Bathroom light tripping rcd

[MICH43L]

My bathroom lights keep tripping the rcd when I switch them on, not just the one circuit, but half the board!

There are 5 led gu10 bulbs on the circuit, plus an extractor fan wired into the switched live and main live (for the timer). The extractor is not yet firmly screwed into the wall.

Here's what I have done so far:
Removed all the led bulbs.
Removed the extractor.
Replaced the extractor (the components seemed to be getting warm, but I think that's normal).
Cut back some length off the hard cable (thinking it was possible kinks in the wire shorting) to the extractor and plugged it in via a Click Flow connector. P clipped everything to the wall nice and stable.

I thought this last change had fixed everything, turned the lights on and off several times no problem.

A few hours later, I turned on the lights and it tripped again.

Next step will be to pull down the ceiling and inspect the feed from the jb (which I think is quite busy) to the extractor.

Unless anyone here can talk me out of it?

 

[EFLImpudence]

As you have discovered, random removal and replacement is not a good method of discovering intermittent faults.

If you don't have the proper equipment to discover where the earth leakage is, you are probably not going to be able to find it.

 

[oldbutnotdead]

First one- are you absolutely sure it is the bathroom lights causing the problem? RCDs don't trip on overload.....you could get a situation where device A is leaking current from neutral to earth. But device A is switched off at the moment so there's no current to leak. As soon as you switch your lights on, current starts to flow on the neutral, leaks at Device A and trips the RCD
Second one- I'm assuming you own the place, if you're renting then get onto your landlord.
Are your LEDs 240v or 12v via a transformer/power supply of some sort?
Are the bathroom lights/extract on their own MCB or are they part of the general lighting circuit (you say JB so I suspect they'll be part of the general setup).
Do you really have to drop the ceiling to get at the junction box- that is very poor design on someones' part (unless it is a maintenance free type)
The investigation phase is very boring. Assuming there are power circuits on that side of the board as well as lights, unplug everything that can be unplugged from those circuit, everything else should have an isolator switch (FCU usually) so switch them off. If there is anything that can't be isolated/unplugged then make a note but don't worry about them at this stage.
Switch your lights on, leave them on and don't switch any other items on that side of the board on (lights mainly including any outside or inside PIR devices which you should have isolated). Does the RCD stay in? If no then start looking at isolating anything that can't be switched/unplugged- possibly at the consumer unit. If yes, start wandering round switching additional lights on (give it 5 or 10 minutes). Does the RCD still stay in? If not, what was the last item you switched on? If yes, start switching your spurs back on, see what happens. If it still stays in then start plugging things back in.
The big trap with RCDs is that most 13A sockets only switch the live- you might think 'can't be the kettle, it is switched off' but it isn't isolated til you actually unplug the thing. If you're unlucky, your FCUs will only switch the live- more work in the investigation phase.

 

[EFLImpudence]

you could get a situation where device A is leaking current from neutral to earth. But device A is switched off at the moment so there's no current to leak. As soon as you switch your lights on, current starts to flow on the neutral, leaks at Device A and trips the RCD

...but it would trip when device A was switched on - or other devices.



As the lights do not trip the RCD every time, it would appear to be accumulated leakage. Edit, or an intermittent fault.
Whether any of these leakages is excessive is impossible to tell for certain, but if this light switch is the only thing that trips the RCD, it would seem that these lights are where the largest amount of leakage is.

The only part of the circuit dependent on the switch being on is the switched live from the switch to the lights and fan, and the lights and fan themselves.

Does anyone disagree?

 

[oldbutnotdead]

...but it would trip when device A was switched on - or other devices.



As the lights do not trip the RCD every time, it would appear to be accumulated leakage.
Whether any of these leakages is excessive is impossible to tell for certain, but if this light switch is the only thing that trips the RCD, it would seem that these lights are where the largest amount of leakage is.

The only part of the circuit dependent on the switch being on is the switched live from the switch to the lights and fan, and the lights and fan themselves.

Does anyone disagree?

All valid points- my money is that there's some sort of Device A (boiler, PIR light, fairy lights, motorised valve) causing an issue maybe or maybe not in conjunction with the lights/fan. Been told too many times things that turn out not to be strictly true (usually to do with 'all I did was x' actually turning out to be that was the last thing they did, they did all sorts of things beforehand but decided they weren't important)

 

[JohnW2]

As the lights do not trip the RCD every time, it would appear to be accumulated leakage. .... Whether any of these leakages is excessive is impossible to tell for certain, but if this light switch is the only thing that trips the RCD, it would seem that these lights are where the largest amount of leakage is. .... Does anyone disagree?

Not much.

If what you say were the explanation, then one would would expect the converse to also happen ... i.e. that if the bathroom lights/fan were 'on' (without a trip having occurred) switching something else on would sometimes cause the trip to happen (even if the bathroom lights were the source of the largest leakage, although not large enough to trip the RCD alone).

In that scenario, one would obviously also expect that whether or not the light switch tripped the RCD would (assuming we are talking about L-E leaks) depend upon what else was switched on at the time.

It could, of course, simply be an intermittent fault in lights/fan or associated wiring which results in a substantial leak sometimes (but not every time) the lights are switched on.

Kind Regards, John

 

[JohnD]

I wonder if the bathroom is steamy and prone to condensation.

Is it worse in cold weather?

 

[EFLImpudence]

actually turning out to be that was the last thing they did, they did all sorts of things beforehand but decided they weren't important)

Yes, that's a good point.

 

[EFLImpudence]

If what you say were the explanation, then one would would expect the converse to also happen ... i.e. that if the bathroom lights/fan were 'on' (without a trip having occurred) switching something else on would sometimes cause the trip to happen (even if the bathroom lights were the source of the largest leakage, although not large enough to trip the RCD alone).

Yes.

In that scenario, one would obviously also expect that whether or not the light switch tripped the RCD would (assuming we are talking about L-E leaks) depend upon what else was switched on at the time.

True. I did not consider the converse.

It could, of course, simply be an intermittent fault in lights/fan or associated wiring which results in a substantial leak sometimes (but not every time) the lights are switched on.

Yes. That's probably it.

 

[JohnW2]

Yes.

That has not been reported, but maybe the OP hasn't tried it.

Yes. That's probably it.

I fear it might be. If, as would then be the case, the leak itself is intermittent, I imagine that, unfortunately, discovering the cause could be a nightmare.

Kind Regards, John

 

[MICH43L]

Thanks for the replies.

They're switching on and off fine again now. Have left it all running while we go around switching other things on, plugging and unplugging fairy lights etc. Nothing trips it. (edit: I know I need to do this in a more thorough methodical way as above when time permits).

Have given what I can see of the 3 core and earth to the fan a good wiggle (as that's the thing that has been disturbed recently). Doesn't break it (but the rest of it is above plasterboard so doesn't prove much). I even jumped around in the loft above!

It's not the units themselves (hitting the light switch with nothing connected still had the same effect).

Yes, it can be cold and damp, but nothing new there.

Assuming that a light switch can't cause the problem? It all looks ok inside.

I might take a look under the floor above to see if I can get to the JB. If so it should be fairly easy to disconnect the 3 core and earth to the fan.