial verification :
1. Continuity of protective conductors :
2. Continuity of ring final circuit conductors :
3. Insulation resistance :
4. Polarity :
5. Impedance Zs :
Question 12 :
State TWO disadvantages of using Method 2 in order to verify the continuity of c.p.c.’s :
GN-3 ( Test Method 2 )
1. Long wander lead :
2. Gives R :
does not provide R :

 

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Question 14 :
State the British Standard number for a transformer used to provide electrical separation :+
GN-3 ( Electrical Separation )
Transformer complies with BS 3535 , Note: Transformer double-wound type :
Question 15 :
List FOUR types of external influence that affect the safety/operation of an electrical installation :
GN-3 ( Electrical Separation )
1. Ambient temperature :
2. Heat :
3. Water :
4. Corrosion :
Question 16 :
Identify the TWO procedures required when verifying the continuity of a ferrous enclosure used as a c.p.c. for a circuit
GN-3 ( Test Method 2 )
1. Inspect the enclosure throughout its length :
2. Carry out low resistance ohmmeter test :
Question 17 :
State in the Correct Sequence the Test required to verify the continuity of a ring final circuit :
GN-3 ( Continuity of Ring Circuit )
1. Identify and measure the resistance of each ring (end to end) r
1 / r :
2 / rn :
2. Apply figure of 8 (cross connection) between phase and neutral conductors at distribution board and then measure resistance between phase/neutral at each socket outlet :
Question 17 : ( con,d )
GN-3 ( Continuity of Ring Circuit )
3. Apply figure of 8 (cross connection) between phase and cpc at origin and measure resistance between phase and cpc at each socket outlet :
Note: where dead Tests are made the supply must be isolated before any work commences:
Question 18 :
The following measurements were taken at the origin of an A :
1 ring circuit. r 1 = 0.4Ω :
2 = 0.67Ω R n = 0.4Ω :
Determine the measured value of resistance at each socket outlet when the ends of the circuit are cross-connected to form a figure 8 :
GN-3 ( Continuity of Ring Circuit )
1. r , 1 + R n = 0.4 + 0.4 = 0.8/4 = 0.2Ω ;
2. r , 1 + r 2 = 0.4 + 0.67 = 1.07/4 = 0.267Ω :
Question 19 :
Identify ONE other test that is automatically performed when undertaking a ring final circuit test :
GN-3 ( Continuity of Ring Final Circuit )
Polarity :
Question 20 :
State FOUR items of equipment/components that may need to be removed prior to carrying out a test for insulation resistance on a circuit :
GN-3 ( Insulation Résistance )
1. Pilot or indicator lamps :
2. Dimmer switches :
3. Touch switches :
4. Electronic r.c.d.’s etc :
Question 21 :
State the test voltage and minimum acceptable value of insulation resistance for the following circuits :
1. 400V 3 phase motor
2. 760V discharge lighting circuit
3. 45V FELV circuit
GN-3 ( table – 61 )
1. 500V d.c. 0.1 MΩ
2. 1000V d.c. 1.0 M
3. 500V d.c. 0.5 M
Question 22 :
State the Correct Sequence for undertaking an insulation resistance test on a filament lamp circuit containing two-way switching :
GN-3 ( Insulation Résistance Testing )
1. Supply must be isolated : ← ← ←
2. All lamps removed :
3. Insulation test between live conductor :
4. Insulation resistance test between live conductors and earth :
5. Two-way switches operated during test
Question 23 :
State the type of test that should be applied where protection against direct contact is by site-applied insulation :
GN-3 ( Site applied Insulation )
1. Test at 3750V a.c :.
2. Apply test voltage for 60 seconds during which time insulation failure or flashover should not occur :
3. Instrument used: Site applied insulation3. Instrument used: Site applied insulation :
Question 24 :
State the THREE specific requirements for verification of polarity with regard to accessories : 612.6 ,
1. All single-pole devices are connected in the phase conductor
2. The centre contact of Edison screw lamps are connected in the phase conductor
3. All socket outlets : wiring has been correctly connected to socket-outlets and similar accessories :
Question 25 :
Identify the test that should be applied to verify polarity after the supply is energised :
GN-3 ( Polarity )
Test to verify correct polarity of the incoming live supply (PES ). Test made at the origin using approved voltage indicator :

Question 26 :
Identify the THREE electrodes used when used with a proprietary earth resistance tester:
GN-3 ( Earth electrode resistance )
1. Main electrode :
2. Potential electrode ( auxiliary electrode ) :
3. Current electrode ( auxiliary electrode ) :
Note: This method can be use for electrodes used for transformers, lightning protection systems etc.:
Question 27 :
State the action to be taken regarding the earthing conductor before measuring the resistance of an earth electrode
GN-3 ( Earth electrode for RCD’s )
Normal 100Ω ← ← ←
Special locations 50Ω
By calculation 50V ÷ 0.5A = 100Ω
Dry 25V ÷ 0.5A = 50Ω
Special Loc,
Question 27 :
State the action to be taken regarding the earthing conductor before measuring the resistance of an earth electrode :
GN-3 ( Earth electrode resistance )
1. Disconnect earthing conductor at MET to avoid parallel earth paths :
2. Do NOT disconnect any protective conductors before isolating the supply :
Question 28 :
State the maximum recommended value of resistance for an earth electrode :
GN-3 ( Earth electrode for RCD’s )
Electrodes having resistances in excess of 200Ω :
will require further investigation.
Note: Electrode resistances obtained in excess of 200Ω :
may indicate unstable soil conditions :
Question 29 :
State the formula used to calculate Impedance
Zs, at the furthest point within a circuit
Zs = Ze + ( R1+R2 ) Where Ze is by measurement or enquiry
and ( R1+R2) by measurement
State the formula used to calculate Impedance Zs, at the furthest point within a circuit :
GN-3 ( Earth Fault Loop )
( Zs = Ze + ( R1+R2 )
Where Ze is by measurement or enquiry and ( R2 ) by measurement :
Question 30 :
State TWO reasons why it is necessary to measure external earth fault loop impedance at the origin of an installation :
GN-3 ( Determining Ze )
1. To verify an earth connection :
2. The value is equal to or less than the value determined by the designer :
Question 31 :
State TWO methods by which the impedance of a circuit may be obtained without operating any r.c.d.’s protecting the circuit :
GN-3 ( Residual current devices )
1. Soft test ( 15mA )
2. By calculation Zs = Ze + ( R1 + R2 )
Question 32 :
Determine the prospective fault current given following information ( Three phase supply 1. Impedance between P and N = 0.25Ω :
2. Impedance between P and E = 0.5Ω :
( General knowledge )
1. 230V ( Uo ) ÷ 0.25 = 920A = 0.92kA
2. 230V ÷ 0.5 = 460A = 0.46kA
3. For three phase multiply P to N value by 2 ( 0.92 x 2 = 1.84kA )
Question 33 :
State the reason for undertaking a prospective fault current measurement at the distribution board at the origin of the installation :
( Prospective fault current )
1. To ensure the adequate breaking capacity of the overcurrent devices :
2. To ensure the adequate breaking capacity of the main switch :
Question 34 :
State the three required electrical Tests required to be undertaken on a 30mA r.c.d. complying with BS 4293
( Functional testing ) Old BS- Only – 200mS
1. 1/2 test - 15mA for 2 seconds - device does not trip ;
2. 1 x test - device tested at full rated current trips within 200mS ( 0.2 seconds ) :
3. 5 x test when tested at 150mS device operates within 40mS :
Question 35 :
State FIVE items of electrical equipment that would require functional testing
( Functional checks )
1. R.c.d.’s :
2. Circuit breakers :
3. Isolators :
4. Interlocks :
5. Switches :

 

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Basic applications MCBs : Apprentice ,
The essential distinction between Type B, C or D devices is based on their ability to handle surge currents without tripping. These are, typically, inrush currents associated with fluorescent and other forms of discharge lighting, induction motors, battery charging equipment etc. BS 7671 specifically refers to Types B and C, and the choice will normally be between these two types :
• Type B devices are generally suitable for domestic applications. They may also be used in light commercial applications where switching surges are low or non-existent.
• Type C devices are the normal choice for commercial and industrial applications where fluorescent lighting, motors etc. are in use.
• Type D devices have more limited applications, normally in industrial use where high inrush currents may be expected. Examples include large battery charging systems, winding motors, transformers, X-ray machines and some types of discharge lighting :
The classification of Types B, C or D is based on the fault current rating at which magnetic operation occurs to provide short time protection ( typically less than 100ms ) against short-circuits. It is important that equipment having high inrush currents should not cause the circuit-breaker to trip unnecessarily, and yet the device should trip in the event of a short-circuit current that could damage the circuit cables :
The tripping characteristics
• Type B devices are designed to trip at fault currents of 3-5 times rated current (In). For example a 10A device will trip at 30-50A.
• Type C devices are designed to trip at 5-10 times In (50-100A for a 10A device ).
• Type D devices are designed to trip at 10-20 times In (100-200A for a 10A device ).
Normal cable ratings relate to continuous service under specified installation conditions. Cables will, of course, carry higher currents for a short time without suffering permanent damage. Type B and C circuit breakers can generally be selected to achieve tripping times that will protect the circuit conductors against normal surge currents in accordance with BS 7671. This is more difficult to achieve with Type D devices, which may require a lower earth loop impedance (Zs) to achieve the operating times required by Regulation 411.4.7 / 411.3.2.3 -
Overcoming unwanted tripping:
Sometimes failure of tungsten filament lamps can trip Type B circuit-breakers in domestic and retail environments. This is caused by high arcing currents occurring at the time of failure and is generally associated with inferior quality lamps. If possible the user should be encouraged to use better quality lamps. If the problem persists then one of the measures listed below should be considered :
A Type C device may be substituted for a Type B device where unwanted tripping persists, especially in commercial applications. Alternatively it may be possible to use a higher rated Type B MCB, say 10A rather than 6A. Whichever solution is adopted, the installation must be in accordance with BS 7671 :
A change from Type C to Type D devices should only be taken after careful consideration of the installation conditions, in particular the operating times required by Regulation 411.4.5 :
Other considerations:
Combined overcurrent and residual current circuit breakers (RCBOs) are available as integrated units or, in one case, as a modular device with a field-fittable clip-on RCD 'pod'. It should be borne in mind that if an RCBO trips it is not always clear whether tripping has been caused by an overcurrent or a residual current. Type B devices should only be used in domestic situations where high inrush currents are unlikely and Type C devices should be used in all other situations.

Short Circuit Capacity: Basic Calculations and Transformer Sizing : ( kVA ) ,

Short circuit capacity calculation is used for many applications: sizing of transformers, selecting the interrupting capacity ratings of circuit breakers and fuses, determining if a line reactor is required for use with a variable frequency drive, etc.
The purpose of the presentation is to gain a basic understanding of short circuit capacity. The application example utilizes transformer sizing for motor loads ,
Conductor impedances and their associated voltage drop are ignored not only to present a simplified illustration, but also to provide a method of approximation by which a plant engineer, electrician or production manager will be able to either evaluate a new application
or review an existing application problem and resolve the matter quickly ,

The following calculations will determine the extra kVA capacity required for a three phase transformer that is used to feed a single three phase motor that is started with full voltage applied to its terminals, or, "across-the-line."

Two transformers will be discussed, the first having an unlimited short circuit kVA capacity available at its primary terminals, and the second having a much lower input short circuit capacity available ,

kVA of a single phase transformer = V x A
kVA of a three phase transformer = V x A x 1.732, where 1.732 = the square root of 3.
The square root of 3 is introduced for the reason that, in a three phase system,
the phases are 120 degrees apart and, therefore, can not be added arithmetically They will add algebraically,

Transformer Connected To Utility Power Line ,

The first transformer is rated 1000 kVA, 480 secondary volts, 5.75% impedance. Rated full load amp output of the transformer is ,

1000 kVA / (480 x 1.732) = 1203 amps :

The 5.75% impedance rating indicates that 1203 amps will flow in the secondary if the secondary is short circuited line to line and the primary voltage is raised from zero volts to a point at which 5.75% of 480 volts, or, 27.6 volts, appears at the secondary terminals. Therefore, the impedance (Z) of the transformer secondary may now be calculated ,

Z = V / I = 27.6 volts / 1203 amps = .02294 ohms :

The transformer is connected directly to the utility power lines which we will assume are capable of supplying the transformer with an unlimited short circuit kVA capacity. The utility company will always determine and advise of the short

With unlimited short circuit kVA available from the utility, the short circuit amperage capacity which the transformer can deliver from its secondary is

480 volts / .02294 = 20,924 amps :

An alternative method of calculating short circuit capacity for the above transformer is:

1203 amps x 100 / 5.75% = 1203 / .0575 = 20,922 amps :

transformer and the value of the short circuit capacity The short circuit capacity is given as 20,900 amps.

Now we are ready to apply a motor to the terminals of the transformer secondary. We must determine the voltage drop which will be
We must determine the voltage drop which will be caused by the motor inrush on start. If the voltage remains within the rated voltage of the motor, then no oversizing ,

of the transformer is required. Motors rated for 460 volts are for use with distribution systems that are rated at
480 volts. The rating system allows a twenty volt drop in the distribution system which may occur along the feeder cables which connect the power transformer to the load.
The NEMA specification for a standard motor is that it requires the motor to be capable of operating at plus or minus 10% of nameplate voltage. Therefore, the voltage drop on inrush should not be allowed to drop below 460 volts less 10%, or, 414 volts ,

The transformer will be asked to supply power to a motor which has a full load amp rating of 1203 amps, which will fully load the transformer. Therefore, we will rate the motor at 460 V x 1203 A x 1.732, or, 958.5 kVA. We will assume that our motor will have an inrush of 600% of its full load rating which will cause an inrush of The transformer will be asked to supply power to a motor which has a full load amp
rating of 1203 amps, which will fully load the transformer. Therefore, we will rate the motor at 460 V x 1203 A x 1.732, or, 958.5 kVA. We will assume that our motor will have an inrush of 600% of its full load rating which will cause an inrush of ,

460 V x 1203 A x 600% x 1.732 = 5751 kVA :

The voltage drop at the transformer terminals will be proportional to the motor load. The voltage drop will be expressed as a percentage of the inrush motor load compared to the maximum capability of the transformer. [2] The transformer has a maximum kVA capacity at its short circuit capability, which is ,

480 V x 20,924 A x 1.732 = 17,395 kVA The voltage drop on motor inrush will be
5751 kVA / 17,395 kVA = .331, or, 33.1% :

The transformer output voltage will drop to 480 x .669, or, 321 volts. Thus, we can see that the transformer is much too small to use a motor that has a full load rating equal to the full load capacity of the transformer

The transformer must be sized so that its short circuit capabilty is equal to or greater than 5751 kVA times 10, or, 57,510 kVA in order to have a voltage drop of 10% or less. Therefore, the short circuit amperage capacity of the transformer to be used must be a minimum of ,



The transformer must be sized so that its short circuit capabilty is equal to or greater than 5751 kVA times 10, or, 57,510 kVA in order to have a voltage drop of 10% or less. Therefore, the short circuit amperage capacity of the transformer to be used must be a minimum of ,

57,510 kVA / (480 V x 1.732) = 69176 amps

 

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A typical 2500 kVA, 5.75% impedance transformer will have a short circuit capacity of 52,300 amps. The next highest standard size transformer at 3750 kVA will have a 6.5% impedance and would have a short circuit output capability of 69,395 amps which will be sufficient. ,


In the particular application discussed, the ratio of the selected standard size transformer kVA to motor kVA is 3750 kVA / 958.5 kVA = 3.91. Thus the transformer rating is 391% larger, or, nearly four times, the rating of the motor. Note the non-linear effect of the impedance rating of the transformers on their short circuit capacities ,

Transformer Connected To An Upstream Transformer ,

The second transformer we will examine will have a finite short circuit capacity available at its primary rather than an unlimited capacity. We will assume that a facility derives its power from the same 1000 kVA transformer mentioned above and that the
second transformer is connected directly to the terminals of the 1000 kVA transformer.
Thus, feeder cables between the two transformers are eliminated and the impedance of cables are not taken into account. However, the smaller the motor leads, the less will be both the short circuit capacity and the voltage delivered to the motor terminals ,

The second transformer, which will have a 480 volt primary and a 480 volt secondary, will be used to power a 20 HP, 3 phase, 460 volt motor which will be started at full voltage. The motor will be the only load on the transformer. The minimum transformer kVA ratings are for use with multiple motors on a single transformer. The 21.6 kVA is calculated as follows:

480 volts x 26 nominal amps x 1.732 = 21.6 kVA

The transformer manufacturers will give a 20 HP motor a nominal full load amp rating of 27 amps, thus allowing no extra capacity:
460 volts x 27 nominal amps x 1.732 = 21.5 kVA ,
One motor manufacturer has rated a 20 HP motor at 26 Full Load Amps, 460 VAC, 205 Locked Rotor Amps, 81% Power Factor. The motor will present a load of , 460 volts x 26 amps x 1.732 = 20.7 kVA ,
The starting motor kVA load with inrush current will be : 460 V x 205 A x 1.732 = 163.3 kVA ,

We will consider using a 30 kVA general purpose transformer to supply the 20 HP motor. The transformer will have a nominal impedance of 2.7% and an ouptut of 36.1 amps at 480 volts. The short circuit current capacity that can be delivered to the 21.6 kVA
transformer by the upstream 1000 kVA transformer is 20,924 amps, or, 17,395 kVA.
The short circuit amperage capacity of a transformer with a limited system short circuit capacity available at its primary is :

transformer full load amps / (transformer impedance + upstream system impedance as seen by the transformer)
Where : upstream system impedance as seen by the transformer = transformer kVA / available primary short circuit capacity kVA
Therefore, ( 36.1 amps / [2.7% + (30 kVA / 17,395 kVA ) = 36.1 / (2.7% + .0017%) = 36.1 / .0287 = 1258 short circuit amps )
The transformer output voltage drop upon motor inrush will be :
motor inrush kVA / short circuit kVA =163.3 kVA / (480 V x 1258 A x 1.732 ) = 163.3 kVA / 1046 kVA =156 = 15.6 % )
A 30 kVA transformer rating is too small as the motor voltage drop will exceed 10% ,

A 45 kVA transformer with a 2.4% impedance and an output of 54.1 amps at 480 volts would have a short circuit capacity of 2034 amps. The voltage drop upon motor inrush would be 9.66% ,

For a single motor and transformer combination, one transformer manufacturer recommends that the motor full load running current not exceed 65% of the transformer full load amp rating. [3] Thus, for our 26 amp motor the transformer rating should be a minimum of 40 amps, or, 33.3 kVA.

The transformer output voltage drop upon motor inrush will be : motor inrush kVA / short circuit kVA =
163.3 kVA / (480 V x 1258 A x 1.732) = 163.3 kVA / 1046 kVA = 156 = 15.6 %
A 30 kVA transformer rating is too small as the motor voltage drop will exceed 10% ,
A 45 kVA transformer with a 2.4% impedance and an output of 54.1 amps at 480 volts would have a short circuit capacity of 2034 amps. The voltage drop upon motor inrush ,
A 45 kVA transformer with a 2.4% impedance and an output of 54.1 amps at 480 volts would have a short circuit capacity of 2034 amps. The voltage drop upon motor inrush would be 9.66%. , A 45 kVA transformer with a 2.4% impedance and an output of 54.1 amps at 480 volts
would have a short circuit capacity of 2034 amps. The voltage drop upon motor inrush
would be 9.66% ,
For a single motor and transformer combination, one transformer manufacturer recommends that the motor full load running current not exceed 65% of the transformer full load amp rating. [3] Thus, for our 26 amp motor the transformer rating should be a minimum of 40 amps, or, 33.3 kVA. ,
Multiple Motors On A Single Transformer ,
The minimum transformer kVA is given by transformer manufacturers so that a transformer may be sized properly for multiple motors. If there are five motors on one transformer, add the minimum kVA ratings and then add transformer capacity as necessary to accommodate the inrush current of the largest motor , The transformer thusly selected will be capable of running and starting all five motors provided that only one motor is started at any one time. Additional capacity will be required for motors starting simultaneously , Also, if any motor is started more than once per hour, add 20% to that motor's minimum kVA rating to compensate for heat losses within the transformer.
Motor Contribution to Short Circuit Capacity ,
When a fault condition occurs, power system voltage will drop dramatically. All motors that are running at that time will not be able to sustain their running speed. As those motors slow in speed, the stored energy within their fields will be discharged into the power line. The nominal discharge of a motor will contribute to the fault a current equal to up to four times its full load current.
With our 1000 kVA, 1203 amp transformer example given above, we will assume that all
1203 amps of load are from motors. The actual short circuit current will equal 20,924 amps
plus 400% of 1203 amps for a total of 25,736 short circuit amps.

