Re-take - Useful Information for 2394 :

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(*5 ) 2394 :

3 b ) ii) Explain why the earthing conductor is connected to the MET when measuring prospective earth fault current .. 2/M

Ans ; This is the condition that exists at the time of a fault and therefore is the only way to determine the maximum fault current to ( EARTH ) when carrying out the test .

C;
in this case the purpose of the test is to ( Determine ) the maximum prospective earth fault current , This will occur when the installation is energised and all earthing arrangements are in place , so the test must be carried out under these conditions .

3 c) i) List the measurements to be taken , at the main switch of a three-phase TN-S system , in order to determine the installation prospective fault current ( Ipƒ ) .. 3/M

Ans ;
• L1 to L2
• L1 to L3
• L2 to L3

C;
There is no need to carry out any other tests to determine ( PFC ) because on a three-phase system the largest fault current will be due to a symmetrical short circuit , that is a short circuit between all line conductors' at the same time . A test between line conductors is an acceptable approximation . if additional tests were included in the answer then this would not make the answer invalid .

The measurement of , L1 to N , L2 to N and L3 to N would be an acceptable Alternative method see answer to ( 3 c ii below )

3 c ) ii) Explain how the recorded value of prospective fault current ( Ipƒ ) is determined following the test in c) ii) above .. 3/M

Ans ; The highest value of the three measurements

C;
3 c ) i) and ii) are linked and the answer to ii) is dependent on the test method used in i) if the answer to i) was to measure between L & N then this answer would be " the largest value x 2 " if the answer to i) included tests to earth then this answer must state 2 the largest line to neutral value x 2 "

 

[Richard Burns]

From Post 753
6 ) Describe , with the aid of a fully labelled diagram , the earth fault loop path for the outside lighting circuit 15 marks .

Answer : Drawing . TN-C-S System Earth Fault .

The fault path is :
from the point of fault
Along the cpc to the MET
from the MET via the earthing conductor to the supplier's PEN terminal
Along the PEN conductor to the supply transformer winding
Through the transformer winding , along the line conductor to the fault

 

[Richard Burns]

Section B

 

[Richard Burns]

Distribution Layout: figure two

 

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Useful junk

Connection to the fixed wiring :

A luminaire is defined in Part 2 of BS-7671: P/30 As

‘ Luminaire. Equipment which distributes, filters or transforms the light transmitted from one or more lamps and which includes all the parts necessary for supporting, fixing and protecting the lamps, but not the lamps themselves, and, where necessary, circuit auxiliaries together with the means for connecting them to the supply .’

Means of connection at lighting points
At each fixed lighting point or position, Regulation 559.6.1.1 requires the fixed wiring to be connected to one of the following:
□ a ceiling rose to BS-67
□ a batten lampholder or a pendant set to BS EN 60598

Batten lampholders
Pendant sets .. Etc

Where a pendant set is installed, the accessory used as the means of connection with the fixed wiring installation is required to be suitable for supporting the mechanical load to be suspended Regulation 559.6.1.5

559.6.1.5 Adequate means to fix luminaires shall be provided .

 

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4 hours Ago # 763 ◄ Look at connector block's drawings Step 2 & Step 3 ..

Take your inspiration from GN-3 P/37 Drawing . Continuity of ring final circuit conductor Exam

 

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BS-7671: have stated the facts .

R. P/34 , Residual current operated circuit breaker with integral overcurrent protection ( RCBO ) A residual current operated switching device designed to perform the functions of protection against overload & / or short-circuit .

RCBOs provide both earth-fault & overcurrent-protection

30mA BS-EN-61009-1 provides :
independent RCD protection to individual circuits offering both the degree of additional protection that may be required by Regulation 415.1 and the minimum of inconvenience following a single-earth-fault ( Regulation 314.1 ).

R. P/26 , Earth-fault current . A current resulting from a fault of negligible impedance between a line conductor and an exposed-conductive-part or a protective-conductor .

R. P/34 , Short-circuit current . An overcurrent resulting from a fault of negligible impedance between ( live-conductors ) refer .

 

[amberleaf]

Measurement of the résistance ( R[SUP]A[/SUP] )
( 50 ) is the maximum safety touch voltage limit :

TT - system .
protected by a RCD the maximum ( R[SUP]A[/SUP] ) values are :

BS-EN-61009-1 .. Uo /230V
BS-EN-61008-1 .. Uo /230V

( Ia ) is the rated residual operating current ( I∆n )
Table 41.5 . Rated residual operating current ( I∆n ) 30 , 100 , 300 , 500 . ( mA )

( R[SUP]A[/SUP] ) with touch voltage of 50V : 1667* , 500* , 167 , 100 . ( Ω )

Verification of the protection by RCD in a TT - system

411.5.3. Where an RCD is used for fault protection , the following conditions shall be fulfilled :
( R[SUP]A[/SUP] ) x I∆n ≤ 50V .

where :
R[SUP]A[/SUP] ) is the sum of the résistances of the earth electrode and the protective conductor connecting it to the exposed-conductive-parts . ( Ω )
I∆n ) is the rated residual operating current of the RCD

The requirements of the regulation are met if the earth fault loop impedance of the circuit protected by the RCD meets the requirements of Table 41.5.

Note 2 : Where ( R[SUP]A[/SUP] ) is not known , it may be replaced by ( Zs )
BS-7671:2011: shall be verified by ; ( R[SUP]A[/SUP] ) or ( Zs ) table 41.5. 50V ÷ 30mA = 1.666666667Ω .. 1667* maximum ( Zs ) earth fault loop impedance
Loop tester ( Ω ) example .
Maximum permissible value is 1667Ω ( RCD = 30mA and contact voltage limit of 50V ) instrument reads 12.74Ω , thus the condition ( R[SUP]A[/SUP] ≤ 50/Ia is respected )

R/P.57 . recap : Note 2 . * The résistance of the installation earth electrode should be as low as practicable . A value exceeding 200Ω may not be stable . refer

RCD is essential for protection , must be tested .

