Unusual RCD tripping

[jonboy1]

I have had a call out to investigate an RCD tripping. Initially this was thought to be caused by a leak from the shower. The installation has been installed poorly with a multitude of junction boxes under the floor (i counted 15 within 2 metres of the fuseboard). I located the problem circuits, 1 no. shower and 1 no. ring circuit. The cables were clear on IR test except for the shower which as soon as it was switched on tripped the RCD. I suspected that there was a problem with the shower although found it unusual as this too rang out clear with 250V IR test to heating element. I checked the ring circuit and this too was clear although when an extension lead was plugged in it tripped the RCD again (extension lead was ok). Then the client informed me that the vacuum cleaner had tripped the RCD from another socket which was on a totally different circuit to the other 2. I have a nagging suspicion that the RCD is faulty but there seems to be too many other variables to consider. Quote the client "we did not have a problem before the shower leak"

Short of beginning to strip the whole installation down and test i am at a loss as to where to start. I checked neutral and earth conductors IR with most of the circuits connected and they were clear, Megger is brand new, polarity is correct, along with voltage. I did find several loose connections in the backs of sockets etc but tightened them up and a completely loose neutral connection at the board. There has been a problem with rodents as well as the leak but all cables tested are clear. It seems that as soon as any substantial load is applied to circuit the RCD trips. Aside from changing the RCD are there any suggestions that you can offer. I have very little confidence in the installation as i found so many faults without even beginning to test.

Open to any useful suggestions.

 

[Amp David]

If your IR test are all ok, then test the RCDs if not already done.

Unless the householder has faulty appliances.

 

[Sintra]

Test RCD with no load connected.

 

[spamwize2]

i agree check rcd may be faulty, but i suspect something they are plugging in

 

[pushrod]

Is the whole CU protected by just a single rcd? check disconnection times if not already done.
It could well be that there are several appliances all contributing a small earth leakage current so that the total is just causing the rcd to trip. If it is this anything with electronics in is a possible culprit eg washing machine, vacuum, fridges etc etc. Getting the client to keep a log of every appliance that was on when the rcd trips might help to identify culprits. See if you can cause the rcd to trip by duplicating which appliances are switched on. Splitting the board so that it is under the control of 2 rcds can help.
Also if you have, can buy or borrow an earth leakage clamp meter then you can test the earth leakage on individual appliances. Hope this is of some use.

 

[kung]

Sounds the way to go with testing RCD on half/full & x5 a fault in the past plus all the tripping prob hammerd it.

 

[jonboy1]

Thanks everyone, will let you know how i get on!

 

[Jason Smith]

If its any help, I went with oldsweat to do a periodic and the RCD was tripping on half current. This house had hardly any of the usual equipment that causes earth leakage, small fridge etc, and most appliances were spanking new, this is probably the only reason the RCD stood up.
What I need to know is, obviously the other end of the spectrum, the RCD I suppose could fail to trip at all ? there must be installations out there with a faulty RCD just waiting.
Had loads of nuisance tripping jobbies, i.e alls well untill the washing machine reaches a certain program, one customer rather than spend out on a new machine,spent more than its value having it tested and repaired- must of had sentimental value, but it was brill for me as I was working on the house when he called, he got probably an ounce of carbon dust from inside the motor, nuisance excessive current to earth sorted !! Sequel is got called again six months later same problem, repair man this time changed the hetaer in the machine. Problem solved.

 

[baldsparkies]

With all those jb's keep a lookout for rogue shared neutrals. They have a nasty habit of tripping the rcd when a load is connected to any one of the shared circuits.
Sounds like you have a Mr DIY infestation in the house.
Thats assuming you have either a split board, or dual rcd set up as per 17th.
If just one rcd feeding all circuits, go for the usefull advice as already given.Also try using half tripp turning circuits on one by one, it has been known to find the offender.

 

[SirKit Breaker]

If the fault isnt the RCD then judging by your comments about JB's etc , its a knocking bet it wants a rewire.

 

[baldsparkies]

If the fault isnt the RCD then judging by your comments about JB's etc , its a knocking bet it wants a rewire.

Would go with that SirKit, but thats when the customer gives you the (This blokes trying to ripp me off look)

 

[Richard]

Check for any transformers on the lighting circuit. I know the lighting circuit appears ok, however it could be a neutral fault backfeeding.

 

[bugsy]

is this a split load board , have you checked to make sure neutrals are in the correct terms

 

[billy110]

Have you ramp tested the RCD as well as disconnection times?

 

[uksel]

i'd look for shared neutrals, also - how long ago was this 'leak' from the shower, maybe some of that water hasn't quite dried out yet?

damp walls?