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

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Currently the national safety standard for electrical installation work in the UK is British Standard 7671 – Requirements for
Electrical Installations. The IEE Wiring Regulations are a code of practice for ensuring safe electrical installations.

Although the IEE Wiring Regulations have no statutory force in the UK, they are referred to as a means of demonstrating compliance with relevant legislation, such as the Electricity at Work Act (1989) and the Building Regulations.

Fault Protection

Protection against electric shock under single-fault conditions. Note: For low voltage installations, systems and equipment,
fault protection generally corresponds to protection against indirect contact, mainly with regard to failure of basic insulation.
Indirect contact is ‘contact of persons or livestock with exposed-conductive-parts which have become live under fault conditions’.

Section 701 concerns locations containing a bath or shower. It is now a requirement under 701.411.3.3 that additional
protection shall be provided for all circuits of the location by the use of one or more RCDs, again, with an operating
current not exceeding 30mA, reference Regulation 415.1.1. As well as items such as electric towel rails and electric showers, this regulation also applies to lighting. Although all of the aforementioned areas require RCD protection, the requirements of Regulation 314.1, Division of Installation, need to be taken into account, when designing and installing the circuit protective arrangements. 314.1
states that every installation shall be divided into circuits as necessary to:

a. Avoid hazards and minimise inconvenience in the event of a fault

b. Take account of danger that may arise from the failure of a single circuit such as a lighting circuit

c. Reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation

 

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Functional switches are required to be suitable for the most onerous duty intended (rated to carry the highest load on that circuit), and should be selected to have a utilization category appropriate for the type of load being switched.

Isolation of a luminaire

The objective of isolation is to enable electrically skilled persons to carry out work on, or adjacent to, parts which would otherwise be live e.g. for a luminaire, replacing a faulty ballast or ignitor.

Electrical Faults – where do they occur ?

Electrical Faults may occur in electrotechnical systems at the following places ,
a) The wiring system ,
b) At cable terminations ,
c) Within accessories, switchgear , contactors and controls ,
d) Within instrumentation and metering equipment ,
e) At protective devices ,
f) At luminaires ,
g) in flexible cables and cords ,
h) in electrical components ,
each of these potential fault situations ;

Electrical Faults in the wiring system :
The electrical designer will choose a wiring system which meets the needs of the client and any relevant regulations , part 5 of the IEE Regulations deals with the selection and erection of equipment and the designer must choose a wiring systems which complies ,

* The wiring system must be suitable for the installed conditions such as temperature , presence of water , vibration , corrosion and solar radiation ,

The electrician must install the wiring system competently and in compliance with the IEE Regulations . for ;
Buried cables must have mechanical protection , and underground cables must be buried at sufficient depth to prevent future damage ,
Cables installed in timber joist must be at least 50mm from the top and bottom of the joist , and the installed wiring system must not reduce the safety of the building structure ,

A suitable wiring system , correctly installed will cause few problems in the future , it is where the human hand has been involved
At each end of the wiring systems there future problems most often occur ,

POWER CIRCUITS :
Showers
Often forming part of modern installations is the electric shower. With sizes now reaching 11kw, it is vitally important that we calculate the correct cable size. Remember the power formula ? An 11 kW shower can draw currents up to 48A !

Cookers
Ovens and cooking devices :
An electric cooker can often have enough parts (top oven, bottom oven, grill etc.) to produce a large amount of current. Although we can apply diversity from the On Site Guide, modern ovens can have a large amount of features that must be taken into account when designing the circuit.

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.

DOMESTIC FINAL CIRCUIT ARRANGEMENTS

The IEE Regulations, specifically the On Site Guide, takes a lot of work out of the design of a domestic installation for a typical installer. This combined with the Building Regulations gives us a quick and easy platform to determine the requirements.

RING AND RADIAL SOCKET OUTLET CIRCUITS
The On Site Guide gives us 3 options for the installation of socket outlets. These can be found in Appendix 8 of the On Site Guide and can be simplified to the following: O/S/G , 158 , Table 8A
A1 : Ring : 30 or 32A : 100m2
A2 : Radial : 30 or 32A : 75m2
A3 : Radial : 20A : 50m2

CITY AND GUILDS 2393 - CERTIFICATE IN THE BUILDING REGULATIONS FOR ELECTRICAL INSTALLATIONS IN DWELLINGS

The City and Guilds have also launched qualifications around the Building Regulations known as the 2393-10
The idea behind this qualification is to enable the allied trades and existing electricians working in the domestic environment to gain an understanding on how the Building Regulations impacts on electrical installations.
It is a 20 question multiple choice paper completed within 40 minutes and covers the following:
• Building Regulations
• Building Work
• Approved Documents
• Building Control
• Compliance with Approved Documents A to M

Part P does not apply in the case of all buildings. It applies to all fixed electrical installations after the suppliers’ meter in buildings or parts of buildings comprising:

• Dwellings
• Dwellings and business premises such as shops and public houses that have a common supply
• Common access areas in blocks of flats such as corridors and staircases but not lifts shared amenities in blocks of flats, such as laundries and gymnasiums.
While Approved Documentation ‘P’ applies to all electrical installation work in dwellings, it is not necessary to notify building control bodies in the following circumstances:

• The electrical installation work is to be undertaken by a ‘Competent Person’ and self certificated*
• When electrical installation work is 'Minor Work' and is not contained within the kitchen or special location and does not involve a special installation

• Competent persons registered enterprises (Competent Persons Scheme)

* Clarify this with your local Building Control before commencing work. Although Part P was designed to enforce standards and increase safety, many council offices simply do not understand the implications of the document and merely insist you are part of a competent persons scheme. This is not true but you do need to notify before you begin work on an installation.

* What types of mechanical protection provide sufficient protection against penetration by nails, screws and the like :

- As an example, steel of 3 mm minimum thickness is generally considered to provide sufficient mechanical protection, except where shot-fired nails are likely to be used. 522.6.6 / 522.6.8

* Do ‘meter tails’ concealed in walls or partitions need to be protected in accordance with Regulations 522.6.6 and/or 522.6.8 :

- Yes. Meter tails concealed in a wall or partition at a depth of less than 50 mm from a surface must be protected in accordance with Regulation 522.6.6. Also, irrespective of the depth from a surface, meter tails concealed in a wall or partition having internal metallic parts (except nails and screws, etc) are subject to the requirements of Regulation 522.6.8. ( 522.6.6, 522.6.8 314.1, 314.2 )

- However, additional protection for meter tails by means of an RCD is not an acceptable option in respect of Regulation 522.6.7 (which in consequence rules out reliance on 522.6.6(v), routing in the ‘safe zones’ alone), or in respect of Regulation 522.6.8(v). Also, for TT systems, the only option remaining is to provide suitable mechanical protection (that is, to comply with Regulations 522.6.8(iv) and/or 522.6.6(iv) as appropriate).

* Does boiler pipework need to have additional equipotential bonding for electrical safety reasons :

- There is no specific requirement in the Regulations for boiler pipework to be supplementary bonded. However, such bonding may be called for in the boiler manufacturer’s instructions, in which case BS 7671 requires those instructions to be followed (Regulation 510.2 refers). Any stated requirement for additional bonding that is considered to be unnecessary should be queried with the manufacturer concerned, and amended installation instructions requested. ( 411.3.3 )

* I am still working on an electrical installation that was designed to the 16th Edition. To which Edition should the installation be inspected, tested, verified and certificated :

- An installation designed and installed to the 16th Edition should be inspected, tested, verified and certificated to that Edition.

* Is an RCD main switch (such as a 100mA time-delayed device) still required in the consumer unit of a new domestic installation forming part of a TT system :

For a domestic installation complying with the 17th Edition where all the final circuits are RCD-protected, an RCD main switch is no longer required, provided that the consumer unit is of all insulated construction.

* Does the device that has to be provided for switching off a bathroom extract fan for mechanical maintenance need to be located adjacent to the fan :

- No, but the device does need to be so placed and marked as to be readily identifiable and convenient for the intended use ( 537.3.2.4 )

* Does the R1 + R2 test confirm& the correct polarity of a radial circuit :

- No, not on its own. Whilst the test can provide an indication of polarity, it needs to be combined with inspection and further testing as required by Part 6 of BS 7671: 2008 ( 611.3, 612.6 )

* Appendix 15 of BS 7671: 2008 gives advice on ring final circuits and sharing/spreading the load around the circuit. Item (iii) suggests that cookers, ovens and hobs over 2 kW should be on their own dedicated circuit. Why can’t ovens of less than 3 kW be connected to a ring final circuit via a suitable connection point such as a socket-outlet or fused connection unit :

- Appendix 15 is intended to give guidance only. Such connection is not prohibited, provided that no part of the ring final circuit will be overloaded as a result. ( 433.1.5 )

 

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* Is it necessary to verify voltage drop during initial verification :

- Verification of voltage drop is not normally required unless there is considered to be a voltage drop problem. ( 612.14 )

* Considering Regulations 134.1.1 and 510.2 which require equipment to be installed in accordance with instructions provided by the manufacturer, are installers now required to check torque settings for connection tightness at consumer units where these are manufacturers instructions.

- Yes. It is necessary to check that all connections are tight, and any specific installation instructions must also be followed.

* In a location containing a shower, what is the horizontal limit of zone 1 for showers without a basin :

- The limit of zone 1 horizontally is 1.2 m from the centre point of the fixed water outlet (the end of the rigid pipe of the fixed water installation) on the wall or ceiling, irrespective of whether the shower head is fixed or on the end of a flexible hose. Beyond zone 1, the general rules of BS 7671 apply, including Regulation 512.2 concerning external influences. In particular, the IP rating of any electrical equipment must be adequate. ( 701.32.4 512.2 )

* Regulation 560.7.7 requires cables for safety circuits, other than metallic screened fire-resistant cables, to be adequately and reliably separated from other circuit cables. In addition to mineral insulated cables, what cables would be exempted from this separation requirement : ( 560.7.7 )

- Soft-skinned cables to BS 7629-1: 2008 would be exempted from the separation requirements as they have a metallic screen and their survival in a fire has been tested in accordance with BS EN 50200. However, cables to BS 8436: 2004 would not be exempted as the product standard does not require their fire resistance to be tested. Irrespective of the above, BS 5839-1 recommends that, for a fire detection and alarm system complying with that standard, the circuits of fire alarm systems should be segregated from the cables of other circuits to minimize the potential for those other circuits to cause malfunction of the fire alarm system.

