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 ))

 

[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 .

 

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High Integrity Consumer Unit or Insulated Dual RCD Consumer Unit ?? What the difference

High Integrity CCUs have two RCD Banks and some separate slots that are not RCD controlled
This allows you to fit Circuit-breakers / RCBOs for those important and sensibly independent circuits like ( Fridge/Freezer, Smoke Alarm, Burglar Alarm ) will not cut power to the tropical fish tank

Manufacturers Literature

High Integrity Boards
A ‘ High Integrity Consumer Unit ’ is one which allows for separation of circuits whilst still protecting all circuits from earth leakage. It does this by using three neutral bars which allows for the use of 2 RCDs and a whole bank of RCBOs.

Split Load Consumer Units
A split load board, in common parlance, is one which is supplied with a Main Switch and RCD. Now that we operate under 17th Edition regulations the implied loading of a split load unit is that Circuit-breakers should only be put on the RCD side while RCBOs are fitted on the main switch side.

Consumer Unit
Suitable for installing into consumer units . BS-EN-60947-3 - Main-switch 100A

High Integrity dual RCD split load unit(s)
Uses two RCD protected sections and a number of ways for dedicated ( High Integrity Circuits ) using 30mA RCBOs

Consumer units ( CCU )
BS-EN-60947-3 - Main-switch 100A

Dual RCD Split Load units
Dual RCD units with two-sections / each protected by a 30mA RCD , Suitable for smaller dwellings

Split Load Units
BS-EN-60947-3 - Main-switch 100A
Split load consumer unit with a small group of circuits on the RCD and all others on independent devices ( RCBOs )

 

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Consumer Units :
All independent circuit

Suitable for installing into consumer units . BS-EN-60947-3 - Main-switch 100A
RCBO - BS-EN-61009-1 .. B40A .. Shower
RCBO - BS-EN-61009-1 .. B32A .. Sockets downstairs
RCBO - BS-EN-61009-1 .. B32A .. Sockets upstairs
RCBO - BS-EN-61009-1 .. B20A .. Garage sockets
RCBO - BS-EN-61009-1 .. B6A .. Smoke alarms
RCBO - BS-EN-61009-1 .. B6A .. Hall / stairs lighting
RCBO - BS-EN-61009-1 .. B6A .. Lighting upstairs
RCBO - BS-EN-61009-1 .. B6A .. Lighting downstairs
RCBO - BS-EN-61009-1 .. B6A .. Boiler
Spare . etc

Consumer Units :
Half-independent circuits

Split Load .
Suitable for installing into consumer units . BS-EN-60947-3 - Main-switch 100A
RCBO - BS-EN-61009-1 .. B40A shower
RCBO - BS-EN-61009-1 .. B6A Smoke alarm
RCBO - BS-EN-61009-1 .. B6A Hall / stairs lighting
RCBO - BS-EN-61009-1 .. B6A lighting upstairs
RCBO - BS-EN-61009-1 .. B6A lighting downstairs
RCD 30mA ~
Circuit-breaker - BS-EN-60898-1 .. B32A / Sockets downstairs
Circuit-breaker - BS-EN-60898-1 .. B32A / Sockets upstairs

Consumer Units :
High integrity
Some independent circuit(s)

Suitable for installing into consumer units . BS-EN-60947-3 - Main-switch 100A
RCBO - BS-EN-61009-1 .. B6A Smoke alarms
RCBO - BS-EN-61009-1 .. B6A Hall / stairs lighting

RCD 30mA ~ .. High Integrity “ Protective conductor current “
Circuit-breaker - BS-EN-60898-1 .. B40A Cooker
Circuit-breaker - BS-EN-60898-1 .. B32A Sockets downstairs
Circuit-breaker - BS-EN-60898-1 .. B6A Lighting upstairs
RCD 30mA ~
Circuit-breaker - BS-EN-60898-1 .. B32A Sockets upstairs
Circuit-breaker - BS-EN-60898-1 .. B6A Lighting downstairs
Circuit-breaker - BS-EN-60898-1 .. B6A Boiler

