RCB Tripping Advice Please

chris301up · Apr 3, 2019

My Son is in the process of redesigning his kitchen and one of the issues is that the electric cooker needs to be moved, approximately another 2 to 3 meters or so.

The current wiring is the old red and black 6mm running from a consumer unit situated some 60 feet away in the front room. This is a small terraced house and we didn't want the problem of ripping up all the upstairs floorboards and chasing out the plaster to replace the wiring, so we thought the easiest way was to purchase a 60amp junction box and extend the wire accordingly.

Today we ran the old wiring through the ceiling joists and then joined a new length of 6mm twin & earth to the exit point where the new cooker socket will be located. Now, what we cannot understand, is that the RCB keeps tripping and disconnecting the main ring main socket circuit.

At this point I will say that there is nothing connected to the end of the new cable, and the MCB for that circuit is in the off position, but this doesn't stop the RCB from tripping.

We initially thought the problem was with the kitchen ring main circuit, but I disconnected this completely and the RCB still tripped. Just as a matter of course, I thought I disconnect the junction box, and 'bingo' all was well. Why on earth would this cause a problem when it's not actually connected to anything and the MCB for that circuit is off? I will say at this point the cooker was working perfectly up until a few weeks ago when we stripped the kitchen out completely.

Just wondered if anyone has had similar issues and maybe have an answer?

Marcus Vaughan · Apr 5, 2019

wirepuller said:
In 40 years working I have never had a faulty joint box.

I agree. It doesn’t make sense. I guess we’ll never know what’s really gone on without a photo...

HappyHippyDad · Apr 5, 2019

chris301up said:
Okay everyone. Have had another look at the problem this morning and can confirm that it looks like the junction box is the cause. When connecting just the junction box to the existing wiring the RCD trips. No extension cable attached at this stage.

Just a bit of trial and error! I connected a standard 30amp junction box, together with the new extension cable, and all is well. RCD not tripping. Nothing else connected to the cable. I'll order another junction box and go from there. Thanks everyone for your kind advice

It is possible that the Junction box is faulty but EXTREMELY unlikely. It would be simple to test if it was the junction box Chris as you would just test for continuity between the neutral and earth terminals. If there is no continuity then the junction box is not faulty.

It is worrying that you have decided by 'trial and error' that a circuit is now safe to use. I realise you are trying to help your son save some money and probably also enjoy feeling useful to him, but you cant possible liven up that circuit until you have had an electrician look at it. Your son's safety is more important than your need to feel/be helpful.

chrisdungan · Apr 7, 2019

Sounds like a neutral /earth connection .
either in the j box or cable end.
have you considered a crimped joint with HD shrink tube instead of a j box

chris301up · Apr 7, 2019

Right everyone. Had a new J/B and fitted it and all is now well. Sorry I don't have one of these so called 'smart phones' so was unable to take any pictures. When this issue raised 'it's ugly head' I did consider crimp and heat shrink tubing as an alternative, but has I'd already contacted the supplier thought I'd wait until I'd tried the replacement.

I have an old friend of mine who works for the council and is a qualified electrician, but is currently off work at the minute following a knee operation, and he said he will be more than happy to call round when he can to check this out for me.

I will say at this point that I tried several other electricians before contacting my friend but none would entertain calling round and checking this out for me.

Thank you all for you kind help and advice

HappyHippyDad · Apr 7, 2019

chris301up said:
Right everyone. Had a new J/B and fitted it and all is now well. Sorry I don't have one of these so called 'smart phones' so was unable to take any pictures. When this issue raised 'it's ugly head' I did consider crimp and heat shrink tubing as an alternative, but has I'd already contacted the supplier thought I'd wait until I'd tried the replacement.

I have an old friend of mine who works for the council and is a qualified electrician, but is currently off work at the minute following a knee operation, and he said he will be more than happy to call round when he can to check this out for me.

I will say at this point that I tried several other electricians before contacting my friend but none would entertain calling round and checking this out for me.

Thank you all for you kind help and advice

Thanks for the update Chris and really glad you decided to get an electrician to have a look. It's good to hear how it ends. Still can't quite believe (without seeing it with my own eyes) that it's the junction box though.

telectrix · Apr 7, 2019

happyhippydad said:
Thanks for the update Chris and really glad you decided to get an electrician to have a look. It's good to hear how it ends. Still can't quite believe (without seeing it with my own eyes) that it's the junction box though.

it might well be the junction box if the cat has pi$$ed on it.

freddo · Apr 7, 2019

Sounds unlikely but I guess anything is possible. Here is a brand new socket with a N-E short, the fault was found during dead testing of a new installation. The fault was an assembly screw trapped inside the socket.