When sizing the transformer for motor loads, the fault current contribution from the motors will not be a consideration for sizing. However, the motor contribution must motors will not be a consideration for sizing. However, the motor contribution must be
considered when sizing all branch circuit fuses and circuit breakers. The interrupting capacity ratings of those devices must equal or exceed the total short circuit capacity ratings of those devices must equal or exceed the total short circuit capacity available at the point of application..

Motor contribution to short circuit capacity must be included when adding a variable frequency drive to the system ,

Do you know what an impedance test is ? Max Earth fault loop impedance is ( Zs=Ze+R1+R2 )
You are testing your ( R1 + R2 ) if there is no continuity of your CPC you will have an open circuit.


Easily check your Earth Loop Impedance compliance!
: Cable size and capacity
: Voltage drop in volt and percent
: Maximum length of run
: Fuse or Circuit Breaker size
: Working Temperature
: Fault level
: Minimum trip current needed to comply with Earth loop Impedance test
: Actual let through current
: Maximum impedance values (Ze) and the actual impedance values (in ohms)
: Total impedance values(Zs) for the complete installation (in ohms)

“ Inspection & Testing before into Service “ 2392-10 Electrical Installations should be Inspected and Tested as Necessary and Appropriate During and the End of Installation , Before they are taken into Service , to Verify that they are Safe to Use ,Maintain and Alter and Comply with Part P of the
Building Regulations and with any Other Relevant Parts of the Building Regulations

 

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Machinery and equipment must be maintained in efficient working order, so it is in good repair and kept safe -
This is required by Regulation 5, of the Provision and Use of Work Equipment Regulations 1998.

What is Three Phase Power ?

Three phase power is a method of electric power transmission using three wires.
Three phase power systems may have a neutral wire that allows the system to use a higher voltage while still allowing lower voltage single phase appliances. In high voltage distributions, it is not common to have a neutral wire, as the loads can simply be connected between phases :
Three phase power is a very efficient form of electrical power distribution. All three wires carry the same current and have a constantly balanced power load. Three phase power does not generally power domestic houses, and when it does, a main distribution board splits the load. Most domestic loads use single phase power.
Conductors used in the three phase power system are colour-coded. Most countries have their own colour codes. The colour codes of the wires vary greatly. There may be a standard for each installation, or there may be no standard at all :
Three phase power flow begins in a power station. An electrical power generator converts mechanical power into alternating electric currents. After numerous conversions in the distribution and transmission network, the power is transformed into the standard mains voltage. At this point, the power may have already been split into single phases or into three phases. With three phase power, the output of the transformer is usually star connected with the mains voltage, 230 volts in Europe and 120 volts in North America :
Electric motors are the most common use for three phase power. A three phase induction motor combines high efficiency, a simple design and a high starting torque. Three phase electric motors are commonly used in industry for fans, blowers, pumps, compressors and many other kinds of motor driven equipment. A three phase power motor is less costly than a single phase motor of the same voltage and rating :
Other systems that use three phase power include air conditioning equipment, electric boilers and large rectifier systems. The main reasons for using the three phase power system are efficiency and economy. While most three phase motors are quite big, there are examples of very small motors, such as computer fans. An inverter circuit inside the fan converts DC to a three phase AC current. This serves to decrease noise, as the torque from a three phase motor is very smooth, and it also increases reliability :

What are Electrical Transformers ?
The name itself offers a simple definition. Electrical transformers are used to transform electrical energy. How electrical transformers do so is by altering voltage, generally from high to low. Voltage is simply the measurement of electrons, how many or how strong, in the flow. Electricity can then be transported more easily and efficiently over long distances :
While power line electrical transformers are commonly recognized, there are other various types and sizes as well. They range from huge, multi-ton units like those at power plants, to intermediate, such as the type used on electric poles, and others can be quite small. Those used in equipment or appliances in your home or place of businesses are smaller electrical transformers and there are also tiny ones used in items like microphones and other electronics :
Probably the most common and perhaps the most necessary use of various electrical transformers is the transportation of electricity from power plants to homes and businesses. Because power often has to travel long distances, it is transformed first into a more manageable state. It is then transformed again and again, or “stepped down,” repeatedly as it gets closer to its destination :
When the power leaves the plant, it is usually of high voltage. When it reaches the substation the voltage is lowered. When it reaches a smaller transformer, the type found on top of electric poles, it is stepped down again. It is a continuous process, which repeats until the power is at a usable level :
You have likely seen the type of electrical transformers that sit on top of electric poles. These, like most electrical transformers, contain coils or “windings” that are wrapped around a core. The power travels through the coils. The more coils, the higher the voltage. On the other hand, fewer coils mean lower voltage :
Electrical transformers have changed industry. Electric power distribution is now more efficient than ever. Transformers have made it possible to transfer power near and far, in a timely, efficient, and more economical manner. Since many people do not wish to live in close proximity to a power plant, there is the added benefit of making it possible for homes and businesses that are quite a distance from power plants to obtain dependable, affordable electricity. Much of the electricity used today will have passed through many electrical transformers before it reaches users. Power distribution :

What are AC Motors ?
There are many different types and sizes of electric motors. Electric motors can be divided into two types: Alternating Current (AC) motors and Direct Current (DC) motors. An AC electric motor requires an alternating current, while a DC motor requires direct current.
AC motors are further subdivided into single phase and three phase motors. Single phase AC electrical supply is what is typically supplied in a home. Three phase electrical power is commonly only available in a factory setting. The most common single phase AC motor is known as a universal motor. This is because this motor can also run with DC current.
This type of motor is very inefficient but can be very inexpensively made. It is also used almost exclusively for small factional horse power AC motors. The other advantage this AC motor has is that the rotational speed of the motor can be easy changed. This type of AC motor is commonly found in mixers, hand drills, and any other application requiring variable speed and low cost and small size.
For larger single phase AC motors, a electrical component known as a capacitor is used to create a second phase from the single phase AC current. This type of AC motor is known as an induction motor and there are two basic types; a capacitor start motor and a capacitor run motor. The capacitor is used to create a second phase from the single phase power source and it is the interaction between these two phases that causes the motor to turn.
This introduction of a second phase eliminates the need for the brushes used in a universal AC motor. This greatly increases the both the efficiency of the AC motor and increases the life expectancy of the AC motor as brushes are a
major source of wear and failure. This type of motor is a fixed speed motor. It is commonly used as the drive for refrigerator compressors, shop air-compressors, and as a general utility type AC motor.
AC motors are usually sized in horsepower. The most common sizes are what are called fractional horsepower motors, i.e. ½ horse power or ¼ horsepower. Larger motors are typically only found in factories, where they can range in size to thousands of horsepower.
AC motors also come with various speed ratings. Speed is usually specified as rotations per minute (RPM) at no load condition. As the motor is loaded down, the speed will slow down. When the AC motor is running at its rated power draw, the speed of the shaft measured in RPM is the full load speed. If the electric motor is loaded too heavily, the motor shaft will stop. This is known as the stall speed and should be avoided. All of these speeds are typically listed on the specification sheet for an AC motor.
Finally, before you order an AC motor, you should determine the mounting type you require, the start up torque, the type of enclosure required, and the type of shaft output required :

 

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What is the Difference between a Generator and Inverter ?
The difference between an generator and an inverter may at first seem simple. However, as more research is done, the issue can quickly become confusing, especially to those who are not technically inclined and familiar with types of electricity. For example, while the definitions of an inverter and generator are clearly distinct, there are such things as inverter generators. However, though the terms may seem contradictory, they can be explained fairly easily.
Before discussing the difference between an inverter and generator, it is first necessary to understand a little about electrical currents. Electricity is divided into two types of currents, alternating current (AC) and direct current (DC). AC, a more common current for home use, works by allowing electrons to flow in two different directions. In DC currents, electrons flow only one way.
An inverter takes existing power that comes in the form of DC current and converts it to AC current. This is a popular option for those wanting to run home electronics in automobiles. Such cars often produce on DC current, which is not compatible with most electronics meant to run off standard outlets. Therefore, an inverter becomes necessary.
A generator, on the other hand, is a machine that converts mechanical energy into energy in an electrical form. In most cases, electric generators are responsible for the energy a home receives. Large-scale electrical generators may be powered by coal, natural gas or nuclear energy. A portable generator commonly uses gasoline, which is burned to create electrical energy. Generators usually produce AC electricity.
Simply stated, the difference between the two is that an inverter is only effective if there is already a source of electrical energy. It cannot generate its own. It can simply convert electrical energy that is already there. On the other hand, a traditional generator cannot make AC current into DC current.
On the other hand, there are things known as inverter generators. These are like traditional generators in that they convert some other form of energy into electrical energy. However, they produce AC power, which is then converted to DC power before being converted back to AC. The reason for this conversion is that the power gained during the process. It allows the generator to be more fuel efficient, as well as operate more quietly than standard generators.
Some people also confuse an inverter with a power converter, even using the terms interchangeably. However, a converter is used to change voltage from one level to another. For example, in Europe, a converter may be used to convert the voltage from 220 to 120, for electrical components meant to run on a lower voltage,

What is IPS ?
IPS, or integrated power systems, is simply a method of ensuring that the power supply needed to keep a place of business functional in the event of a problem with the primary source of energy. With so many of our home and work environments dependent on a steady supply of power, it is no wonder that the concept of IPS has gone from being a good idea to an essential. Here is some background on the concept of IPS and how many companies choose to implement their backup power supply procedures these days :
IPS plans and procedures are nothing new. As far back as the 1940’s, manufacturing facilities relied on backup power stations that could be run with gas generators in the event of a massive power failure. Hospitals also have operated with a full-fledged disaster recovery program that would ensure power to all vital functions, such as oxygen for the patients and enough power to keep operating rooms going in a crisis :
What is different today is that IPS strategies have become more sophisticated as technology has improved and demand for more reliable IPS options has become necessary. Where once a gas generator would be needed to power a small power station, many organizations can now relay on compact battery backups as part of the IPS escalation procedures :
In telephone, everything from switch stations to bridging centres will utilize state of the art battery backup that can last for in excess of twelve hours before losing power. Many IPS plans will still incorporate generator backup as well, usually as a third alternative if it appears that battery backup is about to fail. More frequently, businesses are beginning to incorporate solar panels and battery storage as part of the overall IPS directives for the organization :
The loss of valuable data as a result of a complete shutdown in the face of a power outage could be devastating to any business. Preparing a workable IPS plan, including an escalation procedure for implementing the backup power sources, ensures that even in the face of a short-term problem with a node on the national power grid, life will go on as usual :

What is a DC Motor ?
A direct current (DC) motor is a fairly simple electric motor that uses electricity and a magnetic field to produce torque, which turns the motor. At its most simple, a DC motor requires two magnets of opposite polarity and an electric coil, which acts as an Electromagnets. The repellent and attractive electromagnetic forces of the magnets provide the torque that causes the DC motor to turn.
If you've ever played with magnets, you know that they are polarized, with a positive and a negative side. The attraction between opposite poles and the repulsion of similar poles can easily be felt, even with relatively weak magnets. A DC motor uses these properties to convert electricity into motion. As the magnets within the DC motor attract and repel one another, the motor turns.
A DC motor requires at least one electromagnet. This electromagnet switches the current flow as the motor turns, changing its polarity to keep the motor running. The other magnet or magnets can either be permanent magnets or other Electromagnets. Often, the electromagnet is located in the centre of the motor and turns within the permanent magnets, but this arrangement is not necessary.
To imagine a simple DC motor, think of a wheel divided into two halves between two magnets. The wheel of the DC motor in this example is the electromagnet. The two outer magnets are permanent, one positive and one negative. For this example, let us assume that the left magnet is negatively charged and the right magnet is positively charged.
Electrical current is supplied to the coils of wire on the wheel within the DC motor. This electrical current causes a magnetic force. To make the DC motor turn, the wheel must have be negatively charged on the side with the negative permanent magnet and positively charged on the side with the permanent positive magnet. Because like charges repel and opposite charges attract, the wheel will turn so that its negative side rolls around to the right, where the positive permanent magnet is, and the wheel's positive side will roll to the left, where the negative permanent magnet is. The magnetic force causes the wheel to turn, and this motion can be used to do work.
When the sides of the wheel reach the place of strongest attraction, the electric current is switched, making the wheel change polarity. The side that was positive becomes negative, and the side that was negative becomes positive. The magnetic forces are out of alignment again, and the wheel keeps rotating. As the DC motor spins, it continually changes the flow of electricity to the inner wheel, so the magnetic forces continue to cause the wheel to rotate.
DC motors are used for a variety of purposes, including electric razors, electric car windows, and remote control cars. The simple design and reliability of a DC motor makes it a good choice for many different uses, as well as a fascinating way to study the effects of magnetic fields. Electromagnets

 

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What is MIG Welding ? you’ll see a lot in you careers !! tripping ,
MIG (Metal Inert Gas) welding, also sometimes called GMAW (gas metal arc welding), is a welding process that was originally developed back in the 1940's for welding aluminium and other non-ferrous metals. MIG welding is an automatic or semi automatic process in which a wire connected to a source of direct current acts as an electrodes joins two pieces of metal, as it is continuously passed through a welding gun. A flow of an inert gas (originally Argon ) is also passed through the welding gun at the same time as the wire electrode. This inert gas acts as a shield, keeping air borne contaminants away from the weld zone.
The primary advantage of MIG welding is that it allows metal to be welded much quicker than traditional welding "stick welding" techniques. This makes it ideal for welding softer metals such as aluminum. When MIG welding was first developed, the cost of the inert gas (i.e., argon) made the process too expensive for welding steel. However, over the years, the MIG welding process has evolved and semi inert gases such as carbon dioxide can now be used to provide the shielding function which makes MIG welding cost effective for welding steel.
Besides providing the capability to weld non-ferrous metals, MIG welding has other advantages:
• It produces long continuous welds much faster than tradition welding methods.
• Since the shielding gas protects the welding arc, MIG welding produces a clean weld with very little splatter.
• The versatility of MIG welding means it can be used with a wide variety of metals and alloys
The primary disadvantages of MIG welding are:
• The welding equipment is quite complex (MIG welding requires a source of direct current, a constant source and flow of gas as well as the continuously moving wire electrode). Plus, electrodes are available in a wide range of sizes and made from a number of metal types to match the welding application.
• The actual welding technique used for MIG welding is different from traditional welding practices, so there is learning curve associated with MIG welding even for experienced welders. For example, MIG welders need to push the welding puddle away from them and along the seam.
• The necessity for the inert gas shield means that MIG welding cannot be used in an open area where the wind would blow away the gas shield.
Since it's development in the middle of last century, MIG welding has become commonplace in many manufacturing operations. For example MIG welding is commonly used in the automobile industry because of its ability to produce clean welds, and the fact that it welds metals quickly.

ELECTRICAL INSTALLATION CERTIFICATES NOTES FOR FORMS 1 AND 2 : 17th Edition ,

1. The Electrical Installation Certificate is to be used only for the initial certification of a new installation or for an addition or alteration to an existing installation where new circuits have been introduced.
It is not to be used for a Periodic Inspection, for which a Periodic Inspection Report form should be used. For an addition or alteration which does not extend to the introduction of new circuits, a Minor Electrical Installation Works Certificate may be used.
The "original" Certificate is to be given to the person ordering the work (Regulation 632.1). A duplicate should be retained by the contractor.
(2) This Certificate is only valid if accompanied by the Schedule of Inspections and the Schedule(s) of Test Results.
(3) The signatures appended are those of the persons authorized by the companies executing the work of design, construction, inspection and testing respectively. A signatory authorized to certify more than one category of work should sign in each of the appropriate places.
(4) The time interval recommended before the first periodic inspection must be inserted (see IEE Guidance Note 3 for guidance).
(5) The page numbers for each of the Schedules of Test Results should be indicated, together with the total number of sheets involved.
(6) The maximum prospective fault current recorded should be the greater of either the short-circuit current or the earth fault current.
(7) The proposed date for the next inspection should take into consideration the frequency and quality of maintenance that the installation can reasonably be expected to receive during its intended life, and the period should be agreed between the designer, installer and other relevant parties :

TESTING :
NOTES ON SCHEDULE OF TEST RESULTS

*1 Type of supply is ascertained from the distributor or by inspection.
*2 Ze at origin. When the maximum value declared by the distributor is used, the effectiveness of the earth must be confirmed by a test. If measured the main bonding will need to be disconnected for the duration of the test.
*3 Prospective fault current (PFC). The value recorded is the greater of either the short-circuit current or the earth fault current. Preferably determined by enquiry of the distributor.
*4 Short-circuit capacity of the device is noted, see Table 7.2A of the On-Site Guide or Table 2.4 of GN3
The following tests, where relevant, shall be carried out in the following sequence:
Continuity of protective conductors, including main and supplementary bonding Every protective conductor, including main and supplementary bonding conductors, should be tested to verify that it is continuous and correctly connected.
*6 Continuity Where Test Method 1 is used, enter the measured resistance of the line conductor plus the circuit protective conductor (R1+ R2). See 10.3.1 of the On-Site Guide or 2.7.5 of GN3. During the continuity testing (Test Method 1) the following polarity checks are to be carried out: (a) every fuse and single-pole control and protective device is connected in the line conductor only (b) centre-contact bayonet and Edison screw lampholders have outer contact connected to the neutral conductor (c) wiring is correctly connected to socket-outlets and similar accessories. Compliance is to be indicated by a tick in polarity column 11.
(R1 + R2) need not be recorded if R2 is recorded in column 7.
*7 Where Test Method 2 is used, the maximum value of R2 is recorded in column 7. See 10.3.1 of the On-Site Guide or 2.7.5 of GN3.
*8 Continuity of ring final circuit conductors A test shall be made to verify the continuity of each conductor including the protective conductor of every ring final circuit. See 10.3.2 of the On-Site Guide or 2.7.6 of GN3.
*9, *10 Insulation Resistance All voltage sensitive devices to be disconnected or test between live conductors (line and neutral) connected together and earth. The insulation resistance between live conductors is to be inserted in column 9. The minimum insulation resistance values are given in Table 10.1 of the On-Site Guide or Table 2.2 of GN3. See 10.3.3(iv) of the On-Site Guide or 2.7.7 of GN3.
All the preceding tests should be carried out before the installation is energised.
*11 Polarity A satisfactory polarity test may be indicated by a tick in column 11. Only in a Schedule of Test Results associated with a Periodic Inspection Report is it acceptable to record incorrect polarity.
*12 Earth fault loop impedance Zs This may be determined either by direct measurement at the furthest point of a live circuit or by adding (R1 + R2) of column 6 to Ze. Ze is determined by measurement at the origin of the installation or preferably the value declared by the supply company used. Zs = Ze + (R1 + R2). Zs should be less than the values given in Appendix 2 of the On-Site Guide or Appx 2 of GN3.
*13 Functional testing The operation of RCDs (including RCBOs) shall be tested by simulating a fault condition, independent of any test facility in the device. Record operating time in column 13. Effectiveness of the test button must be confirmed. See Section 11 of the On-Site Guide or 2.7.15 and 2.7.18 of GN3.
*14 All switchgear and controlgear assemblies, drives, control and interlocks, etc must be operated to ensure that they are properly mounted, adjusted, and installed. Satisfactory operation is indicated by a tick in column 14.
Earth electrode resistance The earth electrode resistance of TT installations must be measured, and normally an RCD is required. For reliability in service the resistance of any earth electrode should be below 200 Ω. Record the value on Form 1, 2 or 6, as appropriate. See 10.3.5 of the On-Site Guide or 2.7.12 of GN3.