 

[amberleaf]

R/P.55 . ► recap . The values specified in Table 41.3. for the types & ratings of overcurrent devices listed may be used instead of calculation .

Something I knocked up . ( Zs ) you're Q . Maximum

BS-EN-61557-3

GN-3 ; P/83. Earth fault loop impedance tester , These instruments may also offer additional facilities for deriving prospective fault current
( MT ) Earth fault loop impedance tester . also have the ( PFC ) measurement .

TN- system , example of ( Verification of the protection by Circuit-breaker ) BS-EN-60898-1

Characteristic circuit-breaker ( C ) Table 41.3 16A - Zs - 1.44Ω
Maximum value : of ( Zs ) is 1.44Ω .. the instrument reads 1.14Ω or 202A on Fault current range , it means that the Condition ( Zs x Ia ≤ 1.14Ω )
is respected .

in fact the ( Zs ) of 1.14Ω is less than 1.44Ω .. or the Fault current of 202A is more than ( Ia of 160A )

Fault between Line & Earth , the wall socket-outlet tested , The circuit-breaker will trip within the disconnection time required . ( Protected )

R/P.302 . Fig 3A5 . Type C . Rating 16A - Current 160A ; 16 - 160A

 

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Something I knocked up , Rotation instruments . GN-3 P/84 . 612.12. Check of phase sequence . refer

recap : GN-3 measuring equipment for testing the phase sequence in three-phase distribution system whether indication is given by ;
- mechanical .
- Visual .
- & or audible means .

MEM 100A three-phase distribution board

MFT : Megger - 1730 . Phase rotation / sequence test .

Three phase installation you measure or check that you have your Phase sequence correct right through the whole of the installation . Origin of supply then need be every Distribution boards .

turn onto phase sequence
( V ~ rotation Hz ) 50.0 Hz .. L1 , L2 , L3 . run in that sequence .

L1 - 426V , L2 - 426V, L3 - 426V Indicators , Visual .. ( V ~ )
3 alligator clips ; U1 / red , V1 / blue , W1 / green .

Example only . reversal on leads not red , blue , green . ( demonstrate purposes only )
U1 / blue , V1 / red , W1 / green .. L1 - 426V , L3 - 426V , L2 - 426V . flashing that indicates that there is something wrong

( demonstrate purposes only )
GN-3 P/84 . measuring equipment for testing the phase sequence in three-phase distribution systems whether indication is given by

Approved voltage Indicator . ( Visual means )

Fully compliant with GS-38

Voltage & Continuity Testers with Phase Rotation Test
CombiVolt 1 Voltage/Continuity Tester

Depicts a test carried out . Three phase installation .
Voltage indicators . ( L1 ) is black lead & ( + L2 ) in the black & yellow lead .. D.C. voltage ↯

Black lead ( L1 ) onto line 1 - U2 .
+ L2 ) other fixed lead onto line 2 - V2 . green light against the ( R► ) on the right side of indicator . that tell you the rotation is correct .

( L1 ) onto L2 - V2 .
+ L2 ) onto L3 - W2 . that tell you the phase rotation is correct .

then the other way around ;

L1 onto L3 - W2
L2 onto L1 - U2 .. that tell you the phase rotation is correct .

if you get it round the wrong way . L1 onto L1 - U2 , + L2 onto L3 - W2 . Left hand green light coming on ( ◄ L ) that tell you the phase rotation is Wrong

 

[amberleaf]

TN - system with nominal mains voltage ( Uo = 230V ) Fig 3A4 . BS-EN-60898-1 & BS-EN-61009-1
Protection by circuit breakers with ( Uo of 230V ) disconnection time 0.4 & 5s

( Ia & maximum Zs values could be ) R/P. 301 , 302 , 303 . B , C , D .
Characteristic B . ( Ia (A) Zs ( Ω ) 6A .. Ia (A) 30 . Zs ( Ω ) 7.67 .. ( Zs ≤ 230V ÷ 30A = 7.67Ω )
Characteristic C . ( Ia (A) Zs ( Ω ) 6A .. Ia (A) 60 . Zs ( Ω ) 3.83 .. ( Zs ≤ 230V ÷ 60A = 3.83Ω )
Characteristic D . ( Ia (A) Zs ( Ω ) 6A .. Ia (A) 120 . Zs ( Ω ) 1.92 .. ( Zs ≤ 230V ÷ 120A = 1.92Ω )

Rating / Current

In ) 5 x magnetic settings ; 5 x 6A = 30A
In ) 10 x magnetic settings ; 10 x 6A = 60A
In ) 20 x magnetic settings ; 20 x 6A = 120A

 

[amberleaf]

Who sets these questions ?

The usual forum " pick the Answer apart & Criticise "

Q) A ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) reading at the extreme end of a 25m long 20A radial socket-outlet circuit is taken :
What would be the approximate reading of ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) given that the résistance per metre of 2.5mm[SUP]2[/SUP] cable is 7.41 mΩ/m at 20ºC .

0.37Ω
0.18Ω
0.74Ω
0.27Ω

• Using Singles.

O.S.G. Table 11 , Temperature is not an issue as 20ºC

( - ) for single cable . ◄

( r[SUP]1[/SUP] + r[SUP]2[/SUP] ) same csa (singles)

Length of cable 25m
Resistance of cable/m ( r[SUP]1[/SUP]) = 7.41 , ( r[SUP]2[/SUP] ) = 7.41

r1 ) - 25m x 7.41 / 1000 = 0.185
r2 ) - 25m x 7.41 / 1000 = 0.185

0.185 + 0.185 = 0.37 The answer .