* As the designer of an installation, am I allowed to rely on the RCD element of an RCBO to provide for fault protection in order to allow for loop impedance values greater than given in Table 41.3 :

- Yes, so long as all the other applicable requirements of the 17th Edition are met, including those for protection against overload and short circuit. ( 411.4.4 411.4.5 411.4.9 )

* Are there any particular requirements relating to the mounting height or location of consumer units for electrical installations in new dwellings :

- The provision of access to consumer units is not specifically covered by Building Regulations or BS 7671. However, consumer units need to be so located as to enable reasonable access by the users, including for the purpose of testing the RCDs at regular intervals, and in case of emergency. ( 132.12 341.1 513.1 )

- BSI Draft for development DD 266: 2007 – Design of accessible housing: Lifetime homes – Code of practice, explains how, by following the principles of inclusive design, general needs housing can be made sufficiently flexible and convenient to meet the existing and changing needs of most households, and so give disabled and older people more choice over where they live.
Amongst other things, the code of practice recommends that meters and consumer units should be mounted 1200 mm to 1400 mm from the floor so that the readings and switches can be viewed by a person standing or sitting, and should be positioned to be accessible.

* What is the correct sequence for testing RCDs :

- Preferably, RCDs should be tested in the sequence of: x1 I∆n , x5 I∆n (if required for additional protection), followed by x0.5 I∆n and then finally the test button trip.

- However, some automated test instruments test in the sequence of: x0.5 I∆n followed by the x1 I∆n test, and then x5 I∆n test (if required for additional protection).

- In any case, the test button should be operated last in the sequence

Note: Unless otherwise indicated, all references to ‘RCD’ in this section relate to residual current devices having a rated residual operating current ( I∆n ) not exceeding 30 mA and an operating time not exceeding 40 ms at a residual operating current of 5 I∆n , provided as additional protection in the event of failure of the provision for basic protection and/or the provision for fault protection or carelessness by users (Regulation 415.1.1)

 

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Inspection and Testing of Electrical Equipment : PAT !!!


The following ten questions will indicate the scope and level of background knowledge required, for which it is strongly advised that you should be able to achieve at least 80% correct answers.

1. Place the appropriate number in the box opposite each of the following electrical parameters to indicate the letter by which each is designated:

(a) current (b) voltage (c) resistance (d) electric power


1 – A ; 2 – C ; 3 – I ; 4 – P; 5 − R ; 6 − U ; 7 – V ; 8 - W


(2) Place the appropriate numbers in the boxes opposite each of the following electrical parameters to indicate (i) its basic unit of measurement and (ii) the letter or symbol by which that unit is designated:
………….…………………… (i) ……….. …………. (ii)
(a) current …………………… ( ) ……….. …………. ( )
(b) voltage …………………… ( ) ……….. …………. ( )
(c) resistance ………………….( ) ……….. …………. ( )
(d) electric power ……………. ( ) ……….. …………. ( )

(i) 11 – watt; 12 – hertz; 13 – ohm; 14 – farad; 15 – volt; 16 – ampere(amp)
(ii) 21 – A; 22 – O; 23 – R; 24 – U; 25 – V; 26 – W; 27 - Ω; 28 - α

A) ↔ 2. (a) (i) – 16 (ii) – 21 (b) (i) – 15 (ii) – 25 (c) (i) – 13 (ii) – 27 (d) (i) – 11 (ii) – 26

(3) 100mA is the same as:
(a) 10 A
(b) 1 A
(c) 0.1 A ←
(d) 0.01 A

(4) 2 MΩ is the same as:
(a) 0.002 Ω
(b) 0.02 Ω
(c) 2,000 Ω
(d) 2,000,000 Ω ←

(5) 2mΩ is the same as:
(a) 0.002 Ω ←
(b) 0.02 Ω
(c) 2,000 Ω
(d) 2,000,000 Ω

(6) A portable appliance is fitted with a 5 m cord for which the resistance of the protective conductor is 26 mΩ/m. The total resistance of the protective conductor is:
(a) 26 mΩ
(b) 52 mΩ
(c) 130 mΩ ←
(d) 260 mΩ

(7) The protective conductor resistances of two extension leads are 95 mΩ and 75 mΩ respectively. When connected together in series the combined resistance is:
(a) 0.02 ohms
(b) 0.085 ohms
(c) 0.17 ohms ←
(d) 0.34 ohms

(8) An electrical appliance is rated 230 V, 920 W. When connected to a 230 V supply the load current should be:
(a) 0.25 A
(b) 0.4 A
(c) 2.5 A
(d) 4 A ←

(9) The core colours for the phase, neutral and protective conductors of a 3-core appliance cord should be respectively:
(a) red, black and green
(b) red, black and green/yellow
(c) brown, blue and green
(d) brown, blue and green/yellow ←

(10) The nominal voltage of a single-phase mains electricity supply is:
(a) 230 V d.c.
(b) 230 V a.c. ←
(c) 240 V d.c.
(d) 240 V a.c.

(11) Which one of the following does NOT specifically comprise a user check:
(a) confirming that the plug is correctly connected ←
(b) confirming that the flexible cable is secure in the plug anchorage
(c) confirming that the equipment is suitable for the job
(d) confirming that there are no signs of overheating at the socket outlet

(12) An item of class I equipment incorporating unearthed metal separated from live parts by basic insulation and earthed metal is subjected to several earth continuity tests. The results are found to be inconsistent. This is most likely to be as a result of:
(a) a variation in the earth fault loop impedance of the final circuit providing the mains supply to the portable appliance tester
(b) the unearthed metal being in casual contact with earthed metal ←
(c) variation in the supply frequency
(d) the earthed metal changing temperature

(13) When undertaking a protective conductor/touch current measurement on a 2 kW
Class I heating appliance the maximum permitted current is:
(a) 0.25mA
(b) 0.75mA
(c) 1.5mA ←
(d) 3.5mA

(14) The test voltage for an electric strength test undertaken by the manufacturer on the
basic insulation of IT equipment conforming to BS EN 60950 is:
(a) 230 V
(b) 1000 V
(c) 1500 V ←
(d) 3000 V

(15) A low resistance ohmmeter is used to check the polarity of a 3-core extension lead.
The end-to-end resistance measurements are:
Plug phase pin to socket phase connection – open circuit
Plug neutral pin to socket neutral connection – 0.15 Ω
Plug protective conductor pin to socket protective conductor connection – open circuit
Plug phase pin to socket neutral connection – open circuit
Plug phase pin to socket protective conductor connection – 0.15 Ω
Plug protective conductor pin to socket neutral connection – open circuit
Plug protective conductor pin to socket phase connection – 0.15 Ω

These test results show crossed connections between the:
(a) phase and neutral conductors
(b) phase and protective conductors ←
(c) phase, neutral and protective conductors
(d) neutral and protective conductors

A/Q
1. (a) – 3 (b) – 6 (c) – 5 (d) – 4

2. (a) (i) – 16 (ii) – 21
(b) (i) – 15 (ii) – 25
(c) (i) – 13 (ii) – 27
(d) (i) – 11 (ii) – 26

3. (c) 4. (d) 5. (a) 6. (c) 7. (c) 8. (d) 9. (d) 10. (b) 11. (a) 12. (b) 13. (c) 14. (c) 15. (b)

Revision on motors :
1) looking for R.P.M :
Ns = 60 x f ----------- p ( f = 50 Hz : p = 10 = 5 pair of poles : Ns =( ? ) R.P.M ←←
( 60 x 50 ----------- 5 : Ans ↔ ( 60 x 50 = 3000 ÷ 5 = 600 rpm ) *

2) looking for frequency :
Ns = 60 x f ----------- p ( Ns = 1800 rpm , p = 4 = 2 pair , f = ( ? ) Hz ←←
f = Ns x p ----------- 60 Ans ↔ ( 1800 x 2 ÷ 60 = 60 Hz ) *

3) looking for pair = poles :
Ns = 60 x f ----------- p ( f = 50 Hz : Ns = 750 rpm : p = ( ? ) pair of poles ←←
( p = 60 x f ----------- Ns Ans ↔ ( 60 x50 ÷ 750 = 4 *
↔ p = 4 pair of poles : ( Number of pole = 2 x 4 = 8 ) *

4) looking for RPM :
Ns = 60 x f ----------- p ( f = 50 Hz : p = 10 = 5 pair / poles : Ns = ( ? ) RPM ←←
60 x 50 ----------- 5 Ans ↔ ( 60 x 50 = 3000 rpm *

Level 3 Electro-Technical : Exam Questions Not Multiple Choice Questions with Answers :

Questions
1) A resistor of 28_ is connected to a inductor of 12mH and a capacitor of 24μF. Calculate
the impedance presented to the 50Hz supply.
2) A resistor of 38_ is connected to a inductor of 124mH and a capacitor of 100μF.
Calculate the impedance presented to the 50Hz supply.
3) A resistor of 12k_ is connected to a inductor of 56.92mH and a capacitor of 178μF.
Calculate the impedance presented to the 50Hz supply.
4) A resistor of 164_ is connected to a inductor of 84mH and a capacitor of 18μF. Calculate
the impedance presented to the 50Hz supply.
5) A resistor of 216_ is connected to a inductor of 136mH and a capacitor of 124μF.
Calculate the impedance presented to the 50Hz supply.
6) A transformer has a rated power of 15kVA and a power factor of 0.9 and the losses are
200 Watts. Calculate the overall efficiency.
7) A transformer has a rated power of 8kVA and a power factor of 1 and the losses are
1800 Watts. Calculate the overall efficiency.
8) A transformer has a rated power of 1kVA and a power factor of 0.75 and the losses are
100 Watts. Calculate the overall efficiency.
9) A transformer has a rated power of 24kVA and a power factor of 0.95 and the losses are
1400 Watts. Calculate the overall efficiency.
10) A transformer has a rated power of 12kVA and a power factor of 0.85 and the losses are 600 Watts. Calculate the overall efficiency.

