Hi all,

Recently moved into a new place and I am having issues with the garage electrics.

All was fine for a few weeks but a few days ago, the RCD tripped. I reset it but it tripped straight away. There is one main and one each for the lights and sockets.

If I leave the light one off and the socket one on all is fine. But sometimes (and this is the annoying bit - not always) if I switch the lighting breaker back on it trips the main RCD, whether the lights are on or not. It will work OK sometimes but then trips some time later, normally at night of course! . I have had a look inside and all the connections seem fine and there are no issues I can see with the lighting circuits, but obviously something is amiss. I have reset it and watched it trip after a minute or so without touching anything?

It might be my imagination, but it seems to have started after we had several days of really cold weather followed by a sudden rise in temperature, and consequently there was a lot of condensation in the garage, including the light switches. I thought that maybe it would improve after a couple of days assuming it was condensation causing the trip, but not so.

Any ideas out there please?

Thanks.

John

i assume the RCD switches are sprung to go off, maybe whatever holds it 'on' is weak? new RCD perhaps? if everything else is fine, no shorts etc?

I suspect the damp has highlighted an issue and you are getting earth leakage!

I would check resistances on the L,N And E in the garage and see if anything is amiss... It is either a slightly worn cable, or a dodgy connection somewhere... even a screw terminal not quite tight enough can cause issues,

You have an earth leakage. Since it has coincided with wet weather, check any outside lighting (lamp fittings and switches).

[Edited on 20/1/12 by MikeRJ]

Also check all PVC wiring withing garage and if any external wiring for damage by squirrels/mice/rats

Do you have fluorescent lighting, you may find the control gear inside is leaking to earth causing you your problem, you will not be able to see anything wrong.

Could disconnect each in turn then power up to see which one is faulty.

Thanks for all the input guys

Problem is, it's nothing to do with using the lights, I can leave everything switched off and if I switch only the socket breaker on, the main RCD never trips, but if I put the light breaker on sometimes it trips the main one straight away, other times it can take several minutes, but it eventually will trip it. I can have all the lighting on when I reset it and it makes no difference to when it trips.

The layout is:

Main RCD switch 1 x 40A, 1 x 6A trip for lights, 1 x 20A
2 x double sockets
1 x bayonet light fitting
2 x flourescent strip lights

I would check all the terminal in the light switches and fitting are nice and tight.

It must be a slight short between live and earth on the lighting circuit but before any switches. Cant be to neutral because having the mcb off wouldnt affect it, and cant be after the light switches because they are off too! Also check the perminant live feed to any PIR lights.

Insulation tester is what you need.

Just because the lights aren't on doesn't mean it's ruled out, as soon as you switch the breaker on its supplying power to the cable. If there is a problem with the cable it will trip, light on or off.

[Edited on 20/1/12 by Ben_Copeland]

From what I understand it never trips if only the sockets are on. In which case the sockets are the only ones that are fine.

It looks like it's going to be a long process but might well be best to change everything one by one from the rcd onwards

If you cant get an insulation tester, why not turn off the circuit, remove all fittings, and bring them inside the house to dry them out. It is almost certainly damp thats causing this.

Sounds like you have a high resistance fault possibly due to damp as you have already said, take out all the lamps and disconnect the fluorescent fittings from the wiring, close your light switches and energise the circuit, this will test the wiring if it doesn't trip then its most likely to be in one of the lights.

Terminate any live ends into a terminal block before you turn on.

This will allow you to test without the use of a meter.

re connect the lights one by one until you find the problem fitting.

Thanks to all for the input

Top marks to ernie! damn rodents had nibbled away at about 18", just enough to expose some of the copper and most of the inner sleeving

Replaced the length of wire from consumer unit to light and sorted.

I knew there had been rats before (lots of rat cr*p!) butit was quite old, obviously they left a little gift before they moved on.

Thanks again guys