 

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GUIDANCE FOR RECIPIENTS
This safety Certificate has been issued to confirm that the electrical installation work to which it relates has been designed, constructed, inspected and tested in accordance with British Standard 7671 (the IEE Wiring Regulations).
You should have received an "original" Certificate and the contractor should have retained a duplicate. If you were the person ordering the work, but not the owner of the installation, you should pass this Certificate, or a full copy of it including the schedules, immediately to the owner.
The Certificate should be retained in a safe place and be shown to any person inspecting or undertaking further work on the electrical installation in the future. If you later vacate the property, this Certificate will demonstrate to the new owner that the electrical installation complied with the requirements of British Standard 7671 at the time the Certificate was issued. The Construction (Design and Management) Regulations require that for a project covered by those Regulations, a copy of this Certificate, together with schedules is included in the project health and safety documentation.
For safety reasons, the electrical installation will need to be inspected at appropriate intervals by a competent person. The maximum time interval recommended before the next inspection is stated on Page 1 under "Next Inspection".
This Certificate is intended to be issued only for a new electrical installation or for new work associated with an addition or alteration or to an existing installation. It should not have been issued for the inspection of an existing electrical installation. A "Periodic Inspection Report" should be issued for such an inspection.
The Certificate is only valid if a Schedule of Inspections and Schedule of Test Results are appended : Page 2 of (note 5) ,

ELECTRICAL INSTALLATION CERTIFICATE GUIDANCE FOR RECIPIENTS (to be appended to the Certificate)
This safety Certificate has been issued to confirm that the electrical installation work to which it relates has been designed, constructed, inspected and tested in accordance with British Standard 7671 (the IEE Wiring Regulations).
You should have received an "original" Certificate and the contractor should have retained a duplicate. If you were the person ordering the work, but not the owner of the installation, you should pass this Certificate, or a full copy of it including the schedules, immediately to the owner.
The Certificate should be retained in a safe place and be shown to any person inspecting or undertaking further work on the electrical installation in the future. If you later vacate the property, this Certificate will demonstrate to the new owner that the electrical installation complied with the requirements of British Standard 7671 at the time the Certificate was issued. The Construction (Design and Management) Regulations require that for a project covered by those Regulations, a copy of this Certificate, together with schedules is included in the project health and safety documentation.
For safety reasons, the electrical installation will need to be inspected at appropriate intervals by a competent person. The maximum time interval recommended before the next inspection is stated on Page 1 under "Next Inspection".
This Certificate is intended to be issued only for a new electrical installation or for new work associated with an addition or alteration to an existing installation. It should not have been issued for the inspection of an existing electrical installation. A "Periodic Inspection Report" should be issued for such a periodic inspection.
The Certificate is only valid if a Schedule of Inspections and Schedule of Test Results are appended :

ELECTRICAL INSTALLATION CERTIFICATE GUIDANCE FOR RECIPIENTS (to be appended to the Certificate)
This safety Certificate has been issued to confirm that the electrical installation work to which it relates has been designed, constructed, inspected and tested in accordance with British Standard 7671 (the IEE Wiring Regulations).
You should have received an "original" Certificate and the contractor should have retained a duplicate. If you were the person ordering the work, but not the owner of the installation, you should pass this Certificate, or a full copy of it including the schedules, immediately to the owner.
The Certificate should be retained in a safe place and be shown to any person inspecting or undertaking further work on the electrical installation in the future. If you later vacate the property, this Certificate will demonstrate to the new owner that the electrical installation complied with the requirements of British Standard 7671 at the time the Certificate was issued. The Construction (Design and Management) Regulations require that for a project covered by those Regulations, a copy of this Certificate, together with schedules is included in the project health and safety documentation.
For safety reasons, the electrical installation will need to be inspected at appropriate intervals by a competent person. The maximum time interval recommended before the next inspection is stated on Page 1 under "Next Inspection".
This Certificate is intended to be issued only for a new electrical installation or for new work associated with an addition or alteration to an existing installation. It should not have been issued for the inspection of an existing electrical installation. A "Periodic Inspection Report" should be issued for such a periodic inspection.
The Certificate is only valid if a Schedule of Inspections and Schedule of Test Results are appended :

NOTES ON COMPLETION OF MINOR ELECTRICAL INSTALLATION WORKS CERTIFICATE
Scope
The Minor Works Certificate is intended to be used for additions and alterations to an installation that do not extend to the provision of a new circuit. Examples include the addition of socket-outlets or lighting points to an existing circuit, the relocation of a light switch etc. This Certificate may also be used for the replacement of equipment such as accessories or luminaires, but not for the replacement of distribution boards or similar items. Appropriate inspection and testing, however, should always be carried out irrespective of the extent of the work undertaken.
Part 1 Description of minor works
1,2 The minor works must be so described that the work that is the subject of the certification can be readily identified.
4 See Regulations 120.3 and 120.4. No departures are to be expected except in most unusual circumstances. See also Regulation 633.1.
Part 2 Installation details
2 The method of fault protection must be clearly identified e.g. earthed equipotential bonding and automatic disconnection of supply using fuse/circuit-breaker/RCD.
4 If the existing installation lacks either an effective means of earthing or adequate main equipotential bonding conductors, this must be clearly stated. See Regulation 633.2.
Recorded departures from BS 7671 may constitute non-compliance with the Electricity Safety, quality and continuity Regulations 2002 (as amended) or the Electricity at Work Regulations 1989. It is important that the client is advised immediately in writing.
Part 3 Essential Tests
The relevant provisions of Part 6 (Inspection and Testing) of BS 7671 must be applied in full to all minor works. For example, where a socket-outlet is added to an existing circuit it is necessary to:
1 establish that the earthing contact of the socket-outlet is connected to the main earthing terminal
2 measure the insulation resistance of the circuit that has been added to, and establish that it complies with Table 61 of BS 7671
3 measure the earth fault loop impedance to establish that the maximum permitted disconnection time is not exceeded
4 check that the polarity of the socket-outlet is correct
5 (if the work is protected by an RCD) verify the effectiveness of the RCD.
Part 4 Declaration
1,3 The Certificate shall be made out and signed by a competent person in respect of the design, construction, inspection and testing of the work.
1,3 The competent person will have a sound knowledge and experience relevant to the nature of the work undertaken and to the technical standards set down in BS 7671, be fully versed in the inspection and testing procedures contained in the Regulations and employ adequate testing equipment.
2 When making out and signing a form on behalf of a company or other business entity, individuals shall state for whom they are acting.

 

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MINOR ELECTRICAL INSTALLATION WORKS CERTIFICATE

(REQUIREMENTS FOR ELECTRICAL INSTALLATIONS - BS 7671 [IEE WIRING REGULATIONS ) To be used only for minor electrical work which does not include the provision of a new circuit
GUIDANCE FOR RECIPIENTS
This safety Certificate has been issued to confirm that the electrical installation work to which it relates has been designed, constructed, inspected and tested in accordance with British Standard 7671 (the IEE Wiring Regulations).
You should have received an "original" Certificate and the contractor should have retained a duplicate. If you were the person ordering the work, but not the owner of the installation, you should pass this Certificate, or a full copy of it, immediately to the owner.
A separate Certificate should have been received for each existing circuit on which minor works have been carried out. This Certificate is not appropriate if you requested the contractor to undertake more extensive installation work, for which you should have received an Electrical Installation Certificate.
The Certificate should be retained in a safe place and be shown to any person inspecting or undertaking further work on the electrical installation in the future. If you later vacate the property, this Certificate will demonstrate to the new owner that the minor electrical installation work carried out complied with the requirements of British Standard 7671 at the time the Certificate was issued.

PERIODIC INSPECTION REPORT NOTES:
1. This Periodic Inspection Report form shall only be used for the reporting on the condition of an existing installation.
2. The Report, normally comprising at least four pages, shall include schedules of both the inspection and the test results. Additional sheets of test results may be necessary for other than a simple installation. The page numbers of each sheet shall be indicated, together with the total number of sheets involved. The Report is only valid if a Schedule of Inspections and a Schedule of Test Results are appended.
3. The intended purpose of the Periodic Inspection Report shall be identified, together with the recipient’s details, in the appropriate boxes.
4. The maximum prospective fault current recorded should be the greater of either the short-circuit current or the earth fault current.
5. The ‘Extent and Limitations’ box shall fully identify the elements of the installation that are covered by the report and those that are not, this aspect having been agreed with the client and other interested parties before the inspection and testing is carried out.
6. The recommendation(s), if any, shall be categorised using the numbered coding 1-4 as appropriate.
7. The ‘Summary of the Inspection’ box shall clearly identify the condition of the installation in terms of safety.
8. Where the periodic inspection and testing has resulted in a satisfactory overall assessment, the time interval for the next periodic inspection and testing shall be given. The IEE Guidance Note 3 provides guidance on the maximum interval between inspections for various types of buildings. If the inspection and testing reveal that parts of the installation require urgent attention, it would be appropriate to state an earlier re-inspection date, having due regard to the degree of urgency and extent of the necessary remedial work.
9. If the space available on the model form for information on recommendations is insufficient, additional pages shall be provided as necessary.

EXTENT & LIMITATIONS OF THE INSPECTION ( note 5 ) this will come up !!!!
Extent of Electrical Installation covered by this report :
Limitations : ( see Regulation 634.2 )
This inspection has been carried out in accordance with BS-7671:2008 ( IEE Wiring Regulations ) -
Amended to Cables concealed within trunking conduit , or cables & conduits concealed under floors , in roof spaces & generally
Within the fabric of the building or underground have not been inspected ;
( EXTENT & LIMITATIONS , remember this is with the Client ) ←←←←←

PERIODIC INSPECTION REPORT GUIDANCE FOR RECIPIENTS (to be appended to the Report)
This Periodic Inspection Report form is intended for reporting on the condition of an existing electrical installation.
You should have received an original Report and the contractor should have retained a duplicate. If you were the person ordering this Report, but not the owner of the installation, you should pass this Report, or a copy of it, immediately to the owner.
The original Report is to be retained in a safe place and be shown to any person inspecting or undertaking work on the electrical installation in the future. If you later vacate the property, this Report will provide the new owner with details of the condition of the electrical installation at the time the Report was issued.
The ‘Extent and Limitations’ box should fully identify the extent of the installation covered by this Report and any limitations on the inspection and tests. The contractor should have agreed these aspects with you and with any other interested parties (Licensing Authority, Insurance Company, Building Society etc) before the inspection was carried out.
The report should identify any departures from the safety requirements of the current Regulations and any defects, damage or deterioration that affect the safety of the installation for continued use. For items classified as ‘requires urgent attention’, the safety of those using the installation may be at risk, and it is recommended that a competent person undertakes the necessary remedial work without delay.
For safety reasons, the electrical installation will need to be re-inspected at appropriate intervals by a competent person. The maximum time interval recommended before the next inspection is stated in the Report under ‘Next Inspection.’
The Report is only valid if a Schedule of Inspections and a Schedule of Test Results are appended.

Notes on the formal visual and combined inspection and test record (Form VI.2):
1 Register No - this is an individual number taken from the equipment register, for this particular item of equipment.
2 Description of equipment, e.g. lawnmower, computer monitor.
3 Construction Class - Class 0, 0I, I, II, III. Note that only Class I and II equipment may be used without special precautions being taken.
4 Equipment types - portable, movable, hand-held, stationary, fixed, built-in.
5, 6 Insert the location and any particular external influences such as heat, damp, corrosive, vibration.
7, 8 Frequency of inspection - generally as suggested in Table 7.1 of the Code of Practice for In-Service Inspection and Testing of Electrical Equipment. Inspection - items 17-23 and 28 will be completed if an inspection is being carried out. Inspection and Test - the testing in items 24v and 26 should always be preceded by inspection.
9-11 The make, model and serial number of the item of equipment should be inserted.
12-14 The voltage for which the equipment is suitable, the current consumed and the fuse rating should be inserted.
15-16 The date of purchase and the guarantee should be completed by the client
17 The date to be inserted is the date of the inspection or the date of the inspection and testing.
18 Environment and use. It should be confirmed that the equipment is suitable for use in the particular environment and is suitable for the use to which it is being put.
19 Authority is required from the user to disconnect equipment such as computers and telecom equipment - where unauthorised disconnection could result in loss of data. Authority should also be obtained if such equipment is to be subjected to the insulation resistance and electric strength tests.
20 Socket-outlet/flex outlet. The socket or flex outlet should be inspected for damage including overheating. If there are signs of overheating of the plug or socket-outlet, the socket-outlet connections should be checked as well as the plug. This work should only be carried out by an electrician.
21-23 The inspection required is described in Chapter 14 of the Code of Practice for In-Service Inspection and Testing of Electrical Equipment.
24-27 Tests. The tests are described in Chapter 15 of the Code of Practice for In-Service Inspection and Testing of Electrical Equipment. The tests should always be preceded by the Inspection items 17-23 and 28. The instrument reading is to be recorded and a tick entered if the test results are satisfactory.
28 Functional Check - a check is made to ensure that the equipment works properly.
29 Comments/other tests. Additional tests may be needed to identify a failure more clearly or other tests may be carried out such as a touch current measurement. An additional sheet may be necessary, which should be referenced in the box on this record..
30 OK to use - ‘YES’ should be inserted if the item of equipment is satisfactory for use, ‘NO’ if it is not.

 

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1. SELV – an extra-low voltage system which is electrically separated from Earth and from other systems in such a way that a single-fault cannot give rise to the risk of electric shock. The particular requirements of the Regulations must be checked (see Section 414)
2. Double or reinforced insulation. Not suitable for domestic or similar installations if it is the sole protective measure (see 412.1.3)
3. Basic protection – will include measurement of distances where appropriate
4. Obstacles – only adopted in special circumstances (see 417.2)
5. Placing out of reach – only adopted in special circumstances (see 417.3)

6. Non-conducting locations and Earth-free local equipotential bonding – these are not recognised for general application. May only be used where the installation is controlled/under the supervision of skilled or instructed persons (see Section 418)
7. Electrical separation – the particular requirements of the Regulations must be checked. If a single item of current-using equipment is supplied from a single source, see Section 413. If more than one item of current-using equipment is supplied from a single source then the installation must be controlled/under the supervision of skilled or instructed persons, see also Regulation 418.3.

FOR INSPECTION & TESTING
I/We being the person(s) responsible for the inspection & testing of the electrical installation (as indicated by my/our signatures below), particulars of which are described above, having exercised reasonable skill and care when carrying out the inspection & testing hereby CERTIFY that the work for which I/we have been responsible is to the best of my/our knowledge and belief in accordance with BS 7671:2008, amended to ..............................(date) except for the departures, if any, detailed as follows:
Details of departures from BS 7671 (Regulations 120.3 and 120.4):
The extent

FOR CONSTRUCTION
I/We being the person(s) responsible for the construction of the electrical installation (as indicated by my/our signatures below), particulars of which are de-scribed above, having exercised reasonable skill and care when carrying out the construction hereby CERTIFY that the construction work for which I/we have been responsible is to the best of my/our knowledge and belief in accordance with BS 7671:2008, amended to ................................(date) except for the departures, if any, detailed as follows:
Details of departures from BS 7671 (Regulations 120.3 and 120.4):

FOR INSPECTION & TESTING
I/We being the person(s) responsible for the inspection & testing of the electrical installation (as indicated by my/our signatures below), particulars of which are described above, having exercised reasonable skill and care when carrying out the inspection & testing hereby CERTIFY that the work for which I/we have been responsible is to the best of my/our knowledge and belief in accordance with BS 7671:2008, amended to ..............................(date) except for the departures, if any, detailed as follows:
Details of departures from BS 7671 (Regulations 120.3 and 120.4):

FOR DESIGN
I/We being the person(s) responsible for the design of the electrical installation (as indicated by my/our signatures below), particulars of which are described above, having exercised reasonable skill and care when carrying out the design hereby CERTIFY that the design work for which I/we have been responsible is to the best of my/our knowledge and belief in accordance with BS 7671:2008, amended to................................(date) except for the departures, if any, detailed as follows:
Details of departures from BS 7671 (Regulations 120.3 and 120.4):

FOR DESIGN, CONSTRUCTION, INSPECTION & TESTING
I being the person responsible for the Design, Construction, Inspection & Testing of the electrical installation (as indicated by my signature below), particulars of which are described above, having exercised reasonable skill and care when carrying out the Design, Construction, Inspection & Testing, hereby CERTIFY that the said work for which I have been responsible is to the best of my knowledge and belief in accordance with BS 7671:2008 amended to .......... (date) except for the departures, if any, detailed as follows:
Details of departures from BS 7671 (Regulations 120.3 and 120.4):

Amberleaf here , please tell you Mates about this forum : this forum is Here to help Electricians :
There’s “ NOT “ a lot of forum that is doing this , let DAN & and the Boys ← know this , many thanks Amberleaf ,
DAN your Site has the Strength & Convictions to stand up for Electricians : Big Pat on the Back ,

LEVEL 2 CERTIFICATE IN FUNDAMENTAL INSPECTION, TESTING AND INITIAL VERIFICATION OF ELECTRICAL INSTALLATIONS ( GUILDS 2392-10 )

2392
INTRODUCTION
This three day course covers the theory and practice of the fundamental inspection, testing and initial verification of electrical installations and is based on the syllabus laid down in City & Guilds' 2392-10 Scheme Regulations. Its primary objective is to prepare candidates for assessment leading, for successful candidates, to the award of a City & Guilds ‘Certificate in Fundamental Inspection, Testing and Initial Verification 2392-10'.
The course is primarily about the practical application of Part 6 of BS 7671 and participants must be familiar with much of the terminology used in the Regulations and have a good grasp of their technical requirements.
Gaining familiarity with IEE Guidance Note 3 and its content is also an important aspect of the course, and candidates will need to refer to this, and also BS 7671, during the City & Guilds practical assessment.

LEVEL 2 CERTIFICATE IN FUNDAMENTAL INSPECTION, TESTING AND INITIAL VERIFICATION OF
ELECTRICAL INSTALLATIONS

OBJECTIVES
The course embraces:
* Statutory duties and safe working practices
* BS 7671:2008 requirements for inspection, testing and certification
* IEE Guidance Note 3, Inspection & Testing, 5th edition, guidance and recommendations
* Demonstration of tests and 'hands-on' experience

By the end of the Course participants should be fully aware of:
1. The BS 7671 requirements for initial verification, inspection and testing;
2. The information required to correctly conduct the inspection and testing of a new installation;
3. The statutory and non-statutory requirements and relevant guidance material which apply to the activity of inspecting and testing of electrical installations;
4. The information to be contained on forms, i.e. Electrical Installation Certificates, Minor Works Electrical Installation Certificates and how this information should be recorded.

