Re-take - Useful Information for 2394 :

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Periodic inspection & testing
5.3. Larger and more complex installations the inspector will need to formulate his/her own inspection schedules
5.4. ( x ) Additional forms may be required as clarification . if needed by ordinary persons , or in expansion , for lager or more complex installations

 

[Richard Burns]

(No borrowed neutrals)


GN-3 : 2008 . ISBN 978-0-86341-857-0


2.6.3. Inpection checklist


Listed below are requirements to be checked when carrying out an installation inspection , The list is not exhaustive .





4 ) Circuits to be separated ( no borrowed neutrals ) 314.4.





GN-3 : 2011 . ISBN 978-1-84919-275-0


2.6.3. Inpection checklist


Listed below are requirements to be checked when carrying out an installation inspection , The list is not exhaustive .




5) Circuits to be separated ( no borrowed neutrals ) 314.4.





BS-7671:2001:2008:2011:


P/46 , Where an installation comprises more than one final circuit , each final circuit shall be connected to a separate way in a distribution board , The wiring of each final circuit shall be electronically separate from that of every other final circuit , so as to prevent the inderct energizing of a final circuit intended to be isolated

 

[Richard Burns]

On Rant mode .


GN-3 This Guidance Note is concerned principally with Part 6 of BS-7671: Inspection & Testing Etc
Am asking the (( Question )) What can GN-3 do for you . !!! Help you to pass you're Exams


Periodic testing
GN-3 3.10.2. Test to be made : 621.2.


The tests considered appropriate by the person carrying out the inspection should be carried out in accordance with the recommendations


3.5. Testing to be carried out where practicable on existing installation(s)
see notes 1 & 2


1) The person carrying out the testing should decide which of the above tests are appropriate by using their experience and knowledge of the installation being inspected .
2) Where sampling is applied , the percentage used is at the discretion of the inspector .


Recommendations ... ( Tests )
Protective conductors continuity . Accessories exposed-conductive-parts of current-using equipment & accessories ( notes 4 / 5 )


4) The earth fault loop impedance test may be used to confirm the continuity of protective conductors at socket-outlets and at accessible exposed-conductive-parts of current-using equipment and accessories


5) Generally, accessibility may be considered to be within 3m from the floor or from where a person can stand


- Bonding conductors continuity :
Main bonding conductors to extraneous-conductive-parts
Supplementary bonding conductor


- Ring circuit continuity :
Where there are records of previous tests , this test may not be necessary unless there may have been changes made to the ring-final-circuit


- Polarity :
At the following positions .
• origin of the installation
• distribution boards
• assessable socket-outlets
• extremity of radial circuits


- Earth fault loop impedance :
At the following positions
• origin of the installation
• distribution boards
• assessable socket-outlets
• extremity of radial circuits


- Insulation résistance :
if tests are to be made
between live conductors and earth at main and final distribution boards
6) Where the circuit includes surge protective devices ( SPDs ) or other electronic devices which require a connection to earth for functional purpose , these devices will require disconnecting to avoid influencing the test result and to avoid damaging them .


- Earth electrode résistance :
if test are to be made .
Test each earth rod or group of rods separately , with the test links removed , and with the installation isolated from the supply source .


- Functional tests :
RCDs .. Tests as required by Regulation 612.13.1. followed by operation of the integral test button


Functional tests - of circuit-breakers , isolators and switching devices .. Manual operation to confirm the devices disconnect the supply .


R/P 400 , Inspection schedule , taken at random
4.7. Operation of main switch ( functional check ( 612.13.2. )
4.8 . Manual operation of circuit breakers and RCDs to prove disconnection ( 612.13.2 )
4.15 Single-pole protective devices in the line conductor only ( 132.14.1. ; 530.3.2. )
4.18. RCDs provided for fault protection - includes RCBOs ( 411.4.9 ; 411.5.2 ; 531.2 )
4.19. RCDs provided for additional protection - includes RCBOs ( 411.3.3. ; 415.1. )

 

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2394 .. Initial Verification of Electrical Installations.

Q) from -&-s
Candidates were asked to determine the expected measured values at each stage of a test to confirm ring final circuit continuity.

The candidates were then asked to explain the expected pattern of measured values taken at each socket-outlet when carrying out an earth fault loop impedance test on the circuit.

Some
candidates lost marks because their description was vague and could have been a description for a radial socket-outlet circuit rather than a ring final circuit.