Consumer Unit :
No independent circuits .. “ Dual RCD “

Suitable for installing into consumer units . BS-EN-60947-3 - Main-switch 100A
1) RCD 30mA ~
Circuit-breaker - BS-EN-60898-1 .. B32A Sockets down stairs
Circuit-breaker - BS-EN-60898-1 .. B6A Lighting upstairs
Circuit-breaker - BS-EN-60898-1 .. B6A Hall / stairs lighting
Circuit-breaker - BS-EN-60898-1 .. B6A Boiler
2) RCD 30mA ~
Circuit-breaker - BS-EN-60898-1 .. B40/45A Shower
Circuit-breaker - BS-EN-60898-1 .. B32A Sockets upstairs
Circuit-breaker - BS-EN-60898-1 .. B6A Lights downstairs

 

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Non-statutory Requirements Within BS-7671:2008, States . the following are of particular relevance in terms of (( Safe -isolation ))

Regulation 132.15.1 .. :icon_bs: contains the following fundamental principle:

Effective means, suitably placed for ready operation, shall be provided so that all voltage may be cut off from (( every installation )) from every part thereof and from all equipment, as may be necessary to prevent or remove danger.


Regulation group 537.2 .. contains the requirements relating to (( isolation ))

Regulation group 537.3 .. contains the requirements for switching off for (( mechanical maintenance ))

 

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The requirements of BS-7671 applicable to a device providing isolation

Summary of Requirements

• Must isolate all live supply conductors ( with certain permitted exceptions ) 537.1.2. , 537.1.4. , 537.2.1.1. , 537.2.2.1. , 543.3.4.
• A multipole device is preferable where isolation of more than one live conductor is needed . 537.2.2.5.
• Must be Non-automatic . 537.1.
• The disconnection and separation is to be secure and the device designed and / or installed to prevent unintentional or inadvertent closure . 537.2.2.3.
• Contact position must be externally visible or clearly and reliably indicated . 537.2.2.2.
• Impulse withstand voltage based on the overvoltage category applicable at the point of installation . 537.2.2.1.
• Permitted devices to meet with the relevant requirements of Section 537 and Off-load isolating devices capable of being secured against inadvertent or unauthorised . 537.1.1. , 537.2.2.4.
• Semiconductor devices and certain switching devices are unsuitable as isolating devices . 537.2.2.1.

 

[Richard Burns]

Table 53.4. in this case ; Isolation .
Manufacturing Standards - BS-1363/4

Unswitched fused connection unit BS-1363-4 ( Isolation ) Yes (3) removal of fuse link .


(3) Removal of fuse link .
(3) Device is suitable for On-load isolation , i.e. disconnection whilst carrying load-current .


BS-1363 / 4 : 1995 + A4 : 2012
Specification : for adaptors
Specification : for 13A fused connection units Switched or Unswitched


Fused spur to BS-EN-60947-3 (British standard)

 

[Richard Burns]

R/P 34 . A "skilled person" is defined in Part 2 of BS-7671: as:
"A person with technical knowledge or sufficient experience to enable him/her to avoid dangers which electricity may create."
R/P 29 . An "instructed person" is defined by Part 2 of BS-7671: as:
"A person adequately advised or supervised by skilled persons to enable him/her to avoid the dangers which electricity may create."


A main-switch for a (( consumer’s installation )) is an example of a device that is used for the function of (( isolation ))
Table 53.4. Guidance on the selection of protective, isolation and switching device(s)
BS-EN-60947-3 Isolating switch :
Isolation . Yes .. ( 1,3 )
Emergency switching. Yes
Functional switching. Yes


BS-EN-60947-3
( 1,3 )
Yes = Function provided .
1) Function provided if the device is suitable and marked with the ((symbol )) for isolation , see BS-EN-60617 identify number S00288 .
3) Device is suitable for On-load isolation , i.e. disconnection whilst carrying load-current .

Note 1 : An entry of ( 1 , 3 ) means that the device is suitable for On-load isolation only , if it is marked with the symbol for On-load isolation .

(BS) P/285 . BS-EN-60617 See Note at end of this Table .. Table 53.4. note 1 Appx 1 note .. An entry of ( 1 , 3 )

 

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Guide as denoted by the topic reference numbers shown

ANNEX
AA: List of tables of maximum permitted values of earth fault loop impedance ( Zs ) included in BS-7671
Note: All tables apply for a nominal voltage ( Uo ) of 230 V only, unless otherwise shown.