Participants should also be fully prepared for the practical and written assessments City & Guilds 2392-101/102:

A practical assessment (2 hours), normally conducted one week after the course completion date

A multiple-choice GOLA (Global Online Assessment) - 50 questions in 1 hour 40 minutes,

LEVEL 2 CERTIFICATE IN FUNDAMENTAL INSPECTION, TESTING AND INITIAL VERIFICATION OF
ELECTRICAL INSTALLATIONS

Module 1 Includes reference to statutory requirements and safety aspects, and also covers some of the relevant definitions of BS 7671.
Module 2 Reminds participants of some of the relevant technical requirements of other Parts of BS 7671.
Module 3 Explains the inspection requirements of BS 7671 and makes considerable reference to Guidance Note 3. It has an Inspection Assessment at the end during which the participants, are invited to identify faults by inspection. This is an important Module, since City & Guilds place considerable emphasis on inspection in both the practical and assessments in particular the filling in of the Schedule of Inspections
Module 4 Explains the sequence of tests required, dangers of testing and relevant circuit theory.
Module 5 This module covers basic care of instruments and gives candidates the opportunity to familiarise themselves with the low reading ohm-meter, the module also helps to reinforce the theory or the previous module.
Modules 6-8 Are all concerned with testing. During Modules 6 and 8 delegates receive a demonstration on 'dead' and 'live' tests on two identical Demonstration Boards.
Modules 9-11 Are all concerned with testing. During Module10 delegates receive a demonstration on 'dead' and 'live' tests on two identical Demonstration Boards.
Module 12 Covers certification and reporting. LEVEL 2 CERTIFICATE IN FUNDAMENTAL INSPECTION, TESTING AND INITIAL VERIFICATION OF ELECTRICAL INSTALLATIONS (CITY & GUILDS 2392-10) 2392

General Introduction
Module 1: Preparation for Inspection, Testing and Certification
Module 2 - BS 7671 reinforcement
Module 3 - Inspection of Installations
Module 4 - Introduction to Testing
Module 5 – Low Reading Ohm-meter
Module 6 - Testing (1) Methodology
Module 7 - Testing (1) Practical
Module 8 – Testing (2) Methodology
Module 9 - Testing (2) Practical & Fault Finding
Module 10 – Testing (3) Methodology
Module 11 – Testing (3) Practical
Module 12 - Certification and Reporting

2392-10 PS : Electricians that have NOT Done Testing for a “ Long Time “ I would “ Recommend “ that you Do the 5 DAYS COARSE , And a LOT of Studying , take it for me , its Not a Walk in the Park : If you do the 3 Day Coarse , when you come to the EXAM you head will be up your But big Time !!! Trust me one this One ,
Remember that you have three Days to take that all in : ←
Third day : your on the Boards Testing then , before you Know it doing the Exam !!!!!!!

 

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2392-10 Electricians :
Part P of the Building Regulations for England and Wales was introduced by the government in January
2005, with an aim of reducing the number of accidents in the home related to faulty electrical installations. Similar laws apply in Scotland. It is now a legal requirement for electricians, kitchen, bathroom and gas installers, and all other trades or individuals involved in carrying out domestic electrical installation work to comply with Building Regulations.

Most electrical installations carried out in a property are now notifiable: in other words the local authority
building control must be notified prior to the work being carried out. The exception is if it is carried out, inspected and certified by a person registered with a government-authorised competent person scheme such as NICEIC. Failure to comply with Part P is a
criminal offence and local authorities have the power to require the removal or alteration of work that does not comply with the regulations.

You are advised to have a property maintenance and appliance testing procedure in place. This should
ensure properties are maintained in a safe condition.
1 Carry out regular visual inspections, looking for obvious signs of damage such as scorch marks on
socket outlets and damaged cables :
2 Get the property inspected and tested by a competent person on change of occupancy, or at least every 10 years :
3 Ensure formal inspection and testing more often in higher risk properties where the installation is very old, or where damage has been found in the past
4 Carry out regular inspections on all electrical appliances
Inspection Electrical Appliances :
The Department of Trade and Industry (DTI) strongly advises estate agents, letting agents, landlords and anyone else who lets furnished accommodation to seek independent advice as to who is responsible for the safety of electrical appliances supplied in the course of business.
If you are a landlord and provide any electrical appliances (cookers, kettles, toasters, washing machines, immersion heaters, etc) as part of the tenancy, the Electrical Equipment (Safety) Regulations 1994 requires that you ensure the
appliances are safe to use when first supplied. Each time the property is relet, it will be classed as supplying to that tenant for the first time. So you need to:
Check appliances for signs of damage:
1 cuts or abrasions to the cable covering
2 cracked casing or bent pins
3 loose parts and screws
4 overheating (burn marks)
5 the outer covering of the cable not being gripped where it enters the plug or equipment. Look to
see if the coloured insulation of the internal wires is showing :
* You may need to carry out a formal inspection. It should include removal of the plug cover to check:
1 the cord grip is holding the outer part of the cable tightly :
2 the wires, including the earth wire where fitted are attached to the correct terminals :
3 no bare wire is visible other than at the terminals :
4 the terminal screws are tight
5 there is no sign of internal damage, overheating or entry of liquid, dust or dirt Most of these checks apply to extension leads and their plugs and sockets. But some faults cannot be detected in this way, such as lack of continuous earths, which for some equipment, is essential for safety. All earthed equipment should have an occasional combined inspection and test to look for faults. Combined inspection and testing should be
carried out where there is reason to suspect the equipment may be faulty or damaged or
contaminated, but where this cannot be confirmed by visual inspection. Combined testing should also be
carried out after any repair or similar work to the equipment :
Extension Leads Warning :
Use of extension leads should be avoided where possible. If used, they should be tested as portable
appliances. It is recommended that 3-core leads ( including a protective earthing conductor) be used.
A standard 13 amp, 3-pin extension socket outlet with a 2-core cable should never be used even if the
appliance is Class II (music system, TV and video), as it would not provide protection against electric shock
if used at any time with an item of Class I ( cookers, washing machines, refrigerators, irons, dishwashers ).
Portable Equipment Outdoors :
In domestic premises, all socket outlets, which may be used for portable equipment outdoors, should be
protected by an RCD (a safety device that switches off the electricity automatically when it detects an
earth fault) to provide protection against electric shock . Socket outlets installed below kitchen worktops may
usually be considered to be unavailable for connection of outdoor portable equipment, and
would therefore not be required to be RCD protected. It is wise to exclude socket outlets intended for refrigerators and freezers from circuits which require sensitive RCD protection .
Contractors are assessed against the national standard for the safety of electrical installations,
British Standard BS 7671: Requirements for electrical installations (also known as the IEE Wiring Regulations). They must also comply with the electrical safety requirements of any other applicable Codes of Practice, such as those for fire alarms, emergency lighting. In England and Wales, it is a legal requirement for electrical work carried out in and outside the home to comply with Part P of the Building Regulations.

2392-10 Domestic Electrician : ↑↑↑↑ If you are a landlord, you need to be sure that the electrics in your property or properties are safe. That’s the law.
Dozens of people die and thousands are injured every year through unsafe electrics. If you let property, take note of these statistics – rented properties are potentially more at risk than owner-occupier homes as they tend to get more
wear and tear. Identifying faulty electrical installations can be difficult. Especially in rented properties as tenants
may have carried out electrical work themselves without requesting permission or notifying their landlord. An accident could be waiting to happen, and the electrical installation in one of your houses or flats may not comply with national safety standards and Building Regulations.
( IF your got to send a Note to a Landlord , here it is ) your “ But “ is Covered :

Apprentice Question 1 :
Assessment of general characteristics would not include :
Choose one answer.
(A) Purpose for which the installation is intended to be used
(B) External influences
(C) Length of final circuit cable runs *
(D) Compatibility of equipment
Question 2 :
Where the provision of safety services is required the supply characteristics for the safety services or systems shall be:
Choose one answer.
(A) AC only
(B) Separately assessed *
(c) DC only
(D) Exactly the same as the incoming supply characteristics
Question 3
Characteristics of supply shall be determined by:
Choose one answer.
(A) Inspection
(B) Measurement
(C) Enquiry and calculation
(D) Calculation, measurement, enquiry or inspection *

Question 4 :
When determining maximum demand of an installation:
(A) All circuit breakers and fuse ratings within the installation must be added together
(B) All circuits must be fully loaded
(C) A clip on ammeter must be used during low demand periods
(D. Diversity may be taken into account *
Question 5 :
Every installation shall be divided into circuits as necessary in order to:
(A) Reduce running costs
(B) Reduce final circuit cable lengths
(C) Facilitate inspection and testing and maintenance *
(D) Minimise installation time
Question 6 :
Assessment of general characteristics would include:
(A) Maintainability, safety services and continuity of service *

(B) Cost of installation
(C) Number of distribution boards and or consumer units
(D) Total floor area

 

[amberleaf]

17th Edition Forms :
1 Initial inspection and testing

Forms 1 to 4 are designed for use when inspecting and testing a new installation, or an alteration or addition to an existing installation. The forms comprise the following:
1 Short form of Electrical Installation Certificate (To be used when one person is responsible for the design, construction, inspection and testing of an installation.)

2 Electrical Installation Certificate (Standard form from Appendix 6 of BS 7671)
3 Schedule of Inspections
4 Schedule of Test Results.
Notes on completion and guidance for recipients are provided with the form.

2 Minor works :
The complete set of forms for initial inspection and testing may not be appropriate for minor works. When an addition to an electrical installation does not extend to the installation of a new circuit, the minor works form may be used. This form is intended for such work as the addition of a socket-outlet or lighting point to an existing circuit, or for repair or modification.
Form 5 is the Minor Electrical Installation Works Certificate from Appendix 6 of BS 7671.
Notes on completion and guidance for recipients are provided with the form.

3 Periodic inspection :
Form 6, the Periodic Inspection Report from Appendix 6 of BS 7671, is for use when carrying out routine periodic inspection and testing of an existing installation. It is not for use when alterations or additions are made. A Schedule of Inspections (3) and Schedule of Test Results (4) should accompany the Periodic Inspection Report (6).
Notes on completion and guidance for recipients are provided with the form.

Electrical Protection : Apprentices ,
“ Isolation and Cutting Off Supply “
(a) Does every machine have a means of isolation provided and is it accessible ?
(b) Does every machine have a means by which it can be stopped, e.g. a stop button and is this button of the mushroom head type and easily accessible?
(c) Are isolators in good condition and can the be operated without difficulty? For example, check for broken handles or any impediment in the operation?
(d) Is the system provided with adequate means of isolation back at the mains switchroom and at the respective distribution points? Does every machine have a means of isolation?
(e) Are all the isolation points clearly marked for the circuits they control? Identification is very important and should be looked for in every inspection. This should also include identification of fuse ways within distribution boards and at front and rear of switchboards.
(f) Check to ensure that all circuits have a means of switching off, e.g. lighting and fan switches and are these in good working order and not broken ?
(g) Ask about OFF LOAD isolation and the procedures existing for operation of such...
who does it and by which methods ?
“ Earthing “
Note: visual examinations of the earthing arrangements.
(a) All conductive parts, i.e. metallic enclosures, pipes, radiators, taps etc., must be bonded and efficiently connected to earth.
(b) Check this carefully and if the earthing protective conductor is visible, examine the connections for tightness. They must be as tight as possible, because loose or slack connections give a high resistance and result in danger.
(c) Check colour coding of the earthing protective conductor; this should be green/yellow. 514.3 / 514.4.2
(d) Is the conductor large enough to carry fault currents without destruction ?
(e) How often is the EARTH FAULT IMPEDANCE tested and what are the latest results ?
(f) Is armouring, conduit or trunking used as the earth protective conductor? Check glands for tightness, look for signs of corrosion and damage ,
(g) Ask about the earthing system... do they obtain this from the Supply Authority and how, or do they have an earth rod or a water pipe ? 411.3.1.2
“ Portable Tools “
Note 1: The safest voltage is the lowest practicable voltage. Generally the recommended voltage is 110 volts AC from a step down transformer where the mid point of the secondary 110 volt winding is connected to earth ( CTE ). This limits the shock to earth voltage to 55 volts AC. In confined conducting locations the voltage should be much lower than this, i.e. no more than 50 volts from an unearthed ( or isolated earth ) supply, or 50 volts from a ( CTE ) supply to give a 25 volt shock-earth.
(b) Check the cables and entries, are they damaged?
(c) Are there any taped joints. If so have them replaced ,
(d) Check to see if the metal casing or any other metallic parts of the tool are sufficiently earthed.
Note 2: Double insulated or all insulated (Class II) tools do not require an earth. It is therefore vitally
important to ensure that the casing, cable insulation and plug are not damaged.
(e) If the tool has to be supplied from a 230 volt AC supply ask for RCD (30mA trip) protection.
(f) Are they inspected, tested and maintained regularly ?
(g) Check plugs, fuses, cables and general conditions .
“ Adverse Environmental Conditions “
(a) Firstly, check the environment, i.e. is it:
• Dusty.
• Wet or damp (do they use hosing down operations).
• Corrosive.
• Dirty.
• Adverse weather or just simple weather exposure.
• High temperatures and/or pressures.
• Flammable or explosive atmospheres.
Note: Standard electrical equipment will be seriously affected by these conditions and danger will result. Electrical equipment will have to be selected accordingly to suit the environment so as to combat the consequential problems. There are many British Standards dealing with the requirements for electrical equipment in adverse atmospheres and these should be consulted along with specialist advice.
(b) Check the type of installed equipment against the environment and advise accordingly:
• Dirty, dusty, wet, adverse weather – BS-EN60529.
• Flammable/Explosive areas – BS-EN60079.
• Corrosion – Replace or clean down and repaint with anti-corrosive paint.
• High temperature, pressures – Reposition or replace with suitable equipment.
(c) Check also the installation medium such as cables, conduits etc. It is better to use armoured cables or MICC cables in most environments.

2392-10 Traditional Junction Boxes : ( Regulation 526.3 p-106 : BS-EN60670-22 – BS 6220
unless using a solution such as maintenance free terminals, the access to electrical connections should be
adequate for their safe and proper inspection, testing and maintenance. In this respect, connections should be in a location where they can reasonably be reached and where there is adequate working space.:

Where connections are made in roof spaces and inter-floor spaces the enclosures containing the connections should normally be fixed and provision must be made for their access. Providing these two constraints are complied with, then the
continued use of standard circular junction boxes remains acceptable.

Maintenance Free Connections
Maintenance free terminals provide one solution where accessibility is an issue :

Junction boxes are commonly used during alterations and additions to an installation. With certain exceptions regulation 526.3 requires that every connection shall be accessible for inspection, testing and maintenance.
The Electrical Safety Council Technical Manual states that “a junction box with screw terminals is an example of where connections must be accessible”. The reason is to allow inspection of joints which could have relaxed or loosened over time, a recognised problem with screwed terminals.
Unless provision is made for access, where boarding, carpet or other similar covering is laid over a junction box with screw terminals, it may not be considered accessible and maintenance free terminals should be used.
This is further reinforced in Appendix 15 of the Wiring Regulations which states “Junction boxes with screw terminals must be
accessible for inspection, testing & maintenance or, alternatively, use maintenance-free terminals / connection (Regulation 526.3)”

Junction boxes with screw terminals must be accessible for inspection...

 

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SCHEDULES ******
The attached Schedules are part of this document and this Certificate is valid only when they are attached to it.
............ Schedules of Inspections and ............ Schedules of Test Results are attached. (Enter quantities of schedules attached).

( C&G 2392-10 ) ( 2 days plus 1 day Assessments )
This new qualification has been developed in order to meet the needs of the electrical contracting industry.
It is intended to provide candidates with an introduction to the fundamentals of inspection, testing and initial verification of electrical installations.
It is aimed at practicing electricians who have not carried out inspection and testing since qualifying or who require some update training.
It is also suitable for those coming into the industry with limited experience of inspection and testing.
Candidates who achieve this qualification could progress onto the Certificate in Inspection, Testing and Certification of Electrical Installations (2391-10).

SCHEDULE OF TEST RESULTS

NOTES ON SCHEDULE OF TEST RESULTS :
Type of supply is ascertained from the distributor or by inspection :
( Ze at origin.) When the maximum value declared by the distributor is used, the effectiveness of the earth must be confirmed
Prospective fault current (PFC). The value recorded is the greater of either the short-circuit current or the earth fault current
Preferably determined by enquiry of the distributor

Short-circuit capacity of the device is noted, see Table 7.2A of the On-Site Guide or Table 2.4 of GN3

the following tests, where relevant, shall be carried out in the following sequence :
Continuity of protective conductors, including main and supplementary bonding
Every protective conductor, including main and supplementary bonding conductors, should be tested to verify that it is continuous and correctly connected :

Continuity :
Where Test Method 1 is used, enter the measured resistance of the line conductor plus the circuit protective conductor ( R1 + R2 )
See 10.3.1 of the On-Site Guide or 2.7.5 of GN3, During the continuity testing (Test Method 1) the following polarity checks are to be carried out:
(a) every fuse and single-pole control and protective device is connected in the line conductor only
(b) centre-contact bayonet and Edison screw lampholders have outer contact connected to the neutral conductor
c) wiring is correctly connected to socket-outlets and similar accessories. Compliance is to be indicated by a tick in polarity column 11
(R1 + R2 ) need not be recorded if ( R2 is recorded in column 7 :


Where Test Method 2 is used, the maximum value of ( R2 ) is recorded in column 7.
See 10.3.1 of the On-Site Guide or 2.7.5 of GN3

Continuity of ring final circuit conductors :
A test shall be made to verify the continuity of each conductor including the protective conductor of every ring final circuit
See 10.3.2 : of the On-Site Guide or 2.7.6 of GN3 :

Insulation Resistance
All voltage sensitive devices to be disconnected or test between live conductors (line and neutral) connected together and earth
The insulation resistance between live conductors is to be inserted in column 9
The minimum insulation resistance values are given in Table 10.1 of the On-Site Guide or Table 2.2 of GN3
See 10.3.3 (iv) of the On-Site Guide or 2.7.7 of GN3

All the preceding tests should be carried out before the installation is energised :
Polarity :
A satisfactory polarity test may be indicated by a tick in column 11
Only in a Schedule of Test Results associated with a Periodic Inspection Report is it acceptable to record incorrect polarity ,

Earth fault loop impedance Z
This may be determined either by direct measurement at the furthest point of a live circuit or by adding (R1 + R2 ) of column 6 to
Ze . is determined by measurement at the origin of the installation or preferably the value declared by the supply company used
Zs = Ze + ( R1 + R2 ) Zs should be less than the values given in Appendix 2 of the On-Site Guide or Appx 2 of GN3

functional testing :
The operation of RCDs (including RCBOs) shall be tested by simulating a fault condition, independent of any test facility in the device
Record operating time in column 13. Effectiveness of the test button must be confirmed
See Section 11 of the On-Site Guide or 2.7.15 and 2.7.18 of GN3

All switchgear and controlgear assemblies, drives, control and interlocks, etc must be operated to ensure that they are properly
mounted, adjusted, and installed Satisfactory operation is indicated by a tick in column 14
Earth electrode resistance
The earth electrode resistance of TT installations must be measured, and normally an RCD is required
For reliability in service the resistance of any earth electrode should be below 200 Ω. Record the value on Form 1, 2 or 6, as
appropriate. See 10.3.5 of the On-Site Guide or 2.7.12 of GN-3

NOTES ON COMPLETION OF MINOR ELECTRICAL INSTALLATION WORKS CERTIFICATE

Scope
The Minor Works Certificate is intended to be used for additions and alterations to an installation that do not
extend to the provision of a new circuit. Examples include the addition of socket-outlets or lighting points to
an existing circuit, the relocation of a light switch etc. This Certificate may also be used for the
replacement of equipment such as accessories or luminaires, but not for the replacement of
distribution boards or similar items. Appropriate inspection and testing, however, should always be carried out irrespective of the extent of the work undertaken ,

Part 1 Description of minor works :

1,2 : The minor works must be so described that the work that is the subject of the certification can be readily identified.
4 See Regulations 120.3 and 120.4. No departures are to be expected except in most unusual circumstances. See also Regulation 633.1

Part 2 Installation details :
2 : The method of fault protection must be clearly identified e.g. earthed equipotential bonding and automatic disconnection of supply using fuse/circuit-breaker/RCD.
4 : If the existing installation lacks either an effective means of earthing or adequate main equipotential bonding conductors, this must be clearly stated. See Regulation 633.2
Recorded departures from BS-7671 may constitute non-compliance with the Electricity Safety, quality and continuity Regulations 2002 (as amended) or the Electricity at Work Regulations 1989. It is important that the client is advised immediately in writing.
Part 3 Essential Tests :
The relevant provisions of Part 6 ( Inspection and Testing ) of BS 7671 must be applied in full to all minor
works. For example, where a socket-outlet is added to an existing circuit it is necessary to:
1 : establish that the earthing contact of the socket-outlet is connected to the main earthing terminal
2 : measure the insulation resistance of the circuit that has been added to, and establish that it complies with Table 61 of BS 7671
3 : measure the earth fault loop impedance to establish that the maximum permitted disconnection time is not exceeded
4 : check that the polarity of the socket-outlet is correct
5 : (if the work is protected by an RCD) verify the effectiveness of the RCD
Part 4 Declaration :
1.3 : The Certificate shall be made out and signed by a competent person in respect of the design construction, inspection and testing of the work.
1,3 The competent person will have a sound knowledge and experience relevant to the nature of the
work undertaken and to the technical standards set down in BS-7671 be fully versed in the inspection
and testing procedures contained in the Regulations and employ adequate testing equipment.
2 : When making out and signing a form on behalf of a company or other business entity, individuals shall state for whom they are acting.

