Re-take - Useful Information for 2394 :

[amberleaf]

Guide to Fire Detection & Alarm systems . 2013.

Grade D System:

Cables : Standard in accordance with BS-7671:
Standby supply : Required either primary battery or more usually secondary battery or capacitor .

Supply : An independent circuit not supplying other equipment or regularly used lighting-circuit should be used ( Clause 15.5 ) The isolator of an independent circuit should be labelled “ Smoke Alarms Do Not Isolate “

When a regularly used lighting-circuit supplies the smoke alarms there should be a means of isolating the fire alarms whilst maintaining the lighting labelled “ Smoke Alarms Do Not Isolate “ unless the smoke alarms can be removed from their mounting-plates .

Interconnection : Required with standard cables per BS-7671 colour-coded .

Note : Interconnected smoke alarms etc. . must be connected to the same circuit .

House in multiple occupation with smoke & heat-alarms in common parts : smoke & heat alarms in common parts and smoke & heat alarms in dwellings with pre-payment-meters should be supplied from a permanent landlord’s supply . Then permanent notices should be displayed adjacent to any consumer unit etc. in the dwelling , which states “ Caution . Smoke Alarms Are Not Connected To This Circuit . Isolation / Switching Off At This Point , Or Having No Credit On The Meter , Does Not Isolate The Electrical Supply To The Smoke Alarm “

 

[amberleaf]

All there is to known ( radio linked systems )

( BR ) 2013: 4.4.3 Note : Smoke alarms may be interconnected using radio links , provided that this does not reduce the lifetime or duration of any standby power supply to below 72 hours .

4.4.9. Radio links
Mains - powered smoke alarms may be interconnected by radio links. Provided the lifetime or duration of the standby supply is not reduced to below 72 hours. If these conditions are met the smoke alarms may be connected to different circuits ( as there is no need to isolate all the alarms to work on one )

7.11. Radio Linked System … ( BS-5839-1 Clause 27 )
The Standard recognises that radio linked systems cannot comply with all the requirements for hard-wired systems and that there are advantages & disadvantages in both systems. it is likely that the demand for radio-linked systems will grow , particularly because of the relative ease of installation in existing buildings .

Systems cannot be completely designed from drawings ; it is necessary to test on site . Booster aerials may be required on completion .
Radio links can be used for almost all elements of the system including detectors , manual call points , and sounders . Their advantage and disadvantages are summarised
Advantage and Disadvantages of radio linked systems

Advantages : Reduced hard wiring … Comments : Particularly easy to install in existing buildings
Flexible … Easy to change locations and add elements ( sounders , call points etc. )

Disadvantages :
Interference
Variable signal strength … Comments : Needs to test on site before and after installation
Low-frequency electromagnetic radiation … Comments : Some customers may have concerns
Reliance on batteries … Comments : Cost of periodic battery replacement

 

[amberleaf]

The Electrical Installation 2013 . Fire Detection & Alarm System's

The requirements for the electrical installation in terms of cable types and segregation as well as the main and standby supplies depend upon the system grade

Which summarises the requirements

Electrical supply and wiring requirements of BS-5839-6 dwellings ... ( Clause 15 & 16 )

Grade A : Power supply ( Clause 15 )
A mains supply final circuit's to all parts of the fire alarm system dedicated solely to the fire alarm system , Switches and protective device to be labelled " Fire Alarm : Do Not Switch Off .

Grade A : Standby supply
The standby supply should be capable of automatically maintaining the system in normal operation ( whilst giving an audible and visual indication of mains failure ) for a period of 72 h , after which sufficient capacity should remain to supply the maximum alarm load for at least 15 minutes , Secondary battery to have an automatic charger .

