Insulation Test Problem (sorry!)

[drummonkey]

Hello to you all, and apologies for another question on this topic but I'm new to all this and completely stuck!
I've been testing a Ring Final circuit today with a Megger MFT and got a bizarre reading on one of the IR tests.

On the continuity test I seemingly got correct readings on all the tests, however I never tested Neutral to CPC at the time.

Then when I came to do the IR test on the ring everything was proceeding as planned until I tested Neutral and CPC. The meter just reads 0, not even a smidgen of a reading, am I right in assuming that there is a short between neutral and cpc?

When I then went to find the problem using a continuity test with outgoing Neutral and incoming CPC connected together and vice versa, I gradually get smaller readings towards one section of the ring, so is this where the problem is located?

I also noticed that in most of the sockets, I didn't need to turn the socket on to get my continuity readings whereas I'm sure I did for the Live/Cpc tests, is this indicative of the fault also.

Thanks so much for your assistance, apologies for asking and look forward to your replies

Alan

 

[MikeK]

Then when I came to do the IR test on the ring everything was proceeding as planned until I tested Neutral and CPC. The meter just reads 0, not even a smidgen of a reading, am I right in assuming that there is a short between neutral and cpc?

Almost certainly.

When I then went to find the problem using a continuity test with outgoing Neutral and incoming CPC connected together and vice versa, I gradually get smaller readings towards one section of the ring, so is this where the problem is located?

Probably not. Ring resistance will vary around ring, max furthest away from CU.

I also noticed that in most of the sockets, I didn't need to turn the socket on to get my continuity readings whereas I'm sure I did for the Live/Cpc tests, is this indicative of the fault also

.

Probably not. Could have mix of single and double pole sockets.


Most likely you clipped neutral cable against back box or with screw whaen attaching socket cover.

Divide ring into 2. IR test both halves (like a radial) one will fail this is half fault is on.
\Keep dividing down til identify fault location.

 

[mikeymoo]

You shouldnt need to switch any of the sockets on to get a continuity reading on a ring? They loop in then back out, without going through the switch.

 

[ajelec10]

Mikey he was probably using a plug in adapter (only assuming)

 

[mikeymoo]

good point, he was using a megger mft.

 

[drummonkey]

Thank you so much for replying guys, especially MikeK, your help is most appreciated.

Managed to sort it out today, took a while but got there in the end, biggest problem was It was in an old house and I never wired the ring so I was unsure where the next socket on the ring was!

But all sorted now thanks!

P.s. I was using a socket adaptor with the Megger, thanks for checking though

 

[MikeK]

What did fault turn out to be?

MikeK

 

[drummonkey]

Hi, i found 2 faults on the ring.

In one of the sockets whoever stripped the cable back had obviously used a Stanley blade and slit the neutral insulation right up to the box entry (there was a grommet btw). The other fault was between two sockets but I've no idea what it is, I just split the ring in 2 and made two radials on 20A MCB's.

Must be a fault buried under the floor or in the wall as the cables into the box looked fine.

Thanks again for your assistance, very much appreciated