 

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About the Electrical Testing and Inspection
During the inspection, you can rest assured that we will cover the most obvious danger points and those that are less obvious, including:
• System types
• Live conductors
• Nature of supply parameters
• Supply protective device characteristics
• Means of earthing
• Details of installation earth electrode
• Main switch circuit breaker
• Main protective conductors
• Bonding of extraneous conductive parts
• Method of protection against indirect contact
• Method of protection against electrical shock
• Prevention of mutual detrimental influence
• Protection against indirect contact
• Cables and conductors
• Circuits
• Boards
Emergency Lighting Testing BS 5266
Emergency lighting is required in all premises where people are employed and it is a mandatory requirement to be installed where artificial lighting is installed.

Under the “Fire Precaution (Workplace) Regulations 1999” all Employers, Landlords or Occupiers have a duty to carry out a risk assessment to ensure their premises and activities are able to facilitate safe escape in the event of an emergency.
The Emergency Lighting British Standard BS5266 defines the requirements for the correct installation of Emergency Lighting. Compliance with this standard will ensure that your premises, meets the requirements of the Fire Precaution (Workplace) Regulations.

BS5266 requires inspection & tests should be carried out at the following intervals (Frequencies);

Daily
Monthly
Six-Monthly
Three Yearly
Subsequent Annual Test

Portable Appliance ( Pat Testing )
The law clearly states that all employers have a legal obligation to maintain all electrical equipment in order to ensure a safe working environment. This includes all electrically operated items such as computers, printers, photocopiers, kettles, extension leads, vacuums etc.
Organisations of all types and sizes have a duty to protect their employees and business from this risk and to comply with the Electricity at Work Regulations 1989, Health and Safety at Work Act 1974, The Electrical Equipment (Safety) Regulations 1994, Provision and Use of Work Equipment Regulations 1998
• Replacement of faulty or damaged mains plug (BS1363/A)
• Replacement of damaged or incorrectly rated fuses (BS1362)
• Re-wiring of incorrect connections in the mains plug BS1363/A)
• Repair to faulty cable grips in the mains plug BS1363/A)
• Minor repairs requiring less than ten minutes labour
• Re-test following repair

All Appliances are labelled with the result of the test (pass or fail).

Description of Minor Works :

The minor works must be so described that the work that is the subject of the certification can be readily identified.
See Regulations 120.3 ) This Standard sets out Technical Requirements intended to ensure that Electrical Installations conform to
The Fundamental Principles chapter 13 : as follows , ( Part 3 ) ( Part 4 ) ( Part 5 ) ( Part 6 ) ** ( Part 7 ) ** and 120.4. No departures are to be expected except in most unusual circumstances. See also Regulation 633.1 ,
633.1 : Additions & Alterations , this Requirement of Sections 631 & 632 for the issue of an Electrical Installation Certificate or a
Minor Electrical Installation Works Certificate shall apply to all the work of the Additions or Alterations ,

 

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“ Operation of Overload and Fault Current Devices “

When a fault is noticed , it is usually because a circuit or piece of equipment has stopped working and this is usually because the protective device has done its job and operated , the rating of a protective device should be greater than , or at least equal to , the rating of the circuit or equipment it is protecting , e.g. 10 x 100 watt lamps equate to a total current use of 4.35 amperes ,
Therefore a device rated at 5 or 6 amperes could protect this circuit ,
A portable domestic appliance which has a label rating of 2.7kW equates to a total current of 11.74 amperes ,
Therefore a fuse rated at 13 amperes should be fitted in the plug ,
Protective devices are designed to operate when an excess of current ( greater than the design current of the circuit )
Passes through it , the fault currents excess heat can cause a fuse element to rupture or the device mechanism to trip ,
Dependent on which type of device is installed , these currents may not necessarily be circuit faults , but short-lived overloads specific to a piece of equipment or outlet , the regulations categorise these as overload current & overcurrent , For conductors ,
The rated value is the current-carrying capacity , most excess currents are , however , due to faults , either earth faults or short circuit type which cause excessive currents , whichever type of fault occurs the designer should take account of its effect on the installation wiring and choose a suitable device to disconnect the fault quickly and safely , the fundamental effect of any fault is a rise in current and therefore a rise in temperature , high temperature destroys the properties of installation , which in itself could lead to a short circuit , high currents damage equipment , and earth fault currents are dangerous to the body from electric shock ,
“ Overloads faults “
Adaptors used in socket outlets exceeding the rated load of circuit :
Extra load being added to an existing circuit or installation :
Not accounting for starting current on a motor circuit :
“ Short circuit faults “
Insulation breakdown :
Severing of live circuit conductors :
Wrong termination of conductors energised before being tested :
“ Earth faults “
Insulation breakdown :
Incorrect polarity :
Poor termination of conductors :
“ fuse holder has melted due to overloading “
“ wrong type of starter in fluorescent tube has melted due to excess power demand “
“ poor termination of ( CPC ) circuit protective conductors “ in junction boxes “

Definitions :
“ Overloads current “ – an overcurrent occurring in a circuit which is electrically sound :
“ Overcurrent ” – a current exceeding the rated value
“ Earth fault current “ – a fault current which flows to earth :
“ Short circuit current “ – an overcurent resulting from a fault of negligible impedance between live conductors :

 

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“ Basic electricity “ Apprentice :
All questions about the nature of electricity lead to the composition of matter. All matter is made up of atoms.
Every atom has a nucleus, with positively - charged protons, and neutrons with no charge.
Moving around the nucleus are negatively -charged electrons.
With equal numbers of protons and electrons, their charges cancel each other out, leaving the atom with no overall charge.
An excess of electrons gives an atom a negative charge; a deficiency gives it a positive charge.
In some materials, there are electrons called free electrons, only loosely held by the nucleus.
The more free electrons a material has, the better it can conduct electricity.
Metals typically have lots of free electrons and are good conductors.
In insulators, electrons are bound much more tightly to the nucleus.
They cannot easily move freely, so they are not readily available for electric current.
Semiconductors conduct electricity more easily than insulators but not as well as conductors. They are crucial in electronics

Free electrons

Free electrons are necessary for electric current, but for those electrons to move, they need a complete pathway, or circuit, and there must be a force to make them move. The force from a battery sets free electrons moving.
Like charges repel, so the negative electrons are repelled from the negative terminal. Unlike charges attract, so the electrons are also attracted towards the positive terminal.
They flow in one direction only. This is called direct current or DC. Most circuits in motor vehicles use direct current.
The larger the charge at the positive terminal, the more strongly it attracts free electrons. This attraction acts as a force driving the electrons along. The greater the force, the stronger the electrical current. The force is called electromotive force or EMF. It’s also known as "voltage".
Also affecting the current flow in a circuit is electrical resistance, measured in ohms. All materials have resistance - even good conductors.
Four factors determine the level of resistance:
• Type of material - whether it has enough free electrons;
• Length of the conductor - as length increases, so does resistance;
• Size of the conductor - the larger the conductor, the greater the amount of current it can carry; and
• Temperature of the conductor.
The higher the temperature, the harder it is for electrons to pass through it and the higher the resistance. While all materials have some resistance to current flow, a resistor is a component designed to cause a particular voltage drop in a circuit. It has a set resistance, usually marked or coded on its surface.
Since electric current is the flow of electrons, it's natural to say the direction of current is the direction in which electrons move. However, before the discovery that electric current was the flow of electrons, it was thought the natural way for electricity to move was from positive to negative.
Both concepts are still in use. Current said to flow from positive to negative, is called conventional current. Current said to flow from negative to positive, is called electron current.

Resistance
Electrical resistance is a measure of the degree to which an object opposes the passage of an electric current. The SI unit of electrical resistance is the ohm. Its reciprocal quantity is electrical conductance measured
Resistance is defined as the ratio of the potential difference (i.e. voltage) across the object (such as a resistor) to the current passing through it:
R = V / I
where
• R is the resistance of the object
• V the potential difference across the object, measured in volts
• I is the current passing through the object, measured in amperes
For a wide variety of materials and conditions, the electrical resistance does not depend on the amount of current flowing or the amount of applied voltage. This means that voltage is proportional to current and the proportionality constant is the electrical resistance. This case is described by Ohm's law and such materials are described as ohmic. V can either be measured directly across the object or calculated from a subtraction of voltages relative to a reference point. The former method is simpler for a single object and is likely to be more accurate. There may also be problems with the latter method if the voltage supply is AC and the two measurements from the reference point are not in phase with each other.

Electromagnetic induction

When a conductor cuts across a magnetic field, current flows in the conductor. It flows one way when the conductor cuts the field in one direction, then reverses as it cuts the field in the opposite direction.
The current is called alternating, because it flows one way, and then the other. The term alternating current is often shortened to AC. That's the sort of electrical energy that comes through power outlets. It's also produced by an alternator, as the name indicates.
Moving a wire inside a magnetic field produces a current flow. Similarly, moving a magnet inside a stationary coil of wire, produces the same effect.
If a magnet is rotating in an iron yoke, and a coil of wire is wound around the stem of the yoke to form a complete circuit with the ammeter, this will indicate if current flows.
As the magnet rotates, the ammeter deflects for current flow. For every half-revolution, current flow reverses. Increasing the speed of the magnet increases the amount of electrical energy produced. Electromagnetic induction is applied in alternators and ignition coils.
Electromagnetic induction is the production of an electrical potential difference (or voltage) across a conductor situated in a changing magnetic flux.
Michael Faraday is generally credited with having discovered the induction phenomenon in 1831 though it may have been anticipated by the work of Francesco Zantedeschi in 1829. Faraday found that the electromotive force (EMF) produced along a closed path is proportional to the rate of change of the magnetic flux through any surface bounded by that path. In practice, this means that an electrical current will flow in any closed conductor, when the magnetic flux through a surface bounded by the conductor changes. This applies whether the field itself changes in strength or the conductor is moved through it. Electromagnetic induction underlies the operation of generators, induction motors, transformers, and most other electrical machines.

Electromagnetism
Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. The electric field can be produced by stationary electric charges, and gives rise to the electric force, which causes static electricity and drives the flow of electric current in electrical conductors. The magnetic field can be produced by the motion of electric charges, such as an electric current flowing along a wire, and gives rise to the magnetic force one associates with magnets. The term "electromagnetism" comes from the fact that the electric and magnetic fields are closely intertwined, and, under many circumstances, it is impossible to consider the two separately. For instance, a changing magnetic field gives rise to an electric field; this is the phenomenon of electromagnetic induction, which underlies the operation of electrical generators, induction motors, and transformers. The term electrodynamics is sometimes used to refer to the combination of electromagnetism with mechanics. This subject deals with the effects of the electromagnetic field on the mechanical behavior of electrically charged particles.

Electromagnetic force
The force that the electromagnetic field exerts on electrically charged particles, called the electromagnetic force, is one of the four fundamental forces. The other fundamental forces are the strong nuclear force (which holds atomic nuclei together), the weak nuclear force (which causes certain forms of radioactive decay), and the gravitational force. All other forces are ultimately derived from these fundamental forces. However, it turns out that the electromagnetic force is the one responsible for practically all the phenomena one encounters in daily life, with the exception of gravity. Roughly speaking, all the forces involved in interactions between atoms can be traced to the electromagnetic force acting on the electrically charged protons and electrons inside the atoms. This includes the forces we experience in "pushing" or "pulling" ordinary material objects, which come from the intermolecular forces between the individual molecules in our bodies and those in the objects. It also includes all forms of chemical phenomena, which arise from interactions between electron orbital’s.

 

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Electrical power

Energy is the potential to do work. But work is done only when the energy is released.
A disconnected battery isn't doing work, but it has the potential to do work, so it's a source of energy.
The difference in electron supply at the battery terminals is sometimes called the potential difference - in the case of a standard charged automotive battery, a potential of 12 volts. Tapping this potential means turning one form of energy, the battery's electrochemical energy, into another.
Turning one form of energy into another is called work.
The amount of energy transformed is the amount of work done. When a person's legs turn the pedals of a bicycle, physical energy is being turned into mechanical energy. A power drill turns electrical energy into mechanical energy.
In each case, work is being done, but the power drill is different - it does the work quicker, delivering more mechanical energy. That difference is called Power. Power is the rate at which work is done. The rate of transforming energy. In an electrical circuit, power refers to the rate at which electrical energy is transformed into another kind of energy
The unit of power is the watt. 1 watt is produced when 1 volt causes a current flow of 1 amp. From this comes the power equation: P, the power in watts, equals V, the voltage in volts, multiplied by I, the current in amps.
This calculation is applied just like Ohm's law.
When current flows in a circuit with a resistor in it, the resistor may become hot as it converts electrical energy into heat energy. If this circuit is powered by a 12 volt battery with a current of 2 amps, using the power equation (P=VxI), we can determine that 24 watts of power are being taken from the circuit by the resistor
It is also possible to simplify and transpose the power equation:
• Power equals voltage times current
• Therefore, voltage equals power divided by current
• and current equals power divided by voltage.

Instantaneous electrical power
The instantaneous electrical power P delivered to a component is defined as:
P = I x V where
• P is the instantaneous power, measured in watts
• V is the potential difference (or voltage drop) across the component, measured in volts
• I is the current flowing through it, measured in amperes
If the component is a resistor, then:
P = I2 x R or
P = V2 ÷ R
where
R is the resistance, measured in ohm.

Parallel circuits

In a series circuit, components are connected like links in a chain. If any link fails, current to all the components is cut off.
In a parallel circuit, all components are connected directly to the voltage supply. If any connection or component fails in a parallel circuit, current continues to flow through the rest.
This is one reason why parallel circuits are used in automotive applications like lighting systems. If one lamp fails, current continues to flow through the rest. In a series circuit, all would go out, which could be disastrous.
Also, since all components connect directly to the battery terminals, the metal of the vehicle’s body can become one of the conductors. One terminal of the battery, and one of each component, can be connected anywhere on the body or chassis, to complete the circuit. This is called an earth, or ground connection. It saves a lot of connecting wire.
A feature of a parallel circuit is that the voltage across each component is the same as battery voltage.
No matter how many components are added, or removed, as long as they’re in parallel, the voltage across them will be the same as across each other component, including the battery.
Another feature of a parallel circuit is that the current flowing in each branch is determined by the resistance of that branch.
In a parallel circuit where the resistors in each branch are the same, the current flowing in each branch is therefore also the same. However, the sum of their individual currents is equal to the total current flowing in the circuit.
When the resistance's are not equal, then the current divides in accordance with the value of each resistance, but the total current flow is still the sum of the currents flowing in each branch.

Parallel circuit resistance Say you have a 12 volt parallel circuit with three branches, each with a 12 ohm resistor, and a current flow of 3 amperes. If you add another 12 ohm resistor to the circuit it produces an effect which is the opposite of what might be expected. Current increases from 3 amperes to 4.

This is because, in a parallel circuit, adding more branches provides more pathways, but decreases the overall circuit resistance, so current flow increases.

Total resistance of a parallel circuit is found by turning all the resistances upside down, to make fractions called reciprocals. In this case, each 12 becomes 1/12th.

The 4/12ths are added together, and the answer turned back up the way it was, so that it is 12/4, or 12 divided by 4, which equals 3. 3 ohms is therefore the total resistance in the circuit. Ohm’s law confirms the ammeter reading of 4 amperes. Now, if 2 resistors are removed, what is the result?

1/12th plus 1/12th is 2/12th’s, which, turned back the way it was, is 12 over 2, or 6 ohms. Voltage across the components is still 12 volts, but by Ohm’s law, the new current is 2 amperes. So removing the resistors, in this circuit, halves the current.

Wire sizing Wire size is very important for the correct operation of electrical circuits. Selecting too small a gauge wire for an application will adversely effect the operation of the circuit. This will cause voltage drop and poor performance, or, in extreme cases, the cable will get hot enough to melt the insulation. Selecting too large a gauge increases costs and weight.

The resistance of a cable affects how much current it can carry. The resistance of a cable is determined by its length and its diameter.

The longer the cable and the smaller the diameter, the higher the resistance. The shorter the cable and the larger the diameter the lower the resistance.

To select the correct cable gauge for any given application it is best to refer to a cable chart. Manufacturers and standards bodies use cable gauge charts to define how much current each cable gauge can carry safely and effectively.

Over the years a number of different wire gauges have been used to determine application.

The primary wire gauges are the metric wire gauge and the American wire gauge or AWG.

For example, this 12 Volt circuit is designed for a maximum current flow of 10 Amps. Because of the installation design, the length of the cable used to wire the circuit needs to be approximately 20 feet or 7 meters in length, so using the AWG table as a reference we see that the correct gauge cable to use is 16AWG.

 

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GUIDANCE FOR RECIPIENTS
This safety Certificate has been issued to confirm that the electrical installation work to which it relates has been designed, constructed, inspected and tested in accordance with British Standard 7671 (the IEE Wiring Regulations).
You should have received an "original" Certificate and the contractor should have retained a duplicate. If you were the person ordering the work, but not the owner of the installation, you should pass this Certificate, or a full copy of it including the schedules, immediately to the owner.
The Certificate should be retained in a safe place and be shown to any person inspecting or undertaking further work on the electrical installation in the future. If you later vacate the property, this Certificate will demonstrate to the new owner that the electrical installation complied with the requirements of British Standard 7671 at the time the Certificate was issued. The Construction (Design and Management) Regulations require that for a project covered by those Regulations, a copy of this Certificate, together with schedules is included in the project health and safety documentation.
For safety reasons, the electrical installation will need to be inspected at appropriate intervals by a competent person. The maximum time interval recommended before the next inspection is stated on Page 1 under "Next Inspection".
This Certificate is intended to be issued only for a new electrical installation or for new work associated with an addition or alteration or to an existing installation. It should not have been issued for the inspection of an existing electrical installation. A "Periodic Inspection Report" should be issued for such an inspection.
The Certificate is only valid if a Schedule of Inspections and Schedule of Test Results are appended.

