another cpc continuity question

[disinfo]

Hi,

Last weekend i wanted to test CPC continuity on one circuit consisting of three sockets (in my own house), as per GN3 i did the following;

Bridged the phase of the circuit i wanted to test to the earth terminal
Tested between P+E at all 3 sockets of the circuit
Recorded the highest result as R1+R2

However, reading the electricians guide to the 17th tonight I am slightly confused, in this book you are instructed to bridge Rn+R2 then there is a formula to take the different CSA of the CPC and netural conductors into account, the book then goes on to say this value is R1+R2, but surely this is Rn+R2?

Anyway, as you can see i'm slightly confused


Can anyone explain?

 

[Carpman]

CONTINUITY OF RING FINAL CIRCUIT CONDUCTORS.

test procedure.

STEP

1.Securely isolate supply and identify each end of the ring

2.Measure the phase, neutral and cpc loops. Note values.

3.Connect incoming phase to outgoing neutral and vice
versa.

4.Test between phase and neutral at each socket outlet. If all sockets are on the ring then the results should be substantially the same (within 0.05 ohms) and should approximate to half of the phase or neutral loops.

5.Now connect incoming phase to outgoing cpc and vice versa.

6.Test between phase and cpc at each socket outlet. Again if all sockets are on the ring then the results should be substantially the same (within 0.05 ohms) and should approximate to the sum of the phase and cpc loops divided by 4. If the cpc is of different csa to the phase then results will vary slightly. The highest reading will be R1+R2 for the circuit. Record this in the appropriate column.

7.Re-connect all conductors.


NOTE; The test verifies that the conductors of the circuit are in the form of a ring and that there are no inter-connected loops. R1+R2 is conveniently established and Polarity is also verified.


EDIT: I just noticed that the cct you are testing may not be a ring if this is the case the continuity will be confirmed as follows:-

1.Securely isolate supply.

2.Make a temporary connection between phase and cpc of the circuit to be measured at the distribution board.

3.Measure the resistance between phase and cpc at each point on the circuit low reading expected to confirm cpc.

4.Record the reading at the furthest point on the circuit which should be the highest reading.




Hope this helps

 

[securespark]

Ah, but is the OP's circuit a RFC?

 

[Carpman]

Sorry just noticed that see EDIT.

 

[disinfo]

Ah, but is the OP's circuit a RFC?

Sorry should have said, this is a radial i'm testing.

Carpman, thanks for the instructions but i've already done this. I'm ust puzzled about the difference in methods between the Electricians guide to the 17th i.e. testing between line and neutral with correction for the different CSA sizes and guidance note 3.

Matt

 

[Carpman]

I would personally go by GN3 , I cant personally speak for the Electricians guide to the 17th as i have not seen it.


Stick with the GN3 description you'll be sure its right.

 

[GaryMo]

Bridged the phase of the circuit i wanted to test to the earth terminal
Tested between P+E at all 3 sockets of the circuit
Recorded the highest result as R1+R2

However, reading the electricians guide to the 17th tonight I am slightly confused, in this book you are instructed to bridge Rn+R2 then there is a formula to take the different CSA of the CPC and netural conductors into account, the book then goes on to say this value is R1+R2, but surely this is Rn+R2?

Ignore the silly book and carry on as per your method, line connected to cpc at the consumer unit and measure continuity between line and cpc at all points on the circuit, recording the highest value as R1+R2.