 

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Answers
Two equations are used, depending upon the values of XL and XC:
If XL is larger than XC, then: Z = √ (R2 + (XL- XC)2
If XC is larger than XC, then: Z = √ (R2 + (XC- XL)2
1) A resistor of 28_ is connected to a inductor of 12mH and a capacitor of 24μF. Calculate
the impedance presented to the 50Hz supply.
XL = 2πfL = 3.77_, XC = 1 / (2πfC) = 132.63_, Z = √ (R2 + (XC- XL)2 = 131.87_
2) A resistor of 38_ is connected to a inductor of 124mH and a capacitor of 100μF.
Calculate the impedance presented to the 50Hz supply.
XL = 2πfL = 38.96_, XC = 1 / (2πfC) = 31.83_, Z = √ (R2 + (XL- XC)2 = 38.66_
3) A resistor of 12k_ is connected to a inductor of 56.92mH and a capacitor of 178μF.
Calculate the impedance presented to the 50Hz supply.
XL = 2πfL = 17.88_, XC = 1 / (2πfC) = 17.88_, In this case XL=XC, so Z=R = 12k_
4) A resistor of 164_ is connected to a inductor of 84mH and a capacitor of 18μF. Calculate
the impedance presented to the 50Hz supply.
XL = 2πfL = 26.39_, XC = 1 / (2πfC) = 176.84_, Z = √ (R2 + (XC- XL)2 = 222.56_
5) A resistor of 216_ is connected to a inductor of 136mH and a capacitor of 124μF.
Calculate the impedance presented to the 50Hz supply.
XL = 2πfL = 42.73_, XC = 1 / (2πfC) = 25.67_, Z = √ (R2 + (XL- XC)2 = 216.67_
6) A transformer has a rated power of 15kVA and a power factor of 0.9. and the losses are
200 Watts. Calculate the overall efficiency.
Input power = kVA x Power factor, = 15kVA x 0.9 = 13.5kW
Output power = Input power - losses
Output power = (15kVA X 0.9) - 200 = 13500 - 200 = 13.3kW
Efficiency = (Output/input) x 100%, n = (13300/13500) x 100 = 98.52%
7) A transformer has a rated power of 8kVA and a power factor of 1 and the losses are
1800 Watts. Calculate the overall efficiency.
Input power = kVA x Power factor, = 8kVA x 1 = 8kW
Output power = Input power - losses
Output power = (8kVA X 1) - 1800 = 8000 - 1800 = 6.2kW
Efficiency = (Output/input) x 100%, n = (6200/8000) x 100 = 77.5%
8) A transformer has a rated power of 1kVA and a power factor of 0.75 and the losses are
100 Watts. Calculate the overall efficiency.
Input power = kVA x Power factor, = 1kVA x 0.75 = 0.75kW
Output power = Input power - losses
Output power = (1kVA X 0.75) - 100 = 750 - 100 = 0.65kW
Efficiency = (Output/input) x 100%, n = (650/750) x 100 = 86.6%
9) A transformer has a rated power of 24kVA and a power factor of 0.95 and the losses are
1400 Watts. Calculate the overall efficiency.
Input power = kVA x Power factor, = 24kVA x 0.95 = 22.8kW
Output power = Input power - losses
Output power = (24kVA X 0.95) - 1400 = 22800 - 1400 = 21.4kW
Efficiency = (Output/input) x 100%, n = (21400/22800) x 100 = 93.9%
10) A transformer has a rated power of 12kVA and a power factor of 0.85 and the losses
are 600 Watts. Calculate the overall efficiency.
Input power = kVA x Power factor, = 12kVA x 0.85 = 10.2kW

Level 2 & Level 3 Electro-Technical Question Paper with Answers :

Level 2
1) A transformer has an input power of 20kW and power losses of 920W, the overall
efficiency is
a) 96%
b) 94%
c) 95%
d) 90%

2) What is this component? ( Gate / Anode / Cathode )
a) A transistor
b) A triac
c) A diac
d) A thyristor

3) What are the three main sections of a health and safety policy
a) Statement of intent
b) Organisation
c) Arrangements
d) The manual

4) Under the Management of Health and Safety at Work Regulations 1999, which of these
is an employee NOT entitled to do?
a) Use any equipment or substance after training
b) Report any serious or imminent danger
c) Operate unguarded machinery after training
d) Report employers health and safety shortcomings

5) It is the duty of all employees to:
a) Organise safety lectures
b) Carry out safe working practices
c) Provide suitable safety equipment
d) Repair damaged equipment

6) The sequence of control for a large installation can be MOST simply shown by
a) Wiring diagram
b) Layout diagram
c) Circuit diagram
d) Block diagram

7) A layout drawing shows a proposed cable run. The scale is 1:100 and the length on the
drawing is 65mm, the length of the cable is:
a) 6.5m
b) 17m
c) 42.5m
d) 4.25mm

8) What is meant by the term ‘zone of protection’?
a) Area around a working person
b) Zone around a bath
c) Zone around a lightning conductor
d) The area covered by an earthing system

9) If a ring main circuit has a 32 A fuse 230 V supply the maximum power available at any
one time is
a) 73.36 W
b) 736 W
c) 7360 W
d) 73600 W

10) BS 7671 does not apply to which of the following: (tick all that apply)
a) Aircraft
b) Motor vehicles
c) Mines
d) Outdoor lighting
Level 3

11) Two parallel plates of dimension 30mm by 20mm are oppositely charged to a value of
50mC. Calculate the electric flux density of the electric field.
a) 0.12C/m2
b) 83.3C/m2
c) 0.003C/m2
d) 3000C/m2

12) A 3-phase 4 pole, 50Hz induction motor has a slip of 4%. Rotor speed is:
a) 1500prm
b) 1440rpm
c) 1400rpm
d) 1359rpm

13) Which of these is a definition of ‘reasonably practicable’ in risk reduction
a) Minimum Cost And Effort
b) Major Cost But Minimal Effort
c) A Balance Of Effort And Costs
d) Major Cost With Major Risk Reduction

14) Which two of these are NOT true statements about ACOPs
a) They have a special legal status
b) Failure to observe an ACOP is not a criminal offence
c) Provide guides on practices other than health and safety
d) Can be approved without consent of the Secretary of State

Answers :

1) C Efficiency = Output/Input = (20000-920)/20000 x 100 = 95.4%.
I saw a similar question to this, with GOLA stating 20kVA.
2) D Thyristor. These have anodes and cathodes like diodes, but also have a gate.
3) A, B and C. Yes, they have manuals, but policy does not state it has to be in a manual! It
could be held on-line or in electronic format!
4) C Only manufacturer’s agents or trained authorised personal should remove guards
5) B
6) D
7) A In real life, the cable will be 100 times bigger than the dimension on the drawing.
65mm in m is 0.065. 100 x 0.065 = 6. 5m
8) C This term denotes the space within which a lightning conductor provides protection
against a direct lightning strike by diverting the strike to itself.
9) C P = V x I = 230 x 32 = 7360W
10) A, B and C
11) B Q = 50 x 10-3, A = 30 x 20 x 10-6 m2 OR 0.03 x 0.02 m2
D = Q
A
D = 50 x 10-3 = 83.3 C/m2
600 x 10-6
I have also seen this question with the word FLUX replacing FIELD, although field
is the correct term, as conceptualised by Michael Faraday.
12) B Ns = 1500 rpm. With 4% loss = 1440rpm
13) C
14) C, D
15) C
16) C
17) A They both have the same magnetisation strength. The area under the curve
represents the losses, so the wider the curve, the more magnetisation losses there
are.
18) C Similar to the cage rotor, except the bars are replaced by windings.
A and C. DOL is only used for starting.
19) C A and B would be examples of inappropriate PPE. The HSE don’t prevent accidents
directly, they provide guidance and enforcement.
20) D

 

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Electrotechnical Unit 302 :

A) A prospective earth fault current test needs to be carried out on a domestic
consumer unit which has type B circuit breakers. Some of the lighting circuits have fluorescent fittings.

1. State which instrument(s) can be used.
2. What precautions need to be taken prior to the test.
3. The minimum allowable value(s).
4. Describe the test.
(6 points)
B. Explain the terms
1. Equipotential bonding
2. Exposed conductive part

C. Draw a star-delta transformer arrangement.
1. Fully label all conductors, voltages and currents for a 25kV/400kV step-up system.

2. State two materials used for conductors in the UK generation, transmission and distribution system and why they are chosen.

Note: electro-technical level 2 and level 3 papers,
you will find quite a few questions which relate to this unit. Here are some examples
of what you may be asked (what is covered in the unit and should be known as underpinning knowledge):

_ Statutory safety regulations and safe working practices.
_ Selection of wiring systems and cable sizes
_ Be able to represent an installation using block, schematic, wiring or layout diagrams
_ Describe the generation, transmission, transformation, distribution and delivery of electricity in the UK
_ Describe single-phase and 3-phase supply types, voltages, currents and terminology

A) A prospective earth fault current test needs to be carried out on a domestic
consumer unit which has type B circuit breakers. Some of the lighting circuits have fluorescent fittings.

1. State which instrument(s) can be used.
2. What precautions need to be taken prior to the test.
3. The minimum allowable value(s).
4. Describe the test.

Answers
A) A prospective earth fault current test needs to be carried out on a domestic
consumer unit which has type B circuit breakers. Some of the lighting circuits have fluorescent fittings.

1. State which instrument(s) can be used.
2. What precautions need to be taken prior to the test.
3. The minimum allowable value(s).
4. Describe the test.