Why must we have earth electrodes
The principle of earthing is to consider the general mass of earth as a reference (zero) potential. Thus, everything connected directly to it will be at this zero potential, or above it by the amount of the volt drop in the connection system (for example, the volt drop in a protective conductor carrying fault current). The purpose of the earth electrode is to connect to the general mass of earth.
With the increasing use of underground supplies and of protective multiple earthing (PME) it is becoming more common for the consumer to be provided with an earth terminal rather than having to make contact with earth using an earth electrode.
The tester : The person who carries out the test and inspection must be competent to do so, and must be able to ensure his own safety, as well as that of others in the vicinity. It follows that he must be skilled and have experience of the type of installation to be inspected and tested so that there will be no accidents during the process to people, to livestock, or to property. The Regulations do not define the term 'competent', but it should be taken to mean a qualified electrician or electrical engineer.
Why do we need inspection and testing
There is little point in setting up Regulations to control the way in which electrical installations are designed and installed if it is not verified that they have been followed. the protection of installation users against the danger of fatal electric shock due to indirect contact is usually the low impedance of the earth-fault loop; unless this impedance is correctly measured. this safety cannot be confirmed. in this case the test cannot be carried out during installation, because part of the loop is made up of the supply system which is not connected until work is complete. In the event of an open circuit in a protective conductor, the whole of the earthed system could become live during the earth-fault loop test. The correct sequence of testing would prevent such a danger, but the tester must always be aware of the hazards applying to himself and to others due to his activities. Testing routines must take account of the dangers and be arranged to prevent them. Prominent notices should be displayed to indicate that no attempt should be made to use the installation whilst testing is in progress.
The precautions to be taken by the tester should include the following:
1. -make sure that all safety precautions are observed
2. - have a clear understanding of the installation, how it is designed and how it has been installed
3. - make sure that the instruments to be used for the tests are to the necessary standards ,
4. - check that the test leads to be used are in good order, with no cracked or broken insulation or connectors, and are fused where necessary to comply with the Health and Safety Executive Guidance Note GS38
5. - be aware of the dangers associated with the use of high voltages for insulation testing. For example, cables or capacitors connected in a circuit which has been insulation tested may have become charged to a high potential and may hold it for a significant time. ←←←

Essential Tests :
continuity of protective conductors : satisfactory ( GN-3 )

Insulation resistance:
Phase/neutral…………………………MΩ
Phase/earth …………………………MΩ
Neutral/earth …………………………MΩ
Earth fault loop impedance ………………………… Ω ( Live Test )

Polarity satisfactory

RCD operation (if applicable). Rated residual operating current I∆n ………mA and operating time of ………mS (at I∆n

Notes on the formal visual and combined inspection and test record ( Form VI.2 )

1, Register No - this is an individual number taken from the equipment register, for this particular item of equipment
2, Description of equipment, e.g. lawnmower, computer monitor
3, Construction Class - Class 0, 0I, I, II, III. Note that only Class I and II equipment may be used without special precautions being taken
4, Equipment types - portable, movable, hand-held, stationary, fixed, built-in
5/6 , Insert the location and any particular external influences such as heat, damp, corrosive, vibration.
Frequency of inspection - generally as suggested in Table 7.1 of the Code of Practice for In-Service Inspection and Testing of Electrical Equipment
Inspection - items 17-23 and 28 will be completed if an inspection is being carried out
Inspection and Test - the testing in items 24v and 26 should always be preceded by inspection.
9/11 ,The make, model and serial number of the item of equipment should be inserted ,
12/14 , The voltage for which the equipment is suitable, the current consumed and the fuse rating should be inserted ,
15/16 , The date of purchase and the guarantee should be completed by the client
17 , The date to be inserted is the date of the inspection or the date of the inspection and testing ,
18 , Environment and use. It should be confirmed that the equipment is suitable for use in the particular environment and is suitable for the use to which it is being put ,
19 , Authority is required from the user to disconnect equipment such as computers and telecom equipment - where unauthorised disconnection could result in loss of data , Authority should also be obtained if such equipment is to be subjected to the insulation resistance and electric strength tests.
20 , Socket-outlet/flex outlet. The socket or flex outlet should be inspected for damage including overheating.
If there are signs of overheating of the plug or socket-outlet, the socket-outlet connections should be checked as well as the plug. This work should only be carried out by an electrician
21/23 , The inspection required is described in Chapter 14 of the Code of Practice for In-Service Inspection and Testing of Electrical Equipment.
24 / 27 ,Tests. The tests are described in Chapter 15 of the Code of Practice for In-
Service Inspection and Testing of Electrical Equipment. The tests should always be preceded by the Inspection items 17-23 and 28. The instrument reading is to be recorded and a tick entered if the test results are satisfactory
28 , Functional Check - a check is made to ensure that the equipment works properly
29 , Comments/other tests. Additional tests may be needed to identify a failure more clearly or other tests may be carried out such as a touch current measurement. An additional sheet may be necessary, which should be referenced in the box on this record
30 , OK to use - ‘YES’ should be inserted if the item of equipment is satisfactory for use, ‘NO’ if it is not ,

 

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17th Edition Wiring Regulations Practice : Apprentice ,
Overall Percentage Score , 100%

Unit 1: Special installations or locations ( 100% )
Q1 : Zone O in a bathroom is the ( A ) Area within the bath or Shower , ( p-165 701.32.2 )
Hint !! Extreme end ,
Q2 : Zone 1 in a bathroom is the
Hint !! Not quite the extreme end , ( A ) Area directly above the bath or shower up to 2.25m above finished floor level . ( p-165 701.32.3 )
Unit 2 : Appendices ( 100% )
Q2 : BS-1362 relates to ( A ) Cartridge fuses for use in 13A plugs , ( p-229 BS – Standards )
Hint !! Used with BS- 1363
Unit 3 : Inspection & Testing ( 100% )
Q3 : An insulation Résistance test performed on a 50v a.c . SELV installation should be capable of producing a test voltage of
( A ) 250v dc ( p-158 / table 61 )
Hint !! think about ELV downlighters and the average voltage they use ,
Testing : Q 21 : An insulation résistance test performed on a 230v a.c installation should be capable of producing a test voltage ,
Hint !! what type powers the instrument ? ( A ) 500v DC ( p-158 / table 61 )
Unit 4 : Definitions ( 100% )
O4 : A double insulated hand held electric drilling machine is known as
Hint !! think about where you see the symbol , ( A ) Class II equipment ,
Q5 : BS-7671 IEE Regulations define Extra Low Voltage a.c as Not exceeding ( A ) 50 volts a.c , ( p-31 )
Unit 5 : Selection & erection of equipment ( 100% )
Q6 : where a wall consists of a metallic construction and it is necessary to install cables within that wall , the circuit should
( A ) be RCD protected ,
Unit 6 : protection for safety ( 100% )
Q7 : A device intended for safety reasons to cut off all or part of an installation from every source of electrical energy provides ,
( A ) Isolation ( 537 / 537.2 )
Q8 : what is the maximum Zs for a 32Amp type B circuit breaker protecting a standard ring final circuit ,
( A ) 144Ω ( p-49 / table 41.3 )
Unit 7 : Scope , Object and fundamental characteristics ( 100% )
Q9 : Inspection & Testing of an installation should be completed by ( A ) Competent person )
Hint !! Maybe someone who knows what they are doing :
Q10 ; BS-7671 is a ( A ) Non-Statutory document ,
Hint !! its Not enforceable in Law ,
Unit 8 : Assessment of general characteristics ( 100% )
Q 11 : Non-sheathed cables for fixed wiring , other than protective conductors , should be installed in , ( A ) Conduit or Trunking ,
Q 12 : who is responsible for specifying the first periodic inspection on an installation ?
Hint !! who knows everything about an installation before the Other ?
( A ) the person responsible for the design ,
Q 13 : Inspection & Testing of an installation should be completed by ?
Hint !! maybe someone who knows what they are doing ,
( A ) Competent persons ,
Q 14 : Basic protection protects against ?
Hint !! the most basic of contact ,
Electric shock under fault free conditions ,
Q 16 : Any overcurrent protective device installed at the origin of a circuit must have a breaking capacity of ?
Hint !! what cases the maximum current to flow under fault conditions ,
( A ) Equivalent or more to the prospective short circuit current ,
Q 17 : Non-sheathed cables for fixing wiring , other than protective conductors , should be installed in ,
Hint !! think what the sheathing provides on cable , ( A ) Conduit or Trunking ,
Q 18 : Undervoltage protection is required where the restoration of power may cause ,
Hint !! what can be dangerous if power is suddenly turned on ?
( A ) Unexpected starting of machinery ,
Q 19 : outdoor lighting involves all the following except ,
Hint !! Temporary installation , ( A ) Festoon lighting ,
Q 20 : where a wall consists of a metallic construction and it is necessary to install cables within that wall the circuit should ?
Hint !! needs additional protection , ( A ) be RCD protected ,

 

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PERIODIC INSPECTION REPORT FOR AN ELECTRICAL INSTALLATION
(REQUIREMENTS FOR ELECTRICAL INSTALLATIONS - BS 7671 [IEE WIRING REGULATIONS])
Extent and Limitations of the Inspection :
Extent of Electrical Installation covered by this report ,
Limitations ( see Regulation : 634.2 p-163 ,

Insulation resistance
If the DC resistance tests above fail to identify the cause of a circuit that is causing RCD tripping on its own (i.e. without the aid of the appliances usually connected to it). You may find that repeating the tests described using an insulation resistance tester will yield more information. Since the insulation resistance tester carries out the tests at much higher voltages than the multimeter (typically 500V) it will identify those few failures where the conduction path between a live conductor and earth is only visible at mains voltages.
Take care when performing these tests, it is possible to get a nasty shock off an insulation test meter!
Mitigating the effects of nuisance trips
While it is possible to eliminate most causes of nuisance trips with careful system design and testing, it is always wise to design the system to allow for the possibility of it happening:
* Provide dedicated non RCD protected circuits [see note] for vulnerable equipment such as:
*Freezers
* Central Heating Systems
* Heated Aquariums
* Fire or smoke alarms
* Security systems and lighting
* Computer and IT equipment
* Have as few circuits or devices as possible protected by the same RCD so that a trip impacts as few extraneous circuits as possible. The ultimate solution would use RCBOs for each circuit. Obviously expense has to be weighed against the implications of tripping.
* Use emergency lighting to backup any important lighting circuits that need to be RCD protected (i.e. on TT earthing systems). In particular these should include lighting for:
* Stairs
* Fire escape routes
* Near trip hazards or other difficult to navigate areas
* Near the consumer unit
* Consider using uninterruptible power supplies (UPS) to maintain running of critical equipment.
* Power failure alarms might also be an appropriate measure in some circumstances.
Note: With the advent of the 17th edition of the wiring regulations, one must comply with the requirement that any buried cables that don't have 30mA trip RCD protection, must still be adequately protected from physical damage. This can be achieved either via being buried at 50mm or greater depth in a wall, or with metallic earthed protection such as conduit or by using suitable metal sheathed cables like SWA, MICC etc. Note that new cable types are becoming available to help meet these requirements. Surface mounted cables may also be installed without additional RCD protection in some circumstances since it is assumed they are sufficiently visible to avoid accidental damage from drilling / nailing etc.
System design using RCDs
Some of the system design aspects of using RCDs to good effect are covered in the mitigation section above. However the following basic principles should also applied:
1. Use split load consumer units, to allow circuits that do not benefit from RCD protection to be powered directly.
2. Don't place too many circuits on the same RCD. In particular identify circuits that are likely to have high leakage (e.g. those containing lots of IT other electronic equipment).
3. Where RCDs need to be cascaded, use time delayed types for the upstream device so that trips are contained close to the cause of the fault.
4. Don't place circuits to outside electrics and outbuildings on the same RCD as protects the house circuits.
5. Avoid placing high leakage devices on RCD protected circuits where possible.
6. Design circuits such that the anticipated leakage is no more than 25% of the trip threshold. This will allow for later circuit extension.
7. Ensure accessories and wiring are not placed in excessively damp environments.
8. Don't use lower trip threshold devices that is appropriate for the level of risk present and protection sought.

NOTES ON COMPLETION OF MINOR ELECTRICAL INSTALLATION WORKSCERTIFICATE :

Scope :
The Minor Works Certificate is intended to be used for additions and alterations to an installation that do not
extend to the provision of a new circuit. Examples include the addition of socket-outlets or lighting points to
an existing circuit, the relocation of a light switch etc. This Certificate may also be used for the
replacement of equipment such as accessories or luminaires, but not for the replacement of
distribution boards or similar items. Appropriate inspection and testing, however, should always be
carried out irrespective of the extent of the work undertaken ,

Part 1 Description of minor works :
1,2 The minor works must be so described that the work that is the subject of the certification can be
readily identified.
4 : See Regulations 120.3 and 120.4. No departures are to be expected except in most unusual
circumstances. See also Regulation 633.1

Part 2 Installation details :
2 : The method of fault protection must be clearly identified e.g. earthed equipotential bonding and
automatic disconnection of supply using fuse/circuit-breaker/RCD
4 : If the existing installation lacks either an effective means of earthing or adequate main equipotential
bonding conductors, this must be clearly stated. See Regulation 633.2
Recorded departures from BS-7671 may constitute non-compliance with the Electricity Safety, quality
and continuity Regulations 2002 (as amended) or the Electricity at Work Regulations 1989. It is
important that the client is advised immediately in writing.

Part 3 Essential Tests :
The relevant provisions of Part 6 (Inspection and Testing) of BS 7671 must be applied in full to all minor
works. For example, where a socket-outlet is added to an existing circuit it is necessary to ;
1 : establish that the earthing contact of the socket-outlet is connected to the main earthing terminal
2 : measure the insulation resistance of the circuit that has been added to, and establish that it complies with Table 61 of BS 7671
3 : measure the earth fault loop impedance to establish that the maximum permitted disconnection time is not exceeded
4 : check that the polarity of the socket-outlet is correct
5 : (if the work is protected by an RCD) verify the effectiveness of the RCD

Part 4 Declaration :
1,3 The Certificate shall be made out and signed by a competent person in respect of the design , construction, inspection and testing of the work
1,3 The competent person will have a sound knowledge and experience relevant to the nature of the
work undertaken and to the technical standards set down in BS-7671 be fully versed in the inspection
and testing procedures contained in the Regulations and employ adequate testing equipment.
2 : When making out and signing a form on behalf of a company or other business entity, individuals shall state for whom they are acting ,

 

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SELV and PELV :

According to IEC 60364-4-41 protection against electric shock is deemed to be provided when:
• the nominal voltage cannot exceed an upper limit in accordance with IEC 60449 (50 V AC / 120 V DC)
• the supply is from a safety isolating transformer in accordance with IEC 60742 or equivalent (e.g. motor generator with windings providing an equivalent isolation)
• an electrochemical source (e.g. battery) or another source independent of a higher voltage circuit (e.g. diesel-driven generator),
• mobile sources or certain electronic devices all complying with appropriate standards, where measures have been taken in order to ensure that, even in the case of an internal fault, the voltage at the outgoing terminals cannot exceed the above mentioned levels , or
• when all above conditions are fulfilled and in addition electrical separation with either SELV for unearthed circuits or PELV for earthed circuits is provided
Arrangement of circuits :

IEC 60364-4-41 states that live parts of SELV and PELV circuits shall be electrically
separated from each other and from other circuits. Arrangements shall ensure electrical separation
not less than that between the input and output circuits of a safety isolating transformer ,
Circuit conductors of each SELV and PELV system shall preferably be physically
separated from those of any other circuit conductors. When this requirement is impracticable, one of the following arrangements is required
• Plugs and socket-outlets of SELV and PELV systems shall comply with the following requirements
– plugs shall not be able to enter socket-outlets of other voltage systems : – socket-outlets shall not admit plugs of other voltage systems :
– socket-outlets shall not have a protective conductor contact :

Requirements for unearthed circuits ( SELV ) :
According to IEC 60364-4-41, live parts of SELV circuits shall not be connected to
earth or to live parts or to protective conductors forming part of other circuits
Exposed conductive parts shall not be intentionally connected to :
* earth; or
* protective conductors or exposed conductive conductors of another circuit; or
* extraneous conductive parts.
If nominal voltage exceeds 25 V AC r.m.s or 60 V ripple-free DC, protection against direct contact shall be provided by:
* barriers or enclosures affording a degree of protection of at least IP2X or IPXXB; or
* insulation capable of withstanding a test voltage of 500 V AC r.m.s for 1 minute ,
In general, protection against direct contact is unnecessary if the nominal voltage
does not exceed 25 V AC r.m.s. or 60 V ripple-free DC. However, it may be necessary under certain
conditions of external influences, which is currently under consideration by the IEC.

 

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Why Earth ?
One side of the electricity supply (the neutral) is firmly connected to earth at the substation to prevent the supply 'floating' relative to earth for safety reasons.
Many electrically operated devices (e.g. washing machines, heaters and some lighting fittings) have exposed metalwork which could become live if a fault occurred. Anyone touching it could then receive a shock or even be killed depending on the current flowing through them to earth. To prevent this, an earthing conductor should be provided to all socket outlets, lighting circuits and any fixed appliances to which exposed metal parts are then connected. The earth connection limits the voltage which can appear on the exposed metal parts under fault conditions to a safe value until the fuse blows or the MCB or RCD trips. Note that earthing does not necessarily prevent anyone receiving a shock, but together with the time/current characteristics of the protective device (fuse, MCB or RCD) it should ensure that it is not lethal. It is desirable to make the impedance (resistance) of the earth wiring a low as practicable. (1000A flowing through 0.1 ohm drops 100V! )
Note that exposed metalwork cannot be protected by connection to the neutral because current flowing will cause a voltage drop between the metalwork and true earth. Also, if the neutral connection breaks or the appliance is plugged into a socket with line and neutral reversed (!), the metalwork will be at full mains voltage.
Appliances with an earth connection are called Class I (one): Class II or 'double insulated' appliances incorporate additional insulation to prevent exposed metalwork becoming live, and do not require an earth connection. This means that a 2-core mains lead can be used and internal earth connections are not needed.
A fundamental principle of electrical safety is that no single fault condition should cause a hazardous situation. This is why some of the regulations may appear to be rather stringent: it is better to be safe than sorry.
Who Supplies the Earth ?
The earth connection will usually be supplied by one of the following methods:
a). By the electricity company. Either through the armouring of the supply cable or through a combined neutral and earth conductor. The latter method is termed PME (protective multiple earthing) and requires some special attention (see below). There will usually be a label near the meter indicating a PME system.
b). Through an earth electrode; usually a rod or plate driven into the ground. This method is found where the electricity company cannot easily supply or guarantee an adequate earth conductor; for example, where the supply comes on a pair of overhead wires. The user is generally responsible for the adequacy of the earth electrode.
The method of earthing can normally be found out by tracing the wiring from the meter/consumer unit. It is usually fairly obvious. IMPORTANT! - It is no longer permitted to use a water or gas pipe for the main or only earthing connection. There may, however be earth bonding wires connected onto the water and gas pipes for 'equipotential bonding' (see below). If there is no electricity company earth or dedicated separate earth electrode, then one must be provided. Contact the electricity company if in any doubt.

