RCD both tripping and refusing to trip!?

[Octopus]

yep i didn't have time for three of the NE IR tests and hadn't thought through the rest. Am really grateful for the advice on testing between neutrals etc.

What's also on my mind is that the house seems to have been working fine. It was bought with no certification, I conducted initial testing and from then it didn't trip once.

its a basement and ground floor flat and yesterday I worked on the ground (and kitchen inclusive) floor in other rooms than the kitchen converting pendants to downlighters. I have been really careful to drill around the conductors and core out separate holes into which the conductors will be redirected. In all this I only saw one instance in which a bit of sheathing was scuffed but I guess I have to face the posibility that I missed something.

On the topic of the ceiling there was another thing that really worried me. It is plaster/fire proof board city plus ... three layers on the basis of lard and plaster. the thing that worried me, and counting down from the lard and plaster, was that there was a one cm gap between the first and second layers.

what advice or comments would you make to the owners?

So there is your starting point!

 

[ipf]

Lard......Sounds like it must have previously been a commercial kitchen or takeaway.

 

[Sintra]

Yes and it seemed to be going well until today.

I just cant see how all four circuits on the one RCD (cooker and three power) can be affected when the only other circuits are lighting!? I've not seen evidence of a circuit crossover.

I also don't know how it is possible for an RCD not to trip when tested in one circumstance but to trip as expected in another. This is a burning question for me.

I will also fabricate a "circuit" from the RCD in situ test it in another way.

Is this a split board? Are there lighting circuits on both sides? If so turn off all lighting mcb's and try your rcd.

 

[snowhead]

The only way forward it to assume every single cable on every circuit has been vandalised by persons unknown.
Not forgetting outside as well, e.g any excavations that may have damaged the incoming supply cable.

Start at the begining with all circuits disconnected, test the obvious ones first where you know there has been a problem, cut cables, exploding radios etc.

 

[jaypp]

When I first returned to the job I tinkered with a lighting circuit

its a basement and ground floor flat and yesterday I worked on the ground (and kitchen inclusive) floor in other rooms than the kitchen converting pendants to downlighters

if you used jb to replace pendant and wire d/lights, check connections there (particularly if pendant was loop in/out) and perhaps check 2way from basement re borrowed neutral as stated in other replies (if feed @ switch)
just a thought if n-e tests don't help. also re-check ring continuity and figure of 8 and maybe socket that didn't like your choice of music.