O.S.G. 7.1. Final circuit(s)
Table 7.1. (i) has been designed to enable a ( Radial or Ring-final-circuit ) to be installed without calculation where the supply is at 230V single-phase or 400V three-phase .
For other voltages , the maximum circuit length given in the table must be corrected by the application of the formula : etc

411.3.2. Automatic disconnection in case of a fault .
411.3.3. Additional protection .
525.101. Where fixed current-using equipment is not the subject of a product standard the voltage at the terminals shall be such as not to impair the safe functioning of that equipment . etc

each stage of a test to confirm ring final circuit continuity.

10.3 Test procedures
( 612.2.1. ) .. Testing 10.3.1. Continuity of circuit protective conductors and protective bonding conductors ( ► for ring-final-circuit see 10.3.2. )
( 612.2.2. ) .. 10.3.2. Continuity of ring-final-circuit conductors .

Your Q : !! A Three-step is required to ( verify the continuity of the ) Line , Neutral and Protective-conductors ,
Your Q : ( for the sake of -&-s ) .... Use a low-résistance ohmmeter for this test ............ Yes we all know that we use MFT testers nowadays .

Step 1 .
The line , neutral and protective-conductors are ( identified at ) the distribution board ( in our case here at the Consumer-unit ) and the end-to-end résistance of each is measured separately You're Q , ( see Figure 10.3.2.(i))

You're Q .. Step 1 .
The end-to-end résistance of the line , neutral and protective-conductors are measured separately ... ( initial check for continuity at ends of ring )

Step 2 . The line & neutral conductors are then connected together at the distribution board so that the outgoing line-conductor is connected to the returning neutral-conductor & vice versa . You're Q see Figure 10.3.2. (ii))

Has O.S.G given insight here . refer to
Note : Where single-core-cables are used , care should be taken to verify that the line and neutral conductors of opposite ends of the ring circuit are connected together ... in domestic we use T&E cable . not single-core-cables . with any Q) from -&-s . we can't see the trees from the woods . Yeah .

Figure 10.3.2. (ii) Step 2 . The line and neutral conductors are cross-connected and the résistance measured at each socket-outlet

Step 3 . The above step is then repeated ,
this time with the line and circuit-protective-conductor crossed-connected at the distribution board ( see figure 10.3.2.(iii))

You're Q , The résistance between line and earth is measured at each socket-outlet .

" " The readings obtained at each of the socket-outlets wired into the ring will be substantially the same and the value will be approximately one-quarter of the résistance of the line plus cpc loop résistance . i.e.

" " ( r[SUP]1[/SUP] + r[SUP]2[/SUP] ) / 4 . As before , a higher résistance value will be measured at any socket-outlet wired as ( Spurs )

" " The highest value recorded represents the (( maximum)) ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) of the circuit and is recorded on the Schedule of Test Results .
" " The value can be used to [ determine the earth fault loop impedance ] ( Zs ) of the circuit to verify compliance with the loop impedance requirements of BS-7671: see 10.3.6.

10.3.2. (iii) Step 3 . The line conductors and circuit-protective-conductor are cross-connected and the résistance measured at each socket-outlet
Connection for taking readings of R[SUP]1[/SUP] + R[SUP]2[/SUP] at socket-outlets

This sequence of tests also verifies the polarity of each socket-outlet , Except that where the testing been carried out at the terminals on the reverse of the accessories , a visual inspection is required to confirm correct polarity connections , and dispenses with the need for a separate polarity test .

 

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Accessory
Switches, sockets, ceiling roses etc.

R/P23 . Accessory A device , other than current-using equipment , associated with such equipment or with the wiring of an installation

R/P24 . Circuit
An assembly of electrical equipment (socket outlets, lighting points and switches) supplied from the same origin and protected against over current by the same protective device(s).

 

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On rate mode . O.S.G. refer to

The value can be used to [ determine the earth fault loop impedance ] ( Zs ) of the circuit to verify compliance with the loop impedance requirements of BS-7671: see 10.3.6.

