Live earth fault??

[Kyle_Trainee]

So was testing a house today (new build)
When I came to testing on of the ring finals in the house, when testing insulation resistance the live and earth legs on the ring are clear but live to the earth on cpc’s on the cooker circuit, other ring, downstairs lights and heating its bang down I’m thinking something to do with damp walls? But every time Other circuit tested out fine on IR

 

[timhoward]

If we just talk about that sockets circuit a moment, to clarify things for my little brain:
1) L - MET was 0 Mohms when the sockets own CPC is in MET?
2) L- sockets own CPC is clear when the CPC isn't in the MET?

 

[Kyle_Trainee]

If we just talk about that sockets circuit a moment, to clarify things for my little brain:
1) L - MET was 0 Mohms when the sockets own CPC is in MET?
2) L- sockets own CPC is clear when the CPC isn't in the MET?

Yeah that’s correct ?

 

[pc1966]

Yeah that’s correct ?

Sounds like the L insulation is damaged and on to some shared metalwork (with route back to MET) then.

 

[Dave OCD]

Hmm I don't want to second guess this but I wouldn't be surprised if it turns out to be a result of carelessness by other 'trades' . A blur of nail guns and impact drivers can cause chaos.

 

[timhoward]

Was thinking same. This sort of fault can be a bit of a mare to find.

One possible shortcut - wander lead from MET and test continuity to live at each socket.
Or as alternative you can also just connect one L and one CPC at CU and do a live to cpc continuity test at each socket. (This is using the circuit's cpc instead of a wander lead.)

In my head, with either method the lowest resistance reading should be closest to the fault.

 

[Kyle_Trainee]

Was thinking same. This sort of fault can be a bit of a mare to find.

One possible shortcut - wander lead from MET and test continuity to live at each socket.
Or as alternative you can also just connect one L and one CPC at CU and do a live to cpc continuity test at each socket. (This is using the circuit's cpc instead of a wander lead.)

In my head, with either method the lowest resistance reading should be closest to the fault.

So still struggling with this so when earth connected to MET get continuity at every socket
I’ve identified there’s continuity between downstairs lights cpc and sockets live
then IR testing sockets are down between cooke, kitchen sockets, lights

bugging me that there’s no metal work in the house all wooden stud and normal dabbed walls

 

[Kyle_Trainee]

So still struggling with this so when earth connected to MET get continuity at every socket
I’ve identified there’s continuity between downstairs lights cpc and sockets live
then IR testing sockets are down between cooke, kitchen sockets, lights

bugging me that there’s no metal work in the house all wooden stud and normal dabbed walls

Any be able to answer why there’s no continuity between the L and cooker cpc but IR down

 

[timhoward]

Any be able to answer why there’s no continuity between the L and cooker cpc but IR down

Is it a gas cooker, or touching a metal pipe behind it?

 

[timhoward]

So still struggling with this so when earth connected to MET get continuity at every socket
I’ve identified there’s continuity between downstairs lights cpc and sockets live
then IR testing sockets are down between cooke, kitchen sockets, lights

bugging me that there’s no metal work in the house all wooden stud and normal dabbed walls

Do the readings vary, if so the lowest reading may provide a clue.

I feel for you as these can be horrible to diagnose.
You've done well to find the lights cpc and sockets live bridge.

With both those circuits completely disconnected, is the cooker still giving low IR L to Earth? (you need to check with cooker cpc in earth bar and out).
Keep going!

 

[Kyle_Trainee]

Do the readings vary, if so the lowest reading may provide a clue.

I feel for you as these can be horrible to diagnose.
You've done well to find the lights cpc and sockets live bridge.

With both those circuits completely disconnected, is the cooker still giving low IR L to Earth? (you need to check with cooker cpc in earth bar and out).
Keep going!

The continuity results the kind of just go in a logical order gradually increases the further away from the board I go

with the cooker it’s both down when in and out of the earth bar same the kitchen sockets and pretty much everything else ??

close to ringing one my supervisor only newly qualified and this is a real head messer

 

[timhoward]

close to ringing one my supervisor only newly qualified and this is a real head messer

No shame in that - this is not a trivial one by any means.
Main tip I can offer is to periodically go outside, make a cuppa, and think about what does work. Sometimes the answer hits you between the eyes when you aren't staring at a mass of cables getting more stressed by the minute!

 

[timhoward]

Have you tried pulling main earth and bonding conductors out and continuity testing between affected circuit L's and each of them.
If you are lucky it will only be water or gas, though if a boiler has been fitted there will be connection between them.
While they are out IR results should be clear on all circuits.
While they are out re-test sockets live to kitchen cpc too.

 

[Kyle_Trainee]

No shame in that - this is not a trivial one by any means.
Main tip I can offer is to periodically go outside, make a cuppa, and think about what does work. Sometimes the answer hits you between the eyes when you aren't staring at a mass of cables getting more stressed by the minute!

Thanks for the advice, arranged for another sparky to come and have a look with me tomorrow, I’ll keep you posted ??

 

[Kyle_Trainee]

Thanks for the advice, arranged for another sparky to come and have a look with me tomorrow, I’ll keep you posted ??

So we traced it back to a leg on the ring, one which I was close too yesterday but doubted my self on it, disconnected that from the other showed an IR reading of about 6/7 M ohm, doing that cleared the continuity between the lights and sockets and also bad IR to other ciricuits cpc so replaced leg re tested and all fine and energised

 

[timhoward]

So we traced it back to a leg on the ring, one which I was close too yesterday but doubted my self on it, disconnected that from the other showed an IR reading of about 6/7 M ohm, doing that cleared the continuity between the lights and sockets and also bad IR to other ciricuits cpc so replaced leg re tested and all fine and energised

Well done. It get's easier, I promise!