O.S.G. Table 11 , Temperature is not an issue as 20ºC

• Cable is T&E
Length of cable 25m
Resistance of cable/m

( r1 ) = 7.41............. ( resistance of 2.5mm line-conductor )
( r2 ) = 12.10 ............. ( resistance of 1.5mm circuit-protective-conductor)

r1 ) - 25m x 7.41 / 1000 = 0.185
r2 ) - 25m x 12.1 / 1000 = 0.303

0.185 + 0.303 = 0.488Ω

 

[amberleaf]

When selecting equipment the ( designer / Installer ) should take account of manufacturer's instructions (i.e. is this equipment suitable for the purpose (s)

Just back from changing circuit-breakers for RCBOs 20A , Shop work

Manufactures' instruction's on box . ◄

Operation of the test button of any RCBOs fitted

When newly fitted systems do not trip on the TEST button or using the RCBO tester the problem is normally caused by an earth to neutral fault on the circuit ( PME ) supply

Installers can easily check the RCBO by removing the outgoing terminations ( i.e. busbar and neutral link ) on the RCBO and applying power .

if the TEST button works the fault is in the circuit . ◄

Section 134 .. Erection & initial Verification of Electrical Installations .

R/P.21 , 134.1 Erection
Regulation 134.1.1 , Good workmanship by competent persons or persons under their supervision and proper materials shall be used in the erection of the electrical installation, ( Electrical equipment shall be installed in accordance with the instructions provided by the manufacturer of the equipment. )

Part 5 ; Selection & Erection of Equipment

Chapter 51 , Common Rules
510.3 Every item of equipment shall be selected and erected so as to allow compliance with the regulations stated in this chapter and the relevant regulations in other parts of BS-7671 and ( shall take account of manufacturers' instructions. )

& 511.1. Compliance with Standards .

R/P118 , 514.12.2. Where an installation incorporates an RCD a notice shall be fitted in a prominent position at or near the origin of the installation , The notice shall be in indelible characters not smaller than those illustrated here and shall read as follows : refer

RCD / RCBO .

134 ; is just deals with Erection ( & Verification).

 

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Inspection ..
An action comprising careful scrutiny of an item / system . ( this is the polite way of say it )

Inspection .. R/P.29
Examination of an electrical installation using all the senses as appropriate .

Visual inspection .. which identifies, those defects, which can be apparent to the eye.

 

[amberleaf]

( rule of thumb ) ► This type of calculation must be understood by any student studying for the C&Gs 2394 / 5 Inspection & Testing

• Values given in BS-7671:2011: for ( Zs ) are for when the circuit conductors are at their operating temperature , generally 70ºC

On small rant mode .

Comparing Maximum ( Zs ) & Measured ( Zs )

Simple calculation - rule of thumb , Appendix 14 of BS-7671:

This calculation will allow you to compare your measured values with the values in BS-7671:2011:

in these type of calculations you must always use the worst case values to ensure a safe installation .

Circuit-breaker application . circuit protected by a 32A BS-EN-60898-1 type B
your measured value of ( Zs ) is 0.98Ω

By calculation . 5 x 32A = 160 so , 230V ÷ 160A = 1.44Ω
Maximum ( Zs ) at ( 70ºC ) for your circuit is , 1.44Ω

To find the corrected value you must multiply ( 1.44Ω by 0.8 ) ........ 1.44 x 0.8 = 1.15Ω .

1.15Ω now becomes your maximum value & you can compare your measured value directly to it . without having to consider the ambient temperature or the conductor operating temperature .

Your measured value must be less than the corrected maximum value . in this case it is , & the 32A type B device would be safe to use .

 

[amberleaf]

( rule of thumb ) ▲▲▲

Unfortunately you cannot compare this value to any measured ( Zs ) value that you have .
• Values given in BS-7671:2011: for ( Zs ) are for when the circuit conductors are at their operating temperature , generally 70ºC

 

[amberleaf]

On rant mode .

Just stating the Obvious . C&Gs can ask you any one of these in , Q/As

Gentlemen ; everything you have to known about inspection & testing , is all in GN-3 & BS-7671:2011:

P/396 . Electrical Installation Condition Report .. ( EICR )

Section B reason for producing this Report

Details of the installation . Etc ........
- Occupier : this may not be the owner .
- Estimated age of wiring system in Years
- Evidence of additions / alterations : if Yes , estimate the age in Years
- Installation records available .. regulation 621.1. ???
- Date of last inspection ( date ) That's a good Question . ???

Section D . Extent & Limitation of Inspecting & Testing .

Extent of the electrical installation covered by this report : what does the inspection cover , is it the complete installation or just a part of

Agreed Limitation : including the reasons , Regulation 634.2. are there any areas that are not being inspected , are there circuits which cannot be isolated or tested .

Agreed with : who has the limitations been agreed with .
Operational limitations including the reason : areas not to be entered or access not permitted .

The inspection & testing detailed in this report and accompanying schedules have been carried out in accordance with BS-7671:2008: as amended to ....
What Certificates will be used . Section H , Schedules(s) BS-7671: tell us ; ( EICR ) with Schedule(s) of inspection , & Schedule(s) of test results are attached .

The attached Schedules(s) are part of this document and this report is ( valid ) only when they are attached to it .

it should be noted that cables concealed within trunking and conduit , under floors , in roof spaces , and generally within the fabric of the building or underground , have not been inspected unless specifically agreed between the client and inspector prior to the inspection .

Section E . Summary on the condition of the Installation .
This section is where you would record any concerns which you have about the electrical safety of the installation ,

Extent & Limitation of Inspecting & Testing .. C&Gs
Agreed with : who has the limitations been agreed with . .. C&Gs etc .

Periodic inspection is carried out for many reasons ;
The due date .
Client / customer request
Change of ownership
Change of use .
Insurance purposes .
To inspect the condition of the existing installation , prior to carrying out any alterations or additions .

