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Guidance Note 3. Inspection & Testing > ON SITE GUIDE > Flashcards

ON SITE GUIDE Flashcards

1
Q

meter tails

A
  1. consumer tails - the cables between the electricity meter and the consumer unit & should be insulated & enclosed e.g in trunking or conduit.
  2. suppliers tails - the cables between the suppliers cut out and the electricity meter . should be protected fro mechanical damage.
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2
Q

where gas installation pipework is not separated from electricrical equipment , the following distances shall be followed :

A
  • at least 150 mm away from supply equipment e.g consumer units
  • at least 25mm away from electrical switches , sockets and cables.
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3
Q

Generators can be split into 2 classes

A
  1. Portable generators - with an electrical output rating of up to 10 KVA are used for short term use . e.g one day & are often isolated from earth. fault protection by electrical separation. basic protection by barriers or basic insulation of live parts
  2. Mobile generators - are those used for longer periods and can be excess of 10KVA output.
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4
Q

devices that offer protection against overload

A
  • fuses , circuit breakers & RCBO
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5
Q

protection against electric shock :

A

automatic disconnection of the supply the most common form of protection against electric shock, there are 2 elements :

  1. basic protection - basic insulation around live part sand enclosure or barriers
  2. fault protection - protective earthing , bonding and automatic disconnection in case of a fault.
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6
Q

other methods of protection against electric shock

A
  1. SELV - supplied from isolated safety sources e.g a safety isolating transformer
    - no live parts or exposed conductive parts are connected to earth or protective conductor & have reinforced insulation
  2. PELV- pelv is same as selv except the circuits are not electrically seperated from earth.
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7
Q

automatic disconnection times for TN system

A

a. d.t of not more than 0.4 s required for final circuits not exceeding 63A with 1 or more socket outlets and 32A when supplying only fixed equipment.
- a.d.t of not more than 5 s for final circuits exceeding 32 A & distribution circuits

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8
Q

automatic disconnection times for TT system

A
  • can only be achieved by protecting every circuit with an RCD , hence a time of not more than 0.2 s required for final circuits:
  • not exceeding 63 A with one or more socket outlets
  • 32 a when supplying only fixed equipment.
  • a.d.t of not more than 1 s is permitted for:
    final circuits not exceeding 63 A with one or more socket outlets and distribution circuits.
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9
Q

RCD,s

A
  • a device that opeates when the residual current in the circuit reaches a certain value. they’re required for
  • fault protection ( where earth fault loop impedance id too high to meet the disconnection time )
  • addition protection for socket outlets not exceeding 32 a
  • additional protection for lighting circutis in domestic.
  • for cables without earthed metallic covering installed in walls
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10
Q

when are RCD’s not needed

A
  1. when a risk assessment determines rcd protection is not nessacary. risk assessment must be mentioned on certificate ( always needed in a dwelling )
  2. when cables are installed on the surface , rcd protection isn’t needed.
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11
Q

why are installations divided into circuits

A
  • to minimize inconvenience and avoid hazards in the event of a fault .
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12
Q

where is SPD required ( protection against transient overvoltages ) which leads to :

A
  • serious injury to or loss of human life

- interruption to an installation with a lots of people . e.g offices or universities.

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13
Q

types of Surge protection devices

  • spds should have a protection level lower than the voltage and spds should be of the same make/ manufacturer
A
  1. type 1 - used only where there is risk of direct lightning current and typically installed at origin of the installation.
    type 2 - used at distribution boards
    type 3 - used near terminal equipment
    aswell as combined type spds.
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14
Q

Arc Fault Detection Devices

  • shall be installed at the origin of the circuit to be protected.
A

used for additional protection against fire in AC final circuits. designed to detect low level hazardous arcing that CB’s , Fuses and RCDs are not designed to detect

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15
Q

what is the purpose of protective earthing

A

to ensure that in the event of a fault , sufficient current flows to operate the protective device.
- e.g fuse to blow , rcd to operate and CB to operate in the required time. every exposed conductive part should be connected to the M.E.T

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16
Q

earth electrodes

A
  • can be connected to the M.E.T by the earthing conductor and provides part of the earth fault installation for a TT system. ( shouldn’t exceed 200ohms)
    types of earth electrode
  • earth rods - earth plates
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17
Q

ISOLATION & SWITCHING

A

means of isolation should be provided

  1. at the origin of an installation e.g a linked main switch or a CB should be used as a means to interrupt the supply on load
  2. for every circuit and every item of equipment ( have its own isolating device )
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18
Q

each device for switching off for mechanical maintenance must :

A
  • be capable of switching the full load current
  • clearly in OFF position
  • be designed to avoid unintentional switching own
  • be labelled.
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19
Q

each device for switching off for mechanical maintenance must :

A
  • be capable of switching off the full load current
  • clearly in OFF position
  • be designed to avoid unintentional switching own
  • be labelled.
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20
Q

Functional Switching

A

a switch must be installed in each part of the circuit which may require to be contorolled independently from other parts of the circuit
- switches shouldn’t be on the N conductor alone

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21
Q

Fire fighters Switch

A

a firefighters switch must be provided to disconnect the supply to any exterior electrical installation operating at a low voltage.