Wiring ( Clause 16 ) Cables and cable support systems ( fixings , conduit , trunking ) used for all parts of the critical signal paths and for the final circuit providing low-voltage mains supply to the system should be fire-resisting , This can be achieved by ensuring either that cables are fire resisting or that cable and cable support systems ( fixings , conduit , trunking ) are fire-resisting . ( * ) ◄

Cable segregation
Fire alarm cables to be segregated from cables of other services by , for example :
1 ) Not installing in the same conduit or trunking unless " strong " compartments are used .
2 ) Use of separate sheathed multicore cables .
3 ) Physical separation . Fire cables to be identified by colour .

Grade B : Power supply ( Clause 15 ) As for A ,
Standby supply , As for A
Wiring ( Clause 16 ) As for A - No special requirements
Cable segregation - No special requirements

Grade C : Power supply ( Clause 15 ) As A but may also supply an integral intruder alarm . The isolating protective device should be labelled " Fire / Intruder Alarm : " Do Not Switch Off "

Standby supply
As for A , the standby supply should be capable of automatically maintaining the system in normal operation for a period of 72 h , ( whilst giving the fault warnings ) but after which sufficient capacity should remain to support the maximum alarm load for 4 min .

Wiring ( Clause 16 ) - No special requirements
Cable segregation - No special requirements

Grade D : Power supply ( Clause 15 )
An independent circuit at the dwelling's main distribution board , in which case no other electrical equipment should be connected to this circuit ( other than a dedicated monitoring device installed to indicate failure of the mains supply to the smoke alarms and any heat alarms ) or a separately electrically protected , regularly used local lighting circuit .

Standby supply : As for C
Wiring ( Clause 16 ) - No special requirements
Cable segregation - No special requirements

Grade E : Power supply ( Clause 15 )
The mains supply to smoke alarm(s) and any heat alarms in a Grade E system should comprise a single independent circuit at the dwelling's distribution board . No other electrical equipment should be connected to this circuit ( other than a dedicated monitoring device installed to indicate failure of the mains supply to the smoke alarms and heat alarms )

Standby supply , None
Wiring ( Clause 16 ) - No special requirements
Cable segregation - No special requirements

Grade F : Power supply ( Clause 15 )
The batteries of smoke alarms and any heat alarms in Grade F systems should be capable of supplying the quiescent load of the smoke alarm or heat alarm , together with the additional load resulting from routine weekly testing , for at least one year before the battery fault warning is given , At the point at which the battery fault warning commences , the battery(ies) should have sufficient capacity to give afire alarm signal for at least 4 min or , in the absence of a fire , a battery fault warning for at least 30 days .

Power supply ( Clause 15 ) None .
Wiring ( Clause 16 ) - Not applicable
Cable segregation - Not applicable

( * ) Comprise either
1) Mineral insulated copper sheathed cables , with an overall polymeric covering , conforming to BS-EN-60702-1 with terminations conforming to BS-EN-60702-2
2) Cables that conform to BS-7629 specification for 300/500V fire resistant electric cables having low-emission of smoke and corrosive gases when affected by fire .
3) Cables that conform to BS-7846 Electrical cables - 600/1000V armoured fire-resistant cables having thermosetting insulation and low emission of smoke and corrosive gases when affected by fire .
4) Cables rated at 300/500V ( or greater ) that provide the same degree of safety to that afforded by compliance with BS-7629 .

 

[Richard Burns]

Aico Ei1529RC , has its points .


Fire Alarm Control Switch .
230V Remote Locate, Silence & Test Control Switch - Ei1529RC


• The Test switch allows the user to test the Alarms easily, without having to access the Alarms on the ceiling. **
• Easy installation with 3 core cable: live, neutral and interconnect/control


All the units that can interconnect with the EI1529RC.