The frequency of the periodic inspection and any testing which may be required is dependent of the ( type ) of installation , the environment and type of use . BS-7671: What Edition ?? refer to this as the " Construction , Utilization and Environment . and this can be found in Appendix 5 of BS-7671:

 

[amberleaf]

C&Gs ( EIC ) what is my main purpose Q/As
□ New installation : ✓
□ Addition : ✓
□ Alteration : ✓

P/390 ( EIC ) Description & Extent of the Installation ; What part of the Installation does this certificate cover :

□ New installation : to be ticked if the whole installation is New .

□ Addition to an existing installation : this box be ticked when the work is added to an existing installation , could be a single new circuit , the installation of circuits in an extension .

□ Alteration to an existing installation : this box is used to indicate that the characterises of the existing installation have been altered . this would include extending / altering a circuit and changing the protective-device . the replacement of consumers unit

Supply Characteristics
1 phase 2 - wire 3 phase 4 - wires ... meaning ( Live conductors ) only

Schedule of Test Results This document is a generic document which can be used with either an ( EIC ) or ( EICR )

 

[amberleaf]

[h=4]What are the appropriate testing criteria for a time-delayed RCD whenconnected into a TT system, where the installation was designed prior tothe introduction of the 17th Edition [/h]It would be necessary toverify that the RCD operates within the criteria stated in the relevant productstandard (BS-EN 61008-1) and reproduced in Table 3A ofAppendix 3 - that is between 130 mS & 500 mS

 

[amberleaf]

GN-3 , give us a solution for anything . (( Testing is for this reason ))

re-cap ; GN-3 2.7.7.
Insulation résistance testing is a fundamental test for inspectors . do they have to be a reason . !

The purpose of the insulation résistance test is to verify that the insulation of conductors provide adequate insulation , is not damaged and that live-conductors or protective-conductors are not short-circuited .

Insulation résistance test . ( IR )
Neutral / Earth fault can go unnoticed unless an ( IR ) test is carried out , whether the circuit with the Neutral / Earth fault is protected by an RCD or not .

To suit certain situations !!

Regulation 612.3.1. requires that :
Insulation résistance be ( Measured ) between ( live-conductors ) & ( protective-conductor ) connected to the earthing arrangement .

This means that the insulation résistance test must be carried out between the neutral-conductor & Earth ... your reason here is , Any Short should be picked up at this stage .

 

[amberleaf]

Scenario . (( One way of looking at it ))

Neutral / Earth fault can remain undetected . they do exist

Ohms law . Scenario .
The résistance of the Earth-path : " room for thought " TT system with an earth-rod résistance of ( 100Ω )

( PD , potential-difference ) neutral and Earth .. 30mA to flow to Earth will require a voltage-difference between the neutral-conductor and Earth of ,
3 - volts .. ( 0.03 x 100 ) = 3V .

The resultant ( PD ) between neutral and Earth may be sufficient to cause the current to flow in the circuit-protective-conductor , Hence .
the nature of the fault is ( Load-dependent ) This may cause the RCD to trip randomly at times and the fault may be described as ;

The Pursuit of making (( Unwanted tripping )

 

[amberleaf]

Faults are not always just a single problem & one fault can hide or affect another.

 

[amberleaf]

" Alternating current " its about potential difference ... ( ~ ) in and out .

Current should flow from Line to Neutral . ( a.c ) it will reverse direction 50 times a second, but convention says it flows from Line to Neutral .

BS-7671:2011: tell us of , Types of system earthing . Three-systems . TN-S , TN-C-S ( PME ) , TT - system .

TN-C-S ( PME ) Fig 3.9

Standard - reminds us , RCDs monitors only .

Neutral to Earth faults ..
i) This depends on two-factors .. ( The PD ) potential difference between the neutral conductor & Earth .
ii) The résistance of the earth-path .

Significant neutral to Earth résistance can also exist ; Therefore , TT - , TN-S , can remain undetected . ( IR ) insulation resistance test . C&Gs

TN-C-S ( PME ) .. ( PD ) Neutral & Earth .
if the RCD is to trip due to a Neutral & Earth fault , the ( PD ) between the neutral-conductor and Earth must be sufficient to cause at least some of the returning neutral current to return to the origin via the circuit-protective-conductor rather than via the ( Neutral-conductor )

TN-C-S ( PME ) .. The neutral conductor and Earth are likely to be ( Substantially the same potential ) due to the neutral / earth link in the ( Cut-out ) in such a situation , no current will flow & the RCD will not trip . However .

When the load of the circuit with the neutral / Earth fault is energised , the current flow causes a voltage drop in the neutral-conductor and this voltage drop results in a ( PD ) between it and Earth .

The greater the load , the greater the current flow and hence the greater will be the voltage drop . if the voltage drop is sufficient , some of the returning neutral-conductor will flow through the circuit-protective-conductor , should enough current flow through the circuit-protective-conductor , the RCDs search will " See an imbalance and cause the RCD to operate " Therefore , in a TN-C-S with no load or with a very light load . a neutral / Earth fault my remain undetected .

 

[amberleaf]

Borrowed Neutral . is an infringed by this practice . ?? British ( Standards )

Situation where a Neutral is wired across two or becomes live once you switch the circuit off that you are working on, effectively reversing the live conductor 230V to the neutral part of the circuit you thought you had just isolated.

(( Borrowed Neutral )) it may already be a killer and not know it. ( it's still out there ) cleaning someone also mess .

Regulation 314.4. recap :
Where an installation comprises more than one circuit , each final circuit shall be connected to an separate way in a Distribution-board . Consumer-unit .

The wiring of each final circuit shall be electrically separate from that of every other final circuit . so as to prevent the indirect energizing of a final circuit intended to be isolated .

 

[amberleaf]

Blast from the Past . Extracts

16th Edition ◄► . Isolating timer Fans ..

Does BS-7671 require items of electrical equipment to be isolated locally ?

The answer is that there is no specific requirement for equipment to be isolated locally. However, careful consideration must be given to the positioning of isolating devices.

