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Ring main mcb intermittently tripping

The ring main MCB is intermittently tripping. Only the MCB trips, never the RCD. Presently the MCB will not turn back on, even with no appliances plugged in to the ring. The boiler is spurred off one of the double sockets, but I've switched that fuse off. I've tried switching the MCB with an alternative breaker, but the problem still occurred so the actual MCB seems fine. This happens a hand full of times a month, but can go for over a week without tripping again. If it was an appliance, I'd have thought the breaker would go back on when all plugs are removed. If it was wiring, I'd have thought it would be a constant fault rather than coming and going. Any ideas what could cause such an issue?

4 Answers from MyBuilder Electricians

Best Answer

Get an electrician in to do an insulation test before removing any sockets etc. Then if it is a low reading the circuit could then be broken down by closing the cables at the con unit and testing from point to point until identified. I would bet it’s a fault on one of the accessories either Burnt out or tracking across. Have you any sockets on a damp wall at all? I have known this to occur in the box behind the socket.


Answered 30th May 2019

If it’s been happening for a while I’d say it’s a loose wire that has probably melted the back of a socket our the spur badly by now so won’t take a load at all . I’d recommend getting an electrician in to open all sockets and spur in the ring and check connections , our have you had any work done nails screws through a cable and over time with it heating up gets worse till it’s made full contact across One our all of the live neutral our Earth , and the breaker won’t hold !


Answered 30th May 2019

I agree with Milne, could also be intermittent water or condensation build up if there’s the possibility of exposure somewhere.


Answered 30th May 2019

RCD trip's if balance between live and neutral is excedded. MCB trips on over current. Some times a light bulb blowing can cause MCB's to trip as it causes a spike, so you may have lose connections or broken socket/switch. Get electrician to do a full check on the circuit including insulation resistance test. It may involve disconnecting most if not all the sockets.


Answered 2nd Jun 2019

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