An earth leakage fault has started to appear.

It could be many things, in two senses.

It could be that you have 'many things' each of which is adding a little leakage and that adding just one more has been "the straw that breaks the camel's back". One particular type of 'thing' that can do this is PCs. Have you several PCs running?

The other type of 'many things' is simply that it could simply be one thing which has slowly deteriorated and is now tripping the RCD occasionally. A common culprit for this is an oven element.

It can of course also be a wiring fault where some insualation has worn or a junction box has got water in it but these are relatively rarer (at least in my experience).

The breaker being "very hard to reset" isn't significant I don't think.

If repeatedly tripped my experience is that some RCDs get paranoid and trip again even though the main leakage culprit has been removed. Usually however, if this happens, just remove all the loads, reset the breaker and then turn circuits back on one by one. Of course if you then get a trip when one of the circuits is turned back on you have a good clue as to where the problem is.

All in all it can be quite difficult to find what is causing the trip when it's a bit random (as you're seeing). If it's something like an oven element failing then it almost always gets worse quite quickly and is then easy to find. Otherwise you will just have to try and be as logical as you can when trying to deduce where the problem is.

I'll second that.

At one point, we had a home server and up to 5 PCs, plus 3 printers, 3 satellite boxes, two digital terrestrial boxes and God knows what else running - much less now two of the kids are away at university - and we suffered random trips. I got rid of the RCD and replaced all the breakers with RCBOs, thus spreading the device leakage across different circuits, and we've had no problem since.

Washing machine or dishwasher elements are also a likely culprit too.

Don't forget any outside electrics or outbuildings where ingress of dampness may occur. We've had a couple of trips where an extension lead, being used for battery charging, has got damp inside its socket.

I had a washing machine once that was the culprit. When it got to the spin cycle the computer crashed out!

First disconnect the neutrals one by one off the consumer unit and test for shorts to ground, with and without appliances connected

OOI, how do you go about isolating the supply, before the CU? I've recently had the switch/breaker replaced with a 100A fuse protected with a seal.

I'd have to break the seal to isolate the CU, leaving the only way to isolate to any extent is at the CU.

By "main breaker" do you mean the breaker between the meter and the CU, or something inside the CU? If inside, is it an MCB or an RCD/RCBO? (In case you aren't aware, an RCD or RCBO will have a test button and an MCB will not.)

The CU's main switch will isolate the supply to everything else in the box. You're not looking at disconnecting the supply tails, so you don't need to isolate before the switch.

Just be sure not to touch the upstream side of that switch. Ideally there should be protection on those terminals, but that doesn't seem to be common practice. You could probably put some tape over the screws to prevent mishaps, but it would be nicer if there was an official cover.

Theo

Dont need to. Switch off the main RCD and simply disconnecte te neutrals one by one and check em

I've recently

Well yes, sure there will be mains coming into the main breaker, but that's as far as it goes. You have switched it off so nothing at the busbars.

Pics here:

Only one PC running at the moment.

Unless they are unplugged or physically switched off (not the PC power button), the power input filters will still be connected to the mains and they'll still contribute to the total leakage.

It's usually the kettle, though. Or the toaster. Or the electric shower.

Well, unless it's a worn-out circuit breaker (which happened to us last year).

Yes, it's that 'be sure' bit that makes me want to isolate away from the CU.

It's something I looked at because an electrician just quoted me nearly £500 to fit (and presumably check etc.) an additional MCB to the CU, and connect it to existing cable.

Fit a new seal?

Very true. I was called out to a health centre last week. There was an overnight power cut but one office ring circuit had tripped when the power came back on and was off in the morning. It also tripped when the facility guy tried to turn it back on so I was called out.

ARW snipped-for-privacy@blueyonder.co.uk> wrote in news:vme7ll$5n70$ snipped-for-privacy@dont-email.me:

or don't bother?

If you don't already have a smart meter, you may be able to persuade them to fit an isolator at the same time as doing the meter swap. Or you could get an electrician to do it.

'e's 'avin' a larf.

Should be a half hour work tops, including testing the circuit (assuming it's not something like an entire ring main where they have to unplug everything). £500 is new consumer unit money - not needed unless the existing CU is full or ancient.

Theo

Not just PCs. My Beko tumble drier has the filter where the cable enters before the mains switch. It developed a fault and would trip the RCD when the machine had cooled down after being used. An identical OEM replacement did the same thing after a few years. I've now replaced that one with a completely different filter. Only time will tell if that's any better.