Ei141RC ..Ionisation Alarm ..Hard wire interconnection
Ei144RC.. Heat Alarm.. Hard wire interconnection
Ei146RC ..Optical Alarm ..Hard wire interconnection


• The Remote Control should be wall mounted at standard light switch level ( 1.2m from floor level ) to allow easy access. **


Siting : - Ei1529RC .. 2010.
Position the Remote Control in a location that will allow it to be easily accessed. In the majority of installations this will be in a hallway, possibly next to the master bedroom. It should be installed at the standard light switch height ( 1.2m from floor level ).
If a metal back-box is used it must have a minimum depth of 35mm. Up to four Ei1529RC System Remote Controls can be used in a system


Note: The Ei1529RC Remote Control can be wired from any location within the system. **

The Test switch allows the user to test the Alarms easily, without having to access the Alarms on the ceiling. ◄◄◄


Wiring in some Ionisation Alarms, Heat Alarm, Optical Alarm, Hard wire interconnection. ( LD3 )
► Disabled person by using the Ei1529RC Siting it (1.2m from floor level) to allow easy access


Ei1529RC Can be used in shops with High Ceilings, without having to access the Alarms on the ceiling ( Fire & Safety Officer asked for LD3 )


- The locate option silences all the alarms except the initial activating alarm allowing easy identification of the source of the fire
- The test option will activate all the alarms
- The hush option will temporarily silence any false alarm
- Auto-reset within 10 minutes for locate and hush

 

[amberleaf]

Appendix 12 of BS-7671:2008:
Appendix 12 of BS-7671:2011: Moved Appendix 4 sec 6.4 P421

Taken from Extracts
Verification of voltage drop : 2008:

Verification of voltage drop is now covered in BS-7671, with the introduction of BS-7671:2008
Regulation 612.14 refers .

Note : Verification of voltage drop is not normally required during the initial verification of either a new installation or an alteration or addition to an existing installation. This is because the designer of the electrical work should have sized the circuit conductors so that the voltage drop requirements of Section 525 of BS-7671:2008 are met , having regard to the circuit lengths and design currents .

However , in the case of periodic inspection and testing of an existing installation, the inspector may judge it necessary to verify the voltage drop for a particular circuit ( or circuits ) if he or she has doubts that the voltage drop requirements of section 525 are met for the circuit . This may be case, for example , where there is evidence that a circuit has been extended or that additional load has been connected or it .

a detailed explanation of the voltage drop requirements of Section 525 is beyond the scoop of this book . However , as given in Regulation 525.3 the requirements of Section 525 are deemed to be met if the voltage drop between the origin of the installation ( usually the supply terminals ) and a socket-outlet or the terminals of fixed current using equipment does not exceed that stated in Appendix 12 of BS-7671 For a low voltage installation supplied directly from a public low voltage distribution system , Appendix 12 gives maximum voltage drop of ( 3% ) for lighting circuits and ( 5% ) for other circuits , Greater voltage drop than given in Appendix 12 may be accepted for a motor during starting periods and for other equipment with high inrush currents . Also as before , a higher voltage drop may be accepted for a motor during starting conditions and for other equipment with high in rush currents , provided it is verified that it is acceptable for the equipment ( Regulation 525.4 ) refers

Regulation 612.14 lists the following two ways to verify the voltage drop for a circuit.
• Evaluate the voltage drop by measuring the circuit impedance
• Evaluate the voltage drop using calculations

Evaluation of voltage drop by measuring circuit impedance ( worked example )
Suppose that it is desired to verify that the voltage drop does not exceed ( 5% ) in an existing single-phase 230V 50Hz radial circuit supplying a 20A heating load connected at the end of the circuit . The circuit is supplied directly from distribution board at the origin of the installation . The line and neutral conductors of the circuit have thermoplastic ( pvc ) insulation and their résistance ( R[SUP]1[/SUP] + R[SUP]n[/SUP] ) is 0.3Ω when measured at ambient temperature ? 20°C

As the circuit rating does not exceed ( 100A ) and the supply frequency is 50 Hz . ( R[SUP]1[/SUP] + R[SUP]n[/SUP] ) may be taken to be the circuit impedance ( that is , inductive reactance maybe ignored )

To evaluate the voltage drop , the measured value of ( R[SUP]1[/SUP] + R[SUP]n[/SUP] ) should be increased on the basis of the increase in conductor temperature due to load current , and then multiple by the design current of the circuit ( Ib ) In the absence of better information , a correction factor of ( 1.2 ) should be used to increase the conductor résistance in this case . This assumes an increase in conductor temperature from ( 20°C ) ambient to ( 70°C ) , the maximum permitted operating temperature for thermoplastic insulated conductors .