Table 41.2. - Device type : General purpose (gG) fuses to BS-88-2 fuse systems E ( bolted ) & G ( clip in )
Table Ref . BS-88-2
Disconnection time - ( seconds ) 0.4s General 41.2 (a)
Disconnection time - ( seconds ) 5.0s General 41.4 (a)
Disconnection time - ( seconds ) 5.0s ( RLV ) 41.6 .. Reduced Low Voltage system. .. ( 55V single-phase ) & ( 63.5V three-phase )
( RLV ) 41.6. 32A B - 32 x 5 160 = 0.34Ω - 55V ÷ 160 = 0.34Ω .. Fig 3A4

Table 41.2. - Device type : Fuses to BS-88 -3 fuse system C ... ( Old BS-1361 )
Fuses to BS-88 -3 fuse system C
Table Ref . BS-88-3
Disconnection time - ( seconds ) 0.4s General 41.2 (b)
Disconnection time - ( seconds ) 5.0s General 41.4 (b)

Table 41.2. - Device type : Fuses to BS-3036
Table Ref . BS-3036
Disconnection time - ( seconds ) 0.4s General 41.2 (c)
Disconnection time - ( seconds ) 5.0s General 41.4 (c)

Table 41.2. - Device type : Fuses to BS-1362
Table Ref . BS-1362
Disconnection time - ( seconds ) 0.4s General 41.2 (d)
Disconnection time - ( seconds ) 5.0s General 41.4 (d)

Table 41.3(a) . - Device type : B circuit-breaker to BS-EN-60898-1 & the overcurrent characteristics of RCBO to BS-EN-61009-1
Disconnection time - ( seconds ) 0.4s & 5.0s
Disconnection time - ( seconds ) 5.0s ( RLV ) 41.6

Table 41.3(b) . - Device type : C circuit-breaker to BS-EN-60898-1 & the overcurrent characteristics of RCBO to BS-EN-61009-1
Disconnection time - ( seconds ) 0.4s & 5.0s
Disconnection time - ( seconds ) 5.0s ( RLV ) 41.6

Table 41.3(c) . - Device type : D circuit-breaker to BS-EN-60898-1 & the overcurrent characteristics of RCBO to BS-EN-61009-1
Disconnection time - ( seconds ) 0.4s & 5.0s
Disconnection time - ( seconds ) 5.0s ( RLV ) 41.6

Table 41.5.
Non-delayed RCDs to BS-EN-61008-1 and BS-EN-61009-1 .. for final circuits not exceeding 32A
Disconnection time - ( seconds ) 0.4s
To ensure RCD operation in accordance with Regulation 411.5.3.

Electric shock , protection against
By automatic disconnection of supply , TT system

BS-7671: states three fundamental requirements for fault protection by ADS in a TT system:
• Protective earthing (Regulation 411.3.1.1)
• Protective equipotential bonding (Regulation 411.3.1.2)
• Automatic disconnection in case of a fault (Regulation Group 411.3.2)

Protective devices
For fault protection, Regulation 411.5.2 requires one or more of the following types of protective device shall be used, the former being preferred:
an RCD
an overcurrent protective device such as, a circuit-breaker.

BS-7671: states three fundamental requirements for fault protection by ADS in a TN system:
• protective earthing (Regulation 411.3.1.1)
• protective equipotential bonding (Regulation 411.3.1.2)
• automatic disconnection in case of a fault (Regulation Group 411.3.2)

Protective devices
For fault protection, Regulation 411.4.4 requires one or more of the following types of protective device to be used:
an overcurrent protective device such as a circuit-breaker
an RCD.

Table 41.1 of BS-7671: provides the maximum disconnection times for TN and TT systems for final circuits not exceeding 32 A (Regulation 411.3.2.2 refers).

 

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Sub distribution board .. Sub-mains Etc . see Distribution circuit

P/26 . Distribution circuit . :icon_bs:
A circuit supplying a distribution board or switchgear

A distribution circuit may also connect the (Origin ) of an installation to an outlying building or separate installation , when it is sometimes called a sub-main .

Supply intake .
A term used to describe the location or room housing the main cable and equipment provided by ( DNO ) to provide a supply of electricity to a premises .

 

[Richard Burns]

For Amberleaf:
Radial final circuits, Cooker


Guidance on the requirements of BS-7671: for final-circuits supplying cooker loads.
Maximum circuit cable lengths for typical final circuits supplying cooker loads wired in 70 °C thermoplastic (pvc) insulated and sheathed flat cable to BS-6004 Table 8. The information is intended to enable such circuits to be installed generally without calculation.


