Help with another bizarre RCD problem

[timidez]

Hey guys!

I have a RCD protecting the sockets in a 2-bed flat, everything else is unprotected. Every now and then it will trip when we switch the (unprotected) lights off (any lights, coming from 2 different MCBs). It often happens in the early morning between 6 and 830am and we will use the same lights all day, all night without any further incidents. When the RCD trips I can reset it immediately and it stays on. I've checked the consumer unit (a wylex) and all the connections seem to be at the right places.

My theories:

It's either a hyper-sensitive RCD unit or something to do with moisture/difference in temperatures during the night?

In any case am I right to say the problem will have to be at the unit where the earth cables meet?

I'm not extremely technical but very interested in the subject, I would really appreciate your opinions.

Thank you very much!

 

[ackbarthestar]

It could be one or more of a number of intermittent faults.
1/ Over sensitive RCD
2/ Lighting neutral connected to the socket circuit, or even just switching on a bed-side light.
3/ Time switch coming on in the morning
4/ A possible N-E current imbalance when switching on/off the lights at a time when other appliances are switching on and of (washing machines, dishwashers, CH systems).
5/ external surges, voltages appearing on the earthing conductors

IMO, if you do not have the kit or experience of electrical fault finding then I would get a local electrician in to test the circuits.

 

[oldtimer]

I your central heating timeclock set for 6 - 08:30 ?

 

[timidez]

Thanks for your replies so far!

Ackbarthestar, I was wondering about external surges but there is conflicting information about this on the internet, some people saying RCD is not affected in these circumstances.

Oldtimer, the timer on my boiler is not working, the clock is working fine but the taps are being ignored by the heating system, so the answer is no (although the fault with the timer may be relevant?)

Thank you once again

 

[eckersecker]

Had one trip at various times in a house once. Went back retested circuit , no joy still a mystery. To stop customer losing faith I just changed the RCD and there has been no problems since.

 

[GLENNSPARK]

Place we were at the other week had neusance tripping of an RCD...crappy protius board that one..anyway.....been in and did the usual ....IR n all that which came back good....so thought i`l have a look behind those socket fronts anyway and found all the CPCs had been yanked hard up against the live conductors so seperated them and sleaved individually....not had any neusance tripping there sinse......funny the IR test didn`t pick that up though...........:beatnik:

 

[timidez]

The RCD I have is a Wylex 80A 30ma, protecting 2 32A MCBs. Would you recommend something higher to reduce this sensitivity? I'm almost sure there is nothing terribly wrong here, it's some kind of interference or external surge as suggested by Ackbarthestar.

 

[trev]

I'd do a ramp test first mate, if you have the necessary kit of course. If not, I'd suggest posting up your location we'll have a member near you who would help

 

[Engineer54]

Why don't you just replace this RCD, the chances are, ....no more problems!!
RCD can be fickle things at the best of times. You probably just have an over sensitive unit, it happens!!!

 

[peanutty]

Hi. check tightness of all connection s in cu, had before were RCD tripped randomly when non rcd and rcd circuits operated, (lights, boiler hairdryer on upstairs ring). thought at first was going to be borrowed neutrals but turned out to be loose neutral connection at main switch before rcd!!! if rcd hadn't been tripping no fault would of been picked up till connections had burnt out i guess. hope it helps.

 

[timidez]

If it trips again (hasn't happened since Thursday) I will replace the RCD as suggested. Peanutty, I've done that (checked all cu connections) yesterday, hopefully it will make a difference. It's an annoying problem because there is no apparent reason and it's so random