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Guidance Note 3. Inspection & Testing > navigation of bs7671 > Flashcards

navigation of bs7671 Flashcards

1
Q

index

A

525

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2
Q

part 1

A

110.1 gives a list of items it covers 110.2 what it doesn’t cover

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3
Q

basic protection and fault protection

A

131.2.1. 132.2.2

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4
Q

thermal effects

A

131.3

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5
Q

132.5.1 environmental factors

A

ip ratings to see what requirements are needed.

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6
Q

part 4

A

most often referred to. about electric shocks , over current and thermal effects

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7
Q

410.3 states that we can use one of the following methods to the risk of electric shock

A
  1. automatic disconnection of supply .
  2. separation by SELV.
    3.
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8
Q

protective earthing

3 points to consider

A

exposed conductive part sare connected to a protective conductor ( cpc )

  1. conductors willl comply w chapter 54
  2. a cpc shall be run and terminated at each point in the wiring and at each accessory. whether it’s class1 or class2.
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9
Q

411.3.2.2 and table 41.1

A

gives max disconnection times for final circuits. if don’t get Max times on 41.1 we add an RCD or look at reg419.

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10
Q

411.3.2.3

A

allows 5 s disconnection time for any circuit that is a distribution circuit.

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11
Q

additional requirements for circuits with luminaries

A

requires additional protection by a 30ma RCD

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12
Q

core requirements for TN systems

A
  1. 4.1 - protective earthing
  2. 4.3 - functions of N and cpc ( PEN )can be combined in a single conductor provided no isolating device is installed
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13
Q

devices that may be used for fault protection for tn systems.

A
  1. an over current protective device. e.g a fuse or circuit breaker
  2. RCD - ( can’t use in tncs) operates by looking for differences in live conductors. must be backed up by a CB for L-L OR L-N faults.
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14
Q

selecting the device to achieve disconnection times

411.5.4. cmin ?

A

Uo divided by Zs X cmin - current - look @ tables

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15
Q

what is the difference between circuit breakers

A

type b circuit breakers are the standard ones
type c deals with inductive loads e.g fluorescent lighting
type d cBs are for highly inductive loads. e.g motors.

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16
Q

value in regs books for 41.2 3 nd 4 is tabulated.

A

measured value is 80 % !!!!!!!!!!

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17
Q

TT system

A

use a earth spike so fault path is down the spike into the ground back to the starhoint, completing the loop in that way

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18
Q

basic requirements of a TT system

A
  1. exposed and extraneous conductive parts are still connected to the M.E.T
  2. The MET is connected to the earth electrode
  3. the neutral is typically earthed
    for ADS. RCD & OCPD may be used
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19
Q

if we use ocpd for ads for a tt what equation do we use

A

uo divided by zs X cmin = current

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20
Q

IT systems

411.6

exposed conductive parts are to be earthed
in ac systems the earthing it to limit touch voltage to 50v
V=IxR

A

IT systems are systems in which all live parts are connected to earth ( or connected to earth through a high impedance )

  • during the first fault to earth , the system typically remains safe
  • however if a 2nd fault occurs , there is a high chance of electric shock is apparent
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21
Q

protective devices for it systems

A
  1. insulating monitoring devices (IMDs)
  2. residual current monitoring devices (RCMs)
  3. insulation fault location systems (IFLS)
  4. overcurrent protective device ( OCPD)
  5. residual current devices ( RCD’s)
22
Q

Functional extra low voltage

A

usually no electrical separation between primary and secondary . voltage comes down our primary , along our windings , & down the neutral

23
Q

Reduced low voltage ( RLV) system

A

where we want to reduce the voltage to earth to help maintain safety and where its not always to increase conductor sizes or earth electrode resistances.

24
Q

what is reinforced insulation

A
  • 2 layers of insulation ( both basic and supplementary)

- or 1 layer of insulation that is reinforced.

25
Q

electrical seperation

A

primary and secondary are separated electrically so under fault conditions you wont get an electric shock.
requirements :
1. isolating transformer. 2. 500 v maximum
3. no earth connection on the secondary 4. only for individual items of equipment 5. multiple items of equipment each need their own transformer.

26
Q

electrical seperation

e.g shaver points.

A

primary and secondary are separated electrically so under fault conditions you wont get an electric shock.
requirements :
1. isolating transformer. 2. 500 v maximum
3. no earth connection on the secondary 4. only for individual items of equipment 5. multiple items of equipment each need their own transformer.

27
Q

SELV AND PELV

separated and protective

A

selv and pelv provide extra low voltage through safety isolating transformers. both are extra low voltage systems supplied from safety isolating transformers.