Conventional arrangements for radial final circuits for cookers
Each cooker should be supplied by a radial final circuit dedicated for the purpose, and should be connected to the final circuit by a readily accessible means of interrupting the supply on load - generally a cooker control switch (see Fig 1) or a cooker control unit. For the purposes of this topic, a cooker is a hob unit, an oven/grill or a combination of both.


Fig 1 .. Cooker control switch




The protective conductor current of a cooker may cause unwanted tripping of a 30mA RCD. Where there is concern, a cooker control unit without a socket-outlet may be used.


Fig 2 .. Cooker control unit


A cooker control unit incorporates a main switch for the cooker and a switched socket-outlet. The installation of a cooker control unit can lead to accidents due to trailing cables and/or portable equipment being located near to hot surfaces. Where a cooker control unit is provided, it should be positioned so as to minimize the risk of such accidents.


One dedicated circuit of suitable rating may be used to supply two or more cookers, an oven/grill and a separate hob unit for example, where they are installed in the same room. In such cases, the cookers may be connected to the final circuit either individually by means of a cooker control switch or cooker control unit, or collectively by means of one such unit common to all the cookers (see Fig 3).


A typical radial final circuit supplying two cookers


Fig 3


A 30/32 ampere circuit is generally suitable for most household cookers (4 heating rings, a grill and an oven) but a circuit of higher current rating may be necessary for cookers having additional cooking facilities and/or larger capacity ovens.


13 A socket-outlets in a TN or TT system (including the socket-outlet in a cooker control unit) are required by Regulation 411.3.3 to be protected by a 30mA RCD .


The protective conductor current of a cooker may cause unwanted tripping of a 30mA RCD. Where there is concern, a cooker control unit without a socket-outlet may be used.

 

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P/28 . 2011: Extraneous conductive parts :icon_bs:
A ( conductive-part ) liable to introduce a potential , generally Earth potential . and not forming part of the electrical installation .

Extraneous conductive parts ( Basic’s )

Understanding the definition

First part: ‘ A conductive-part ’ .. In order to be conductive, an item must be formed of metal or some other conducting material.
In most situations, only parts made of metal need to be considered as conductive-parts

Second part: ‘ liable to introduce a potential, generally Earth potential ’
That is to say, is the item liable to introduce a potential to a person (or livestock) who may be in contact with another potential

To introduce a potential to such a person, the item must not only be at a potential, but must also be able to introduce the potential. Introduction of the potential requires two- things. The first is that the item (or a conducting item in electrical contact with it) must be accessible to be touched by a part of such a person’s body.

The second is that any electrical resistance through which the item is connected to the source of its potential (such as the resistance connecting an item with Earth potential) must not be so great as to prevent the potential being introduced to a person (due to voltage drop in the resistance).

Third part: ‘ and not forming part of the electrical installation ’

This part of the definition limits extraneous-conductive-parts to being items which do not form part of the electrical installation in question.
Therefore, items which may be extraneous-conductive-parts include the following, which are referred to in Regulation 411.3.1.2 of BS-7671 with regard to main protective equipotential bonding

Water installation pipes
Gas installation pipes
Other installation pipework and ducting
Central heating and air conditioning systems
Exposed metallic structural parts of the building

In addition, any other non-electrical items which fall within the definition may be extraneous-conductive-parts.

 

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( BS P/277 ) Standard / Title BS-88

Old to New , fuses

BS-88:
The term “ BS-88 series “ when used in the Regulations , means BS-88-1 , -2 , -3 . ( BS-88-1 BS-88-2 BS-88-3 ) part 1 , 2 , 3 .

BS-88-1: 2007: Low-voltage fuses – Part 1 : General requirements .

BS-88-2 : 2010: Low-voltage fuses Part 2:
Supplementary requirements for fuses for use by authorized persons (fuses mainly for industrial applications) - Examples of standardized systems of fuses A to J

BS-88-2 : 2010: has replaced BS-88-2.2.:1989. and BS-88-6:1988 which have been withdrawn .

BS-88-3: 2010: Low-voltage fuses Part 3:
Supplementary requirements for fuses for use by unskilled persons (fuses mainly for household and similar applications) - Examples of standardized systems of fuses A to F.