Earthing of Electrical Installation :
Each circuit requires an earth conductor to accompany (but kept separate from) the line and neutral conductors throughout the distribution. Where the distribution is in the form of a ring, the earth connection must also complete the ring.
The bare tails of earth conductors must be insulated with green/yellow sleeving from the exit from the cable sheath to the earth terminal.
All metal boxes should be connected to the earth; either through a short tail covered with green/yellow sleeving to the socket earth terminal or directly by the earth conductor for a switch box.
Equipotential Bonding
As mentioned elsewhere, a fault current flowing in the earth wiring will cause the voltage on that wiring to rise relative to true earth potential. This could cause a shock to someone touching, for instance, the case of a faulty washing machine and a water tap at the same time. In order to minimise this risk, an 'equipotential zone' is created by connecting the services to the main earthing point. Such services are:
• Water Pipes
• Gas Pipes
• Oil Pipes
• Central Heating
• Metallic Ventilation Trunking
• Exposed Parts of Building Structure
• Lightning Conductor
• Any other Metallic Service

WHY DO LIGHT BULBS ALWAYS BLOW WHEN YOU SWITCH THEM ON, AND WHY DO THEY BLOW FUSES ?
An ordinary incandescent "light bulb" consists of a thin tungsten filament in a glass envelope containing an inert gas. The filament has a relatively high resistance, and thus gets hot - hot enough to give out useful amounts of light as well as lots of heat - when current is flowing through it. The inert gas prevents the hot tungsten rapidly oxidising, as it would in air, or rapidly evaporating, as it would in a vacuum. It does, however, reduce efficiency, by conducting heat away from the filament. (Different gases and pressures are selected for different applications: for example, krypton and xenon are advantageous because they convect less and prevent evaporation better than argon/nitrogen, and therefore allow a hotter, more efficient, filament to be used while maintaining lamp life. Note that quartz halogen bulbs are different again: here, evaporated tungsten is re-deposited on the filament, thus allowing it to be hotter still while maintaining its life.)
Tungsten, being a metal, has a resistivity which increases as its temperature rises. Therefore, when you switch on a lamp, it presents a much lower resistance than normal to the passage of electricity, and so your beefy electricity supply will drive through a great deal more current than normal while the filament heats up, putting it under thermal stress as it expands. This on its own encourages the filament to give up and break, but it is exacerbated by the fact that any thinned section will incur extra stress, as it will heat up more quickly than the rest of the filament (being thinner), present a higher resistance, and thus dissipate even more than its fair share of the (increased) power. This will tend to thin it further, rapidly, and hence lead to a point of failure.
How do you deal with it? Well, using a rotary on/off dimmer, where you always have to switch on the lamp at its lowest brightness, will help a lot. A dimmer will reduce the maximum available light output slightly. You can also fit negative temperature coefficient thermistors in series with the bulb. These have a resistance/temperature characteristic with the opposite slope to that of the filament, so give a "soft start" until they themselves warm up. Again, you will lose a little brightness, and waste a little energy in the hot thermistors. I am not aware of any "off the shelf" products containing thermistors, probably because they need to be selected for the wattage of lamp required.
It should be noted, however, that it is probably counterproductive to try to keep a light bulb alive for too long. This is because the thinned filament will be taking less current, so the light output will be reduced, and the tungsten that has evaporated from it will be deposited on the inside of the glass, reducing efficiency by blocking some of the light.
As regards blowing the fuse, this is never directly due to a broken filament falling onto the lead-out wires, and thus presenting a much lower resistance, but is due to the gas or vaporised filament in the bulb becoming ionised. The high temperature and large electric field (full mains voltage across a very small gap) which occurs when the filament breaks can cause the gas to go into a conducting state, and the plasma will "spread" until it shorts out the lead-out wires, because it presents a much lower resistance than the filament. This causes a "pop" due to rapid heating, and has been known to cause the envelope to explode. Light bulbs usually have built-in fuses to deal with this, but as they are built down to a price, they aren't always effective.
If you plug in a new light bulb and it only lasts a few seconds, leaving a white pattern on the glass, this is because it has cracked at some point, letting air in. When energised, the filament has oxidised to white tungsten oxide, which condenses on the glass in a pattern corresponding to the flow of air inside as the lamp is switched on.
Oh, by the way, "extra-long life" bulbs seem to be a con. They just run at a lower temperature than normal bulbs, thus lasting longer, but being a lot less efficient. There is no justification for the extortionate prices charged for them.

 

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Cables in contact with polystyrene

Do not let electrical cables come into contact with polystyrene. It slowly leaches the plasticiser out of the PVC, so that it becomes stiff and brittle. Sometimes it looks like the PVC has melted and run a little.

* Shaver sockets incorporate special isolating transformers which provide an earth-free output. The primary (input) side requires an earth which is connected internally to the transformer core.

Protective Multiple Earthing (PME.)
With PME. the neutral and earth conductors of the supply are combined. The supply company connects the neutral solidly to earth frequently throughout the distribution network. At the customer's connection point the company supplies an 'earth' (which is actually connected to the neutral) to which all the installation earths and equipotential bonding are connected. Note that within the installation, the earth and equipotential bonding are kept separate from the neutral in the usual way.
With PME. there is a potential danger in that if the combined neutral/earth conductor of the supply became broken (very unlikely but nevertheless possible), the voltage on the earth conductors could rise towards the full supply voltage. It is most important therefore that equipotential bonding is rigorously applied in installations supplied by PME. The minimum size of main bonding conductor is 10 sq mm but may need to be up to 25 sq mm depending on the size of the incoming neutral/earth conductor: the supply company will advise you.
Electricity System Earthing Arrangements
Mains electricity systems are categorised in the UK according to how the earthing is implemented. The common ones are TN-S, TN-C-S and TT. You will sometimes see these referred to in questions and answers about mains wiring.
Note that in these descriptions, 'system' includes both the supply and the installation, and 'live parts' includes the neutral conductor.
First letter:
T The live parts in the system have one or more direct connections to earth.
I The live parts in the system have no connection to earth, or are connected only through a high impedance.
Second letter:
T All exposed conductive parts are connected via your earth conductors to a local ground connection.
N All exposed conductive parts are connected via your earth conductors to the earth provided by the supplier.
Remaining letter(s):
C Combined neutral and protective earth functions (same conductor).
S Separate neutral and protective earth functions (separate conductors).
TN-C No separate earth conductors anywhere - neutral used as earth throughout supply and installation
TN-S Probably most common, with supplier providing a separate earth conductor back to the substation.
TN-C-S [Protective Multiple Earthing] Supply combines neutral and earth, but they are separated out in the installation.
TT No earth provided by supplier; installation requires own earth rod (common with overhead supply lines).
IT Supply is e.g. portable generator with no earth connection, installation supplies own earth rod.
Inside or nearby your consumer unit (fuse box) will be your main earthing terminal where all the earth conductors from your final sub-circuits and service bonding are joined. This is then connected via the 'earthing conductor' to a real earth somehow...
TN-S The earthing conductor is connected to separate earth provided by the electricity supplier. This is most commonly done by having an earthing clamp connected to the sheath of the supply cable.
TN-C-S The earthing conductor is connected to the supplier's neutral. This shows up as the earthing conductor going onto the connection block with the neutral conductor of the supplier's meter tails. Often you will see a label warning about "Protective Multiple Earthing Installation - Do Not Interfere with Earth Connections" but this is not always present.
TT The earthing conductor goes to (one or more) earth rods, one of them possibly via an old Voltage Operated ELCB (which are no longer used on new supplies).
There are probably other arrangements for these systems too. Also, a system may have been converted, e.g. an old TT system might have been converted to TN-S or TN-C-S but the old earth rod was not disconnected.

 

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Consumer Units
Live parts must be contained inside enclosures or behind barriers providing a degree of protection of at least IX2X or IPXXB. 416.2.1
The horizontal top surface of a readily Accessible barrier or enclosure must provide a degree of protection of at least IX4X or IPXXD. 416.2.2
All installations must be divided into separate circuits so as to comply with the following :
- avoid danger and inconvenience if a fault develops
- allow safe maintenance, inspection & testing
- prevent any danger that may be caused by the loss of supply to a single circuit e.g. a lighting circuit
- reduce the possibility of nuisance tripping of RCDs by equipment with high cpc currents produced in normal use e.g. computers
- prevent electromagnetic interference between items of electrical equipment
- prevent the accidental energising of an isolated circuit .
314.1

A double pole main switch or linked circuit breaker must be installed as close as possible to the incoming supply at the origin of the installation. 537.1.4
Unless specifically labelled or suitably identified, all 13A socket outlets must be 30ma RCD protected. 411.3.3
Fire detection circuits must be supplied independently of other circuits and not protected by an RCD protecting multiple circuits. 560.7.1
Fire detection .cables, not including metal screened fire resistant cables, must be adequately segregated from cables supplying other circuits. 560.7.7
Extra Low Voltage circuits should not be run in the same wiring system as 230v circuits unless all ELV cables and conductors are insulated for 230v or separated by an earthed metal screen. 528.1
All electrical equipment must be accessible for operation, inspection & testing , maintenance and repair. 132.12
Before an installation or an addition / alteration to an installation is energised, inspection and testing must be carried out to ensure the requirements of BS-7671 have been met and an appropriate Certificate must then be issued. 134.2.1, 610.6, 631.1
Any defects found in the existing installation must be recorded on the Electrical Installation Certificate or Minor Electrical Installation Works Certificate. 633.2
A single pole fuse or circuit breaker must be used with the line conductor only. 132.14.1
Only a linked circuit breaker that breaks all related line conductors can be used with an earthed natural conductor. 132.14.2
All final circuits must be connected to a separate way in the consumer unit. 314.4
In a ccu the natural conductors and cpc's should be connected to their respective terminals in the same order as the phase conductors are connected to the mcb's. 514.1.2

An unfused spur may be connected to the origin of a radial or ring final circuit in the consumer unit. 433.1
All protective devices must be labelled. 514.8.1
A periodic inspection notice must be fixed on or next to the ccu. 514.12.1
Where applicable an RCD notice must be fixed on or next to the ccu. 514.12.2
Where the installation contains wiring colours to two versions of BS-7671 a warning notice must be fixed on or next to the ccu. 514.14.1
A voltage warning notice is only required where a nominal voltage exceeding 230v exists. 514.10.1
A durable copy of the schedule from the electrical installation certificate must be fixed next to or placed inside the consumer unit. In addition to circuit details the schedule must also contain information about the protective measures used in the installation ie automatic disconnection of supply, electrical separation , SELV , RCD. 132.13, 514.9
All literature supplied with fire detection equipment must be made available to the occupant of the dwelling. 560.7.12
Fuses and mcb's must have a breaking capacity greater than or equal to the maximum PFC at the point where the device is installed. 432.1 A lower breaking capacity is allowed if another fuse or mcb with the necessary breaking capacity is installed on the supply side and the energy let-through of both devices will not damage the fuse or mcb on the load side. 434.5.1, 536.1
Consumer units must be spaced at least 150mm away from gas pipes unless there is a pane of non combustible insulating material separating them. OSG p18
In areas subject to flooding, consumer units should preferably be installed above flood water level. OSG p161
Overcurrent protection devices must comply with one or more of the following standards :

Bs 88-2.2 .
Bs 88-6 .
Bs 646 .
Bs 1361 .
Bs 1362 .
Bs 3036 .
Bs en 60898-1 & -2 .
Bs en 60947-2 & -3 .
Bs en 60947-4-1, -6-1 & -6-2 .
Bs en 61009-1 .
533.1

MINOR ELECTRICAL INSTALLATION WORKS CERTIFICATE : p-335 / 336

GUIDANCEFOR RECIPIENTS (to be appended to the Certificate)
This Certificate has been issued to confirm that the electrical installation work to which it relates has been
designed, constructed and inspected and tested in accordance with British Standard 7671, (the IEE Wiring
Regulations). You should have received in ‘original’ Certificate and the contractor should have retained
duplicate. If you were the person ordering the work, but not the owner of the installation, you should
pass this Certificate, or copy of it, to the owner.
A separate Certificate should have been received for each existing circuit on which minor works have been
carried out. This Certificate is not appropriate if you requested the contractor to undertake more extensive
installation work., for which you should have received an Electrical installation Certificate.
The Certificate should be retained in safe place and be shown to any person inspecting or undertaking
further work on the electrical installation in the future. If you later vacate the property, this Certificate
will demonstrate to the new owner that the minor electrical installation work carried out complied with
the requirements of British Standard 7671 at the time the Certificate was issued.

MINOR ELECTRICAL INSTALLATION WORKS CERTIFICATE :
(REQUIREMENTS FOR ELECTRICAL INSTALLATIONS - BS 767 ( IEE WIRING REGULATIONS )
To be used only for minor electrical work which does not include the provision of new circuit

Agreed limitations on the inspection and testing ← with Client ,

Declaration
I/We certify that the electrical installation work, as detailed in part 1 of this certificate, do not impair the safety of the existing installation, that the said works have been
designed, constructed, inspected and tested in +accordance with BS 7671:2008 * ( IEE Wiring Regulations), amended to the date shown* and that to the best of my/our
knowledge and belief, the time of my/our inspection, complied with BS 7671 except as detailed in Part 1 of this certificate.
This form is based on the model shown in Appendix 6 of BS 7671: 2008

239- Inspection Testing & Certification of Electrical Installations Exam : Part B scenario :
Solution to terminating the underground SWA supply cable :
-&-'s question may lead you to terminate the SWA of the underground supply cable, since the question informs you. "You are NOT allowed to use the supply companies earthing system as a means of earthing the outhouse" However -&-'s mention nothing about earthing the supply cable itself. It is difficult to decide whether -&-'s are just testing the candidates knowledge of this situation VERY thoroughly or alternatively offering a red-herring to mislead the unwary candidate. Whichever is the reason for this question, it caused many exam candidates a great deal of difficulty and lost time trying to decide what the solution was.

The actual solution stems from BS 7671 regulation 542.1.8 part of this reg states , ←

"If the protective conductor ( i.e. the swa ) forms part of a cable, the protective conductor shall be earthed only in the installation containing the associated protective device" This therefore has to be the main house end. See the only possible solution below :
( Main house CCU / TN-C-S / Systems ) MET : ←←

part B scenario : gave many candidates a difficult time. Here you were presented with a TN-C-S system installed in a domestic property, and an underground supply cable is being used to supply an external outhouse. However the electricity supply company will not allow you to use their means of earthing for the outhouse. So how do you provide a means of earthing for the outhouse? Where do you earth the supply cable? What checks must you make on the underground supply cable? Why can't you use the main house TN-C-S system as a means of earthing the outhouse ?

 

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Many candidates continue to get the value of Zs wrong for the circuit in question in part B of the exam.
A common error when completing questions involving schedule of test results is to forget to indicate functional tests have been performed and found satisfactory/unsatisfactory. To tick the tick box when completing details of ring final circuits, ensuring to indicate continuity of ring final conductors have been performed.
Failure to record the type of earthing system, i.e. TN-S, TN-C-S, TT,
Failure to record the value of Ze, PFC, Nominal voltage, Nominal frequency, are common errors.
Test procedures
A very common question is to explain in detail how to perform an insulation resistance test, often on a lighting circuit. Candidates regularly fail to state the instrument used which is an 'Insulation Resistance Ohm-meter' (Not a Megger! You will not gain any marks if you answer a Megger) Many candidates fail to identify the test voltage required for typical 230/240 volt installation which is 500 volts and the acceptable test value which is 0.5 Meg-ohm or greater (again due to change under 17th edition to a minimum acceptable value of 1.0 Meg-ohm) City and Guilds usually deliberately pick a lighting circuit that is stipulated as having two way switching, just to see if the candidate mentions to test the strappers in BOTH positions.
Failure to mention testing the insulation resistance of both strappers will lose you marks. Be warned!
Candidates regularly make mistakes when answering RCD questions. Often the question or specifications usually given in part B will make reference to a specific type of RCD for example a 30 mA RCD. Candidates are then asked to state the actual test current applicable to test this type of RCD. Candidates regularly incorrectly state the answer as x1/2 x1 and x5 instead of x1/2 = 15mA x1 = 30mA and x5 = 150mA

'Memorandum of Guidance on the Electricity at Work Regulations 1989'
This may help you somewhere on your 2391 ,

5. General :

1. The majority of the regulations are directed at hardware requirements. Installations are required to be of proper construction; conductors must be insulated or other precautions taken; there must be means of cutting off the power and means for electrical isolation. The hardware requirements are complemented by a group of regulations stating principles of safe working practice. Regulation 14, which covers live working, is of particular importance.
2. The scope of the EAW Regulations is limited by the definition of danger and injury solely to risks arising from an electrical source and does not include, for example, control-system faults and consequent hazards such as aberrant machinery behavior.
3. The EAW Regulations revoke a number of specific regulations, but a number remain which either overlap or appear to overlap, for example
1. the Electricity Safety, Quality and Continuity Regulations 2002 (as amended): see the introduction to the Memorandum of guidance.
2. the Low Voltage Electrical Equipment (Safety) Regulations 1988 (made under the Consumer Protection Act 1987);
3. the Building (Scotland) Regulations 2004: these give deemed to satisfy status to BS7671 Requirement for Electrical Installations (also known as the Institution of Electrical Engineers Wiring Regulations, 16 th Edition); and
4. the Cinematographic (Safety) Regulations, 1955.
If demarcation between these sets of regulations and the EAW Regulations is unclear in a particular case, then details should be passed to HSE, via the Enforcement Liaison Officer.
4. Appendices 1 and 2 of the Memorandum of guidance list publications relating to electrical safety.

6. Enforcement
1. There is no expectation that inspectors should change their general approach to enforcement. However, particular attention should be paid to the enforcement of reg 14. (Work on, or near, live conductors).
2. In situations where the 1908 Regulations previously applied or where HSW Act was used, inspectors should now enforce the EAW Regulations.
3. There should be no difference in enforcement between situations in which no specific regulations previously applied and those which were regulated
4. Nothing is required by the EAW Regulations which is not already the norm in the best undertakings.
5. The EAW Regulations will apply to electrical work in domestic premises. Such work will fall to HSE to enforce.
6. Expert assistance to prove the presence of electricity should not be necessary when contemplating enforcement action. Circumstantial evidence should suffice to indicate that electricity is present and that the EAW Regulations apply. Such evidence could include:
1. that the equipment carried a plate indicating that it worked at mains voltage;
2. that the equipment was connected to a supply via a 3-pin plug;
3. that the premises were supplied with electricity for lighting which was working; and
4. that a person on the premises paid an electricity bill.
In court, an expert witness should be able to use such evidence to express a professional opinion as to the dangers which were present or likely to occur.
7. It may also be possible to use an on-site electrician to measure voltages and use his or her measurements in evidence.
8. An improvement notice may be appropriate it conductors are inadequately protected against damage; for example, not routed through conduit, tubing or armouring in premises where the risk of physical damage is apparent. In particularly arduous conditions, e.g. construction work, stronger action may be considered.
9. Exposed and accessible live conductors or a lack of earthing could justify a prohibition notice. Lack of earthing can only be proved by measurement; simple observation is never adequate.

7. Interpretation (Reg 2)
1. The definitions of danger and injury are linked but distinguished to accommodate those circumstances when persons must work on or so near live equipment that there is a risk of injury, ie where danger is present and cannot be prevented.
2. Danger includes danger to the public.
3. The definition of electrical equipment excludes items which only generate electricity adventitiously, eg as static.
4. Earthing and isolation are defined in regs.8 and 12 respectively.
8. Duties (Reg 3)
1. Regulation 3 imposes duties only on employers, employees, the self-employed, and mine or quarry managers. In other cases HSW Act ss.3 and 4 will apply.
2. All duties are limited by the phrase "to matters which are within his control", apart from reg.3(2)(a) which is similar to HSW Act, s.7(b). Some large industries tend to produce written rules which clearly define the extent of an individual's control but it will often be the case that there is overlapping liability where several individuals and/or bodies corporate are duty holders.