While it is important that all the requirements of BS-7671: regarding isolation are adhered to, the following comments regarding the isolation of single-phase electrical equipment are offered for consideration:

Regulation 461-01-01 requires that each circuit must be capable of being isolated from each of the live supply conductors, except as required by Regulation 460-01-04, which states that, for TN-S or TN-C-S systems, the neutral conductor need not be isolated.

Regulation 537-02-02 permits the use of overcurrent protective devices, such as circuit-breakers to BS-EN-60898-1 and RCBOs to BS-EN-61009, to be used as isolators.

Remote isolation
Where isolation is remote, precautions must be taken to prevent equipment from being inadvertently or unintentionally energised (Regulations 461-01-01 and 476-02-02). This effectively means that overcurrent devices must be capable of being locked in the off position.

Where rewireable fuses to BS-3036 are used, the fuse controlling the circuit to be isolated could be removed and put in a safe place where it could not be replaced without the knowledge of the person working on the circuit.

This means of isolation would not be suitable for isolating a timer fan in a windowless room because, in isolating the fan, the lighting circuit which supplies it is also isolated

The artificial light in a windowless room has been switched off when work is to be carried out on the fan. A lead light could be used to provide light but this introduces a trip hazard. ( PS, buy a head torch .. LED )

Three-pole isolating switch is your ( Practical solution ) Safe isolation . in the case of timer fans in windowless room it is recommended in the interests of safety.

 

[Richard Burns]

For Amberleaf:
BS-7671:2008: Requirements for electrical installation(s) ... 542.4.

Main Earthing Terminal MET)

Disconnection of ..........

1 ) Means for disconnecting the earthing conductor

Regulation 542.4.2 of BS-7671 requires means for disconnection of the earthing conductor be provided at or near the Main Earthing Terminal (MET) of an installation. The purpose of the means of disconnection is to allow measurement of the external earth fault loop impedance ( Ze ) and, where the installation forms part of a TT system , measurement of the installation earth electrode résistance.

Regulation 542.4.2 is reproduced as follows for ease of reference

Regulation 542.4.2
‘ To facilitate measurement of the resistance of the earthing arrangements, means shall be provided in an accessible position for disconnecting the earthing conductor. Such means may conveniently be combined with the main earthing terminal or bar. Any joint shall be capable of disconnection only by means of a tool. ‘
As Regulation 542.4.2 does not stipulate a particular arrangement for the means of disconnection, any suitable arrangement may be used which meets all the requirements stated in the regulation. Examples of suitable arrangements are given in Figures 1 and 2.

Fig 1, shows an arrangement in which the earthing conductor is withdrawn from its terminal at the MET, by the use of a tool (a screwdriver), in order to facilitate the resistance measurement of the means of earthing, and then replaced and re-secured into the terminal after the measurement has been made. This arrangement is not suitable for situations where the end of the earthing conductor at the MET cannot be conveniently manoeuvred, such as within an enclosure in which there is insufficient room or where the diameter of the earthing conductor is too large to provide sufficient flexibility.

Fig 2 , shows an example of a MET incorporating a bolted link which is opened or removed by the use of a tool ( such as a spanner ) in order to disconnect the earthing conductor, and then reinstated and re-secured after the resistance measurement to the means of earthing has been carried out.

Whatever arrangement is provided as the means for disconnection of the earthing conductor, in addition to the requirements of Regulation 542.4.2 mentioned earlier, the requirements of the Electricity at Work Regulations and those of Section 522 of BS-7671 must be met.

Regulation 9 of the Electricity at Work Regulations requires that ‘ if a circuit conductor is connected to earth or to any other reference point, nothing which might reasonably be expected to give rise to danger by breaking the electrical continuity or introducing high impedance shall be placed in that conductor unless suitable precautions are taken to prevent that danger ’.

For example, where a joint or bolted link is provided, it must be arranged to ensure the integrity of the conductor. The connection or link must not be able to be removed in such a way as would give rise to danger. Ways of achieving this would normally include one or more of the following:

• Disconnection requires a deliberate act using a tool .... This is an explicit requirement of Regulation 542.4.2
• The joint or link should be accessible only when the installation is isolated
• The joint or link should be accessible to skilled persons only

• Section 522 of BS-7671 requires that the means for disconnection must be protected where necessary against external influences (such as vandalism, unauthorized interference, damp, corrosion, dust, vibration or mechanical impact).

Earthing conductor at the MET. Earthing conductor is withdrawn from its terminal for testing purposes. Withdrawal is a deliberate act involving the use of a tool.

Example of MET with disconnectable link

Testing : ( MET )
542.4.2. To facilitate measurement of the résistance of the earthing arrangements ,
Mean's ; shall be provided in an accessible position for disconnecting the ( Earthing-conductor ) Such means may conveniently be combined with the main-earthing-terminal or bar .

Any joint shall be capable of disconnection only by means of a tool .
Main Earthing Terminal : (MET)

1. The requirement to have a Main Earthing Terminal (MET)
Regulation 542.4.1 of BS-7671 requires a Main Earthing Terminal (MET) be provided for every installation.
The MET is required to connect the following to the earthing conductor of the installation, as illustrated in Fig 1 (Regulation 542.4.1 refers):

i) The circuit protective conductors
ii) The protective bonding conductors
iii) Functional earthing conductors (if required)
iv) Lightning protection system bonding conductor, if any (see Regulation 411.3.1.2).

MET connecting various conductors to the earthing conductor, as required by Regulation 542.4.1.