10.3.6. Earth fault loop impedance :
612.9. The earth fault loop impedance ( Zs ) is required to be determined for the furthest point of each circuit . it may be determined by :
► direct measure of ( Zs ) or
► direct measure of ( Ze ) at the origin and adding ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) measured during the continuity test ( 10.3.1. & 10.3.2. ) [ Zs = Ze + ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) ] or
► Adding ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) measured during the continuity tests to the value of ( Ze ) declared by the distributor ( see 1.1. (iv) & 1.3. (iv)

The effectiveness of the distributors earth must be confirmed by a test . etc

What lets us down badly is not understanding the very basics . it's all in books

 

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Please read the Q )

re-cap Inspection & testing .. my point is ( drawings )

Answer
disconnect conductors at a suitable point on the circuit

5 c) Describe how the continuity of the ring-final-circuit test is to be carried out on Circuit 9 once the circuit has been safely insulated and secured .

Step 1
• Test the conductor end-to-end loop résistance
• Record results r[SUP]1[/SUP] , r[SUP]N[/SUP] , r[SUP]2[/SUP]

Step 2 ... Interconnect line of outgoing leg with neutral of incoming leg and line of incoming leg with neutral of outgoing leg .

Step 3 ... Interconnect line of outgoing leg with cpc of incoming leg and line of incoming leg with cpc of outgoing leg
• Test line to cpc at each socket-outlet
• Record highest value as R[SUP]1[/SUP] + R[SUP]2[/SUP]
• Reinstate the circuit

-&- are saying don't waffle on , time is precious in Exams .

Comments ...
Answering these types of questions using bullet point is clear and easy way to see that no part are missed out and that the test is complete .

A drawing may be used in place of the interconnection statements such as :


GN-3 P/37 refer Figure 2.2b . Figure 2.2c . connector block etc

Step 1
cross connect line and neutral ... drawing may be used in Exams

This may be easer that writing the connection descriptions in full . There is no set sequence for step 2 & 3 but all three steps must be detailed in order to score well on this question

Tip : Failure to identify that at each step test are carried out at each socket-outlet will lose several marks .

 

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612.2.2. Continuity : Test be made to verify the continuity of ( each-conductor )
Continuity of ring final circuit conductors including circuit-protective-conductor(s) of every ring-final-circuit must be verified .

if the conductors are the same size
if the protective conductor has a reduced CSA , the résistance of the protective loop will be proportionally higher than that of the line , neutral loop

O.S.G. 10.3.2. / 612.2.2. Three step test is required to Verify the continuity of : ( Step 3 )

Step 3 10.3.2 (iii)
Line-conductors & circuit-protective-conductors ( CPC ) crossed connected .
The résistance between line & earth is then measured again at each outlet , The highest value recorded represents the maximum ( R[SUP]1[/SUP] + R[SUP]2[/SUP] ) of the circuit and can be used to determine the earth-loop-impedance ( Zs ) of the circuit .

This test also verifies the polarity at each socket-outlet

 

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Main earthing terminals
MET testing . R/P160

the regulations have stated the facts
As called for in Regulations 542.4.1. & 542.4.2. as MET is required for every installation .

One of the principal purposes of the MET is to provide for disconnection of the earthing-conductor from circuit-protective-conductors and bonding-conductors , So that the external line to earth loop impedance ( Ze ) can be measured .

542.4. Main earthing Terminals or Bars

542.4.2
The means of disconnection must involve the use of a tool .. can be ( Bars / Spanner or Terminals / Screwdriver ) may be provided in the form of a disconnectable link , (( with any connections' to MET providing reliability & continuity ))

Protective Conductor(s)

Including :
Earthing conductor(s)
Circuit-protective-conductor(s)
Main-protective-conductor(s)
Supplementary-protective-bonding-conductor(s) where required

 

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R/P 53 . 411.3.1.2. Protective equipotential bonding

Where an installation is contained in more than one separate building , Regulation 411.3.1.2. calls for a MET .. ( & equipotential bonding ) for each building

411.3.1.2 In each installation :
Main protective bonding conductor(s) shall connect to the main earthing terminal extraneous-conductive-parts including the following :

i) Water installation pipes
ii) Gas installation pipes
iii) Other installation pipework & ducting
iv) Central heating and air conditions systems
v) Exposed metallic structural parts of the building

 

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System earth fault loop impedance ( Zs ) s)) system ..

Earth fault loop impedance ( Ze ) e )) external to the installation .
The external earth fault loop impedance ( Ze ) is one of the supply characteristics to be recorded can only be measured by testing at the origin of the installation .

