Re-take - Useful Information for 2394 :

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Initial Verification ,

Order of tests
Order of tests ( Prior ) To the installation being Energized ( After the completion of Inspection )

• Continuity of protective conductors including , main and supplementary bonding 612.2.1.
• Continuity of ring final circuit conductors 612.2.2.
• Insulation résistance 612.3.
• Protection by SELV , PELV or by electrical separation 612.4.
• Basic protection by a barrier or an enclosure provided during erection 612.4.5.
• Polarity .. for example , at lighting switches . 612.6.

• Where the - earth electrode is part of the installation 612.7. “ Earth electrode to Earth shall be measured “
- Alternatively for a TT system the installation earth electrode résistance may be approximately measured with the incoming supply energized and the main switch OFF , using an earth fault loop impedance test instrument .

Order of tests to be carried out with the supply connected

 

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Order of tests to be carried out with the supply connected

• Earth fault loop impedance 612.9.

• RCDs used for :
i) Where RCDs are applied for protection against fire 612.8.
ii) Fault protection , or 612.8.1. (a) (2) TN- system & (b) (2) TT system .. ( ADS )
iii) Additional protection 612.10.
Prospective fault current 612.11.
( Check ) Phase sequence, maintained for multiphase circuits 612.12.

• Functional testing of RCD ( using test facility in device ) 612.13.1.
Where :
- fault protection ... is to be provided by an RCD .
- additional protection ... is to be provided by an RCD .

• Functional testing of : Equipment . 612.13.2.
- switchgear
- controlgear assemblies
- drivers
- control and interlocks

• Verification of voltage drop 612.14.
Note : Verification of voltage drop is not normally required during initial verification .

 

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Appendix 1 of the HSE Memorandum of guidance on the Electricity at Work Regulations 1989 lists , HSE Guidance Note GS-38 .
Electrical test equipment for use by electricians as a publication being particularly relevant to regulations : are

( 10 - connections )
( 14 - work on or near live conductors )
( 16 - persons to be competent to prevent danger and injury )

 

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The Health and Safety Executive HSR 25

Memorandum of guidance on the Electricity at Work Regulations 1989 is intended to help (( duty holders )) meet the requirements of the regulations

 

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The purpose of providing (( Isolation )) is so that live parts (( normally energised )) can be safely isolated (( separated )) from their source(s) so that work may be carried out on , or near parts without the risk of Electric shock .

it should be noted that isolation is an OFF-load function .

 

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The human body has known limits:
Under normal conditions, voltage limit = 50V

To comply with wiring regulations the earth fault loop impedance in Ohms, multiplied by the rated tripping current of the RCD in amperes must not exceed 50V

For an RCD with a rated tripping current of 30mA, the maximum permissible earth fault loop impedance is calculated as follows: Zs (max) = 50 / In = 50/0.03 = 1666.666667 ( 167Ω )

Table 41.5.
Rated tripping current of the RCD 30mA – Maximum permissible earth fault loop impedance ( Zs / Ω ) 1667Ω (*)
Rated tripping current of the RCD 100mA – Maximum permissible earth fault loop impedance ( Zs / Ω ) 500Ω (*)
Rated tripping current of the RCD 300mA – Maximum permissible earth fault loop impedance ( Zs / Ω ) 167Ω

 

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16[SUP]th[/SUP] Edition : Principal requirements for isolating devices .

537-02-02 . calls for the isolating distance between contacts ( in the absence of international agreement , normally taken to be not less than 3mm in the open position . to be not less than that called for in BS-EN-60947-3 . 17th Edition Table 53.4. Isolating switch . BS-EN-60947-3

 

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Basic’s : The purpose of providing Isolation is to cut Off the supply from the installation , Or part of it (( for safety )) persons carrying out modification or electrical maintenance to affected circuit(s)

513 Accessibility : :icon_bs:
Designer’s selection of types of devices and their positioning in order to expedite ready access for operation , inspection and testing and maintenance of devices . as required by Regulation 513.1.