Answer:
1. PFC tester or loop tester with PFC function (as shown). The voltage range the meter will work on is from 50V to 480V, which is taken from the supply it is plugged into. It measures the current between line and neutral across an internal impedance inside the tester: PFC =
I = V/R = 230/0.5 = 460A. The meter will return a value from 0A up to ≈50kA.
The value can also be ascertained by calculation or determined by other means. ( 16th edition 713-12-01, ↔ 17th edition 612.11 )

2. This is a live test, you may be measuring live energised conductors (when using clip-on leads) so be very careful. As this is not the first live test, you will have already informed persons, put up warning signs, informed persons who could be affected by a ‘live’ test etc, but your tutor needs you to say this.
The other precautions required for a PFC test are for the person who is conducting the test to:
i) Check the condition of the test instrument and probes/leads for soundness
ii) Check test leads and probes conform to HSE GS 38
iii) Since you are working with live terminals, be careful not to touch any live part
3. To 16th edition:
Semi-enclosed (re-wire able BS 3036) SA1 = 1kA etc SA2 SA4
Cartridge fuses BS:1361 Type 1 = 16.5 kA Type 2 = 33kA

BS:88-2.1 = 50kA at 400V
BS:88-6 = 16.5kA at 230v & 80kA at 400v
BS EN 60898 MCBs (or old type MCB’s BS:3871)
M1 = 1kA / M1.5 = 1.5 kA / M2 = 2kA and so on
So, check your reading against the time current graphs for the relevant device to get an actual disconnection time.
.g. a 32A BS EN 60898 type B (BS3871 type 2) MCB has a reading of 460A, giving a
disconnection time from Appendix 3, fig.3.4 of 01.s to 5s (>160A), which is acceptable.

4. Measure the Prospective Fault Current at the origin of the supply.
Check that the test instrument, leads, probes and crocodile clips (if any) are suitable for the
purpose, and in good serviceable condition (to GS38).
Observing all precautions for safety, connect the instrument to the incoming energised
supply to measure a phase to neutral value.
Check the polarity indicator (if any) on the instrument for correct connection.
Using the PFC / Loop tester set the selector switch to PFC and the range switch to the
highest setting i.e. 2000A and test for the PFC value.
Reduce the range switch to a lower setting to obtain a more accurate value.
Measure the PSCC (Line (Phase) to Neutral) & PEFC (Line (Phase) to earth), measure at
the most remote socket and record the highest value as the PFC. Note: for 17th edition the
term ‘line’ must be used, for 16th edition, ‘phase’ is used.
Record this value in the Supply characteristics page and the Schedule of test results.
Ensure the breaking capacity of the main protective device is
capable of breaking the PFC (434-03-01 – 16th edition, 434.5.1 – 17th edition)
For 3-phase installations the PFC recorded is twice (2x) the maximum single-phase value measured.
instrument does not have a prospective fault current range, the readings given by the above
procedure are fault loop impedances (in ohms). Use a BS EN 61557-2 or BS EN 61557-3
compliant meter, which will deliver 20 to 25A for up to two cycles. To convert each of these
readings into a prospective fault current, divide them into the measured value of phase to
neutral voltage.
For example, if the voltage measured at the time of the test is 230V and the measured value
of fault loop impedance between phase and neutral at the origin is 0.05_.
Maximum prospective short-circuit = 230 / 0.05 = 4600 A (or 4.6 kA) current (line (phase) to neutral).
If Ze is known and the loop tester does not have the facility to measure earth fault current,
it can also be calculated by using the formula below:
Ipf = Uo / Ze Where Ipf = Earth Fault Current, Uo = Nominal Phase to Earth Voltage, Ze = External Earth Fault Loop Impedance

A.) If the test
LCD, display : Main status indication LED : Range switch : Test Button : PS, always remember Polarity :

B. Explain the terms

1. Equipotential bonding :
2. Exposed conductive part :

B. Explain the terms

1. Equipotential bonding
2. Exposed conductive part
1.Equipotential bonding: 16th / 17th edition: ‘Electrical connection maintaining various
exposed-conductive-parts and extraneous-conductive-parts at substantially the same potential.’

This involves joining together metalwork that is or may be earthed so that it is at the same
potential to prevent shock from between those pieces of metal as the earth system handles a fault.

2. Exposed conductive part: ** 16th edition: A conductive part of equipment which can be
touched and which is not a live part but which may become live under fault conditions.’
** 17th edition: ‘Conductive part of equipment which can be touched and which is not
normally live, but which can become live when basic insulation fails.’
This refers to items like the metallic covers of electrical equipment which will normally be
at earth potential, but which may develop a voltage if the fault current goes through the equipment.

C. Draw a star-delta transformer arrangement
1. Fully label all conductors, voltages and currents for a 25kV/400kV step-up system.

2. State two materials used for conductors in the UK generation, transmission and distribution system and why they are chosen.
Aluminium is used for high voltage conductors on overhead pylons on the Supergrid, National grid and to large industry. Aluminium has a slightly higher resistivity than copper ,←← but is much lighter, the main reason it is chosen for overhead lines. The aluminium
conductors are on the outside woven like a rope around a steel core, which provides mechanical strength.
Copper is used for underground cabling in the transmission and distribution systems or where weight is not an issue. It is also used for medium industry right down to domestic supply due to its low resistivity. Although Gold has lower resistivity, it is not used due to its high cost.

C. Draw a star-delta transformer arrangement.
1. Fully label all conductors, voltages and currents for a 25kV/400kV step-up system.

2. State two materials used for conductors in the UK generation, transmission and distribution system and why they are chosen.

examples of what you may be asked (what is covered in the unit and should be known as underpinning knowledge):
_ Statutory safety regulations and safe working practices.
_ Selection of wiring systems and cable sizes
_ Be able to represent an installation using block, schematic, wiring or layout diagrams
_ Describe the generation, transmission, transformation, distribution and delivery of electricity in the UK
_ Describe single-phase and 3-phase supply types, voltages, currents and terminology

 

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Protective Conductors :

Where the protective conductor is formed by conduit , ( 543.2.7 ) trunking , ducting or the metal sheath and/or armour of a cable ,
The earthing terminal of each accessory shall be connected by a separate protective conductor to an earthing terminal incorporated in the associated box or other enclosure ,

Except where the circuit protective conductor is formed ( 543.2.9 ) by a metal covering or enclosure containing all of the conductors
Of the ring , the circuit protective conductor of every ring final circuit shall also be run in the form of a ring having both ends
Connected to the earthing terminal at the origin of the circuit ,

A switching device shall Not be inserted in a protective ( 543.3.4 ) conductor unless :
* the switch has been inserted in the connection between the Neutral point and means of earthing ; and
* the switch is linked switch arranged to disconnect and connect the earthing conductor for the appropriate source , at substantially the same time the related live conductors ,

Where electrical monitoring of earthing is used , no ( 543.3.5 ) dedicated devices ( e.g. operating sensors , coils ) shall be connected
In series with the protective conductor , ( see BS-4444 )

Earth Electrode Résistance :

Where the Earthing system incorporates an Earth Electrode ( 612.7 )
As part of the installation , the Electrode Résistance to Earth shall be measured ,

Where the installation incorporates an Earth Electrode , the ( 612.1 ) test of Regulation ( 612.7 ) shall also be carried out before the Installation is energised ,

If any test indicates a failure to comply , that test and any preceding test , ( 612.1 ) the results of which may have been influenced by fault indicated , shall be repeated after the fault has been rectified ,

Where Fluorescent or Discharge lighting is involved , a factor of 1.8 is used to take into consideration control gear :
Fluorescent fitting will have a current rating off ?
80W x 1.8 ÷ 230 = 0.63A

Light levels :

Light levels available where the camera is to be used are an important consideration. shows some typical light levels.
When choosing a suitable camera for a particular environment, it is best to select one that is specified at approximately ten times the minimum light level for the environment. One that is specified at the same level of light will not produce the clear
images needed, because the camera will not have enough light to ‘see’.

Environment : Typical light level
Summer sunlight : 50,000 lux
Dull daylight : 10,000 lux
Shop/office : 500 lux
Main street lighting : 30 lux
Dawn/dusk : 1–10 lux
Side street lighting : 3 lux
Typical light levels

 

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Are you installing smoke alarms ? Are you confused when it comes to the 17th Edition ? Too many conflicting views ? We have put together a little smoke and fire alarms guide to the 17th edition.
Smoke alarms can be connected to a lighting circuit – this is the preferred circuit
The alternative is wiring on a dedicated circuit

Who says this?
Most reputable smoke alarm manufacturers.
The IEE , NICEIC , ECA , and SELECT

The 17th Edition : does not make any reference to domestic smoke alarm installations in the whole document.
Why are some manufacturers saying that smoke alarms should be wired on a dedicated circuit ?
They are misinterpreting the requirements of Chapter 56 – Safety Services. This makes reference to fire detection and alarm systems, but in section 560.10 it refers you to BS 5839 for the specific requirements. Appendix A makes it quite clear that BS 5839 : Pt 1 , is the document being referred to. This standard is for commercial systems , it is not the standard for domestic smoke alarms systems, this is BS- 5839 : Pt 6 ,
In the absence of specific advice in the 17th Edition for domestic smoke alarm systems
to Grade D (mains with a back-up battery), follow the recommendations of BS-5839 : Pt 6 ,

What are these recommendations exactly?

Clause 15.5 states that Grade D smoke alarms can be wired from either…
* ‘An independent circuit at the dwellings main distribution board, in which case no other electrical equipment should be connected to this circuit’.
* Or ‘A separately electrically protected, regularly used lighting circuit’.
* Note that RCD protection is not mentioned. Therefore, an RCD protected circuit is acceptable.
* Hard-wired systems must be on a single final circuit.
* Radio – linked systems must be on a single final circuit.
* Radio – linked systems can be on separate lighting circuits.

- Temporary Electrical Installations for Structures ,
Amusement devices and booths at fairgrounds , Amusement parks and circuses ,

The protective measures of no-conducting location and earth-free local equipotential bonding are Not permitted , ( 740.410.3.6 )
Where the type of system earthing is TN-: ( 740.411.4 )

* a PEN conductor shall not be used downstream of the origin of the temporary electrical installation ,
* the final circuits for the supply to caravans or similar shall not include a PEN conductor ,

Where a generator supplies a temporary installation , ( 740.551.8 )
Forming part of a TN, TT , or IT system , care shall be taken to ensure that the earthing arrangements are in accordance with the regulations ,

- The following types of protective device may be used for fault protection in a TN system , ( 411.4.4.)

