MCB trip problem

[autolycusd]

I recently wired a new upstairs light and power circuit. (The entire upstairs is being converted from bungalow to house). An electrician then came and checked my work and connected the circuits up to a new consumer unit. A couple of nights ago, a day after some new plastering was done, the MCB for the upstairs lights and the RCD for that side of the board tripped. (I hope i'm using the right terminology). I was lucky i noticed almost at once because it took out the fridge and freezer late at night just as i was retiring downstairs.

Anyway, the RCD switch reset OK, but the MCB would not. It clicked back down immediately with a bit of a nasty bang. I tried for two days to contact the electrician, but he's not picking up or ringing back. So today i reset the MCB and all seemed fine for a minute or so and the upstairs lights worked OK. Then the MCB tripped again.

Could anyone please give me any idea what the problem might be? Thanks in advance.

 

[Chri5]

Look in the area that was plastered, Wet and juice don't work well together.

Remove all fittings in the plasterers work zone and check for moisture and plaster. Also check for loose or lost terminations in any fittings that were in the same area.

 

[autolycusd]

Thanks Chri5 - there was only really one switch and one lamp on the light circuit in the plastered room and i can't see anything suspicious there. In fact i tried the circuit with these two fittings disconnected this morning and got the result i described.

I had hoped the fact that there was a delay of up to a minute before the trip might point to something - or at least rule out something?

 

[JohnD]

we've had some cold nights

it might also be condensation (humidty from drying plaster) inside an accessory. I always like to brush out backboxes after any plastering or decorating

Agree about inspecting all the recently touched stuff, a wire might have come out e.g. when it was being pushed into the backbox, or nipped by a screw.

Guess how I know that.

 

[ajrobb]

An MCB delay of a minute indicates it is the thermal element in the MCB that tripped. For instance, you might be drawing up to 10 A on a 6 A circuit.

 

[JohnD]

...the MCB would not. It clicked back down immediately with a bit of a nasty bang....

and yesterday it was magnetic. Maybe it is drying out, but it could also be copper burning away.

 

[autolycusd]

Thanks guys. So in practical, non technical terms, might it just sort itself out in time as the plastering dries or should i be doing something? If so, what? As i said, the accessories are removed - just bare/tape insulated wires. And presumably any damp in the power sockets would not affect the lighting circuit?

 

[JohnD]

you should be trying to find the fault.

 

[1john]

You need an insulation resistance tester to track this fault down or an electrician who knows what he's doing. Focusing on the plastering causing the fault could be the wrong thing to do as it could be completly unrelated. Saying that, was any plasterboarding done afterwards, have you ran your cables in a manner that they may be damaged by screws or nails. have the cables been pulled tight in places, are they ran next to or crossing over heating pipes?

 

[JohnD]

what's that about your sheep?

 

[1john]

 

[JohnD]

EGO amo meus ovis cocta

you love your sheep?

the Ego is redundant

 

[1john]

EGO amo meus ovis cocta

you love your sheep?

the Ego is redundant

Not quite. clicky

 

[JohnD]

the Ego is redundant

and it is not a good translation

 

[1john]

I can do alot of things, but I aint no linguist. I will remove it if you like. OP, sorry this has gone off track.