 

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Whereas Circuit-breaker is an : (( On-Load device ))
Circuit-breaker (( Duties )) Make or Break both normal & abnormal currents .. Manual or Fault-conditions

Circuit-breaker BS-EN-60898-1 (3) Table 53.4. :icon_bs: Guidance on the selection of protective-device’s
(3) - Device is suitable for (( On-load isolation )) i.e. disconnection whilst carrying load-current .

 

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RCD’s work on the principle of a (( load )) being in balance - that is, the current on the Line-conductor is equal to that flowing out of the Neutral-conductor. (( resi / dual-current ))

 

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Chapter 53 : 530.3.4. - BS-EN-60947-3 . (( Consumer Units ))
For an installation with a 230V single-phase supply rated up to 100A that is under the control of Ordinary persons :


Switchgear and controlgear assemblies shall either comply with BS-EN-60947-3 and Regulation 432.1. or be a consumer unit incorporating components and protective devices specified by the manufacture complying with BS-EN-60947-3 , including the conditional short-circuit-test . refer


Main Switch controls all circuits .. 17th Edition High Integrity
Main Isolator(s) BS-EN-60947-3 .


BS-7671:2008:2011: P/286
BS-EN-60947-3 : 2009 .. ( British standard )
Switches
Disconnectors .. disconnector (or isolator)
Switch disconnectors , and
Fused combination units


• Disconnector (or isolator) This switch is a manually-operated, lockable, two-position device (open/closed) which provides safe isolation of a circuit when locked in the open-position .. (( being locked in either the ON or OFF position. When locked in the ON position it will no longer operate as an isolator Positive indication of the opening of the contacts is only given when the green stripe can be seen on the dolly.
• Its characteristics are defined 60947-3: disconnector is not designed to make or to break current


R/P 35 . Switch-disconnector - A switch which , in the Open-position , satisfies the isolating requirements specified for a disconnector
R/P 28 . Fused connection unit - A device associated with the (( fixed wiring of an installation )) by which appliances may be connected , and having provision for a (( replaceable cartridge fuse link ))


Spur
Switched fuse connection unit ; in this case .

A switched fuse has a fuse in series with the switch .

R/P 29 . Isolator . A mechanical switching device which , in the Open-position , complies with the requirements specified for the isolating function . An isolator is otherwise known as a disconnector

Manufacturing Standards . BS-EN-60947-3
100A DP Incomer (( Main Switch )) .. Short-circuit 3kA BS-EN-60947-3
Product contents: 100A Switch disconnector.
100A Double Pole . Main switch Isolator(s) BS-EN-60947-3 .
Wylex 100A DIN mounting switch disconnector. BS-EN-60947-3.2.

Product contents: 100A Main Switch
Short-circuit 16kA BS-EN-60947-3 .. Enclosure material / High Impact Polystyrene

 

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313 : Supplies :icon_bs:

Prospective short circuit current ( PSCC ) at the origin of the installation .
This is the maximum current which could flow between live-parts as close as you can measure to the meter . (( do not confuse this with )) Earth-fault-current

Single-phase supplies where the protective device for the supply is no greater than 100A , a fault current of 16kA may be assumed provided that the current rating of individual protective devices does not exceed 50A .

 

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(( Protective devices )) have to comply with certain requirements . Basic’s

BS-EN-60898-1 & BS-EN-61009-1 protective devices must carry a current of at least 1.13 times the device ratings for 1 hour without operating
However – they must operate within 1 hour at a maximum of 1.45 times their rating.