The voltage drop ( Vd ) for the single phase circuit in this example is (\) therefore given by :
( Vd ) = measured value of ( R[SUP]1[/SUP] + R[SUP]n[/SUP] ) x 1.2 x Ib
therefore (\) Vd = 0.3Ω x 1.2 x 20A = 7.2V

A voltage drop of ( 7.2V ) is equivalent to ( 3.13% ) given by 100% x 7.2V ÷ 230V . it has therefore been verified that , in the case of this example , the voltage drop in the circuit does not exceed ( 5% )

Evaluation of voltage drop using calculations ( Worked example )
The calculation method mention in Regulation 612.14 , as an example , is to use diagrams or graphs showing maximum cable length versus load current for different conductor sizes with different percentage voltage drops for specific nominal voltages, conductor temperatures and wiring systems .

In the absent of such diagrams or charts , the voltage drop for a circuit may be calculated by using the tabulated values of voltage drop given in Appendix 4 of BS-7671: in accordance with the instructions given in item 6 of that appendix , To do this , it will be necessary to ascertaining the type and size of cable by inspection , and to estimate the length of run for the circuit .

 

[amberleaf]

Maximum earth fault loop impedance values for overcurrent protective devices in common use , ( for Fault Protection )
Extracts :

Why do you need to test , Earth-fault-loop-impedance !! .... Under Earth fault conditions RCD will trip out before 0.04s .

Under earth-fault-conditions , a circuit which relies on the protective measures ( ADS ) for fault protection is generally required to be disconnected under fault conditions within the maximum time permitted by BS-7671: for that type of circuit or location .

Tables 41.2 , 41.3 , 41.4 of BS-7671: give the maximum permitted values of ( Zs ) for different types of overcurrent protective devices and different maximum permitted disconnection times .

A indicated above , it is generally necessary to adjust the values obtained by the test before comparing them with the maximum permitted values given in BS-7671: This is because the values referred to in BS-7671: are based on the conductors having been heated up by the passage of load current , which increases their résistance , whilst test results are usually obtained when the conductor temperature is somewhat lower . Detailed advice on correction factors is given on IET Guidance Notes 3 & 6 .

Alternatively , as a rule of thumb , the measured value of ( Zs ) should not exceed ( 0.8 times ) the relevant value given in BS-7671: such as in Tables 41.2 and 41.4.

limiting values of measured earth fault loop impedance when measured at ambient temperatures up to ( 20°C ) These limiting measured values are based on ( 80% ) of the values given in BS-7671: for ( 0.4 second & 5 second disconnection ), as appropriate .

Note : that the value to be recorded in the schedule of test results is the measured value .
if the protective device is not of a type whose maximum permitted ( Zs ) value is given in BS-7671: then , as a rule of thumb , the measured value should not exceed ( 0.8 times ) the value given by the formula on the first page of Appendix 3 of BS-7671:

2008: 243
2011: 295

 

[amberleaf]

Working like a Trojan , don't have much spare time . Hi Karl

Re-cap

O.S.G. reminds us - The use of RCBOs will minimize inconvenience in the event of a fault and is applicable to ALL systems
RCBO - type of protective-device
Overload .
Short-circuit .
Earth-fault .

O.S.G. P/70 Choice of protective-device .
The selection of protective device ( Depends upon )
i) prospective fault current
ii) circuit-load characteristics
iii) cable current-carrying-capacity
iv) disconnection time limit

O.S.G. P/80 There is no general requirements to ensure electrical continuity across the metallic frame of an item of furniture unless the frame has been designed to be used as a protective-conductor . 543.2.1. , 543.2.6.