For practical reasons, the MET is normally situated at or near the origin of the installation (that is, the position where the electrical energy is delivered)

(Means of earthing) ....................... TN- TT systems

Example of the use of the earthing bar as a MET in an item of main switchgear

R/P 26
Distribution board :
An assembly containing switching or protective devices ( e.g. fuses , circuit-breakers , residual current operated devices ) associated with one or more outgoing circuits fed from one or more incoming circuits , together with terminals for the neutral and circuit-protective-conductors . refer

R/P 25
Consumer unit : .. ( CCU )
may also be known as a consumer control unit or electricity control unit . refer

Examples of brass terminal bars or blocks used as a MET


MET incorporating a bolted link to permit the disconnection of the earthing conductor for testing purposes

 

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Verification of earth fault loop impedance test - results .. ( Implications )

Verification : R/P 36
All measures by means of which compliance of the electrical-installation with the relevent requirements of BS-7671: are checked , comprising inspection , testing and certification .

612.1. recap
it is important to recognise that BS-7671: requires the inspector not only to test the installation but also to compare the results ;
with relevant design criteria ( or with criteria within BS-7671: )

On the question of danger from any test .. this must be assessed by the Inspector for the given situation .

Earth fault loop impedance testers . BS-EN-61557-3 . ( Part 3 )

( Earth-fault-loop ) in the eyes of C&Gs .. Verification
Reason : this instrument functions by creating , in effect an Earth-fault for a brief moment . Instrument should only allow an Earth-fault to exist for a maximum of ( 40mS )

4.5. GN-3 has advocated , This means that the instrument should cut off the test current after ( 40mS )

Connected to a circuit via , a Plug .. ( Circuit-loop ) 612.9. ( Zs )
By " flying leads " connected separately to Line , Neutral , Circuit-protective-conductor .

612.9. Where protective measures are used which require a knowledge of earth-fault-loop-impedance ... The relevant impedances shall be :
Measured

Reporting : R/P 33 . Communicating the results of periodic inspection and testing of an electrical installation to the person ordering the work .

Periodic testing : 3.10.
621.2. The periodic testing is supplementary to the inspection of the installation

3.8. Requirements for inspection & testing
The purpose of periodic inspection and testing is to provide an engineering view on whether or not the installation is in a satisfactory condition where it can continue to be used in a safe way .

if you have conducted the inspection & test of an installation thus far correctly , then you should have already carried out a form of polarity test .
You have done this using your senses during the inspection , prior to picking up an instrument .

re-cap Inspection: R/P 29 .
Examination of an electrical installation using All the senses as appropriate .

Polarity : 2 different scenarios ... ( Dead or Live testing ) that require a polarity test
- origin of the installation ... The polarity of the main-supply must be correct .
- distribution boards ... The polarity of the main-supply must be correct .
- accessible socket-outlets .
- extremity of radial circuits ... All polarities of socket outlet(s) must be verified

Testing to be carried out where practicable on existing-installations ......... ( protective-conductor(s)
Earth fault loop impedance , At the following positions :
- origin of the installation .
- distribution boards .
- accessible socket-outlets .
- extremity of radial circuits . ( contd )

R/P 27 . Electrical-installation ( abbr : Installation ) An assembly of associated electrical equipment having co-ordinated characteristics to fulfil specific purposes .

 

[Richard Burns]

For Amberleaf
Diagrams


General


1) Introduction
2) Identification of site services
3) Requirements of BS-7671
3.1 ) Simple installations
3.2 ) Large complex installations


Introduction
Every electrical installation should be provided with appropriate documentation for operational, maintenance, fault finding, inspection, testing and safety reasons. Such documentation, for example, might include:


- single line (or schematic) diagrams
- circuit charts or circuit schedules
- certification and reports
- information for satisfying the relevant parts of the Electricity at Work Regulations 1989 (EWR), such as risk assessments, method statements and isolation procedures, as appropriate


This topic addresses the requirements of BS-7671 for providing diagrams for identification of circuits and equipment in electrical installations.


Identification of site services
For most industrial and commercial installations it is important to be able to identify exactly where hidden services, such as supply cable routes, water services and gas services are located. Without such identification, any site excavation work could cause damage to those services and, more importantly, cause injury or death to persons carrying out such works. Accurate records, including drawings, should preferably be made at the time services are being installed before trenches are backfilled and hidden from view. However, such records are not generally required for the purpose of identifying services in installations in domestic premises.
Where required, cable routes should be identified on drawings to accurately record their position. This may be achieved, for example, by recording the distance from some fixed object that is not expected to change for the foreseeable future, such as a building. A typical drawing showing the position of cable routes and other services is shown in Fig 1.


Example of site layout diagram identifying routes and positions of cables and other services

Requirements of BS-7671


A legible diagram, chart or table or equivalent form of information is required by Regulation 514.9.1 to indicate:


i) the type and composition of each circuit (points of utilisation served, number and size of conductors, type of wiring)
ii) method used for protection against electric shock for compliance with Regulation 410.3.2
iii) the information necessary for the identification of each device for performing the functions of protection, isolation and switching, and its location
iv) any circuit or equipment vulnerable to a particular test, such as computer and communications equipment


for simple installations the foregoing information may be given in a Schedule , A durable copy of the schedule relating to a distribution board shall be provided within or adjacent to each distribution board .


There are several ways of providing the aforementioned information depending on whether the installation is simple or a more complex one. Examples of how to provide the information required by Regulation 514.9.1 for a simple installation and a complex installation are given in items 3.1 and 3.2, respectively.


3.1. Simple installations
For smaller installations, such as in a domestic premises, the information required by Regulation 514.9 (see item 3) may be provided in a circuit schedule. In such cases, the schedule should be legible and be adequately protected from damage or deterioration, for example, by enclosure in a clear plastic folder. Nevertheless, the completed schedule should be fixed within or adjacent to the distribution board or consumer unit. A typical example of a schedule, using a copy of the Schedule of Test Results, based on the model form given in Appendix 6 of BS-7671 is shown in Fig 2 .
Example of completed Schedule of Test Results based on model form in Appendix 6 of BS-7671



3.2. Large complex installations
Providing a completed copy of one or more circuit schedules is unlikely alone to be sufficient for large complex installations, such as an installation in industrial or commercial premises. For those installations, comprehensive information, including site layout diagrams, schematic diagrams, circuit diagrams, cable route plans, as-fitted diagrams are generally required to accompany a series of circuit schedules (refer item 3.1). An example of a typical single-line diagram showing such additional information is shown in Fig 3.
Example of single-line diagram showing installation layout

Diagrams .. 514.9

 

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What's in a Question . ??

