***Cont../ Useful Information for Electricians & Apprentices***

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O.S.G.. The use of other methods’ of determining Maximum Demand is Not Precludedwhere Specified by the Installation Designer

FirstlyI make no Apologies for the Way am Writing on any Matters . it can be a first day Apprentice or some one Needing aJog of Memory .
Sowe are all in the Same Boat . “ To Learn “

For the Apprentices . The Day we stop learning is the Day we hang Upour Tool-Bag

CookerDesign Current Calculations

Thefirst thing you have to do is get Your Head around the Calculations !!

(From a Design point of View ) 2392-10

DomesticInstallation Oven(s) & Hob(s) are to be Calculated upon their MAXIMUM LOADING
Startwith a simple Calculation ( An Oven has a rating of 2kW ) 2000

(I = P/V ) Formula … I = 2000 ÷ 230V = 8.70A …. Weare Using the Unit Amps


2392-10/ Domestic Installation Oven(s)

Ovenhas 4 Rings ( 2 x 1kW ) & ( 2 x 1.5kW ) & Grill ( 2kW ) & Oven (3kW )

-Controlled via a CookerSwitch with a Socket outlet .

Asa Designer . we’ll have to Apply Diversity ??

Important )- Diversity allowance to be Applied to the FULL LOAD CURRENT for CookingAppliances .

TheO.S.G. is telling us . Purpose of the Final Circuit fed from theConductors )
O.S.G.Table 1B p/97 – column (3) Cooking Appliances → At the Top of the Page Note : Type ofPremises ( 2392-10 → Household Installations ) Domestic Installation(s)

DomesticInstallation(s) Only O.S.G. - 10A + 30% f.l – Full Load ) of connected Cooking Appliances in the Excess of 10A+ 5A if a socket-outlet is incorporated in the Control Unit . ( C.C.U. ) – 45A + 13A Socket Switched with Neon .

Fromyour point of View ( The First 10A ofthe rated current plus 30% of the reminder ( Plus) 5A if the Control Unit incorporates s Socket.

Calculations)- You bank “ Hold OFF“ the first 10 Amps of the Maximum Load Current )
The10A will be used at the End of the Calculations’

-So your Work out the Total Power Rating & then calculate the Full Load Current

Calculations)- Power = ( 2 x 1 ) + ( 2 x 1.5 ) + ( 2+ 3 ) = 10kW

I= 10000 ÷ 230V = 43.48A … round it up to the first four numbers43.47826087 ( 48 ) 43.48A

UsingDiversity allowance stated ↑↑ ( 43.48A sub 10A = 33.48A )

I= 33.48 x 30 ÷ 100 = 10.04A

Youradding the ( 5A ) for Socket outlet . I = 10A + 10.04 + 5A = 25.04A )- Asa Designer this is your Expected Current Demand .

Remember )- Supply Cables Rated to suit DesignCurrent ( Iz )

 

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Emergency Switching :icon14:

Whatare the requirements for Emergency Switching in relation . to

• Full Load Current .
• Hand – held devices .
• Identification of Emergency Switching devices .
• Positioning & Accessibility .
• Positioning & Identification .
• Further Danger .

 

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Firefighters Switch :

A Fire-fighter’s Switch is a Device intended for Use by Fire Service . ( Although ) NotExclusively SO :speechless:

It’spurpose is to ( De-energise ) designated parts of an Installation . That operateat a voltage in ( Excess of Low Voltage ) Neon Lighting .

 

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2392-10: :speechless:

542: Earthing Arrangements .

542.1.General Requirements .
542.1.1.The Main Earthing Terminal . Etc
542.1.2. TN-S .
542.1.3. TN-C-S .
542.1.4. TT or IT .

Chapter54 . p/124
EarthingArrangements & Protective Conductors .

542- Earthing Arrangements . p/126
543- Protective Conductors . p/128
544- Protective Bonding Conductors . p/134 .

ProtectiveConductors .
Areconductors provided for the purposes of Safety . for some measures of Protection Electric Shock . Reg - p/27

Look– fig 2.1 / p32 . Earthing & Protective conductor .

 

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2392-10:

-&-s . Q ) How many Types of EarthingSystem are recognised by BS-7671:2008 . :icon14:

A) 312.3.1. p/38 :- Types of System are . [ TN-C : TN-S : TN-C-S : TT : IT :

 

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2392-10:

TheEarth Fault Loop Impedance ( Zs ) for a Consumer’sCircuit is determined by ? :icon14:

(R1 + R2 ) + Ze

Part 2 Definitions - P/36 :

 

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TheProspective Short Circuit Current at the Origin of the Consumer’s Installationmust be taken into account when ??
Selectingthe type of Overcurrent Protective Device to be installed .

Wherepracticable Main Protective Bonding Conductor . to the Gas services in abuilding should be made within .
[600mm of the Meter on the Consumer Side ] :speechless:

O.S.G.P/27 (- Main Protective Bonding Conductors are required to connect the followingMetallic Parts to the ( Main Earthing Terminal) 411.3.1.2.
Extraneous-conductive-part : A Conductive part such as a Metal Pipe . ( LIBLE )to introduce Earth Potential into the Building.