 

[amberleaf]

Why we do certain tests .
The regulation's tells us " Initial Verification "

Why do we need to test the continuity of protective conductor's
612.2.1. Continuity of protective conductors including main protective bonding conductor's
17th Edition - Supplementary protective bonding conductor's (where required )

it is essential to ensure that all circuit-protective-conductor's & main protective bonding conductor's are continuous .
otherwise , an exposed-conductive-part , an extraneous-conductive-part or the earth-terminal of a point or accessory could be left without an effective connection to Earth , giving no ( Fault-protection ) in the event of an earth-fault .

Fault-protection : Comprises
411.3.1.1. • Protective-earthing .
411.3.1.2. • Protective-equipotential-bonding .
411.3.2. • Automatic-disconnection in case of a fault . ADS

Fault protection is provided by limiting the magnitude and duration of voltages , that may appear under earth-fault-conditions between simultaneously accessible exposed-conductive-parts of equipment and between them and extraneous-conductive-parts or earth .

Whilst the primary purpose of testing for protective conductor continuity is to ensure that such continuity exists , the result ( R[SUP]1 [/SUP]+ R[SUP]2[/SUP] ) test can be used to determine the earth fault loop impedance at the point or accessory at which the test is applied.

The wander lead method . ( R[SUP]2[/SUP] )
This method is used principally for testing ( Protective-conductor's ) that are connected to the main earthing terminal , main equipotential bonding conductors , circuit protective conductors & so on .

612.2.2. Continuity of ring final circuit conductor's .. ( Continuity , a complete circuit ) Loop
Measure between two points in a circuit with MFT tester

612.2.2. A test shall be made to verify the continuity of each conductor , including the protective conductor , of every ring final circuit .
The cables of a ring final circuit start at the outgoing terminals of a ( CCU ) or ( DB )
Connect to all the points in the ring , and return to the same outgoing terminals , The line & neutral conductors must from a complete unbroken loop without interconnections as must the circuit protective conductors .

Single cable's - same size of conductor's ... Conduit or Trunking .

T&E Circuit-protective-conductor 1.5mm[SUP]2[/SUP] - ( 1.67 times )
Line / Neutral 2.5mm[SUP]2[/SUP] ÷ 1.5mm[SUP]2[/SUP] = 1.67

" Dead Test "
T&E Note :- the readings obtained as : ( Little r )
End to end résistance of the line conductor = ( r[SUP]1[/SUP] )
End to end résistance of the neutral conductor = ( r[SUP] N[/SUP] )
End to end résistance of the circuit-protective-conductor = ( r[SUP]2 [/SUP] )

The line and neutral conductors should have equal résistances , if the circuit-protective-conductor has a smaller cross-sectional area than the line and neutral , its résistance should be higher .

In the case of a ring circuit having 2.5mm[SUP]2[/SUP] Live conductor's ( L / N ) and a 1.5mm[SUP]2[/SUP] circuit-protective-conductor , the résistance of the Cpc should be about ( 1.67 times ) that of the line or neutral conductor.

? readings T&E Line & neutral = 0.20Ω
? readings T&E Line & circuit-protective-conductor = 0.27Ω

Socket-outlet-circuit
The length represents the total ring cable loop length and does not include any Spurs .
As a rule of thumb for rings , unfused spur lengths should not exceed ( 1/8 the cable length ) from the spur to the furthest point of the ring .

402 Generic Schedule of Test Results . * Where there are no spurs connected to a ring final circuit this value is also the ( R[SUP]1 [/SUP]+ R[SUP]2[/SUP] ) of the circuit .