* an Overcurrent protection device ,
* an RCD ( in which case the circuit should also incorporate overcurrent protective device ,

Note : Compliance with regulations 411.4 shall be verified by :
* measurement of earth fault loop impedance ;
* verification of the characteristics and / or the effectiveness of the associated protective device ,

Part 2: Definitions for the classification of persons

„ The 17th edition identifies three categories of people
„ * A skilled person who has technical knowledge to enable them to avoid electri
cal dangers
„* An instructed person who has been adequately advised or supervised to
avoid electrical dangers – e.g. facilities manager
„* An ordinary person – typically a member of the general public

FAIRGROUNDS , AMUSEMENT PARKS AND CIRCUSES

Temporary Electrical Installations for Structures, Amusement Devices and Booths at Fairgrounds, Amusement Parks and Circuses – a proposed new Section for BS 7671:2008, 17th Edition of the IEE Wiring Regulations. Currently, there is no Part or Section of BS 7671:2001(2004) covering such installations but information can be found in IEC 60364-7-740 and HD 60364-7-740. The proposed Section 740 of BS
7671:2008 is based on the CENELEC Harmonised Document HD 60364-7-740, of which, the UK is to incorporate the technical intent of that standard. (Please note that Regulations and Sections quoted within this article are from the proposed BS-7671:2008 and may be subject to
The Scope of Section 740
Section 740 recognises that some installations are exposed to many differing and onerous circumstances, as they are frequently installed,
dismantled, moved to a new location then installed and operated again. To compound problems, such installations can be exposed to the
elements, open to the general public, house animals and livestock and be operated as a place of work. The equipment must function without
compromising safety, therefore, the installation has to be fit for purpose and be designed to cope with ever-changing conditions.
The permanent electrical installation, from which the temporary system is supplied, or the building in which the temporary system is
housed, is excluded from the scope, nor does the scope apply to the internal electrical wiring of machines (see BS EN 60204-1).

Electrical Supplies
The nominal supply voltage of temporary electrical installations in booths, stands and amusement devices should not exceed 230/400 V ac or
440 V dc. Supplies can be obtained from a number of sources:
* from the public network, i.e. the DNO ,
* generators, i.e. those mounted on trucks owned by the touring event ,
* from privately owned supplies, i.e. a local factory with sufficient spare capacity , There can be any number of electrical sources supplying the temporary system and it is of paramount importance that line-and neutral
conductors from different sources are not interconnected. Where the supply is obtained from the DNO any instructions given must be adhered to. Supplies obtained from the DNO would preferably be TN-S but this isn’t always possible. A TN-S system has the neutral of the source of energy connected with earth at one point only, at, or as near as is reasonably practicable, to the source of supply. The consumer’s main earthing terminal is typically connected to the metallic sheath of the distributor’s SWA service cable. Where the available supply is TN-C-S, the supply should not be used in that form, i.e. a TT system should be created. The reason is that the ESQCR prohibits the use of a TN-C-S system
for the supply of a caravan or similar construction. Where continuity of service is important, IT systems may be used for dc applications only.

Protection against electric shock
At the origin of each electrical supply, to all or part of the installation, an RCD, with a rated residual operating current not exceeding 300mA, is to be installed to provide automatic disconnection of supply. As there will be further RCDs downstream of this point, this RCD should be of the
S-type, complying with the requirements of BS EN 61008-1 or BS EN 61009-1 and incorporate a time delay in accordance with BS EN 60947-2, to provide discrimination with further RCDs protecting final circuits. For supplies to ac motors, RCDs. should be the time-delayed or the
S-type where necessary to prevent unwanted tripping. The protective measure of protection by obstacles is not permitted on this type of installation, however, placing out of arm’s reach is acceptable for electric dodgems ,

Additional protection
All final circuits in the installation, e.g. lighting, socket-outlets rated up to32 A, mobile equipment connected by a flexible cable and rated up to 32 A are to be protected by an RCD having a rated residual operating current not exceeding 30 mA. The requirement for additional protection relates to the increased risk of damage to cables within an installation of this nature.

Lighting circuits incorporating emergency luminaires, with self-contained batteries for example, should be protected by the same RCD
protecting that lighting circuit. This requirement for additional protection does not apply to:
* SELV or PELV circuits – this measure alone is deemed to be a protective measure in all situations ,
* circuits protected by electrical separation
* lighting circuits placed out of arm’s reach – provided they are not supplied by socket-outlets, i.e. those manufactured to BS 1363 or
BS EN 60309-1; luminaire supporting couplers or plug-in lighting distribution units excepted

Supplementary bonding
Particular care must be taken in areas where livestock are housed as they are sensitive to small potential differences. To minimise potentials,
supplementary bonding should be installed to connect all exposed conductive-parts and extraneous conductive-parts that can be touched by livestock. Where a metal grid is laid in the floor, or extraneous-conductive-parts are accessible, they should be included within the supplementary bonding of the location. It is important to note that animal excrement and urine is very corrosive and so all supplementary bonding connections should be enclosed in a suitable enclosure.

THE INSTALLATION
Wiring systems
Conduit, cable trunking and ducting, tray and ladder systems can be used but must, of course comply with the manufacturer's instructions; the
following standards apply:
* conduit systems BS EN 61386 series
* cable trunking systems/cable ducting systems BS EN 50085
(particular parts only)
* tray and ladder systems BS EN 61537

 

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Cables
All cables should be fire rated and meet the requirements of BS EN 60332-1-2. Cables of type H07RNF or H07BN4-F (BS 7919)
together with conduits complying with BS EN 61386-23 are deemed to satisfy this requirement. Cables should have a
minimum rated voltage of 450/750 V, except that, within amusement devices, cables and cords having a minimum rated voltage of 300/500 V
may be used. Where cables are buried in the ground, the route should be marked at suitable intervals and be protected against mechanical damage.

Electrical connections
Joints should not be made in cables except where necessary as a connection into a circuit. Where joints are made, these should be either using
connectors in accordance with the BS-7671, the manufacturer’s instructions or the connection should be made in an enclosure with a degree of
protection of at least IP4X or IPXXD. Where strain can be transmitted to terminals the connection should incorporate cable anchorage(s).

External influences
Electrical equipment should have a degree of protection of at least IP44.

Switchgear and controlgear
Switchgear and controlgear should be placed in cabinets which can be opened only by the use of a key or a tool, except for those parts designed
and intended to be operated by ordinary persons.

Isolation
It is a requirement that every electrical installation of a booth, stand or amusement device has its own means of isolation, switching and
overcurrent protection, these devices should be readily accessible. There are similar requirements for supplies to amusement devices. Additionally, each distribution circuit should be provided with its own readily accessible and properly identified means of isolation.
A device for isolation should disconnect all live conductors – line(s) and neutral conductors.

Examples of devices used for isolation are:
* circuit-breaker
*RCD
* plug and socket arrangement

Luminaires
Every luminaire and decorative lighting festoon-chain should have a suitable IP rating and be securely attached to the structure or support
intended to carry it. Its weight should not be carried by the supply cable, unless it has been selected and erected for this purpose.
Luminaires and decorative lighting festoon-chains mounted less than 2.5 m, i.e. arm’s reach, above floor level or could be otherwise accessible to incidental contact, should be firmly fixed, sited and guarded to prevent risk of injury to persons or ignition of materials. Access to the fixed light source should only be possible after removing a barrier or an enclosure, which should only be possible by the use of a tool. Lighting festoon-chains should use H05RN-F (BS 7919) cable or equivalent, they may be used in any length provided the overcurrent protective device in the circuit is correctly rated. Luminous tube, sign or lamps with an operating voltage higher than 230 V/400 V a.c., e.g. neon signs, are to
be installed out of arm’s reach or be adequately protected from accidental or deliberate damage. A separate circuit should be used which should be circuit should be used which should be controlled by an emergency switch. controlled by an emergency switch.
The switch should be easily visible, accessible and marked in accordance with the requirements of the local authority.
Luminaires in shooting galleries and other sideshows where projectiles are used should be suitably protected against accidental or deliberate damage. When transportable floodlights are used, they should be mounted so that the luminaire is inaccessible to no instructed
persons. Supply cables should be flexible and have adequate protection against mechanical damage.

Safety isolating transformers and electronic converters
Safety isolating transformers should comply with BS EN 61558-2-6 or provide an equivalent degree of safety. Each transformer or electronic
converter should incorporate a protective device which can be manually reset only; this device should protect the secondary circuit.
Safety isolating transformers should be mounted out of arm’s reach or be mounted in a location that provides equal protection, e.g. in a panel or
room that can only be accessed by a skilled or instructed person, and should have adequate ventilation. Access by competent persons for
testing or by a skilled person competent in such work for protective device maintenance should be provided. Electronic converters should
conform to BS EN 61347-2-2. Enclosures containing rectifiers and transformers should be adequately ventilated and the vents should not be
obstructed when in use.

Plugs and socket-outlets
An adequate number of socket-outlets should be installed to allow the user's requirements to be met safely. In booths, stands and for fixed
installations, one socket-outlet for each square metre or linear metre of wall is generally considered adequate. Socket outlets dedicated to lighting circuits placed out of arm’s reach should be labelled according to their purpose. When used outdoors, plugs, socket outlets and couplers should comply with BS EN 60309-2, or where interchange ability is not required, BS EN 60309-1.

FIRE RISK
Luminaires and floodlights
Luminaires and floodlights should are to be fixed so that a focusing or concentration of heat is not likely to cause ignition of any material.

Electric motors
An electric motor which is automatically or remotely controlled and which is not continually supervised should be fitted with a
manual reset protective device against excess temperature.

Electrical supply to devices
At each amusement device, there should be a connection point readily accessible and permanently marked to indicate the following essential
characteristics:
* rated voltage
* rated current
* rated frequency

Electric dodgems
Electric dodgems should only be operated at voltages not exceeding 50 V a.c. or 120 V d.c. The circuit should have an electrical separation
from the electrical supply by means of a safety isolating transformer in accordance with BS EN 61558-2-4 or a motor-generator set.

Low voltage generating sets
It is very important that all generators are located to prevent danger and injury to people through inadvertent contact with hot surfaces and
dangerous parts. The electrical equipment associated with the generator should be mounted securely and, if necessary, on anti-vibration mountings. Where a generator supplies a temporary installation, forming part of a TN, TT or IT system, care should be taken to ensure that the earthing arrangements are adequate and, in cases where earth electrodes are used, they are considered to be continuously effective. In reality this means that the drying of the ground, in summer, or freezing of the ground, in winter, should not adversely affect the value of earth fault loop impedance for the installation. The neutral conductor of the starpoint of the generator should, except for IT systems, be connected to the
exposed-conductive-parts of the generator.

