Was woken by my son at 3am who told me the power was off. Seems to be the downstairs lighting circuit that trips the whole thing but I’m puzzled why. No lights were on at the time. Nothing has been done to that circuit recently. The whole thing is quite sensitive anyway such that a bulb blowing might trip it as well but that’s usually pretty obvious.

I’ve pulled one switch cover off to check the wiring but not sure where to start looking really. Beginning to wonder if a rodent could be to blame.

Any suggestions?

External lights on pir?

If the RDC direct I’d tripping it means there is earth – line fault.

Duff rcd or trip ?

Had a light circuit tripping for dud rcd also had one that was due to a leak that just filled a light fitting.

No external lights on a PR although there may be an outside light actually. I’ll check.

Earth line fault? You mean a poor earth or stuff shorting to earth somewhere?

How mouse proof is your house?

Yes, external light on the same circuit but no PR.

I wondered about a wet light fitting but can’t see any sign of it.

Maybe worth swapping the RCD to check I guess.

Couldn’t guarantee no mice but not aware of any at the moment. It is that time of year though….

Earth to line voltage is what I mean. If it is really bad you will be able to see a low resistance with cheap multimeter

Sounds like you’ve got a single RCD – sometimes when a lamp fails the filament can short to earth causing the RCD to trip.
I would first check any external equipment for water ingress, even when isolated (via a single pole device) a neutral earth fault can exist, which could trip the RCD.

Ok. No sign of water ingress, plus it’s not really rained for a while and didn’t last night.
I’ve checked what wiring I can see (switches and fittings) and all looks fine.
The puzzle is why it went off in the middle of the night. Makes me wonder if it was a furry animal but then how on earth you start finding that!

How have you narrowed it down to the downstairs lighting circuit?

Ask an electrician to check for nuisance tripping at the RCD, insulation resistance, etc

Have a look for water internally, leaky shower tray upstairs maybe?

If you can manage without it (by using table lamps) switch that circuit off at the consumer unit for 24 hours and see if it’s the cause

Its a bit difficult to fault find remotely as it’s useful to see the type of consumer unit you’ve got, how it’s laid out etc. (any chance of a photo?).

Firstly, it sounds like its the RCD thats tripping as all or part of the house is dead.

Can the RCD be reset with all the MCBs on?

If not then which MCB is causing it to trip/fail to set? (lighting probably). Is it just that MCB?

Can you get the RCD to set with just the lighting MCB on? If so, go round turning on your light switches one by one to see which one causes the trip to occur.

RCD trips are extremely difficult to pin down. The last one I had was due to a faulty neutral on Western Power’s pole outside the property. I was suspicious about it being external as I couldn’t replicate the fault but it was only when I did what is known as an earth fault loop impedence check that I saw an occasional fluctuation in the readings which confirmed it for me.

Based in Pembrokeshire so probably a million miles away from you but if by any chance you’re reasonably local I’d happily take a look for you (FOC).

Rich.

It probably didn’t go off by itself, your son presumably tried to use something or switch on a light to realise? I would concentrate on where he might have been at the time.

Last two times ours tripped, laptop lead fell off the windowsill and the live end dropped in the cats water bowl which popped the charger and the RCD, the second time my wife knocked her glass of water over on the bedside table, and it ran down the back and filled up the USB wall charger which had 4 usb ports on its upper side.

Heater elements in dishwashers, washing machines and ovens can also cause a trip when they pop so if one of them was finishing its cycle when you went to bed that could be the cause.

(also, as not mentioned yet, presumably you have gone round and unplugged every single item to prove it to the downstairs lighting circuit?)

Most probably the dreaded earth to neutral fault. Bloody pain in the arse. I’ve ended up moving both of my ring mains on to the non RCD protected side of the board due to this (I suspect creeping damp in our case) just to keep the power on. Haven’t got round to finding the fault yet…… Lazy git that I am.

Anyway, you (or an electrician) will need to remove the neutrals one by one for each circuit resetting the RCD each time to isolate which circuit is causing the issue. Because earth and neutral are common at the main supply fuse head the problem can be any circuit in the system and not necessarily the one you expect.

Finding the earth neutral short within the problem circuit will involve an insulation/resistance tester and a logical approach. I tend to split down the circuits into two halves and see which half is down, then split that half again and so on until the leg of cabling or faulty outlet is found.

Sometimes I find nothing as it was just some rogue moisture in a fitting that has since dried up and the RCD can be reset without tripping.

Thanks for all the advice and offers of help. I know it’s really hard to diagnose at a distance (and I’m in Northumberland unfortunately rwamartin – but thanks) but I was just making sure I’d not missed anything really obvious.

Everywhere that could be wet seems to be dry as far as I can tell without lifting floorboards, etc.

My first thought was the dishwasher but it’s definitely that lighting circuit. Turn them all off, turn the main back on, turn them all back on again and it’s that one that trips the whole thing. The house has been extended but it’s the original downstairs lighting circuit that’s doing it.

Need to track down an electrician I think.

Thanks!