R/P 390 ( EIC ) supply characteristics . External loop impedance ( Ze [SUP]2[/SUP] ) by enquiry of by measurement . ( direct-measurement )
R/P 397 ( EICR ) supply characteristics . External loop impedance ( Ze [SUP]2[/SUP] ) by enquiry of by measurement . ( direct-measurement )

R/P 31 . Origin of an electrical installation . The position at which electrical energy is delivered to an electrical installation .
R/P 32 . Origin of temporary electrical installation . Point on the permanent installation or other source of supply from which electrical energy is delivered to the temporary electrical installation . refer GN-3 P/53 Zs = Zdb + ( R[SUP]1[/SUP] +R[SUP]2 [/SUP])

Direct measurement : -&-s
This indicates that a test is required and the results are not to be established by using a calculation . for example , where you are asked to describe the direct measurement of earth fault loop impedance , then a description of the test procedure is required , Describing an R[SUP]1[/SUP] +R[SUP]2 [/SUP]test and then stating how to determine the value by calculation using Zs = Ze + ( R[SUP]1[/SUP] +R[SUP]2 [/SUP]) will result in on marks being awarded for the answer

2394 : -&-s Q) Which of the following is not a method for determining prospective-earth-fault-current at the origin of an installation ?
A) Calculation using the measured Zs and the supply voltage .

( Ipƒ ) Prospective fault current is measured to determine the maximum fault current which may occur , Any impedance measurement taken at the end of a circuit will be higher than that at the origin of the circuit , As a result the value obtained from the calculation is not going to produce the maximum value .

 

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• O.S.G. Table 11 - 2.5mm[SUP]2[/SUP] / 1.5mm[SUP]2[/SUP] cable has a résistance of 19.51mΩ per metre
The résistance of 54 metres is : 54 x 19.51 / 1000 = 1.05Ω , 1.05 ÷ 4 0.26Ω

R[SUP]1 [/SUP]+ R[SUP]2 [/SUP]for the circuit is 0.26Ω
Zs = Ze + R[SUP]1 [/SUP]+ R[SUP]2 [/SUP]0.24Ω + 0.26 = 0.5Ω

• An installation has seven circuits . Circuit 1 . 4 . 6 have insulation résistance of greater than 200MΩ
Circuit 2 .3 . 5. & 7 . have résistance values of 50 . 80 . 60 . 50 , Calculate the total résistance of the circuit .

1 ÷ 50 = 0.02 , 1 ÷ 80 = 0.0125 , 1 ÷ 60 = 0.016666666 , 1 ÷ 50 = 0.02 :- 0.02 + 0.0125 + 0.016666666 + 0.02 = 0.069
1/50 + 1/80 + 1/60 + 1/50 = 0.069 .. R = 1 ÷ 0.069 = ****Ω

 

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( little rs & Big Rs )
You will not be the first to fall short at understanding the little rs & big Rs
R/P 402 : Schedule of test results . Ring final circuit continuity ( Little rs 10 , 11 , 12 )
Big Rs , Continuity Ω ( R[SUP]1 [/SUP]+ R[SUP]2 [/SUP]) 13* , * 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

( Little rs 10 , 11 , 12 ) r[SUP]1[/SUP] , r[SUP]N [/SUP], r[SUP]2[/SUP] , are the end-to-end ring final circuit readings
R[SUP]1[/SUP] ) is the maximum résistance of the line-conductor for a circuit .
R[SUP]2[/SUP] ) is the maximum résistance of the circuit-protective-conductor for a circuit
( R[SUP]1 [/SUP]+ R[SUP]2 [/SUP]) is the test reading value of the two-resistances added together
( R[SUP]1 [/SUP]+ R[SUP]N [/SUP]) is done to help confirm polarity so does not need recording

Note : that spurs from the ring-final-circuit will give higher readings

 

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At random . Q/As word for word .

2394 & 2395 Inspection & Testing
Section B :
Remember that the answers to the following questions must relate to the scenario contained in the Source Document .

Q) Describe how a test is carried out to determine the prospective fault current at the origin of the installation by direct measurement
A) Secure the area around distribution board
Access incoming live terminals
Using a PFC tester ( or EFLI tester set to kA )
Confirm test leads comply with GS-38
Connect to incoming supply side Line & Earth
Measure PEFC
Connect it incoming supply side Line & Neutral
Measure PSCC
Record highest result as the PFC
Reinstate the DB

▼▼▼▼▼ There may be improvement in the 18th Edition here GN-3
C) In the case there have been no previous questions relating to the preparation such as type of instrument etc. and so this information needs to be included in the answer. ◄◄ Your Q )

Tip . Failure to identify that the test leads must comply with GS-38 will lose several marks . It is vital to remember that the earthing and all protective bonding conductors are connected whilst this test is carried out .