 

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Diversity in this installation can now be applied . O.S.G. Table A2 - ( 9 )
Ring final circuit(s) diversity is calculated at 100% for circuit ( 1 ) and 40% for circuit ( 2 )

( 100% ) - Ring final circuit ( 1 ) 32A
( 40% ) - Ring final circuit ( 2 ) 32A .. by calculation : 32A x 40% = 12.8A .. (( 100% / 32A - 40% ))

 

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O.S.G. Table A2 - ( 1 ) Lighting
Lighting can be calculated using 66% of the total demand
Two lighting circuits at 6A = 12A .. 12 x 66% = 7.92A

 

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O.S.G. Table A2 - ( 5 )
Shower : which would be classed as an (( Instantaneous water heater )) would have no diversity allowable .

However , only the rated load of the appliance should be used , Not the rating of the protective device .
By calculation : Shower 10.000 ÷ 230 = 43.47A

 

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O.S.G. Table A2 - ( 6 ) Immersion heaters are (( thermostatically controlled water heaters’ )) No diversity allowable .. Only the total load should be calculated : Immersion heater 3000 ÷ 230 = 13A

 

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( British Standards ) :icon_bs:
BS-EN-60947-3 applies to switches, disconnectors, switch-disconnectors and fuse-combination units

What’s in a Name :
100A double pole 2 module 100A main-incomer

100A Main-switch ... BS-7671:2008:2011:
100A Isolator-switch
100A Main-isolator 2-pole modular
100A Isolator-switch-disconnector double pole 2 module
100A main switch isolator disconnector
100A Isolator Incomer-switch

100A Main Switch BS-EN-60947-3. or BS-EN-60947-3.2.

A common example of a single device used to isolate a group of circuitts is a (( main-switch )) permitting isolation of all the circuits in a dwelling

A means of isolation and switching the supply On-load must be provided as near as practicable to the origin of every installation . The means of isolation ans switching is required to be a main linked switch or a linked circuit breaker , regulation 537.1.4. refer

Completing paperwork for Certification & Inspection & Testing of electrical installations to BS-7671: 2008:2011:

Electrical Installation Certificate ( EIC ) P/391
Main-switch (( or )) Circuit-breaker

BS and BS(EN) numbers for switchgear
Isolator ( Main-switch ) Designation BS-EN-60947-3
Type and No . of poles .......

Complete all entries adding details of RCD where it is part of the main-circuit-breaker .

Rated residual operating current IΔn = ........... mA , and operating time of ........... mS ( at IΔn ) ( applicable only where an RCD is suitable and is used as a main-circuit-breaker )

 

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Being replaced , grounds of convenience of operation . Split-loads . etc
Periodic inspection

BS-3036 fuses - which are still in Service in many older premises .

As they have a relatively low short-circuit breaking capacity rating of between ( 1kA and 4kA ) depending on the category of duty .

P/71 . O.S.G. Table 7.2.7.(i) rated short-circuit capacity

Semi-enclosed fuse to BS-3036 with category of duty .

Device designation S1A ...... Rated short-circuit capacity ( kA ) 1kA
Device designation S2A ...... Rated short-circuit capacity ( kA ) 2kA
Device designation S4A ...... Rated short-circuit capacity ( kA ) 4kA

Each fuse-holder should be checked to confirm that the size of fuse wire is correct and that both the fuse-holder and the carrier have not been damaged .

Before installing or reusing rewireable fuses , The following factors should be considered .

Extracts :

• For reasons of protection against overload , Regulation 433.1.101 . requires
That the rated current of the fuse must not exceed 0.725 times the current-carrying-capacity of the lowest rated conductor in the circuit-protected
The effects , therefore , of choosing such a fuse is that the cross-sectional area of the cable may need to be greater than if another type of protective device had been chosen , such as a cartridge fuse , a circuit breaker or an RCBO , A possible alternative to increasing the cable size might be to replace the BS-3036 fuse with one having a suitably reduced rated current ( In ) if that rated current is not less than the maximum sustained current expected to be carried by the circuit in normal service ( Ib )

Regulation 533.1.1.2. requires fuses having fuse links ( fuse-wire or cartridge ) likely to be removed or replaced by persons other than skilled or instructed persons to be of a type that complies with the safety requirements of BS-88-3 BS-3036 or BS-1362 . Regulation 533.1.1.2. also states that fuses should preferably be a type that cannot be replaced inadvertently by one having a higher nominal current , This requirement and preference are met if the fuse carrier will not fit into the base of a fuse having a lower rating . example , a 30A rewireable fuse carrier must not fit into either a 15A or a 5A fuse base .

