Long story short: I did some electrical work and now my RCD is randomly tripping. What have I done wrong?

Long story long: first day of the holidays so time for some DIY bodgery.

In the eaves cupboard in the attic there were mains cables hanging down joined with terminal blocks to wire in a socket. Bit shoddy looking.

I was concerned that these might get snagged when chucking stuff in the cupboard or could even potentially short on something metal so I decided to replace them with a proper junction box and neaten up the wiring.

I flipped the breaker for that circuit and confirmed it was definitely dead first with a lamp and then with a circuit tester in the socket and then directly on the wires themselves. Then finally the good ol’ tentative back of the hand. All good.

But shortly after, while installing the new junction box, the main RCD tripped. 😕 No idea why or how anything I was doing could have tripped it. Capacitive current from my body maybe?? I wasn’t wearing a nylon shell suit or anything.

Anyways, I finished up, reset the breaker and the RCD, checked the socket still worked, and everything seemed good.

Then at 2am, about six hours after I finished this work, the main RCD tripped again. I reset it and went back to bed. It tripped again some time overnight.

It’s back on at the moment but I’m just waiting for it to go again.

Question is: what the hell have I done? It wasn’t exactly complex electrical work. Not much more than wiring a plug. Can’t see how I could have got it wrong.

Any thoughts?

while installing the new junction box, the main RCD tripped

So not the RCD relating to this circuit?

You’ve disturbed some unseen earthing connection?

The main RCD has coincidentally gone faulty?

Some other electrical fault?

On the fact of it, replacing 3 leftover bits of choc block with a proper junction box would seem to be a no brainer.

Random issue – not directly related to what you’ve done but maybe you disturbed something else????

So not the RCD relating to this circuit?

Correct. I flicked the individual breaker for the circuit before starting work (marked 2 in photo), but while working the main RCD (big one at the left) tripped for some reason.

You probably just touched the earth to neutral and that tripped it.

Check back along the wires for possible insulation breaches where a short could be happening.

have you re-checked the wiring in the plug socket? (I assume that’s what thats the back of)

if the wiring behind was that shoddy, it wouldnt be suprising if the wiring in the socket was done well either.

If you touched neutral and earth together during the work it will have caused the RCD to trip.

I’ve tripped a main RCD workign on a ‘switched off’ circuit – electrician said it’s possible to do this if you ‘short’ a circuit.

My guess is there’s another nest of wires above where you were working with similarly shoddy connections that you’ve disturbed.

Ah didn’t realise that earth/neutral would trip the RCD even if the breaker was already thrown. That explains that part at least.

Perhaps the RCD developed a fault as a result of that? Likely?

Check back along the wires for possible insulation breaches

What I can see looks fine, but I can only see what’s in that photo.

have you re-checked the wiring in the plug socket?

Good shout, I’ll have a nosey.

this is how someone added a couple of spurs at my house.

At the other end they’d never used/disconnected them and just taped the ends of the wires up…

[url=https://flic.kr/p/X3E6Zx]012[/url] by luke burstow, on Flickr

Could the trip in the might be a coincidence? Any light bulbs blow over night that might have caused the RCD to trip out ?

Nice, I like how they chose to make a really dodgy connection just next to the copper pipes too. What could possibly go wrong? 😉

Yeah, the breakers just disconnect each live circuit, the neutrals are all on a bus together so if you short any part of that bus to earth, the main RCD will trip.

Could the trip in the might be a coincidence? Any light bulbs blow over night that might have caused the RCD to trip out ?

Not that I’ve noticed, and it tripped twice during the night, at least 30 minutes apart (not sure when the second one was).

That makes sense, thanks colp. Every day’s a school day.

So is it possible I knackered the main RCD in the process?

No you won’t have damaged the RCD

Based on the work done I think the most likely explanation is that you’ve got an exposed earth wire very close to an exposed neutral. (Could be a cut in the insulation where the wired have been stripped)

I’d whip the covers off the junction box and socket off to see what you can find.

If all’s good inside both you could be looking at an internal cable fault on one of the sections you’ve manipulated

Well it didn’t trip again but I don’t trust it.
So I took the face off the socket and rechecked the new junction box just to make sure. All good.

I bought one of those cheap socket testers from B&Q and it gives the socket the all clear BUT interestingly reports a missing earth on other sockets in the attic! Yikes!

My little circuit tester shows good continuity on the earth going into and out of the junction box. So the “disturbed some other unseen wiring” theory is looking plausible. (Or they were just never wired properly in the first place!)

Now I have to spend all day reshuffling the attic to get decent access to the other sockets. 🙁

Sorted!

One of the other sockets also had dodgy wiring. Presumably to save on the exorbitant cost of a nice safe junction box, the muppet just had three cables going into one socket (main in, main out, plus a spur to another socket).

Stuffing the resulting nest of wires into the back of the socket damaged the earth wire which sheared off.

So three double sockets on that side of the attic had no earth connection 😯

All ripped out now and replaced with a proper separate junction box and single spurs to the sockets. And unsurprisingly the socket tester is now much happier.

Thanks for your help all. 😀

How about the breaker thats in the ‘ON’ position but marked ‘Not in Use’? Probably got another abandoned cable sitting somewhere that is now live 😯

I’ve got one the same. The breaker is wired up but don’t know where it ends up…

Bizarrely I think that was for the doorbell!

There is an old transformer on the wall next to the fuse box which connected to the bell. I could probably turn that breaker off… probably…