INSPECTION AND TESTING The temporary installation
The electrical installation between its origin and any electrical equipment should be inspected and tested after each assembly on site. Internal
electrical wiring of roller coasters, electric dodgems, etc., are not considered as part of the verification of the electrical installation. In special
cases the number of the tests may be modified according to the type of temporary electrical installation. The HSE offers guidance on the
inspection and testing of the temporary electrical installation in the publication HSG 175 – Fairgrounds and Amusement Parks: Guidance on Safe Practice.

BS 1363 – 13 A plugs, socket-outlets and adaptors
BS 7919 – Electric cables. Flexible cables rated up to 450/750V, for use with appliances and equipment intended for industrial and similar environments
BS EN 50085 – Cable trunking and cable ducting systems for electrical installations
BS EN 60204-1 – Safety of machinery. Electrical equipment of machines. Specification for general requirements
BS EN 60309-1 – Plugs, socket-outlets and couplers for industrial purposes. General requirements
BS EN 60309-2 - Plugs, socket-outlets and couplers for industrial purposes. Dimensional interchange ability requirements for pin and contact-tube accessories
BS EN 60332-1-2 – Tests on electric and optical fibre cables under fire conditions. Test for vertical flame propagation for a single insulated wire or cable. Procedure for 1 kW pre-mixed flame
BS EN 60947-2 – Low-voltage switchgear and control gear. Circuit-breakers
BS EN 61008-1 – Residual current operated circuit-breakers without integral overcurrent protection for household and similar uses (RCCBs).
General rules
BS EN 61009-1 – Residual current operated circuit breakers with integral overcurrent protection for household and similar uses (RCBOs). General rules
BS EN 61347-2-2 – Lamp controlgear. Particular requirements for d.c or a.c. supplied electronic step-down convertors for filament lamps
BS EN 61386 – Conduit systems for cable management. General requirements
BS EN 61537 – Cable management. Cable tray systems and cable ladder systems
BS EN 61558-2-6 – Safety of power transformers, power supply units and similar. Particular requirements for safety isolating transformers for general use
IEC/HD 60364-7-740 – Electrical installations of buildings – Part 7-740: Requirements for special installations or locations – Temporary electrical installations for structures, amusement devices and booths at fairgrounds, amusement parks and circuses
HSG 175 – Fairgrounds and Amusement Parks: Guidance on Safe Practice ISBN 978-0-7176-6249-4

 

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Low power supply sources : ( 560.6.10 ) limited to 500W for 3-hour duration or 1500W for 1-hour duration
However ,
* the batteries may be of the gastight or valve regulated maintenance – free type ; and
* the minimum design life of the batteries shall be 5 years ,

Multiphase circuits , it shall be verified that the Phase sequence is maintained , ( 612.12 )

Connections :

Every connection shall be accessible for inspection , ( 526.3 ) testing and maintenance , except for the following :
* a joint designed to be buried in the ground ,
* a compound filled or encapsulated joint ,
* a connection between a cold tail and the heating , element as in ceiling heating , floor heating or a trace heating system ,
* a joint by welding , soldering , brazing or appropriate compression tool
* a joint forming part of the equipment complying with the appropriate product standard

Wiring systems : ( 132.7 )
The choice of the wiring system and the method of installation shall include consideration of the following ,
* the nature of the location ,
* the nature of the structure supporting the wiring ,
* accessibility of wiring to persons and livestock ,
* voltage ,
* the electromechanical stresses likely to occur due to short-circuit and earth fault currents ,
* electromagnetic interference ,

Safety of machinery - Electrical equipment of machines - Part 1: General requirements

Amusement Devices and Booths at Fairgrounds, Amusement Parks and Circuses

IEC 60204-1:2005+A1:2008 is applicable to the electrical equipment or parts of the electrical equipment that commences at the point of connection of the supply to the electrical equipment of the machine and operate with nominal supply voltages not exceeding 1 000 V for alternating current (a.c.) and not exceeding 1 500 V for direct current (d.c.), and with nominal supply frequencies not exceeding 200 Hz. The technical content is therefore identical to the base edition and its amendment and has been prepared for user convenience. A vertical line in the margin shows where the base publication has been modified by amendment 1. This consolidated version consists of the fifth edition (2008) and its amendment 1 (2008). Therefore, no need to order amendment in addition to this publication.

Safety Circuits :
In addition to a general schematic diagram, full details of all electrical safety sources shall be given. The information shall be maintained and displayed adjacent to the relevant distribution board. A single-line diagram is sufficient. ( 560.7.9 )

Bonding on sink ?

Probably not.
On-Site Guide section 4 states that:
Supplementary bonding is required by BS-7671 / 701.415. in some locations.
(Generally in Special Locations. A kitchen or utility room is not one of these).
However, if the installation meets the requirements for earthing and bonding (i.e. Main earth connection and Main bonding of gas and water, metal waste pipes etc. 411.3.1.2 ) then there is no specific requirement for supplementary bonding of:
• Kitchen sinks, pipes or draining boards
• Metallic boiler pipework
• Metal furniture in kitchens
• Locations containing bath or shower providing the requirements of BS-7671:2008 701.415. are met. ( Disconnection time of 0.2 for, TT 0.4 for TN and RCD protection).

How close to a sink/basin can sockets be located ?

BS7671:2008 does not specify any minimum distance for socket outlets to be sited from a sink.
Regulation 512.2.1 requires external influences to be considered when selecting equipment for a particular location.

The regulation requires all equipment to be of a design appropriate for the situation in which it is to be used. Sockets that are used in domestic installations are not splash resistant, are therefore not suitable for installation close to any sink or draining board.
It is recommended that socket outlets and other accessories should be located at least 300mm, measured horizontally from a sink or draining board, where they are unlikely to be splashed.

Does the dispensation in Regulation 701.415.2 to omit supplementary bonding in a bathroom apply to TT systems ?

Yes it does apply to TT systems.
Regulation 701.415.2 states that supplementary bonding may be omitted where:
• i) All final circuits in that location comply with 0.4 sec disconnection
• ii) All final circuits in that location are protected by RCD
• iii) Main bonding to extraneous conductive parts is intact.
In this case TT systems are treated in the same way as TNC-S & TNS.

Is a time-delayed RCD main switch required in the consumer unit of a new domestic installation supplied by a TT system ?

Provided that the consumer unit is of all insulated construction and all the final circuits are RCD-protected, a time-delayed RCD main switch is not required.

I am measuring a Zs of 140Ω on my final circuits. Table 41.3 gives a maximum of 1.44Ω. I know that a Ze below 200Ω on a TT system is acceptable (Table 41.5 note 2). Is my Zs ok ?

Yes it is acceptable. As long as your circuit is protected by an RCD. In this case (at the front end) they should be RCBOs to give double pole isolation. The maximum Zs which ensures the operation of a 30mA RCD (circuits not exceeding 32A) is 1,667Ω . (Table 41.5) . Regarding your Ze measurement. A Ze greater than 200Ω is considered unstable and it may be prudent to install further electrodes.

TT circuits require a disconnection time of 0.2 seconds. (BS7671 Table 41.1).
How can this be achieved when the Max Loop Imp Tables in BS7671 only deal with 0.4 and 5 seconds ?
BS-7671:2008 ,
The note below Table 41.1 states that:

TT disconnection time of 0.2 secs up to 32A & 1 sec over 32A (411.3.2.4) is achieved by:
1. an Overcurrent Protective Device and
2. Equipotential Bonding (connected to all extraneous metallic parts).

Then the disconnection times for TN systems can be used ie. 0.4 seconds up to 32A & 5 secs over 32A (411.3.2.3)
On – site Guide Section 3 Disconnection Times for TT circuits. The required disconnection times for TT systems can (except in the most exceptional circumstances) only be achieved by protecting every circuit with an RCD.

BS-7671:2008 / 411.3.2.2 On – site Guide Section 3

 

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Should I identify black or grey as neutral on harmonised single phase cables ?
Technically, when any cable is over-sleeved or marked (with the exception of single-core green/yellow which must not be over-sleeved or marked), the over-sleeve or marking takes precedence over any colour underneath and therefore any combination can be used.

However, a convention has been generally accepted of over sleeving or marking the black with green/yellow (CPC) and the grey with blue (Neutral).

The thinking behind this has been done with the aim of helping disassociate the colour black with neutral and the shade of grey being a neutral colour.

How Long Can Meter Tails Be ?
The length of Tails from the Meter to the Consumers Distribution Board or Consumer Unit is at the discretion the Local Electricity Company.

Generally the maximum length of tails allowed is 3 metres. For longer distances it is common practice to install a Double Pole Isolation Switch at the Meter Position and install tails or a Sub-Main to the Consumers Distribution Board. Care should be taken to install adequate mechanical protection to the Tails or Sub-Main cable.

SWA is preferable if the cable is not to be clipped direct to surface. Minimum size of Meter Tails is 25 sq mm Onsite Guide Section 2

Building Regulations confirm...

...that when a hole is cut into a fire rated ceiling to fit a downlight, the fire stopping ability of the ceiling is impaired. In the event of a fire, flames could penetrate through the light fitting and spread to the floor above with the subsequent risk to life and property. The downlight itself can also be a source of fire due to the high temperature of lamps and the promixity to flammable material.

To provide total peace of mind and total protection, a Fire hood downlight cover should be installed over the light fitting if the ceiling is a fire separating element. Fire hoods will stop the spread of fire for at least 60 minutes. In fact, recent tests by Chiltern International have demonstrated that Fire hood downlight covers can give added peace of mind by providing up to 2 hours protection from fire.

When Fire hood / downlight covers are fitted as part of the ceiling structure they become in effect a permanent fixture. This means that the fire protection with Fire hood remains even when fashion may dictate a change of light fittings.

“Building Regulations 2000 Approved Document P allocates full responsibility to the electrician to make good the fire performance of any fire-rated floor/ceiling/wall after carrying out an electrical installation and legal action can be taken for non-compliance. Many, so called fire rated downlight fittings/covers are only tested in a small number of ceiling constructions and consequently this leaves the electrician vulnerable to “legal action” if the solution that he uses is wrong for the installation."