• To meet the requirements of Regulation 434.5.1. a rewireable fuse . like any other overcurrent protective device , must be chosen such that its rated short-circuit breaking capacity is not less than the maximum prospective fault current at the point the fuse is installed .

The only exception is where back-up protection is provided by another device , meeting specified requirements , Complying with the requirements of Regulation 434.5.1. may appear difficult with BS-3036 fuses

BS-3036 fuses
As they have a relatively low short-circuit breaking capacity rating of between ( 1kA and 4kA ) depending on the category of duty .

However , BS-3036 fuses , or indeed other type of overcurrent protective device of rated current up to and including 45A incorporated in a consumer unit , are considered adequate for prospective fault current levels up to ( 16kA ) provided that :

• The consumer unit complies with Part-3 of BS-EN-60439: 1991
• The consumer unit is fed by a single-phase supply
• The service cut-out has an HBC fuse to BS-1361 rated at not more than 100A ( Annex ZA of BS-EN-60439 refers )

Single element of Tinned copper wire of the appropriate diameter , Table 53.1. BS-7671:

 

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( Functional switching ) P/28
An operation intended to switch “ On or Off “ refer .

Inspection & Testing

( Functional switching ) is included among the items requiring inspection in BS-7671:2011:
R/P 400 - The Schedule of Inspections (( Lists )) Selection of appropriate functional switching devices

BS-7671: States the facts . items requiring inspection for an ( EICR )

Other devices which are permitted are : Table 53.4. “ States “
Circuit-breakers to BS-EN-60898-1 , BS-EN-60947-2 , BS-EN-61009-1 . and RCDs to BS-EN-60947-2 , BS-EN-61008-1 , BS-EN-61009-1
However ; Circuit-breakers and RCDs are primarily circuit-protective-devices and , as such they have not been designed for frequently switching loads On & Off

An Isolator is an Off-load device & a Switch is an On-load device. (( Light switch ))
537.5.2.3. Off-load isolators ( disconnectors ) fuses and links shall not be used for (( Functional switching ))

BS-7671: tell us , Functional switching (( Control ))
( EICR ) The presence and condition of appropriate devices in accordance with Regulation 537.5.1.1. must be Verified
Correct operation of the functional devices as required by Regulation 537.1.3. & 537.2.2. must also be confirmed

537.5.1.1. According to the intended function(s) every device provided for isolation or switching shall comply with the relevant requirements of this Section .
Note : Table 53.4. provides information on selection .

537.1.3. Each installation shall have provision for disconnection from supply .

( DNO ) - Where the distributor provides a means of disconnection complying with Chapter 53 at the origin of the installation and agrees that it may be used as the means of isolation for the part of the installation between the origin and the main linked switch or circuit-break required by Regulation 537.1.4. the requirement for isolation and switching of that part of the installation is satisfied .

Note : A cut-out fuse may be withdrawn only by a person authorized to do so by the distributor .. ( DNO )

537.2.2. Devices for Isolation

( EICR ) - Inspection Schedule P/400 for domestic and similar requires a (( functional check of the manual operation of , Main-switch(s) item 4.7.
Circuit-breaker(s) and RCDs item 4.8.

Further checks would be required on larger installations , Where the sample checklist in Appendix 6 of BS-7671: Lists Functional Switching as part of the inspections .

Functional Testing ; The requirements for functional testing in :
Regulation 612.13.1.
Regulation 612.13.2. include

Functional switching , Functional testing includes that installed electrical equipment is working as it ( Should )