RCD tripping

Theres your problem. It could be a neutral to earth fault. Get it tested properly with a good ohmmeter, preferably one that is used for electrical installations, rather than a cheap £10 one from Wilko.

It sounds very much like you have an earth neutral short.

I had one for years.

The only way to ID is to first of all ID which ring - switch off the whole CU and disconnect each neutral in turn and measure neutral to ground resistance. (You should remove all un-pluggable appliances first) .

Then when you have the circuit Id'ed you need to measure neutral to ground resistance..as you get closer to the short, resistance will decrease.

After that it is a matter of inspection.

If the rings and spurs check out, it may well be an appliance. Electric motors have been known to short a turn to ground.

Note that this is a tedious step by step process of elimination and an electrician is going to charge.

Thanks for the explanation. He has managed to get an electrician in who should be working on the problem as I type.

Just out of interest when isolating the neutrals do you have to do all of them as it is a split CU and the the other half of the CU is working as it should?

An update. The sparky has been and isolated the issue to the upstairs lighting circuit but owing to the mixture of wiring systems ie loop-in at the rosette and loop-in at the switch has not been able to solve the problem yet. Owing to having to go to another job he has isolated the upstairs lights which has allowed all the other circuits on that RCD to work and will come back later to do some more testing. My SiL did say he spent quite a time at one switch on the middle floor.

Second that!, it needs some current to flow _before_ that will show up as a fault as such..

Second to the good multimeter!, if you can find one a second hand Fluke is a very good choice may not have all the bells and whistles but manage fine with mine in an Electronics workshop!..

No. Just the ones associated with the trip

I got an antique AVOMeter Mk II for £45 at a antique shop. So nice to have a reliable meter with a moving needle again

My downstairs RCD tripped one evening a couple of weeks ago, for no obvious reason. Narrowed the issue down to the outside lighting circuits so turned if off. Couldn't see anything obviously wrong with the lighting, and some of it would require ladder work to access, so I changed the screw terminals in various junction boxes for Wagos, not seeing anything wrong as I did so, and turned the power back on. Been OK since but it must be a coincidence.

Water getting in? It could trip when it rains and then the fault clears when it's dried out? Or something similar with a slug or other conductive beastie.

Theo

For quite a few years we had an RCD trip, seemingly at random until I realised it happened when my wife was roasting meat. This in itself didn't make a lot of sense since there were no problems with baking. However it then dawned on my that above but not quite to the side of the hobs was the unswitched oven fuse which got partially covered when the hob lid was raised. eg:

Don't think so. Not had much rain lately and everything external is well sealed.

For a few weeks the living room intruder sensor had been triggering during the night, the alarm sounding long enough to wake me but not long enough to bother the neighbours. Once that happened at about