Types of Smoke Alarm Sensor : The following smoke alarm sensor types are suitable for different applications.

Optical :
Sensitive to larger smoke particles produced by smouldering fires like furniture. Suitable for mounting in landings and hallways to reduce false alarms from kitchens but not in steamy areas near to showers or bathrooms.
Ionisation :
Sensitive to smaller invisible particles in smoke which can be produced from cooking. Suitable for dusty or occasionally Smokey locations as they are less sensitive to more dense smoke particles. More likely to cause false alarms than the Optical when near kitchens.

Heat:
Not sensitive to any smoke.

Suitable for kitchens but only when linked to smoke detectors which are mounted in circulation areas such as hallways and landings.

Sitting :
Must be at least 300mm from a wall, corner or light fitting.
On sloping ceilings sensors must be 900mm (horizontally) from apex.At least one on each floor area (hall & landing).One sensor between lounge or kitchen and bedrooms.

Linking :
A mains voltage system requires linking between sensors with 3 core & earth cabling, however radio frequency or Radio Link bases can be used to prevent the need for wiring.

Sounders :
Each mains or battery operated sensor must incorporate an integral sounder.

Part P of the building Regulations deals with Fire Safety in dwellings.

For the Deaf & Hearing Impaired : Smoke & Heat Alarms
People with hearing difficulties require a different approach to fire protection, a conventional alarm sounder will not be sufficient for their needs.

System Features & Benefits :
• Control panel with rechargeable battery back-up, mains power supply lead and 13 amp Plug
• High intensity integral strobe light
• Auxiliary socket for connection of additional optional strobe lights
• Vibrating pad for placing under a pillow or mattress
• Capability for interconnection of up to 12 smoke alarms
• Test button on control panel for testing the system
• Connections are monitored to check integrity of system
• Alarm clock input facility
• Remote trigger option
• Pager output facility

 

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Inefficient Incandescent (GLS) Lamps to go ←←
Over an eight year period the ‘old type GLS’ land inefficient lamps will disappear from the shelves of suppliers and their sale will be prohibited within the EU. The EU directive begins in September 2009 with lamps of 80 Watts or higher, as well as all frosted (non-energy saving) lamps.

By 2012, most lamps of greater than 7 watts will be withdrawn from sale. Special purpose incandescent lamps (e.g. those used in household appliances such as ovens or fridges, traffic lights, infrared lamps etc.) are meant to be exempt from the measure, as they cannot fulfil the efficiency requirements and most of the time there is no alternative lamp technology.

The table below shows when certain requirements will be enforced and also displays some examples of the types of lamps, commonly used in households that will be affected by the new requirements.

* 1 Sept 2009 Lamps rated at 100w or more must carry an energy rating of C or better. All others may carry E : Lamp types prohibited from retail (common in households) [1] Clear incandescent and conventional halogen lamps rated at 100w or more [2] All frosted lamps excluding those carrying an energy rating of A (CFLs) * 1 Sept 2010 Lamps rated at 75w or more must carry an energy rating of C or better. Lamp types prohibited from retail (common in households) Clear incandescent and conventional halogen lamps rated at 75W or more : * 1 Sept 2011 Lamps rated at 60w or more must carry an energy rating of C or better. Lamp types prohibited from retail (common in households) Clear incandescent and conventional halogen lamps rated at 60w or more * 1 Sept 2012 Lamps must carry an energy rating of C or better All clear incandescent and conventional halogens : Lamp types prohibited from retail (common in households) ( Halogen lamps rated B & C still ok ) * 1 Sept 2013 Raising of quality requirements followed by a review * 1 Sept 2016 Lamps must carry an energy rating of B or better with 1 exception : Lamp types prohibited from retail (common in households) All lamps carrying an energy rating of C except special cap halogens (C rating

Spotlamps and other directed or reflected lamps will not be regulated until a second directive is drawn up at the end of 2009.

Halogen lamps with special caps like G9 do not exist with energy classes better than C. They are needed on the market as there are luminaires that can only take such lamps. Therefore further improvements can only be achieved by imposing requirements on the luminaires themselves, which the Commission is planning to do in a measure currently under preparation and to be tabled in 2009.

Halogen dichroic spots & floods which are widely used in surface mounted and recessed lighting applications, have a higher light output for power used and therefore lamps with an energy rating of C or better will not be phased out.

 

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to view the effects of installing a floodlight at various angles :

domestic locations is a 250 or 500 watt tungsten halogen floodlight controlled by a movement sensor (passive infra-red, PIR).

90o - At an angle of 90 o degrees from the vertical, the light is shining directly outwards, making it impossible for onlookers to see any criminal activity.

At 67o, the problems persist as at 90o degrees, making your "security" light a serious security risk.

45 o - The floodlight has an opening angle of 72o degrees, and so the light needs to be angled at less than half that (i.e. less than 36o) to illuminate the background (in this case, a wall).

At 22o, the floodlight begins to become a security aid. The house wall is illuminated, and so any intruder is highlighted against the background even if (as in this case) the background (i.e. the gate) is dark. However, when standing close by, the light source is still visible, which impedes the ability of a nearby witness to identify an intruder.

O o - Pointing a floodlight directly downwards is the best solution. The background wall is illuminated, and the bulb of the floodlight is no longer visible, making it easier on the eye. However, the floodlight is still over-powered (in this case, a 500W bulb); such a bulb will always generate strong shadows for people to hide in. The best overall solution is a floodlight pointing directly downwards whilst using a low powered bulb (60-120W will aid onlookers, without generating glare).

 

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Wiring within the trunking should be to a maximum of 45% of the available capacity in line with IEE wiring regulations.

* It is important to maintain electrical continuity between the cover and the base for the integrity of the system, and adherence to standards.

 

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The customer

Following initial verification, BS 7671 requires that an Electrical Installation Certificate, together with a schedule of test results and an inspection schedule, should be given to the person ordering the work. Until this has been done, the Regulations have not been met.
Sometimes the person ordering the work is not the end-user, e.g. the builder of a new housing estate sells the individual houses to various occupiers. In these cases it is recommended that copies of the inspection and test certificates, together with a test results schedule, are passed on to the new owners.

Handover to customer

Handover of the installation to the customer is the final task. This should include a tour of the installation, an explanation of any specific controls or settings and, where necessary, a demonstration of any particularly complicated control systems. The operation and maintenance manuals produced for the project should be formally handed to the customer at this stage, including copies of the Electrical Installation Certificate, the Schedule of Test Results and the Inspection Schedule

Activity
1. Obtain copies of the Electrical Installation Certificates, Inspection Schedules and Schedules of Test Results for your home or the site that you are currently working on. If the building is old enough these will also be accompanied by one or more Periodic Inspection Reports. If you can, compare these with the current installation to see if any alterations or additions have been made since they were prepared.

2. Have a look at any test equipment you have access to and see when and how it was last calibrated and when it is next due for calibration.

3. If you have not done any ‘real’ inspection and testing before, you might like to’ work shadow’ someone while they are carrying out an inspection and testing of an installation

Functional testing of residual current devices (RCDs)

Where a residual current device (RCD) fails to trip when pressing the integral test button, this would indicate a mechanical fault within the device itself, which should therefore be replaced.

When a residual current device fails to trip when being tested by an RCD tester, this would suggest that there is a fault with the RCD and that it should be replaced. It maybe that there is an issue with the cpc; however a test of the earth-loop impedance would prove whether this is satisfactory or not.

If the RCD does trip out, but not within the time specified, then a check should be made that the test instrument is set correctly for the nominal tripping current of the device under test. If the correct tripping current was selected then this indicates that the would fail to give the protection required and, therefore, would need replacing.

A RCD is fitted to the circuit for safety and protection. If the device is not working, then the installation is not protected and people and livestock are at risk of electric shock

Initial verification procedures

In order to make sure that this work is carried out satisfactorily the inspection and test procedure must be carefully planned and carried out and the results correctly documented .
We inspect and commission material after the completion of work for three key reasons to ensure:

* compliance with BS 7671
* compliance with the project specification (commissioning )
* that it is safe to use.

 

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Portable Appliance Testing - PATS

Examples of Bad Practice

No matter how well maintained you believe your electrical system to be there can be faults or unsafe areas that need correcting. Below are some of the more common problem areas.

Common Office Hazards

Incorrect Fuse Rating

Incorrect Polarity

Un-earthed appliances

Splits in cables

Trapped cables, between objects. (example: between desks and walls)

Trapped Cables (example; in floor boxes)

Overloading of sockets by 'piggy-backing' extension leads

Incorrect use of extension cables

Use of double adapters

Unsheathed pins on plugs

Un-earthed metal frame desks

Trailing leads

Water vessels near to electrical points

No access to sockets to disconnect in an emergency

Equipment such as fan heaters getting clogged and overheating

Dust clogging electrical equipment

Extension Leads

Extension leads are also considered as portable equipment and 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 A 3-pin extension socket-outlet with a 2-core cable should never be used even if the appliance to be used is Class II, as it would not provide protection against electric shock if used at any time with an item of Class I equipment.

** Class I equipment is earthed and contains metal parts, e.g. storage heaters, washing machines
** Class II equipment is not earthed and is usually in a plastic case, e.g. hairdryers, fans

Guidance for Schools & Colleges

Headteachers and others responsible for the safety of pupils and staff need to ensure that electrical equipment is regularly maintained and electrical hazards are identified and dealt with promptly.

The Health and Safety at Work Act and The Electricity at Work Regulations cover the legal requirements for electrical safety and apply to all places for work, including educational establishments.

Under the Regulations, every employer has a duty to ensure that all reasonable precautions are taken to achieve electrical safety. In the case of schools and colleges, the headteacher will normally be regarded as the principal 'duty holder'. The principal duty holder is required to:

• ensure that installation, repair and maintenance work is only carried out by competent persons
• confirm the safety of equipment by arranging periodic inspection and testing and any necessary maintenance work
• implement and maintain safety procedures for all electrical equipment in use.