22
Q

LABELLING

A
  • labelling of each item of switchgear and control gear .
  • labelling of earthing and bonding conductors at their connection
  • labelling of protective devices
  • labelling of each isolating device
  • near the origin of every installation a label for periodic inspection and testing
  • and Diagrams indicating : number of , type of , & see of cables , method of protection against electric shock and any circuit or equipment vunreble to tests. e.g insulation resistance test
23
Q

LABELLING

  • labelling for if theres 2 colours of wiring that don’t comply to the current bs7671.
A
  • labelling of each item of switchgear and control gear
  • labelling of earthing and bonding conductors at their connection
  • labelling of protective devices
  • labelling of each isolating device
  • near the origin of every installation a label for periodic inspection and testing
  • and Diagrams indicating : number of , type of , & see of cables , method of protection against electric shock and any circuit or equipment vunerable to tests. e.g insulation resistance test
24
Q

rcd labelling would say what :

A

TEST 6 MONTHLY. BY pressing TEST button.

25
Q

installation considerations :

  • a cable passing through a joist , underfloorboards or ceiling support must :
  • max diameter of hole should be 0.25 x joist depth
A
  • when a cable is installed under a floor or above a Celling it must be run in a position that it is not liable to damage by contact with the floor or ceiling.
  1. be at least 50mm from the top or bottom.
  2. have earthed armouring/ or an earthed metal sheath.
  3. be inclosed in trunking or steel conduit
  4. be provided w mechanical protection e.g so nails can’t penetrate
  5. form part of a selv or pelv circuit.
26
Q

a cable installed in a wall :

A
  1. buried at least 50mm grin the surface or
  2. be protected by a 30ma RCD and installed in a zone either horizontally 150mm of the top of the wall or vertically within 150mm of the angle formed by 2 walls.
  3. have earthed armouring or metal sheath
    4 be enclosed in trunking or steel conduit
  4. provide mechanical protection and form part of a SELV or PELV.
27
Q

PROXIMITY TO ELECTRICAL AND OTHER SERVICES

A

electrical services must be protected from harmful mutual effects. for example , cables should not be in contact with or run alongside gas pipes.

28
Q

Band 1 ( extra low voltage ) and Band 2 circuits ( low voltage ) must not be contained in the same wiring unless :

band 1 - 50 v ac or 120 dc
band 2 - 51v - 1000 v ac and 121 - 1500 v dc.

A
  • every cable is insulated for the highest voltage present

- the cables are installed in different compartments.

29
Q

SEPARATION OF GAS INSTALLATION PIPEWORK :

  • gas installation pipes must be spaced
A
  • at least 150mm away from the electricity supply equipment

- at least 25mm away from electrical switches , sockets and cables.

30
Q

Equipment having a protective conductor exceeding 10ma should be connected by :

A
  1. being permanently connected.

2. or a flex cable that is of a CSA not less than the line conductor.

31
Q

the wiring of every circuit and distribution circuit having a protective conductor current likely to exceed 10ma must have high integrity protective conductor connections complying with :

A
  • a single protective conductor having a CSA not less than 10mm
  • a single copper conductor having a csa of not less than 4mm .
32
Q

for a final circuit with socket outlets or connection units where the protective conductor is likely to exceed 10ma , the following arrangements should be met

A
  • a ring final circuit with a ring protective conductor , require high integrity conductor connections
  • a radial circuit with a protective conductor connected as a ring OR an additional protective conductor provided by ducting or metal conduit.
33
Q

all current carrying single core cables must be..

A

enclosed in conduit or trunking and have a degree of protection of IP4X OR IPXXD.

  • must only be removable by a tool.
34
Q

where electrical equipment is installed within purpose built items of furniture the following criteria should be met :

A
  • socket outlets supplying items of furniture must be protected by a 30ma RCD.
  • cables of band 1 and band 2 circuits to be kept apart .
  • cables of band 1 and band 2 which are often hidden , need to be mechanically protected from damage.
35
Q

Consumer Units in Dwellings.