( Ipƒ ) 612.11. Prospective fault current
Regulation 612.11. requires that the prospective fault current under both short-circuit and earth-fault conditions be measured , calculated or determined by another method , at the origin and at other relevant point in the installation .

GN-3 . 4.5. Instruments conforming to BS-EN-61557-3 will fulfil the above requirements
These instruments may also offer additional facilities for deriving prospective fault current . The basic measuring principle is generally the same as for earth fault loop impedance testers . ETC . refer

GN-3 4.5. Earth fault loop impedance testers .
These instruments operate by circulating a current from the line conductor into the protective earth , This will raise the potential of the protective earth system

To minimise electric shock hazard . etc This means that the instrument should cut off the test current after 40mS Etc refer

 

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BS-7671:2008:2011: Voltage-drop PS I will not type this out again

612.14. Verification of voltage drop
Where required to verify compliance with Section 525 , the following options may be used .
i) The voltage drop may be evaluated by measuring the circuit impedance .
ii) The voltage drop may be evaluated by calculations , for example , by diagrams or graphs showing maximum cable length v load current for different conductor cross-sectional areas with different percentage voltage drops for specific nominal voltages , conductor temperatures and wiring systems .

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

Written Examination 2395-302 Read the Qs) Good luck in Exams

Q/As 3 a) i)
Q) Explain the cause of voltage drop within an installation ( 3mk )
A) Volt drop is a product of the conductor resistance and the load current .
Com) The question refers to voltage drop that occurs normally within the installation which is caused by the conductor résistance and the current flowing , Do not confuse this with the causes of excess voltage drop due to poor design or overloading of the circuit

3 a) ii) State the two methods of determining voltage drop ( 2mk )
A) Measurement & Calculation
[h=4]Com ) it is not acceptable to carry out a direct measurement of voltage drop using volt meter(s) The circuit conductors must be at their normal operating temperature , the circuit under full load and there must be no variation in the supply voltage during the test , The methods given are as a result of the measurement of conductor résistance and the reference to charts or tables giving the details of voltage drop . These are not the figures in tables in Appendix 4 of BS-7671: which are generic design details for the calculation of appropriate cable sizes .[/h]
3) b) i) A radial circuit has a load current (Ib) of 28A at 230V ac and has a combined live-conductor résistance of 0.16Ω at 20°C .
Determine the voltage drop for this circuit , Show all calculations' ( 5mk )

A) Voltage drop = ( R[SUP]1[/SUP] + R[SUP]N[/SUP] ) x Ib x 1.2
So Voltage drop = 0.16 x 28 x 1.2 = 5.376V
Com ) The use of the conductor résistance and load current together with the 1.2 multiplier to compensate for the difference in conductor temperature at the time of test and the normal operating temperature of the conductors when maximum résistance and hence maximum voltage drop will occur .

3 b) ii ) if the radial circuit supplies a machine lathe , determine whether the voltage drop in b (i) above complies with BS-7671: ( 5mk )
A) Maximum volt drop - 230V x 5% = 11.5V ......... As 5.376V is equal to or less than 11.5V so complies

Com ) Alternative calculations such as : max voltage drop = 5% V drop = 5.376 ÷ 230 x 100 = 2.3% which is less than 5% So Ok
may be used and will attract the same marks .

(( 5.376 ÷ 230 = 0.023373913 x 100 = 2.3% ))

Tip . It is important to show the calculations because in this type of question where an error is made in the calculation candidates are only penalised once for the error .
The remainder of the answer is marked based upon the incorrect figure produced and , providing the process is correct , marked accordingly , Candidates could have completely the wrong answer for 3 b (i) but based upon their incorrect figure from that calculation achieve full marks for 3 b (ii ) providing their calculation and conclusion is correct .

GN-3 P/59 2.7.20. Verification of voltage drop . Section 525 .
612.14. Where it may be necessary to verify that voltage drop does not exceed the limits stated in relevant product standards of installed equipment BS-7671 : provides two options to do so , Where no such limits are stated , voltage drop should be such that it does not impair the proper and safe functioning of install equipment .

Voltage drop problems are quite rare but the inspector should be aware that long runs and / or high currents can sometimes cause voltage drop problems .

refer to GN-3 .