Domestic accommodation - general .. Change of occupancy / 10 years .
Domestic accommodation - rented house and flats .. Change of occupancy / 5 years .

GN-3 3.5. Routine checks
Electrical installations should not be left without any attention for the periods of years that are normally allowed between formal inspections . In domestic premises .. refer

Q) An domestic installation has been in use for 10 years . Which test procedure is most appropriate
i) minor works
ii) initial verification

Recommended initial frequencies of inspection of electrical installation(s) .. Note 8 .

A) iii) periodic inspection & test ..
GN-3 table 3.2. Maximum period between inspections & testing .

8 , The person carrying out subsequent inspections may recommend that the interval between future inspections be increased or decreased as a result of the findings of their inspection .

10 , The Landlord & Tenant Act 1985 requires that properties under the Act have their services maintained . Periodic inspection & testing is the IET recognised method of demonstrating this .

iv) portable appliance testing

3.7. Frequency of periodic inspections
Extracts :

In short the inspector being a competent person should apply engineering judgement when deciding upon intervals between inspection and testing an installation and may use the recommendations of table 3.2.

in the case of domestic & commercial premises , a change in occupancy of the premises may necessitate additional inspection and testing .

The formal inspections should be carried out in accordance with Chapter 62 of BS-7671:
621.2. This requires an inspection comprising a detailed examination of the installation , carried out without dismantling or with partial dismantling as required , together with the appropriate tests of Chapter 61 .

 

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Q) your on your own . C&Gs .. During an inspection and test a dangerous condition is noticed , What is the correct procedure . ??

Q) What does not form part of ( test documentation )

Your Q , This Safety certificate has been issued to confirm .. etc
R/P 392 . (2) This Certificate is only valid if accompanied by the Schedule of Inspections & the Schedule(s) of test Results

re-cap ; ( Generic ) Schedule of test Results

i) Electrical installation certificate .. ( EIC )
ii) Test result schedule
iii) Inspection schedule
iv) designer's specifications ..

 

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Q) What is not acceptable for an Earth-electrode . A) you're call !!

i) Rods and tape
ii) Earth plates
iii) Lead sheath of supplier's cable .
iv) Underground water pipes .

542.2. Earth electrode(s)
542.2.3. Suitable earth electrodes shall be used . The following types of earth electrode are recognized for the purpose of the Regulations :
i) Earth rods or pipes .
ii) Earth tapes or wires .
iii) Earth plates .
iv) Underground structural metalwork embedded in foundations .
vi) Lead sheaths and other metal covering of cables , where not precluded by Regulation 542.2.5.

542.2.5.
The use , as an earth electrode . of the lead sheath or other metal covering of a cable shall be subject to all of the following conditions :
i) Adequate precautions to prevent excessive deterioration by corrosion .
ii) The sheath or covering shall be in effective contact with Earth .
iii) The consent of the owner of the cable shall be obtained .
iv) Arrangements shall exit for the owner of the electrical installation to be warned of any proposed change to the cable which might affect its suitability as an earth electrode .

542.2.6.
A metallic pipe for gases or flammable liquids shall not be used as an earth-electrode . The metallic pipe of a water utility supply shall not be used as an earth-electrode . refer

 

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Manufactures' instructions ( LD3 )
Optical
Ionisation
Heat

Interconnecting Alarms
in the UK it is recommended that the following coloured cores are used .. for example with triple flat 6243Y cable

230V supply .. Brown
Neutral .. Gray / sleeved blue at terminations . ◄
Interconnect .. Black .

 

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528 Proximity of Wiring Systems to Other Services
528.1. proximity to electrical services

Voltage Bands . P/36
Defined in Part 2 BS-7671:

Band I ( ELV ) extra low voltage .
Not exceeding 50V a.c. or 120V ripple-free d.c. whether between conductors or to Earth .

whereas power wiring operating at 230V/400V is classified as Band II .
Low . Exceeding extra-low voltage but not exceeding 1000V a.c. refer .

Section 528 sets out the requirements where cables of different voltage bands are to be run in close proximity , requiring either all associated cables to be rated to the highest voltage present ;

Regulation 528.1 (i) or segregation provided between cables of different bands . (iii) , (iv) , (v) or (vi)

528.1. proximity to electrical services
(i) Every cable or conductor is insulated for the highest voltage present .
(iii) The cables are insulated for their system voltage and installed in a separated compartment of a cable ducting or cable trunking system .
(iv) The cables are installed on a cable tray system where physical separation is provided by a partition .
(v) A separate conduit , trunking or ducting system is employed .

(vi) For a multicore cable , the cores of the Band I circuit are separated from the cores of the Band II circuit by an earthed metal screen of equivalent current-carrying-capacity to that of the largest core of a Band II circuit .

 

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Band II P/36

Band II contains the voltages for supplies to household and most commercial and industrial installations .
Low voltage ( LV ) will normally fall within voltage Band II .

Note : Band II voltages do not exceed 1000V a.c. rms or 1500V d.c.

 

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Further detectors might be necessary if a risk assessment justifies their provision .

Scope
This part of BS-5839 gives recommendations
The recommendations apply to both new & existing domestic premises.

Fire detection and fire alarm systems for buildings

BS-5839-6 : Fire detection and fire alarm systems for buildings , Part - 6 Code of practice for design , installation . commissioning and maintenance of fire detection and fire alarms systems in domestic premises .

