I'll try and give you the full story here, so bear with me if it looks like an epic.
For the impatient, the summary is this: last night the RCD tripped out while I was using an electric drill. None of the MCBs tripped. From that point on, as soon as I apply a load to any socket the RCD trips again.
Right. From the top. I have been refurbishing my kitchen over the last couple of months.
Structurally, I have had a wall taken down to open the kitchen up into a pantry area - no electrics were involved.
Electrically, I have taken one spur off an existing double socket and fitted an SFCU and terminal box ready for the extractor hood, and another off another existing socket to supply power to the new built-in gas
Neither of these new appliances are wired in as yet, and the cables have been earthed to the terminal boxes and the live and neutral wires fixed into connection blocks.
Other than that, I have replaced all the sockets and switches with new ones and I can assure you they have been fitted far better than the existing ones were.
All this work was completed a couple of weeks ago and everything has been fine.
On Wednesday I got to the point where I was fitting the wall cabinets. In a momentary lapse of concentration I managed to nick a power cable while drilling into the wall, which obviously tripped the RCD.
So, amid a bunch of expletives, I dug the wire out of the wall, chopped out the damaged bit and rejoined it with connector block. I switched the power back on and everything was fine once again.
Last night I was fitting the final wall cabinet. As I started to drill the third hole the RCD tripped. Again, none of the MCBs tripped. I'm 99.9999% certain that this drilling was not in the vicinity of any electrics (once bitten and all that) and it certainly wasn't the 3rd hole that did it, as the bit had barely scratched the plaster when the circuit tripped.
At this point, I couldn't reset the RCD; it simply tripped every time I switched it on.
I went all round the house and unplugged and/or switched off everything
At this point I should mention that I basically have four circuits in the house: 2 lighting and 2 power. There are actually three other power circuits for the shower, cooker and garage but as none of these are required they are all switched off with their respective MCBs.
Anyway, after switching everything off I was able to reset the RCD.
The first thing I switched on was the combi boiler. Everything still fine.
Next, being keen to get the job in hand finished, I picked up the drill and squeezed the trigger. *trip*
Okay, the boy's getting a little impatient now after being unceremoniously dumped from his PS3 game. I switch on the TV socket. *trip* Switch it back off again.
Right. Let's try something less juicy. The cordless telephone. Brilliant, that works. Next I try a micro-hifi system. That works too. I switch on the microwave, which is currently giving staunch service in the dining room, and that lights up it's clock. So I press the start button and *trip*
*reset* *trip* *reset* *trip*
I go round and switch off the few things that were on.
B#gger! I could really do with the fridge and freezer working. *trip*
On the plus side, I can keep the combi running, so we have heat, and the lighting circuits seem unaffected.
I should note that it doesn't matter which of the two power circuits the load is applied to, the RCD still trips. Even if the other circuit is switched off with its MCB.
Frankly, I'm stumped.