 

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If adhesive tape is used , then it has been bicoloured : ( PEN )

* PEN ; conductors’ ( when insulated ) are either
Green & yellow : throughout their length . with blue markings at the terminations : or

Blue : throughout their length . with Green & yellow : markings at the terminations :

* Bare conductors’ are painted or identified by a coloured tape , sleeve or disk ,

 

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Electrical Supply July 2009

a) Provision of supply
The supply into a hazardous area should be directly from a main switch isolator and not from a ring main feeding other parts of the site. The switch isolator must isolate all live and neutral conductors.

b) Type of Supply
The form of earthing defines the types of electrical supply used on a site.
* TT system, a system having one point of the source of energy directly earthed, the exposed-conductive-parts of the installation being connected to earth electrodes electrically independent of the earth electrodes of the source;
* TN system, a system having one or more points of the source of energy directly earthed, the exposed-conductive-parts of the installation being connected to that point by protective conductors;
* TN-C system, a system in which neutral and protective functions are combined in a single conductor throughout the system;
* TN-S system, a system having separate neutral and protective conductors thought the system;
* TN-C-S system, a system in which neutral and protective functions are combined in a single conductor in part of the system;
* IT system, a system having no direct connection between live parts and Earth, the exposed-conductive-parts of the electrical installation being earthed.

For new installations the electrical supplies into a hazardous area should be TT, although TN-S, may be acceptable.

TN-C-S (PME) may only be used on existing installations subject to an
appropriate, documented, risk assessment being carried out and that the
installation is subjected to regular checks on the current on the diverted neutral
current. For these installations it may be more practical to install a “derived TT
system” for the equipment in the potentially hazardous area.
b) Cable sizing
All electrical power cables must be designed and sized by a competent electrician/designer.
The design and cable sizing needs to take into account a variety of factors including:
* Length of the cable(s),
* Proposed method of installation (e.g. underground buried, underground in duct, above ground on trays),
* Type of load (motors, heaters)
* The maximum load, (most LPG pump motors, especially single phase, take a high starting current),
* Current

Information on cable design is available from tables in the 17th Edition Electrical Regulations ,

c) Voltage
Tests should be carried out installations to confirm there are no excessive voltage drops. (e.g. due to length of cable, connections from the incoming supply to contactors/cables, contactors/switches.) The voltage drop to the extremity of the circuit should not exceed 5%; more information in BS7671.

The available voltage at any motor should remain within the tolerances specified by the motor manufacturer both for start up and during running.

d) Protection against Electric Shock
When a different type of supply is used for the hazardous area compared with the supply to other parts of the site there must be a suitable separation, typically in excess of 2.5 metres, between un-insulated components to prevent
inadvertent contact between the two.

e) Site Earthing
Site earthing is required for all sizes of storage vessel, when the installation is fitted with electrical equipment, the primary requirement being protection against electric shock. This is not the same as the earthing required for the dissipation of static electricity; see
5 i). Earthing figures for bonding should meet those given in BS 7671.

An earth-bonding conductor should be run back to a primary earthing point at the source of energy. For a TN-S system this is where all metallic parts will ultimately be bonded.

The electrical supply must have a suitable effective earth. A “split” earth bar and test socket should be installed for each installation to allow testing of the earthing efficiency.

Bonding to other services must be connected to earth and comply with BS7671.

Notes:
• The armour of SWA cable should not be used as an earth conductor.
• Installations using cathodic protection systems for corrosion protection of vessels or pipework require special consideration and expert advice should be sought. the current rating of the type, the type of load (e.g. motor, heater etc), its short circuit capability and earthing impedance values, which need to be evaluated on site to ensure compliance with BS7671.

g) RCDs
Every power circuits into potentially hazardous areas should be protected by a Residual Current Device (RCD) being capable of disconnecting all poles including neutral of the circuit having a disconnection time of not more than 30ms.

h) Generators
Special precautions are required when a generator is to be used either during normal operations or more importantly in emergencies (see BS7671).

5. Installation of Equipment
a) Motor overload/low voltage protection

BS 7671 requires that every electric motor having a rating exceeding 0.37 kW be provided with control equipment incorporating means of protection against overload of the motor. Every motor needs to be provided with means to prevent automatic restarting after a stoppage due to a drop in voltage or failure of supply.

b) Cables
Cable conductors should only be of copper.
Power cables with integral mechanical protection are preferred, non-armoured cables can only be used providing the cable is protected by another method against mechanical damage.
Earthing cable sizes need to be assessed for each site prior to installation. 25mm2 should be adequate for most installations, should a smaller cable be considered then the appropriate calculations need to be carried out before installation.

c) Glands
Cable glands should be suitable for the relevant zone or area, the type of equipment being connected, the connection thread and for the cable being used. They should also maintain the Ingress Protection of the equipment.

d) Auxiliary equipment
Any auxiliary electrical equipment (e.g. solenoid valves) should be suitably protected (e.g. using an individual RCD) in the event of failure of the equipment. This protection should not be incorporated into hazardous area enclosures unless written approval is received from the manufacturer.

e) Enclosures of equipment for use in potentially Hazardous/Protected Areas
Any modification of the enclosures after dispatch from the manufacturer will invalidate the electrical certification for use in hazardous areas and must not be carried out.

f) Emergency Switch
A suitable switching device for emergency use should be fitted outside the potentially hazardous areas or separation distance (whichever is greater). When operated this would disconnect all electrical supplies (live and neutral conductors) to the associated equipment. It may be preferable to leave some auxiliary circuits live; e.g. lighting for the area, gas detection systems etc.

Except where failure to start after a brief interruption would be likely to cause greater danger; the installation should incorporate a system so that following the loss of power (e.g. power cut) power is not restored automatically but needs to be reset manually by an authorised person. This may be incorporated with the switching device in the above paragraph.

g) Isolation
Where required by BS7671 and BSEN60079–14 a means to secure the isolation in the off position shall be provided for the equipment in the potentially hazardous areas.

h) Switching off for mechanical maintenance
A means of switching off and isolating the power supply for mechanical maintenance should be provided for any electrical equipment in accordance with BS7671 and BSEN60079-14.

 

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i) Earthing
Earthing arrangements should be assessed for each site prior to installation. Metallic sections of an installation should be designed, installed and tested to confirm they are electrically connected. For equipment not mounted on common
steelwork each component may need to be electrically connected, using an appropriately sized conductor, back to a single point.
The use of electrical connections across mechanical joints is not necessary providing, after installation, electrical conductivity is checked and confirmed to be acceptable. This should be checked periodically at intervals not exceeding 2 years.

Consideration should be given as to whether earthing of metallic items within a distance of 2.5 metres is also required. e.g. adjacent metallic fencing. Care should be taken to ensure that surface features (e.g. powder coating) do not render surfaces insulating.

For installation the incorporate Cathodic Protection systems suitable measures will need to be taken to ensure the parts of the installation protected by the CP system are not connected to the electrical system earth. Electrical isolators (with static build up protection) may need to be incorporated into the installation.

system are not connected to the electrical system earth. Electrical isolators (with static build up protection) may need to be incorporated into the installation.

j) Static earthing
Before connecting a vessel to a local earth rod an assessment is required to see if this would affect the protection of the total installation. It may be necessary to supply a separate “clean” earth for a delivery tanker earth connection.

k) Sodium lamps
Due to the potential hazard of ignition if a lamp is dropped or falls sodium lamps should not be installed within or above zone 0 or 1 areas. Before changing such lamps above zone 2 areas the area should be checked to confirm there is no flammable atmosphere present.

l) Redundant cables or cores
Any redundant cables/cores should either be removed or terminated in a suitable enclosure.

m) Multistrand cables
To prevent loose strands the terminations of these cables should be fitted with crimped or similar ends.

6. Testing/documentation
a) Initial inspection
All new installations and equipment should be subject to a detailed inspection as part of the commissioning, suitable documentation should be issued on satisfactory testing of the installation. Typical information is given in Appendix 1.
On completion DSEAR requires a register of the electrical components, their relevant zone of installation and the equipment approvals. Typical register layout is given in Appendix 2

b) Periodic Inspection
This is the routine inspection of all equipment, systems and installations and information is given in BS EN 60079-17. An assessment should be made, and recorded, at the time of issuing the initial inspection of:

˃The type of inspections required usually visual or close
˃ The period between inspections.

installations these are normally 12 months but must not exceed 3 years)

Visual and close inspections can be carried out without removing any covers or isolating the power.
The results of all inspections should be recorded.

c) Detailed inspection
In addition to any other periodic inspections a detailed inspection should be carried out at intervals to be determined by the competent electrician (usually not exceeding 5 years) or after any modifications to equipment and/or wiring. Modifications being defined as any change to the wiring, circuits or the replacement of items that are not identical to the one removed.

The next electrical survey will be due no later than ------------ 12 months from the
date of this document. ---------- (Delete as applicable.)
Signed: -------------- Name: ------------
Date: ----------
Qualification for hazardous area work: -------------------

This Schedule relates only to Certificate/Report Reference

Cable type :
A ) PVC/PVC cables
B ) PVC cables in metal conduit
C ) PVC cables in non-metal conduit
D ) PVC cables in metal trunking
E ) PVC cables in non-metal trunking
F ) PVC/SWA cables
G ) XLPE/SWA cables
H ) Mineral Insulated cables
Other ?
Extent covered by this schedule

Stripping out of Redundant Installation

1) All redundant installations shall be stripped out as far as practical. Where this exercise could lead to any future confusion labels shall be installed giving clear concise instructions.

2) Where the stripping out of redundant installation is specified, the work shall be carried out with the same care and attention as for a new installation, and the Contractor shall ensure that no damage to the building fabric or equipment ensues.

3) Under no circumstances shall the Contractor allow any of his own, or any other Contractor’s or Sub-Contractors operatives to disconnect or cut a live cable, or cut conduit / trunking containing ANY cables.

 

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extract taken from wiring maters 2009

Conclusion
When carrying out additions or alterations to existing electrical installations, the reconfigured aspect of the electrical installation should comply with BS 7671:2008. The installer does not simply take responsibility for the newly installed or reconfigured element of the installation but all parts of the circuit(s) worked on - including the need to comment on the continued suitability or
otherwise of the equipment belonging to the distributor - this includes the condition of the metering equipment,
supply and meter-tails, distribution equipment and the earthing and bonding arrangements. If the client does not want to pay for
upgrades to existing equipment, this does not absolve the installer from responsibility, nor does a disclaimer.