BS-88-3: 2010: has replaced BS-1361:1971 which has been withdrawn .

 

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Point to Note here . Etc .
► BS-88-2 is also numbered BS-HD-60269-2: 2010. R/P283
► BS-88-3 is also numbered BS-HD-60269-3: 2010. R/P283

BS-HD-60269-2 . Low-voltage fuses . Part 2 Supplementary requirements for fuses for use by ( Authorised persons ) fuses mainly for Industrial application .
Examples of standardized system of fuses A to M

BS-HD-60269-3 . AMD1 / BS-88-3 :2010 AMD1 . Low-voltage fuses . Part 3 Supplementary requirements for fuses for use by ( Unskilled persons ) fuses mainly for household or similar application .
Examples of standardized system of fuses A to F

BS-HD-60269-2: 2010.
Low-voltage fuses . Part 3 Supplementary requirements for fuses for use by ( Authorized persons ) fuses mainly for Industrial application .
Examples of standardized system of fuses A to J

BS-HD-60269-2: 1995.
Low-voltage fuses . Supplementary requirements for fuses for use by ( Authorized persons ) fuses mainly for Industrial application .
(( Replaced by BS-88-2 :2007 . and bs-en-60269-1 : 2007 and withdrawn 1/3/2010 .

What the Regulations have to say . ( BS )

BS-HD-60269 Low-voltage fuses .

BS-HD-60269-2: 2010.
Low-voltage fuses . Part 3 Supplementary requirements for fuses for use by ( Authorized persons ) fuses mainly for Industrial application .
Examples of standardized system of fuses A to J (( also numbered BS-88-2 : 2010. ))

BS-HD-60269-3: 2010.
Low-voltage fuses . Supplementary requirements for fuses for use by ( Unskilled persons ) fuses mainly for household or similar application .
Examples of standardized system of fuses A to F (( also numbered BS-88-3: 2010 ))

BS-HD-60269-3: 1995. .
Low-voltage fuses . Supplementary requirements for fuses for use by ( Unskilled persons ) fuses mainly for household or similar application .
(( Replaced by BS-88-3:2007 and BS-EN-60269-1:2007 and withdrawn , 1/3/2010

 

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BS-88 fuses each have an assigned breaking range and utilisation category designated by two letters such as ‘gG’. The first letter indicates the breaking range and the second indicates the utilisation category.

The breaking range is the range of prospective currents within which the breaking capacity of the fuse is assured. Some BS-88 fuses have only a partial-range breaking capacity and although they are able to interrupt short-circuit fault currents they are not designed to interrupt overload currents. Such fuses are designated by the letter ‘a’ in the first letter position.

The utilisation category relates to the ability of a fuse to fulfil its purpose for a particular type of application. The utilisation category of a fuse is designated by one of the following letters in the second letter position:

G . use for general application
M . use for protection of motor circuits
D . time-delay fuse
N . non-delay fuse

By applying this method of categorisation to the example given at the beginning of this item, it will be seen that a ‘gG’ fuse is a fuse with a full-range breaking capacity for general application. Other examples are:

gM . a fuse with a full-range breaking capacity for the protection of motor circuits
aM . a fuse with a partial-range breaking capacity for the protection of motor circuits

aM . fuse is usually an industrial fuse with an operating characteristic designed to protect inductive loads e.g. motors. Using a general purpose 'gG' fuse in such an application could lead to nuisance operation because the fuse cannot

It should be noted that, where their characteristics are suitable for the motor starting current, ‘gG’ fuses may be used, and often are used, for the protection of motor circuits.

 

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Definition of Fuse .
A Fuse is a device that , by the fusion of one or more of its specially designed and proportioned components , open the circuit in which it is inserted and breakers the current when this exceeds a given value for a sufficient time . The fuse comprises all the parts that from the complete device ( BS-88- )

A Fuse therefore a complete device consisting of fuse-holder, consisting of fuse-base and fuse-carrier and fuse-link .

Definition of Fuse Link .
A Fuse-link is a device comprising a fuse-element or several fuse elements connected in parallel enclosed in a cartridge , usually filled with an arc-extinguishing medium and connected to terminations , the fuse-link is a part of a fuse which requires replacing after the fuse has operated . ( BS-88- )

from this definition that the “ fuselink “ is part of the fuse popularly but incorrectly referred to as a “ fuse “ and that the internal part which melts is called the “ element “ .