MainProtective Bonding Conductor is the Electrical Interconnection between the MainEarthing Terminal & the incoming Metallic Services : Water / Gas .

TN-C-S. Earthing arrangements .

Regulations544.1.1. p/134 . & Table 54.8 / p134

IETwiring regulations – 17[SUP]th[/SUP] Edition . The required size of the Main Bonding Conductor is ( 10.0mm[SUP]2 [/SUP] ) for supplieswith a Neutral Conductor of ( 35.0mm[SUP]2 [/SUP] ) or Less

Becauseof this You will be required to use ( 10.0mm[SUP]2 [/SUP] ) Single Core Earth Cable toconnect both the Incoming ( Water pipe ) & the Incoming ( Gas pipe ) to theMain Earthing Terminal inside the Consumer Unit . ( CU )

 

[jeremy]

I've skimmed through the last few pages, mostly initially with a "WTF" expression, which then becomes an "AAAAH, I get it". I thank you.

 

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2392-10:

Q)- A single-phase circuit using 2.5mm[SUP]2 [/SUP] single-core PVC cables in conduit supplies adesign current of 20A .
If the cables are 15m long & have a rated voltage drop of ( 18mV/A/m ) the actual VoltageDrop will be . ????

A)- ( 18mV/A/m ) x 20A x 15m ) ÷ 1000 = 5.4V

2392-10: -&-s

Duringthe Testing Line of an Electrical Installation .Which Test would be carried out first . ????

612.2.1– Continuity of Protective Conductors . ◄
612.3.– Insulation Résistance . ( IR )
612.6. – Polarity .
612.9.– Earth Fault Loop Impedance .

 

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Megger ( 1552 / 1553 ) :speechless:

SetUp :

RCD Touch Voltage selection ( To select either 25V or 50V )

1 )With the instrument turned OFF . hold down the Yellow test button & turn the left hand rotary switch to any ON position .
2 )Keep the button held down until the instrument displays the “ SET “ Warning .
3) Now release the TEST button .
4) Pressthe TEST button again to view the currentsetting for the Touch voltage .
Thedisplay shows the touch voltage limit . 50V

Note: The MFT can also display the measuredTouch Voltage on a bar-graph display .

Ifthe touch voltage display is Active . a bar-graph display will also appear .

5) Press the ORANGE( buzzer ) button to change the touchvoltage limit setting . 25V / 50V
6) Press the BLUE (RCD ) button to turn the bar-graphdisplay ON or OFF .
7) Press the TESTbutton to exit from the set-up menu .

 

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Isolation& Switching : :49:

537.2.1. Every circuit shall be Isolated from the Live Supply.

Threepoints of Isolation .
Origin– 537.1.4.
DistributionBoards – 537.2.1.1.
FinalCircuits – 537.2.1.1.

MustIsolate all ( Phases) but not necessarily the Neutral– No link in CPC
Note (- 537.2.1.7.
Isolationat the Origin .

TN-S Phases or Lines & Neutrals
TN-C-S Phases only but both Lines & Neutral where access is Obtained by UnskilledPersons – 537.1.4.
TT- Both Line & Neutral .

 

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Isolation& Switching : :49:

537.4.2.8.
Plugs& Sockets are NOT suitable for EmergencySwitching .

 

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MainElements of Circuit design for conventional Circuits . :juggle2:

•Determine Design Current . actual flow of current through the cables ( Ib )less diversity where appropriate .
•Select type & size of protectivedevice ( In )
•Apply any correction factors to reduce self heating of cables ( It )
•Select type & size of cable fromAppendix 4 ( Iz )
•Determine whether volt drop is satisfactory for Length . Loading & routingof cables .

Note (- 2392-10
Inmost practical applications where an Installation already exists you may havethe choice of Type but only Size .

ApplyingElectrical Design . Cable Sizing .

LoadCurrent ( I ) & design current ( Ib )
Effectivecontinuous current flow through a circuit
-Basic Calculation : P = V . I or I = P/V

Whencalculating Design Current with inductive loading & where there isinsufficient information available apply a factor ( 1.8 ) to the power consumption . App 1 – Table1A O.S.G. note 2 - I = P x1.8 / V

Alternatively. if the powerfactor is known then apply ( P = V x I x Cos Ø or P = √3 x V[SUP]L [/SUP]x I[SUP] L [/SUP] x Cos Ø )

ApplyingElectrical Design . Cable Sizing .

DesignCurrent ( Ib )
Maximum Demand 311.1. ( MD )

Diversitymay be taken into account when determining MaximumDemand
Diversity– O.S.G. Appendix 1 . Table 1A . 1B .

Point to Note : Not all circuits run at their full powerrating .
CookerCircuit - Minus first ( 10A ) then 30% of the rest add( 10A ) to the Total + 5A for Socket / Outlet .