- to ensure the ongoing use of such enclosures , the installer must confirm the following :

A

-made of the non combustible material.
installers will encounter old consumer units not complying with 7671.
1. confirmation of all conductor connections are correctly located in terminals and tight and secure.
2. there are no signs of overheating
3. all barriers are still in place

36
Q

it must be verified for all conductor / busbar connections :

A
  • terminals are not clamping onto insulation
  • conductors are not damaged
  • permitted no. of conductors and correct placing
  • no undue mechanical strain.
37
Q

wiring systems in escape routes

A
  • must be as short as possible
  • cables in escape routes should not be installed within arms reach unless provided w protection against mechanical damage.
38
Q

where cables are in escape routes , the cable management systems must be :

A
  1. conduit systems - non flame propagating
  2. cable trunking systems of non flame propagating type.
    - cables should have a resistance to fire rating
39
Q

LOCATIONS CONTAINING A BATH OR SHOWER

  • due to the presence of water , there is increased risk of electric shock . additional requirements are :
A
  • all low voltage circuits to be protected by 30 ma RCD
  • all circuits passing ZONE 1 & 2 must be protected by 30ma RCD
  • socket outlets are NOT allowed 3 meters of zone1
  • protection to the ingress of water
40
Q

INSPECTION AND TESTING.

  • inspection before testing
  • done with installation disconnected from the supply,
A
  • every installation needs to be inspected and tested.
  • if the tests are satisfactory , a signed electrical installation cerifitcate aswell as a schedule of inspection and test results is given to the person ordering the work.
41
Q

INSPECTION.

what is the purpose of verifying equipment to ensure it is properly selected and erected and nothing is visibly damaged.

A

inspection checklist:

  1. connection of conductors
  2. ID of conductors
  3. selection of conductors for current carrying capability and voltage drop.
    4.methods of protection against electric shock
    - basic protection by barriers or insulation
    - fault protection by automatic disconnection of supply.
    5 - presence of danger notices , diagrams?
    6 - earthing arrangements , adequate of switchgear ETC.w
42
Q

TESTING. if anything were to fail , the test must be repeated , as with any earlier test that could have been influenced by the failure.

A 
testing checklist:
1. continuity of conductors 
a. protective conductors B. ring final 
2. insulation resistance 
3. polarity 
4. earth electrode resistance.
and the you have your live testing
  1. earth fault loop impedence
2. prospective fault current 
3. functional testing        e.g RCD testing.
43
Q
  1. CONTININUITY OF PROTECTIVE CONDUCTORS

ze - external impedance
zs - earth fault loop impedance.

A

2 methods.

1. r1 + r2. (Ze) + (r1 + r2) = Zs

44
Q
  1. CONTININUITY OF PROTECTIVE CONDUCTORS

ze - external impedance
zs - earth fault loop impedance.

A

2 methods.
1. r1 + r2. (Ze) + (r1 + r2) = Zs

  1. wandering lead.
45
Q
  1. CONTINUITY OF RING FINAL CONDUCTORS
A

3 STEPS.

  1. end to end resistance to find r1 r2 and rn. test LL then N-N then E-E
  2. test between L-N
  3. test between L-E
46
Q
  1. INSULATION RESISTANCE.
  • make sure any lamps disconnected and voltage sensitive equipment removed.
  • tests made at the distribution board or consumer unit with the main switch OFF.
A

500 v dc = minimum resistance of 1

47
Q
  1. POLARITY
A
  • Same as test method 1 for the continuity of protective conductors.
  • after connection of the supply , correct polarity must e confirmed using a voltage indicator or test lamp.
48
Q

EARTH FAULT LOOP IMPEDENCE ( Zs) is determined by

A
  1. direct measurement of Zs
  2. Ze + ( r1 +r2) = Zs
    ze can be measured using a line earth loop impedance tester with the earth disconnected from the M.E.T.
49
Q

measurement of prospective fault current:

A
  • should be done with all bonding in place at the distribution board between live conductors and earth.
  • for 3 phase supplies , the max prospective fault level will be approximately twice the single phase to neutral value.
50
Q

verification of voltage drop

A

appendix 4

51
Q

operation of RCD’s

A

operates when the residual current reaches a certain value and is a P.D that A.D.S when theres a imbalance is detected between L & N
- the tests are made on the LOAD side of the RCD.

Guidance Note 3. Inspection & Testing (14 decks)

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