 

[brucelee]

Hi mate No worries keep up the good work

 

[Richard Burns]

on behalf of Amberleaf
Learning curve : what is Parallel-paths
Megger 1552 . ... MFT

TN-S converted to TN-C-S (PME)

1) - Live test

Switch the tester over to (PFC) prospective fault current .
(Green setting)

(PFC) Test between line & neutral ..( short-circuit-fault) reading 1.86kA ... just making a point, so example readings (kA)
(PFC) Test between line & earth ..(earth-fault) reading 1.84kA & Parallel-paths

► (kA) (Green PFC) Loop .. reading *.** kA

The(PSCC) of a circuit is the largest Prospective Fault Current (PFC) in a single-phase-system, this would be the larger of the earth loop (PFC) and the Neutral loop (PFC)

612.11. Prospective fault current .. Ipƒ

prospective short-circuit-current .. (PSCC) .. short-circuit .
&
prospective earth-fault-current shall be measured ..(PEFC) .. earth-fault

measured at the origin or at other relevant points in the installation

R/P 31, Origin of an installation. The position at which electrical energy is delivered to an electrical installation .

The requirements are that the (PSCC) & (PEFC) are to be measured .. (also at the other relevant points in the installation)
A relevant point is a point where a protective device, required to operate under fault-conditions, has been installed, etc.

To prove that in the event of a fault the protective device can handle the fault current (at the point of installation) without danger.

Parallel-paths, what is Parallel-paths

► Learning curve : All circuit-protective-conductors & main-protective-bonding-conductors are connected through the (MET) via earthing-conductor down to the substation ↓↓↓↓

At origin . Measurement of (PEFC) earth-fault-current .. with Parallel-paths in place . 1.84kA worst case scenario .

At origin . Measurement of (PEFC) earth-fault-current .. with Parallel-paths removed . 1.66kA .. small reading . Just earthing conductor connected

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 having a difference in potential under normal operating conditions .

The highest reading measured is the "worst case scenario" and is the one that will be entered onto the schedule of tests
Domestic, circuit-breakers can safely break 6kA( 6000A) in the event of a fault BS-EN-60898

 

[amberleaf]

GN-3 2008: 3.10.3. (c) Polarity
Tests should be made to verify that : 1) the polarity is correct at the meter and distribution board .

BS-7671: P/402 , Schedule of Test Results .. Top left-hand corner . Correct supply polarity confirmed [ ]

O.S.G. P/99 . it is important to confirm that :
After connection of the supply , correct polarity must be confirmed using a voltage indicator or a test lamp ( in either case with leads complying with the recommendations of HSE Guidance Note GS-38 . refer to

GN-3 : P/47
Polarity testing
The polarity of all circuits must be Verified before connection to the supply . refer
Alternatively polarity can be verified by visual checking core-colours at terminations , Thus:
Verifying the installer's connections . Whatever method is used , polarity checks are required at all points on a circuit .

Note : The continuity test and ring-continuity test may confirm polarity

R/P 192 . Polarity . A test of polarity shall be made and it shall be verified that :
i) every single-pole control and protective device is connected in the line conductor only
iii) wiring has been correctly connected to socket-outlets and similar accessories

O.S.G. Correct polarity must be confirmed using a voltage indicator or a test lamp

Correct incoming polarity

T5-1000 Electrical Tester

Safe isolation procedure .. 100A Isolator
Lock off , padlock

Main switch is in the OFF position
1) firstly testing for voltage between the incoming line & neutral-conductor ....... right sided little window will indicate ( Orange ) 230V
This shows a voltage present as highlighted but does not tell you which one of these terminals is ( line ) it could be either one .