9. Systems, work activities and protective equipment (Reg 4)
1. Regulation 4 acts as a catch-all requirement.
2. Due to the broad definition of system (reg 2), reg 4 covers almost every conceivable electrical danger: from an exploding lithium battery in a calculator to the output side of a power station.
3. Systems in vehicles are covered by reg 4, but note should be taken of reg 32 in relation to ships, aircraft and hovercraft.
4. Regulation 4(3) embraces all work which could lead to electrical danger, although such work may not be associated with an electrical system. This would include work in the vicinity of electrical equipment and insulated or uninsulated conductors. The requirement does not limit proximity to conductors, live or dead, but rather regulates the work activity so as not to give rise to danger.
5. Regulation 4(3) is almost always applicable to work on or near underground cables, in which situations the standards of the Construction (GP) Regulations, reg 44 should be maintained, viz electrical isolation by disconnection and secure separation from sources of electrical supply. However, reg 14 should be used if there has been a failure to switch off the supply to such cables before undertaking work. That said, the circumstances of each case will dictate which regulation should be used.
6. The duties in reg 4(4) are not qualified by "so far as is reasonably practicable' and link with reg 14(c) ensuring that protective equipment provided is always suitable for the purpose.
10. Strength and capability of electrical equipment (Reg 5)
1. The assigned rating of electrical equipment represents the extent to which it may be used in an assessment of the adequacy of equipment strength and capability in foreseeable conditions of actual use; but may not necessarily represent all factors to be considered. A technical judgement by a competent person will often be needed to determine adequacy.
2. If a failure has occurred it may be relatively easy to prove a contravention. However, expert support will be required except where a deficiency is obvious and requires no technical proof.

 

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11. Adverse or hazardous environments (Reg 6)
1. Regulation 6 addresses extrinsic effects which are reasonably foreseeable. For example, in order to prove a contravention of reg.6, it is not necessary to show that electrical equipment is or has been exposed to a flammable atmosphere, but only that it is foreseeable that it could be so exposed.
2. The Memorandum of guidance gives general advice on the different hazardous environments covered by reg 6, and makes reference to relevant standards and publications.
12. Insulation, protection and placing of conductors (Reg 8)
1. This regulation is an example of where the EAW Regulations extend protection to anyone exposed to electrical danger from electrical equipment, including those not at work
13. Earthing and other suitable precautions (Reg 8)
1. This regulation applies to any conductor and not just to metal. It also allows other suitable means of preventing danger as an alternative to earthing.
2. The duty to prevent danger arising is activated only when a relevant conductor becomes charged.
3. Regulation 4 requires that systems are constructed so as to prevent danger; but in the event that danger arises because a conductor which should be earthed is not, reg.8 also becomes relevant.
4. As regards adequate earthing, the use of a conductor with a small cross-sectional area, which is not capable of carrying a heavy current for the duration of the fault, is not acceptable.
5. Inspectors should continue to press for the use of reduced voltage lighting and power tools, e.g. 110v centre tapped to earth in the working environments described in para 19 of the Memorandum of Guidance (e.g. construction work).

14. Integrity of reference conductors (Reg 9)
1. Regulation 9 is fully explained in the Memorandum of guidance.
15. Connections (Reg 10)
1. The definition of danger means that connections have to be mechanically and electrically suitable to prevent the risk of electrical injury.
16. Means for protecting from excess current (Reg 11)
1. The due-diligence defence in reg 29 is important when enforcing this requirement because, in theory, it is impossible in an absolute sense to prevent danger arising before any excess current protection device operates.
17. Means of cutting off the supply and for isolation (Reg 12)
1. This regulation cannot be used to require means to prevent non-electrical hazards arising from the use of electrical controlled systems.
2. Permit-to-work systems relying on a warning notice may be encountered. Where such systems are well established, tried and tested they could represent adequate isolation. However, they need to meet the minimum requirements of this regulation and when assessing such systems, inspectors should seek expert assistance, where appropriate.
3. Regulation 12 covers electrical equipment which may become charged by means other than connection to the supply, e.g. through capacitance or induced current arising from proximity to other live conductors.
4. There are no voltage limits.
18. Precautions for work on equipment made dead (Reg 13)
1. Regulation 13 may apply during any work, be it electrical or non-electrical.

19. Work on or near live conductors (Reg 14)
1. This regulation is very important and should be used to reduce the incidence of live working and to ensure strict precautions are adhered to when such work is carried out.
2. All 3 conditions stipulated in the regulation must be met before live working is permitted.
3. "Reasonable in all the circumstances" (reg 14(b)) means that all necessary precautions must be taken to ensure it is reasonable for someone to be asked to work.
4. Regulation 14(c) could imply that in the absence of injury no precautions can be required in advance. This would mean that notices requiring such precautions could not be issued. This interpretation is not correct because:
1. it would not be reasonable to work in a situation where the necessary precautions had not been taken; and
2. in order to take precautions it is necessary to foresee the potential harm, and such precautions will only be suitable if they are adequate to prevent the harm foreseen.
Therefore, if an inspector judges that the precautions taken will not prevent injury, he or she could issue a notice citing an apparent breach of reg 14.
5. Inspectors should question all live working wherever they find it. This could be in many establishments and also where peripatetic electricians are working.
6. The issue of accompaniment during live work is touched upon in the Memorandum of guidance. The presence of a colleague who could render assistance if safe to do so could prevent injury or mitigate its extent.
20. Working space, access and lighting (Reg 15)
1. This regulation only applies to the period during which work is being carried out.
2. It can be used to prevent the storage of goods etc in front of switchboards on the basis that the act of operating switching device is considered to constitute work on the equipment in question.

21. Competence to prevent danger and injury (Reg 16)
1. If competence is in doubt, inspectors should enquire into:
1. technical knowledge, and
2. experience
in relation to the work activity being undertaken. Clearly, more knowledge is required of those involved in high voltage work compared to those doing 25-volt test work.
2. HSE specialist support is available for assessing electrical competence (via the ELO).
3. The regulation does not require authorisation of competent persons but in conjunction with regs 4 and 14 such authorisation may be required, when necessary, to avoid danger.
4. The regulation does not specify any age limitations. The key requirements are adequate and relevant knowledge and experience, or an appropriate degree of supervision to allow persons to work safely and possibly to acquire those attributes.
22. Defence (Reg 29)
1. The defence only becomes relevant once it has been established that an offence has been committed. It should not affect the judgement of the duty holder as to the steps he or she should take to meet an absolute requirement
2. Employers may suggest that they have taken reasonable steps to meet their obligations by the delegation of responsibility to adequately qualified and instructed staff. This approach is pre-empted by the specific duties placed upon employers and others by reg 3.
3. HSE electrical specialists may be able to provide technical support in relation to a due diligence defence.

23. Exemptions (Reg 30)
1. Any applications for an exemption should be forwarded, together with a full report, to the Local Authority Unit.
24. Disapplication of duties (Reg 32)
1. The EAW Regulations apply to all vehicles, except those exempted by this regulation
2. Sea-going ships are exempt in relation to normal shipboard activities under the direction of the Master, whether they are in dock or under way in an inland waterway or at sea.
3. The term sea-going is not defined in these or any other health and safety regulations, but the intended meaning is clear and common to other regulations (eg Docks, COSHH).
4. The reference to any person in reg 32(b) includes the employer.

Appendix
Key issues on which the EAW Regulations And Electricity (Factories Act) Special Regulations 1908 And 1944 (Plus Exemptions) differ
1. Appendix 3 of the Memorandum of guidance gives information on reg 17 of the old regulations in relation to the new provisions. The minimum dimensions for switchboard passage-ways are given tacit approval.
2. Regulation 14 of the EAW Regulations covers all live working not just work on switchboards above 650 volts.
3. There is no specific requirement under the EAW Regulations for the display-of an electric shock placard or an abstract of the 1908/1944 Regulations. Occupiers should be told to remove abstracts but advised to retain placards where these are appropriate (see page 32, para 23 of Memorandum). There is no objection to occupiers displaying the new regulations in placard form if they desire.
4. There are no voltage bandings in the EAW Regulations.
5. There are differences in definitions between old and new. In particular conductor and danger have different meanings in the EAW Regulations.
6. Regulation 5 of the EAW Regulations corresponds to reg 1 of 1908 but is confined to the prevention of electrical danger. It does not cover machine malfunctions from electrical faults. All at risk are covered by reg 5, not just employees.
7. Under reg 6 of the EAW Regulations (as opposed to reg 27 of 1908) it is no longer necessary to show that equipment is or has been exposed to a flammable atmosphere. A foreseeable exposure will suffice.
8. Regulation 8 of the EAW Regulations applies to all conductors, unlike reg 21 of 1908 which only applied to exposed metalwork.
9. Regulation 13 of 1908 required the earthing of mobile generators. Under the EAW Regulations, reg 8 permits alternative approaches where earthing is not practicable.
10. The EAW Regulations contain no specific requirement for the written authorisation of competent persons, although authorisation may be required when necessary to avoid danger.

 

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Electrical Safety and you : ( HSE )
INTRODUCTION :
Electricity can kill. Each year about 1000 accidents at work involving electric shock
or burns are reported to the Health and Safety Executive (HSE). Around 30 of
these are fatal. Most of these fatalities arise from contact with overhead or
underground power cables.
Even non-fatal shocks can cause severe and permanent injury. Shocks from faulty
equipment may lead to falls from ladders, scaffolds or other work platforms.
Those using electricity may not be the only ones at risk: poor electrical
installations and faulty electrical appliances can lead to fires which may also cause
death or injury to others. Most of these accidents can be avoided by careful
planning and straightforward precautions.
This leaflet outlines basic measures to help you control the risks from your use of
electricity at work. More detailed guidance for particular industries or subjects is
listed on pages 6 - 8. If in doubt about safety matters or your legal responsibilities,
contact your local inspector of health and safety. The telephone number of your
local HSE office will be in the phone book under Health and Safety Executive. For
premises inspected by local authorities the contact point is likely to be the
environmental health department at your local council.
WHAT ARE THE HAZARDS ?
The main hazards are:
■ contact with live parts causing shock and burns (normal mains voltage,
230 volts AC, can kill);
■ faults which could cause fires;
■ fire or explosion where electricity could be the source of ignition in a
potentially flammable or explosive atmosphere, e.g. in a spray paint booth.
ASSESSING THE RISK :
Hazard means anything which can cause harm. Risk is the chance, great or small, that someone will actually be harmed by the hazard.
The first stage in controlling risk is to carry out a risk assessment in order to
identify what needs to be done. (This is a legal requirement for all risks at work.)
When carrying out a risk assessment:
■ identify the hazards;
■ decide who might be harmed, and how;
■ evaluate the risks arising from the hazards and decide whether existing
precautions are adequate or more should be taken;
■ if you have five or more employees, record any significant findings;
■ review your assessment from time to time and revise it if necessary.
The risk of injury from electricity is strongly linked to where and how it is used.
The risks are greatest in harsh conditions, for example:
■ in wet surroundings - unsuitable equipment can easily become live and
can make its surroundings live;
■ out of doors - equipment may not only become wet but may be at
greater risk of damage;
■ in cramped spaces with a lot of earthed metalwork, such as inside a tank
or bin - if an electrical fault developed it could be very difficult to avoid
a shock.
Some items of equipment can also involve greater risk than others. Extension
leads are particularly liable to damage - to their plugs and sockets, to their
electrical connections, and to the cable itself. Other flexible leads, particularly
those connected to equipment which is moved a great deal, can suffer from
similar problems.

REDUCING THE RISK
Once you have completed the risk assessment, you can use your findings to
reduce unacceptable risks from the electrical equipment in your place of work.
There are many things you can do to achieve this; here are some.
Ensure that the electrical installation is safe
■ install new electrical systems to a suitable standard, e.g. BS 7671 Requirements
for electrical installations, and then maintain them in a safe condition;
■ existing installations should also be properly maintained;
■ provide enough socket-outlets - overloading socket-outlets by using
adaptors can cause fires.
Provide safe and suitable equipment
■ choose equipment that is suitable for its working environment;
■ electrical risks can sometimes be eliminated by using air, hydraulic or hand powered
tools. These are especially useful in harsh conditions;
■ ensure that equipment is safe when supplied and then maintain it in a safe
condition;
■ provide an accessible and clearly identified switch near each fixed machine
to cut off power in an emergency;
■ for portable equipment, use socket-outlets which are close by so that
equipment can be easily disconnected in an emergency;
■ the ends of flexible cables should always have the outer sheath of the cable
firmly clamped to stop the wires (particularly the earth) pulling out of the
terminals;
■ replace damaged sections of cable completely;
■ use proper connectors or cable couplers to join lengths of cable. Do not
use strip connector blocks covered in insulating tape;
■ some types of equipment are double insulated. These are often marked with
a ‘double-square’ symbol . The supply leads have only two wires - live
(brown) and neutral (blue). Make sure they are properly connected if the
plug is not a moulded-on type;
■ protect light bulbs and other equipment which could easily be damaged in
use. There is a risk of electric shock if they are broken;
■ electrical equipment used in flammable/explosive atmospheres should be
designed to stop it from causing ignition. You may need specialist advice.
Reduce the voltage
One of the best ways of reducing the risk of injury when using electrical equipment
is to limit the supply voltage to the lowest needed to get the job done, such as:
■ temporary lighting can be run at lower voltages, eg 12, 25, 50 or 110 volts;
■ where electrically powered tools are used, battery operated are safest;
■ portable tools are readily available which are designed to be run from a
110 volts centre-tapped-to-earth supply.
Provide a safety device
If equipment operating at 230 volts or higher is used, an RCD (residual current
device) can provide additional safety. An RCD is a device which detects some, but
not all, faults in the electrical system and rapidly switches off the supply. The best
place for an RCD is built into the main switchboard or the socket-outlet, as this
means that the supply cables are permanently protected. If this is not possible a
plug incorporating an RCD, or a plug-in RCD adaptor, can also provide additional safety.

RCDs for protecting people have a rated tripping current (sensitivity) of not more
than 30 milliamps (mA). Remember:
■ an RCD is a valuable safety device, never bypass it;
■ if the RCD trips, it is a sign there is a fault. Check the system before using it
again;
■ if the RCD trips frequently and no fault can be found in the system, consult
the manufacturer of the RCD;
■ the RCD has a test button to check that its mechanism is free and
functioning. Use this regularly.
Carry out preventative maintenance
All electrical equipment and installations should be maintained to prevent danger.
It is strongly recommended that this includes an appropriate system of visual
inspection and, where necessary, testing. By concentrating on a simple, inexpensive
system of looking for visible signs of damage or faults, most of the electrical risks
can be controlled. This will need to be backed up by testing as necessary.
It is recommended that fixed installations are inspected and tested periodically by
a competent person.
The frequency of inspections and any necessary testing will depend on the type of
equipment, how often it is used, and the environment in which it is used. Records
of the results of inspection and testing can be useful in assessing the effectiveness
of the system.
Equipment users can help by reporting any damage or defects they find.
Work safely
Make sure that people who are working with electricity are competent to do the
job. Even simple tasks such as wiring a plug can lead to danger - ensure that people
know what they are doing before they start.
Check that:
■ suspect or faulty equipment is taken out of use, labelled ‘DO NOT USE’ and
kept secure until examined by a competent person;
■ where possible, tools and power socket-outlets are switched off before
plugging in or unplugging;
■ equipment is switched off and/or unplugged before cleaning or making
adjustments.
More complicated tasks, such as equipment repairs or alterations to an electrical
installation, should only be tackled by people with a knowledge of the risks and the
precautions needed.
You must not allow work on or near exposed live parts of equipment unless it is
absolutely unavoidable and suitable precautions have been taken to prevent injury,
both to the workers and to anyone else who may be in the area.
Underground power cables
Always assume cables will be present when digging in the street, pavement or near
buildings. Use up-to-date service plans, cable avoidance tools and safe digging
practice to avoid danger. Service plans should be available from regional electricity
companies, local authorities, highways authorities, etc.
Overhead power lines
When working near overhead lines, it may be possible to have them switched off if the owners are given enough notice. If this cannot be done, consult the owners

about the safe working distance from the cables. Remember that electricity can
flash over from overhead lines even though plant and equipment do not touch
them. Over half of the fatal electrical accidents each year are caused by contact
with overhead lines.

Mac : can you put the ( HSE ) stuff in the Doc , Useful Information for Apprentices , please Sorry about that . Amberleaf

 

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Definitions : Earth Fault Current :
A Fault Current which flows to Earth ,

Earth Fault Loop Impedance :
The Impedance of the Earth Fault Current Loop starting and ending at the point of the Earth Fault .
This Impedance is denoted by ( Zs )
The Earth Fault Loop comprises the following , starting at the point of Fault :
* the Circuit Protective Conductor ,
* the Consumers Earthing terminal and Earthing Conductor ,
* for TN-Systems , the return path ,
* for TT and IT Systems , the Earth return path ,
* the path through the Earthed Neutral point of the Supply Transformer and the Transformer Winding ,
* the Phase Conductor from the Transformer Supply to the point of Fault ,

BS 7671:2008
(i) The Electrical Installation Certificate required by part 6 : should be made out and signed or otherwise
authenticated by a competent person or persons in respect of the design, construction, inspection and testing of the work

(ii) The Minor Works Certificate required by Part 6 : should be made out and signed or otherwise authenticated by
a competent person in respect of the design, construction, inspection and testing of the minor work.
(iii) The Periodic Inspection Report required by part 6 : should be made out and signed or otherwise authenticated
by a competent person in respect of the inspection and testing of an installation
(iv) Competent persons will, as appropriate to their function under (i) (ii) and (iii) above, have a sound
knowledge and experience relevant to the nature of the work undertaken and to the technical standards set
down in these Regulations, be fully versed in the inspection and testing procedures contained in these
Regulations and employ adequate testing equipment
(v) Electrical Installation Certificates will indicate the responsibility for design, construction, inspection and
testing, whether in relation to new work or further work on an existing installation .
Where design, construction, inspection and testing are the responsibility of one person a Certificate with a
single signature declaration in the form shown below may replace the multiple signatures section of the model form

FOR DESIGN, CONSTRUCTION, INSPECTION & TESTING
I being the person responsible for the Design, Construction, Inspection & Testing of the electrical
installation (as indicated by my signature below), particulars of which are described above, having
exercised reasonable skill and care when carrying out the Design, Construction, Inspection & Testing,
hereby CERTIFY that the said work for which I have been responsible is to the best of my knowledge
and belief in accordance with BS 7671 :2008, amended to .............(date) except for the departures, if
any, detailed as follows.
(vi) A Minor Works Certificate will indicate the responsibility for design, construction, inspection and testing of
the work described on the certificate.
(vii) A Periodic Inspection Report will indicate the responsibility for the inspection and testing of an installation
within the extent and limitations specified on the report.
(viii) A Schedule of Inspections and a Schedule of Test Results as required by part 6: should be issued with the
associated Electrical Installation Certificate or Periodic Inspection Report.
(ix) When making out and signing a form on behalf of a company or other business entity, individuals should
state for whom they are acting.
(x) Additional forms may be required as clarification, if needed by ordinary persons, or in expansion, for larger
or more complex installations.
(xi) The IEE Guidance Note 3 provides further information on inspection and testing on completion and for
periodic inspections ,
ELECTRICAL INSTALLATION CERTIFICATES NOTES FOR FORMS 1 AND 2
1. The Electrical Installation Certificate is to be used only for the initial certification of a new installation or
for an addition or alteration to an existing installation where new circuits have been introduced.
It is not to be used for a Periodic Inspection, for which a Periodic Inspection Report form should be used.
For an addition or alteration which does not extend to the introduction of new circuits, a Minor Electrical
Installation Works Certificate may be used.
The "original" Certificate is to be given to the person ordering the work (Regulation 632.1 A duplicate
should be retained by the contractor.
2. This Certificate is only valid if accompanied by the Schedule of Inspections and the Schedule(s) of Test
Results.
3. The signatures appended are those of the persons authorized by the companies executing the work of
design, construction, inspection and testing respectively. A signatory authorized to certify more than
one category of work should sign in each of the appropriate places.
4. The time interval recommended before the first periodic inspection must be inserted (see IEE Guidance
Note 3 for guidance).
5. The page numbers for each of the Schedules of Test Results should be indicated, together with the total
number of sheets involved.
6. The maximum prospective fault current recorded should be the greater of either the short-circuit current or
the earth fault current.
7. The proposed date for the next inspection should take into consideration the frequency and quality of
maintenance that the installation can reasonably be expected to receive during its intended life, and the
period should be agreed between the designer, installer and other relevant parties