Normative References
The following references have been amended;

BS 5839-1:2013, Fire detection and fire alarm systems for building(s) Part - 1: Code of practice design, installation, commissioning and maintenance of systems in non-domestic premises

 

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Limitation of false alarms

12.2 Recommendations

iv) In Grade D and E systems, means should be provided for silencing fire alarm signals that result from, for example, a fault in a detector. This may comprise a means for isolation of mains power to the detector.

Since such faults are likely to be relatively rare, it is acceptable for the means of isolation to involve the use of a tool. However, isolation of power to any detector should not result in isolation of power to other electrical equipment, such as lighting, in the premises.

Note 1 , A number of manufacturers use a fixed base for the electrical connections, and the smoke or heat alarm can be readily removed by use of a tool-operated release tab, et

6 Monitoring of circuits

6.2 Cont.
Note : This standard contains no recommendations for monitoring of wiring or power supplies in Grades D, E or F systems. However, BS-EN-14604 requires that mains-powered smoke alarms (which are used in Grades D and E systems) incorporate a green mains-on indicator, which is continuously illuminated when mains power is present. BS-5446-2 makes the same requirement for heat alarms.

 

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Generally, doors are considered the weak link in sound reduction but caution is needed with this assumption

► BS 5839-6 , recommends that, if an audible alarm is intended to rouse sleeping persons, a sound level of 75 dB(A) ought to be achieved at the bedhead when all doors are shut, although this will not guarantee that every person will be awakened, particularly if they are under the influence of alcohol or drugs.

 

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Categories of System :
There are three Categories of ( LD ) systems for Life protection in Dwellings that can be installated , depending on the fire Risk & Regulations .

Point to Note :
BS-7671:2008 + Amd 1 2011: (( Electrical Connections ))
526.6. There shall be no appreciable strain on the connections of conductors .

 

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They are a reason for me downloading this Stuff . I'll make it clear shortly . off to work

Standards in Approved Document B Building Regulations for flats , thus intended for stay put fire policy then only the part 6 devices are required

The only time this can be viewed differently is when there is a duty of care toward the occupants of the dwelling
landlord(s) has a duty of care

Commentary in ( Part - 6 )

13.1.2. Audibility ))

A fire detection and fire alarm system only provides satisfactory protection of life if it is capable of rousing the principal occupants of the dwelling from sleep (e.g. the adult occupants in a typical single-family dwelling). No particular sound pressure level is certain to rouse all occupants of a dwelling in all circumstances. Depth of sleep varies during the course of the sleep period and also varies from one person to another. Greater sound pressure levels are often required to rouse children from sleep than are necessary in the case of adults. BS 5839-1 recommends that, if an audible alarm is intended to rouse sleeping persons, a sound level of 75 dB(A) should be achieved at the bedhead when all doors are shut, although this will not guarantee that every person will be awakened, particularly if they are under the influence of alcohol or drugs.

Most fire detection and fire alarm systems in dwellings comprise smoke alarms, which are usually fitted in, at least, the circulation areas, such as hallways and landings. BS 5446-1:2000 requires that the sound output of a smoke alarm be at least 85 dB(A) at three metres. Most domestic doors attenuate sound by around 20 dB; greater attenuation can occur in the case of solid doors, such as fire doors. It is therefore unlikely that a smoke alarm on, for example, the upstairs landing of a two-storey house will produce a sound level of 75 dB(A) at the bedhead in each bedroom, particularly if the bedroom doors are shut; levels of 55 dB(A) to 65 dB(A) are more likely. There appears to be no evidence to show that lives are being lost due to inadequate audibility of the fire alarm signal from smoke alarms, except where people are incapacitated to such a degree that even much higher sound levels would not waken them. This might be because, in their own homes, people can be roused by an unusual sound of relatively low level compared with the sound level that may be required to wake them in premises with which they are unfamiliar (e.g. a hotel).

BS-5839-6 : Fire detection and fire alarm systems for buildings , Part - 6 Code of practice for design , installation . commissioning and maintenance of fire detection and fire alarms systems in domestic premises .

BS-5839-6 :2013: Fire detection and fire alarm systems for buildings . Code of practice for the design , installation , commissioning and maintenance of fire detection and fire alarms systems in domestic premises .

BS-5839-6 :2013: give recommendations for the planning , design , installation , commissioning and maintenance of fire detection and fire alarms systems in domestic premises that are :

□ Designed to accommodate a single family
□ Houses in multiple occupation that comprise a number of self-contained units , each designed to accommodate a single family
□ Sheltered housing , including both the domestic units and the common areas

the recommendations apply the both New & Existing domestic premises

Recommendations for routine attention are also given.
The systems covered in BS-EN-5839-6 : 2013 range from those comprising a single self-contained smoke alarm to systems of the type described in BS-5839-1 . The recommendations of this part of BS-5839 may also be applied to the fire detection components of combined domestic fire and intruder alarm systems or fir and social alarm systems .

BS-5839-6 :2013: applies to forms of domestic premises , including bungalows , multi-storey houses . individual flats and maisonettes , mobile homes , sheltered housing , housing providing NHS supported in the community ( as defined in Heath Technical Memorandum 88 [1]) mansions , shared houses and houses divided into several self-contained single-family dwelling units . it does not apply to hostels , caravans or boats ( other than permanently moored boats used solely as residential premises ) or to the communal parts of blocks of flats or maisonettes . it does not apply to any premises used for purposes other than as ( domestic premises ) e.g. small shops , factories or similar premises used solely as places of work /

BS-5839-6 :2013: is intended for , Etc installers and other responsible for implementing fire precautions in domestic premises , it is not intended for occupiers , for whom advice is published by the Government . However , recommendations are given for simple systems that may ne installed by non-specialists

The recommendations refer principally to fire detection and fire alarm systems installed for the purpose of life safety . However , recommendations are given for systems that are also intended to protect property .

Supersession :
This part of BS-5839-6: 2013 . supersedes BS-5839-2:2004 . which is withdrawn .

 

[Richard Burns]

Refer post 797 and 799 re sound output of smoke alarms at bedhead