2) Test between line & earth " line " incoming terminal appears to be " line " on the incoming polarity check
....... right sided little window will indicate ( Orange ) .. 230V

3) final check on the incoming polarity , test between neutral & earth , no ( 0 ) voltage present , This proves that neutral & earth are at the same voltage , if the incoming supply was ( back to front ) you would get a voltage indication here . ( neutral & earth ) reversal of polarity .. 230V

• it proves that the line incomer terminal is in fact ( Line ) correct polarity

Lock off , padlock .. still in place , 100A isolation switch :
Checking safe isolation !! checking that the main-switch is really isolated .
Check the operation of the voltage tester ( T5-1000 Electrical Tester ) is the outgoing side of the main-switch still be live .
Checking the line out-going terminal of the dead side ( bottom side of ) the isolator to earth , you should get No Readings . " Dead "

recap - you have proved , the incoming supply has been connected properly with correct incoming polarity

 

[amberleaf]

Speed up your Laptop or PC

if your Windows computer has become slow and unresponsive , then unneeded files and programs could be clogging it up . A simple hard-drive clean-up can boost its performance and make for speedier surfing . Here how :

Left-hand , One click on mouse
1 . Click the " Start " button ( bottom left-hand corner on your screen ) Choose " All Programs " from the menu that appears .

2 . Click on " Accessories folder " and choose " System tools folder " from the menu . Click on " Disk Cleanup "

3 . Select the drive you want to clean up , and click " OK " (C:) !!!
4 . Click " Clean Up Systems Files " for more categories of files to delete .

5 . Choose what you want to remove .
For example . temporary set-up files . recycle bin files and files left over from old software updates . Click " OK " and then click " Delete Files "

 

[amberleaf]

Inspected first & tested secondly
Initial verification , New installation is not allowed to fail . Fails are only relevant to periodic reporting .

 

[amberleaf]

On rant mode .

Method 2 : or " Wander lead test "
relevant column on the test schedule Continuity ( Ω ) R[SUP]2 [/SUP]column 14 .

When will I used the Method 2 :
Confirm that you have a protective-conductor in place ( R[SUP]2[/SUP] ) Water , Gas pipes copper .

The main-protective-bonding-conductor , Equipotential Bonding .
Parallel path's must be eliminated for this test , measuring this cable alone . main-protective-bonding-conductor .. ( A to B )

Evaluation of Test Results

Candidates were asked to determine whether a stated value for the measured resistance of a given main protective bonding conductor was acceptable. Candidates were therefore expected to use given information to determine the expected value of resistance and compare

given main protective bonding conductor was acceptable. Candidates were therefore expected to use given information to determine the expected value of resistance and compare this with the stated measured value. Some candidates carried out the correct calculation but failed to identify the units applicable to their answer and so losing marks.

A large number of candidates incorrectly stated that the maximum value for the resistance of a main protective bonding conductor was 0.05 Ω. This value is applicable where access to the bonding connection is not possible and a test is made between two extraneous conductive parts (GN-3 Page 35). This value is not the maximum permitted resistance of the main protective bonding conductor.

GN-3 - 2008: ( R[SUP]2[/SUP] )
To confirm the continuity of a bonding conductor , the leads from the instrument are connected to each end of the conductor and a reading is taken .One end of the bonding conductor and any intermediate connections with services may need to be disconnected to avoid parallel paths

This method can also be used to confirm a bonding connection between extraneous-conductive-parts where it is not possible to see a bonding connection e.g. where bonding clamps have been " built in " The test would be done by connecting the leads of the instrument between any two-points such as metallic pipes between which a bonding connection was required and looking for a low ( minimal deflection ) reading of the order of 0.05Ω or less

GN-3 - 2011: ( R[SUP]2[/SUP] ) P/35
Testing bonding conductors & Earthing conductors
To confirm the continuity of these protective conductors , Test method 2 may be used

This method can be used to confirm a bonding-connection between extraneous-conductive-parts where it is not possible to see a bonding connection e.g.
where bonding clamps have been " built in " The test would be done by connecting the leads of the instrument between any two-points such as metallic pipes and looking for a low reading of the order of 0.05Ω ( it should be noted that not all low-résistance ohmmeters can read this low )

 

[amberleaf]

Chief Examiners’ report – December 2012

Testing

Another common incorrect answer given by candidates was that the continuity of main-protective-bonding-conductors could be carried out using either the ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) method or, worryingly, an earth fault loop impedance tester.