LightingCircuits :
Domesticlighting ( 66% ) is assumed to be on Continuously .

PowerCircuits :
1[SUP]st[/SUP] Circuit = Full Rating . 2[SUP]nd[/SUP] Circuit 40% & all Other Circuits . ◄◄

Diversity applies to groups of circuits or / & cables supplying groups of circuitssuch as a Sub-mains distribution boards .

 

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560.7. Circuits for SafetyServices shall be Independent of Other Circuit . :vanish:

Does NOT include Smoke Alarms & Emergency Lightingthat are ( Battery Powered ) & supplied by a ( Charging Circuit ) i.e. Lights .

 

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AppropriateBritish Standard or do a “ Risk Assessment“ :35:

• SafetyServices to be Installed to allow adequate duration equipment to be suitable tolast for the duration of Escape .
•560.5.3. – Continual ( IT ) insulation monitoring devices that give an Audibleor Visual indication of the first fault in the System .

Selection& Erection (- Safety Services . :rolleyes4:

Classification of a SafetySystem .

i)Non-automatic supply .
ii)Automatic – Self Starting .

AutomaticSupply is Classified by the following time it takes to get ( Fully Operational )

- No breaks – UPS .
- Very short breaks - < 0.15s
- Short breaks - > 0.15 < 0.5s
- Lighting breaks - > 0.5s < 5s .
- Medium breaks - > 5s < 15s
- Long breaks - > 15s .

 

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Ido fell the Humble MCB is in theBackground now . The RCD has taking Front Row . :aureola:

TimeDiscrimination :

Isachieved by delaying the Opening of the ( RCD or MCB ) upstream ( RCD or MCB ) untilthe downstream ( RCD or MCB ) has Opened & cleared the Fault .
Thetotal clearing time of the downstream ( RCD or MCB ) MUSTbe LESS than the time setting of the upstream ( RCD or MCB ) & the upstreammust be able to withstand the Fault Current for the time setting period .

Thereforethe upstream ( RCD or MCB ) must be acategory which has been designed & tested for this purpose .

MCBs- To determine timediscrimination it is only necessary to compare the Time / Currentcharacteristic curves of the Two Devices to ensurethat NOoverlap Occurs .

RCBOs – have taking a primaryrole in Industry now - RCD/MCB . ( B & C . curves ) C forLighting . B forPower .

 

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2392-10: Your first role is a Designing . second is Electrician . :aureola:

Forthe Protection of Lighting Circuits the “ Designer “ must select the CircuitBreaker with the Lowest Instantaneous trip current compatible with the inrushcurrents likely to develop in the circuit

 

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Whatis an Insulation RésistanceTest ( IR ) :aureola:

AnInsulation Résistance Test measures the total Résistance of a products’ ( Cable) Insulation System(s)
Itis also useful test to perform when doing preventative maintenance on ( Cable ) overtime .

Whatis an Insulation RésistanceTest ( IR )
Measuring& Recording long term Stability of Insulating Materials over time .

InsulationRésistance Testing . as a Tester . – The Test results can provide usefulinformation about a ( Cable Integrity ) & can yield clues when itsInsulation should be Replaced .

 

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InsulationRésistance (- 2392-10 . from -&-s point of View . :aureola:
InsulationRésistance measurement is preformed inorder to ( Assure Safety ) against ElectricShock through Insulation .

 

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ContinuityFunctions. :aureola:

Apprentices(- ParallelRésistance Paths - Interferingcurrent in measured circuit will influence the TestResults.

From-&-s point of View (- “ Nulling“ / Test Leads Résistance beforeperforming Continuity Measurement

When measuring Insulation Résistance betweeninstallation conductors all Loads must bedisconnected . ( & all SwitchesClosed ) Mains Voltage Switched OFF

“Functionality “

Regulation 612 – BS-EN 61557.

ElectricalSafety in Low-voltage distribution systems up to 1000V. A.C. & 1500V . D.C. .
Regulationsp/31 ( Low . Exceeding extra-low voltagebut not Exceeding 1000V . A.C. & 1500V . D.C. . between conductors.
Equipmentfor Testing . Measuring or Monitoring of Protective Measures .

Thecircuit under test must be Switched OFF .de-energised & Isolated before test connections are made when carrying outInsulation & Continuity Tests .

612.2. & 612.2.1.
Continuityof Protective Conductor(s) & Main Protective Bonding Conductor of New orModified Installation(s) must be verified before carrying out an Earth FaultLoop Impedance . or RCD test .

 

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Loop Impedance .:aureola:

Isa Live Test. which is carried out on a circuit to check the Résistance of the Line conductor to Earth.

Thisshows if the current created under Fault Conditions will trip the MCB .

Apprentices: Refered to as Earth Fault Loop Impedance .
-&-s . Extremely Important Test to verify the System is Safe.

TheEarth Loop Impedance test measures therésistance of the path that a ( Fault Current ) would take between Line & Protective Earth
Thismust be low enough to allow sufficient current to flow to trip a MCB