28
Q

selv

A

in selv systems both conductors are isolated from earth and conductors of other wiring systems
- when the voltage is low enough it is often used in places where risk may be higher e.g bathrooms

29
Q

pelv

A

in pelvic systems 1 conductor is earthed but otherwise same as selv & is used in systems that require an earth connection for electrical interference control ( EMC ) or to detect broken conductors.

30
Q

use of rcds for additional protection

A
  • when used they should not exceed 30ma
  • the use of a rcd as a sole means of protection is not appropriate and must be used with one of the following measures :
  • ## pg 73
31
Q

supplementary equipotential bonding

A

is designed to reinforce the faradays cage principle within an installation. usually used where if the 50 V dc touch voltage were exceeded greater danger may arise than in a normal installation. e.g bathrooms
- may also be used to limit the touch voltage if disconnection times are not achievable in 419.3

32
Q

supplementary equipotential bonding

A

is designed to reinforce the faradays cage principle within an installation. usually used where if the 50 V ac touch voltage were exceeded greater danger may arise than in a normal installation. e.g bathrooms ,
- may also be used to limit the touch voltage if disconnection times are not achievable in 419.3

33
Q

basic insulation of live parts

A

live and neutral conductors must be completely covered by insulation and must only be removable by destroying it.

34
Q

barriers and enclosures

A
  1. 2.1 states that live parts are protected to prevent access from objects in accordance to IPXXD OR IP2X which is finger proof - 12.5 ml by 80 ml
    - regulation 416.2.2 requires horizontal top surface to be at least IP4X - this is 1mm
35
Q

416.2.4 where it is possible to gain access to a enclosure containing live parts, this shall only be possible if :

A
  • by the use of a key or tool

- where the barrier has a protection of at least ip2x to prevent live parts contacting the key or tool.

36
Q

protective measures for application where installation is under supervision of a competent person

A
  • non conducting location
  • protection by earth free equipotential bonding
    electrical seperation
37
Q

placing out of reach

A

1.25m sideways 2.5m Up

38
Q

electrical separation of supply to one or more current usingg equipment

A

exposed conductive parts are connected by protective bonding conductors. these bonding conductors are not earthed.

  • there are limits on the length of wiring
  • additional precautions are there to protect the wiring system from damage and insulation failure.
39
Q
  1. when ADS is not feasible.
A

aimed at limiting touch voltage to 50 V

  1. 2 - permits reducing voltage to a certain level
  2. 3 - local eqi bonding to lower the touch voltage.
40
Q

arc fault detection devices

A
  • recommended to provided extra protection against fire caused by arc faults in final circuits.
  • AFDDs are to be placed at the origin of circuits to be protected.
41
Q

consumer units in domestic properties need to

A
  • be of a non combustible material

- be enclosed in a enclosure or cabinet of non combustible material

42
Q

what is a AFDD

A
  • it is a circuit breaker that operates ( opens) when an arc fault is detected. - outwardly they look similar to an RCD and have a test button to check operation.
  • may also be part of a combined device , along with an CB , RCD or ever RCBO.
43
Q

Cables for evacuation in an emergency

A
  • cables must meet BS for fire conditions
  • not be installed in arms reach
  • cable system of non flame propagating type
44
Q

Luminares must be :

A
  • suitable for the location
  • have the appropriate IP rating
  • limited surface temperature
  • prevent build up of dust
45
Q

combustible materials.

A
  • fire propagating structures. e.g grenfell.
46
Q

what is chapter 43 about

A
  • overload & overcurrent
  • fault current - referred to as fault of negligible impedance
    ocpd will disconnect all Line conductors.
47
Q

protection of line and neutral conductor

A
  • L & N conductors are both to be protected from overcurrent
48
Q

nature of protective device

A
  • each device must be able to make and break the current.
49
Q

protection against overload

A
  • links to cable calculations. 1. ib 2. it etc
  • if reewireble we bring a factor
  • buried cables bring another factor
50
Q

radial vs ring

A
  • can’t cover as much floor area w radial
  • ## ring circuit t uses a lot less copper so cheaper
51
Q

part 5 of bs7671 mutual detrimental influence

A
  • selecting and installing equipment in such a way to avoid harmful effects influenced by different systems being installed in close proximity to each other.
52
Q

types of RCD.

A

type A - used for general purposes
type Ac - can’t detect D.C. e.g vehicle charging. if theres an earth leak it will stop the rcd working.1
type F -
type B -

Guidance Note 3. Inspection & Testing (14 decks)

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