Re-take - Useful Information for 2394 :

[Richard Burns]

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 )

 

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Definitions

Three definitions, which are helpful in identifying suitable devices for performing , Isolation and understanding the requirements for Isolation are included in BS-EN-60947-3 Low-voltage switchgear and controlgear .

:icon_bs: Switches , disconnectors , switch-disconnectors , fuse-combination units . These are for the disconnector , The switch-disconnector

Disconnector : A mechanical switching device which , in the Open-position , complies with the requirements specified for the ( Isolating function )

A disconnector is capable of opening and closing a circuit when either a negligible current is broken or made , or when no significant change in voltage across the terminals of each of the poles of the disconnector occurs such as when the load has been switched Off . it is also capable of carrying currents under normal circuit conditions and carrying for a specified time currents under abnormal conditions , such as these of short-circuit .

BS-7671: considers a device meeting the applicable requirements of a disconnector can be called either a ( disconnector or an isolator )

Switch (( mechanical )) A mechanical switching device capable of making , carrying and breaking currents under normal circuit conditions which may include specified operating overload conditions and also carrying for a specified time currents under specified abnormal circuit conditions such as those short-circuit .

A switch may be capable of making , but not breaking , short-circuit .

Switch-disconnector : A switch which , in the Open-position , satisfies the isolating requirements specified for a disconnector .

Part 2 : Definitions of BS-7671: considers a device meeting the applicable requirements of a switch-disconnector can be called either a switch-disconnector or an isolating-switch .

 

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Secure :

The Electricity at Work Regulations 1989 ( EWR ) requires , by (( its )) definition of isolation , Regulation 12 , That the disconnection and separation for isolation is secure ; that is , reliable and unlikely to (( Fall ))

The ( EWR ) also requires that a device for isolation has either a (( means to physically prevent the isolator form being inadvertently reclosed or that a work system is in place to prevent reclosure ))

A device for isolation should be designed and / or installed so as to prevent unintentional or inadvertent closure such as may be caused by mechanical shock , accident knocks or vibration . refer Regulation 537.2.2.3. :icon_bs:

 

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Disconnector & Switch-disconnector
The disconnector and the switch-disconnector are suitable devices for performing isolation :
i) The disconnector being an Off-load making and breaking device (( Isolator ))
ii) The switch-disconnector being an On-load making and breaking device (( an Isolation-switch ))

However ;

Where a disconnector is used , the disconnector should be interlocked with the load-switching-device of the circuit such that the load is disconnected by the load-switching-device before the disconnector opens to isolate the circuit . Conversely , when re-energizing the circuit , the interlocking should be arranged such that the disconnector has to be closed before the load-switching-device is able to reconnect the load .

Alternatively , provision should be made for securing the disconnector against inadvertent or unauthorised operation . This could be achieved by padlocking the disconnector to prevent its operation or locking it in a lockable area or enclosure . :icon_bs: Regulation 537.2.2.4. refer

 

[Richard Burns]

Guide to the Building Regulations P/61


Extractor fans
A suitable 230V extractor fan may be installed in Zone 1 , 2 , and outside the Zones .
if an extractor fan is installed in Zone 1 or 2 , it must be protected against the ingress of moisture to at least IPX4 .


An extractor fan supplied from a lighting circuit for a bathroom without a window should have its own means of isolation , as otherwise replacement or maintenance of the fan would have to be carried out in the dark . An Isolation-switch for a fan with an overrun facility will need to be triple-pole ( switch wire , line and neutral ) and must be installed outside Zones 0 , 1 , 2 .

Moulded (( Isolator-switch )) single gang , triple-pole 10A.. isolating switch marked with isolator symbol


Description
Standard : BS-EN-60669-1 , BS-EN-60947-3 .
Provides local isolation of fans with or without timers whilst the rest of the circuit remains live, Enables repair or routine maintenance of fan(s)


( British standards ) P/285 / P286 .
Appendix 1 ( normative )
BS-EN-60947-3 : Switches , disconnectors , Switch-disconnectors and fuse-combination-units .


( British standards )
BS-EN-60669 .. Switches for household and similar fixed electrical installations .
BS-EN-60669-1: 1999 + A2 :2008: General requirements . This replaces BS-3676 .

 

[Richard Burns]

Marking(s)

Some product standards , for example those to BS-EN-60947-3 require the product to be marked with a symbol to indicate its suitability for isolation .

Drawing : Left to Right


The Left-hand column shows devices for (( Off-load-isolation ))
The Right-hand column shows devices for (( On-load making , breaking , isolating .