RCD tripping

[wumpty]

Hi

We have had a problem with the RCD (Wylex 100/2) tripping at random times (sometimes during the night) over the last week or so. Yesterday it tripped and within a minute tripped again.

To narrow down the source of the problem I initially switched off ALL of the MCBs protected by the RCD. My aim was to switch each one back on individually to find which circuit was causing the fault.

The RCD continued to trip even when the MCBs were all off. Would this be a fault with the RCD device?

Strange thing is that between 2000 last night and now (0930) no tripping has occurred.

Thanks for any advice,
Steve

[Adam_151]

What size tripping current is your RCD? 30ma? 100ma? (100/2 just tells us it can switch 100A and is a two pole device)

Is this the main switch in your consumer unit?

Anyway, my money is on a neutral->earth fault, the mcbs only switch the phase and not the neutral so switching them off will not remove the fault (however it might have an effect because the load on the system has an influcence on how much current goes astray)

If it hasn't tripped since last night, then that could be due to a lightly loaded local distribution network (did I mention that it can be affected by external things? ) What type of earthing system do you have? TT? TNS? TNC-S? if you don't know then a picture of your meter area and consumer unit area would be usful. But equally, I suppose, it could be an intermittant fault

An electrician would find the fault by conducting insulation resistance tests on all the circuits, as the fault is quite likely to be a direct short between the two, it could probably be located using an ordinary multimeter (but unless you are really sure on what you are doing, probing around in a CU is not such a great idea... same goes for the trial and error method of disconecting neutrals until it goes away). If you have drilled any holes or hung any pictures recently though, it might be easy to find the fault...

[wumpty]

Quote:

What size tripping current is your RCD? 30ma? 100ma? (100/2 just tells us it can switch 100A and is a two pole device)

Hi, it's 30ma

Quote:

Is this the main switch in your consumer unit?

Yes, part of a split load unit.

Quote:

Anyway, my money is on a neutral->earth fault, the mcbs only switch the phase and not the neutral so switching them off will not remove the fault (however it might have an effect because the load on the system has an influcence on how much current goes astray) If it hasn't tripped since last night, then that could be due to a lightly loaded local distribution network (did I mention that it can be affected by external things? ) What type of earthing system do you have? TT? TNS? TNC-S? if you don't know then a picture of your meter area and consumer unit area would be usful. But equally, I suppose, it could be an intermittant fault An electrician would find the fault by conducting insulation resistance tests on all the circuits, as the fault is quite likely to be a direct short between the two, it could probably be located using an ordinary multimeter (but unless you are really sure on what you are doing, probing around in a CU is not such a great idea... same goes for the trial and error method of disconecting neutrals until it goes away). If you have drilled any holes or hung any pictures recently though, it might be easy to find the fault...

Don't know what type of earthing it is, I'll try to get some photos when I'm home.

I'm not an electrical expert by any means, so are you saying that the RCD could be sensitive enough to trip by problems outside of the house?

Haven't created any holes in walls lately either! Thanks for the reply.