Advice on RCD tripping

[peterhyper]

I was called to a job with a light circuit fault tripping the RCD. There are numerous 12 volt downlights on the circuit so I did lives to CPC and got 0.3 Megs on an IR test. I switched off all MCBs controlled by the second RCD and there was no tripping from the faulty light circuit, but once any one of the 3 ring circuits (all on seperate 32 amp MCBs) were switched on, it caused the second RCD to trip. So I suspected a borrowed neutral, but when I moved the circuit over to the other RCD side (where the ring circuits were on) it still tripped.

I had limited time due to this being a short notice job, but I did double check all the circuits were on the correct side of their RCD with no cross 'contamination' (I like that word). Any suggestions appreciated as to whether I overlooked the obvious (it wouldn't be the first time)?

 

[James]

Has all the hallmarks of a n to earth fault somewhere.

 

[Midwest]

I’ve embarrassed myself by trying to locate such faults in limited time. I would now tell a client, I would do the work on day rate and it would take as long as it takes.

That said, if I couldn’t locate the fault, I would not be expecting payment. Catch 22.

 

[Pretty Mouth]

Has all the hallmarks of a n to earth fault somewhere.

Agree. Downstairs circuit = outside light. Upstairs circuit = rats in the attic.

 

[Lucien Nunes]

It's hard to follow which circuits are on which RCD and what is tripping. But if only one RCD ever trips, if the cause is an N-E fault it will normally be found on a circuit controlled by the RCD that trips, even if it trips when circuits on the non-tripping RCD are loaded.

 

[peterhyper]

things.

I’ve embarrassed myself by trying to locate such faults in limited time. I would now tell a client, I would do the work on day rate and it would take as long as it takes.

That said, if I couldn’t locate the fault, I would not be expecting payment. Catch 22.

I took it on at my hourly rate, but it could be a pain to resolve as there must be around 25 downlights (12 volt), as well as it serving a number of under cabinet lights and some upstair lights (yes a bodge of a job). I will be able to find the fault, but the problem is how many hours will it take, and how many hours will the customer be prepared to pay for. Touch wood I have always eventually found the faults I've dealt with, but I have on occasions reduced the bill if I felt I was a little slower identifying the fault than I should have been.

It's an interesting point you make regards not asking for payment if you can't find the fault, because as above I will be able to find it, but how many hours it will take is another thing.

 

[Pete999]

I took it on at my hourly rate, but it could be a pain to resolve as there must be around 25 downlights (12 volt), as well as it serving a number of under cabinet lights and some upstair lights (yes a bodge of a job). I will be able to find the fault, but the problem is how many hours will it take, and how many hours will the customer be prepared to pay for. Touch wood I have always eventually found the faults I've dealt with, but I have on occasions reduced the bill if I felt I was a little slower identifying the fault than I should have been.

It's an interesting point you make regards not asking for payment if you can't find the fault, because as above I will be able to find it, but how many hours it will take is another thing.

You should advise your client that fault finding is a matter of elimination, and as such can take some time, if thet agree to foot the bill then all good, if they expect you to come in spend a few mins looking and find the fault, then an explanation is required or just walk.

 

[westward10]

We normally allow two to fours hours depending on the nature of the circuit, this is normally to find and report the issue but nine times out of ten once you find it you can resolve it at the same time. For this type of circuit four hours and allow £20 sundries for possible repairs.

 

[peterhyper]

You should advise your client that fault finding is a matter of elimination, and as such can take some time, if thet agree to foot the bill then all good, if they expect you to come in spend a few mins looking and find the fault, then an explanation is required or just walk.

I did advise them of the situation, but their English is a tad limited but I have emailed their adult son who contacted me (he speaks perfect English) to make him fully aware of the situation, and that potentially every downlight might have to be removed to check the connections, and that could take some time, and if the downlights are fitted in tight (which they likely are) then some filling painting might be required afterwards. So I've asked him to confirm that he and his parents are happy for me to proceed on that basis.

I will be happy if he says to leave it as I'm not desperate for the work.