Semi-enclosed fuse . ( BS-3036 ) or rewirable fuse .. Semi-enclosed fuse requires a relatively large overcurrent to blow it.
Consists of a base , a carrier ,
the fuse element and some form of protection , such as an arc-résistance tube , to limit the emission of flame .
i) Fuse-carrier
ii) Fuse-element
iii) Fuse-contact
iv) Arc-résistance tube

( Fuse ) is designed to self-destruct .
Fuse operation .
All fuses operate in the same way . a conductor of limited cross-section is heated by current passing through it until it melts . represented in a time current characteristic for the fuse . On melting , a brake is caused in the element , at which an electric arc is established .

The Pre-arcing time . Theory . is dealt with under “ Time / current characteristics “

Other definitions relating to fuses can be found in BS-7671: refer :icon_bs:

R/P 28 . Mechanism of fuse operation . Etc .
Fuse :
A device which , by the melting of one or more of its specially designed and proportioned components , “ Opens “ the circuit in which it is inserted by breaking the current when this exceeds a given value for a sufficient time . The fuse comprises all the parts that form the complete-device .

Fuse-carrier . The movable part of a fuse designed to carry a fuse-link .

Fuse-element . A part of a fuse designed to “ Melt “ when the fuse-operates

Fuse-link. A part of a fuse , including the “ fuse-element(s) “ which requires replacement by a new or renewable fuse-link after the fuse has operated and before the fuse is put back into service .

 

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Fuse Reference ( BS , British Standards )

Existing BS-7671:2008: BS-88-2-2.
BS-7671:2008: 2011) BS-88-2 .. This is a bolted type fuse that is recognised internationally as fuse-system ( E ) Table 41.2. / Table 41.4.

Existing BS-7671:2008: BS-88-6.
BS-7671:2008: 2011) BS-88-2 .. This is a clip in type fuse that is recognised internationally as fuse-system ( G ) Table 41.2. / Table 41.4.
Type ( G ) clip in , fuses only have nominal values up to 125A , The values of current associated with the ( 0.4 & 5s ) disconnection times in these figures are used to generate the ( Zs values ) in tables 41.2. & 41.4 .

Existing BS-7671:2008: BS-1361.
BS-7671:2008: 2011) BS-88-3 .. This is a cartridge type fuse that is recognised internationally as fuse-system ( C ) Table 41.2. / Table 41.4.

Different Ratings . Table 41.4. 2008: Table 41.4. ( 2011)
Comparison of ( Old - BS-1361 ) and ( New – BS-88-3 )
2008: 5A ,15 , 20 , 30 , 45 , 60 , 80 , 100 .
( 2011) 5A , 16* , 20 , 32* , 45 , 63* , 80 , 100 .

Standard changes , these now require specific reference to : BS-88-2 to differentiate with BS-88-3 fuses .
As three standards have been incorporated into a single standard

Appendix 1 ( Normative )
( BS-88) . The term “ BS-88 series “ when used in these Regulations , means BS-88-1 , -2 , -3 .

BS-76712011) Part 2 includes a section on symbols that are used in the Wiring Regulations .
Fuses. the symbols ( gG ) and ( gM ) are defined . “ Protection “
General purpose ( gG ) class “ gG “ utilisation category of fuses to BS-88-2 - general use . 411.4.6.
Motor protection ( gM ) class “ gM “ utilisation category of fuses to BS-88-2 - motor circuit application . 411.4.6.

O.S.G. 1.1. Scope . ( Introduction )
This Guide is restricted to installation(s) :
313.1. i) at a supply frequency of 50 hertz
ii) at a nominal voltage of 230V a.c. . single-phase or 400 / 230V a.c. . three-phase
iii) ( DNO ) supplied through a distributors cut-out having a fuse or fuses rated at 100A or less to one of the following standards :
- BS-88-2
- BS-88-3
- BS-88-6

• BS-1361 Type ( II ) Note : BS-1361 was withdrawn in March 2010 , and replaced by BS-88-3
• BS-88-6 was withdrawn in March 2010 , and replaced by BS-88-2 .

re-cap O.S.G. 2011:
fuses complying with these withdrawn standards will be found in existing installations for many years to come .

Distribution Network Operator ( DNO ) .. supplied through a distributors . PS , Companies