Two socket circuits not allowing RCD reset

daveb · Mar 22, 2018

hi folks,

Been asked to go look at a job tomorrow as his RCD is not resetting - customer sent me some details and from what I can determine is this....

It’s only socket circuits that are on the RCD side of the board. The downstairs socket circuit and the kitchen socket circuit are both off - all other socket circuits on the RCD side are on.

When he tries to flick either one of these circuits it trips the RCD? He’s unplugged everything he says, but still wouldn’t make sense as to why both circuits would all of a sudden not allow a reset?

It’s in the country so am wondering if it’s rodent damage or something on both circuit cables?

Octopus · Mar 22, 2018

My guesses would be water ingress, rodent damage or DIY ...

only a site visit and some inspecting and testing will tell any more ....

I would also be checking to see if the circuits are linked in any way too, i.e. legs in the wrong MCB's

daveb · Mar 22, 2018

He’s assured me that there’s not been any DIY done so I hope that this actually is the case.

Yes definitely worth checking the legs as you say, but surely if these had been mixed up when it was done, the RCD would trip instantly no?

I absolutely hate fault finding - until I find it and then it feels amazing

HappyHippyDad · Mar 22, 2018

It does feel good when you find it doesn't it Dave!
I used to get panicky about fault finding, then you slowly get some experience, then you enjoy it as it's something a bit different. I feel like a detective!

HappyHippyDad · Mar 22, 2018

ps.. in response to you tripping RCD you just need to get there and IR the sockets. Hopefully one leg will show a fault (once youve split the ring somewhere), then you slowly narrow it down... without rushing if you can

Richard Burns · Mar 22, 2018

The fault would appear to be a direct contact fault rather than a progressive fault unless the RCD has been tripping intermittently before. Because it is two circuits I might suspect that the rings were wired with crossed over legs and that now a line is connected to earth (somewhere) either circuit causes the trip as load current is shared on the circuits.

Octopus · Mar 22, 2018

daveb said:
Yes definitely worth checking the legs as you say, but surely if these had been mixed up when it was done, the RCD would trip instantly no?

No .......... if I understand your OP correctly, they are both protected by the same RCD, so you won't get any "inbalance" if that makes sense.

Deleted member 9648 · Mar 22, 2018

N-E fault.
Rcd trips when a load is applied from either ring because a parallel path exists for the return current through the fault.

daveb · Mar 22, 2018

Thanks guys - very helpful

Will also be a good chance to try out my new toy that arrived this week... my earth leakage meter (Megger DCM305e)

Des 56 · Mar 22, 2018

wirepuller said:
N-E fault.
Rcd trips when a load is applied from either ring because a parallel path exists for the return current through the fault.

Thats what I would expect other than he stated all other socket circuits on the RCD side are on
There again,it could be that these "other sockets"are not loaded

Toneyz · Mar 22, 2018

Time to get the insulation resistance tester out!

littlespark · Mar 23, 2018

Site visit needed.

Number of times I've gone to RCD problem and the customer has said everything is unplugged....
Nothing is unplugged, just switched off....
Except the fridge/freezer... its still on.
And the TV.. It's on standby
Wifi router.... cos they have a bad case of FOMO
Outside socket.... "Its not outside... its in the shed!"

Of course it may be something more serious; rodents, damp,
but youll find it

daveb · Mar 23, 2018

Problem sorted...

Went out to discover that it was actually only the kitchen sockets that was tripping RCD.

Ran continuity tests which told me of broken neutral somewhere and a short between neutral and earth. After initially suspecting a faulty boiler or faulty fridge (disconnected them both) the problem was still there so started popping off sockets.

Luckily - second socket I popped off I found a loose neutral which had come out and was pressing against the back of the metal socket.

Problem solved

Thanks all for the comments

Midwest · Mar 24, 2018

daveb said:
Will also be a good chance to try out my new toy that arrived this week... my earth leakage meter (Megger DCM305e)

Where did you get that from, Test Meter tell me the things out of stock!

Pete999 · Mar 24, 2018

daveb said:
hi folks,

Been asked to go look at a job tomorrow as his RCD is not resetting - customer sent me some details and from what I can determine is this....

It’s only socket circuits that are on the RCD side of the board. The downstairs socket circuit and the kitchen socket circuit are both off - all other socket circuits on the RCD side are on.

When he tries to flick either one of these circuits it trips the RCD? He’s unplugged everything he says, but still wouldn’t make sense as to why both circuits would all of a sudden not allow a reset?

It’s in the country so am wondering if it’s rodent damage or something on both circuit cables?

Are the Ns for these connected to the right N bars? although he has stated "no DIY work done, or none that he would admit to, worth checking that out imo"