RCD Main switch Keeps tripping

[leighdilley]

Please can anyone help? I know very little about electrics or the jargon, so I apologies now if i call things the wrong names.
I had an extension built about a year ago and they removed my old fuse box with fuse wires and installed a new fuse box with RCD, trip, mcbs etc.
The problem is, that over quite a few months (not sure when it started) the main trip switch keeps tripping, it can happen day or night, several times a day, or not for weeks - so, totally random. Thing is, the smaller MCBs(?) never trip so we cannot isolate the problem. Is this normal that the main trip goes and not the smaller ones? someone suggested that my switch may be faulty. Anyone have any suggestions please?

 

[Adam_151]

Is it a split load board?, if so, what is on the RCD protected side?, I would expect to see things like sockets and showers here.

Prime candidates for tripping the RCD are are things with certain types of heating elements (they can get damp and start to 'leak' to earth), certain types of motors (carbon dust from worn down brushes can provide a path to earth) and things involving water, or outside-ness, so short list here of things that might be doing it.

Washing machine, Immersion heater, Electric cooker, Outside/garden lighting.

Also, Computer stuff by design leaks a bit to earth, so if you have lots of computers that could also do it, or it has been known for the PSU to become faulty and leak far more than it should.

To narrow down the circuit that is causing this, it is neccessary to not just disconnect live, but also neutral to the circuit (as a neutral-> earth fault can trip an RCD), and this can only be done by opening the CU (fuse box) up and disconnecting the neutral wires from the bus bar....so its not really a job for someone who does not really know what they are doing , I'd reccommend though, leaving stuff like the washing machine unplugged (not just switched off), and the immersion heater switched off at the double pole switch that should be nearer it, but if you can't eliminate it as one of the common culprits, its probably best to call in a spark who can hopefully find the fault by doing insulation resistance tests to find which circuit the fault lies on

 

[Qedelec]

As always, sound advice, Adam.
Would like to add that it is possible to have a faulty RCD which will need specialist equipment to detect. Had one over the holidays which tripped if a light switch (not on the RCD side) arc'd, or the MCB served by the RCD was switched off. I found that it also tripped between 10 and 20mA leakage on the phase to earth side

 

[leighdilley]

Thanks Adam for your advice. My board has the main trip switch on the right hand side and then 8 other switches (MCBs)(with sockets, cookers, lights ,etc) to the left.

We tried turning off and unplugging every socket over night the other night, and the power didnt trip (but then it seems to happen irregularly anyway). but the next day it tripped again 5 times, but the 3rd time that day that our power went the whole street went (and our switch didnt actually trip that time). Nothing happened during the next day but the next night the whole local area including street lights went. I spoke to the electricity board and they said that the damaged cable had now been replaced. Our power hasnt tripped since (although only been a few days). Do you think that it is possible the the street power was somehow tripping our power and if so, why is it that no one elses seems to keep going all the time?