RCD trips a few minutes after lights turned on

[harpoon]

Hi all,

I am trying to diagnose the following problem.

After coming back from holiday, we noticed that our RCD keeps tripping a few minutes after our kitchen lights have been turned on. If the kitchen lights are kept switched off, then everything is ok.

The lights were GU10 spotlights connected to a dimmer switch. Replaced the dimmer switch with a trailing edge dimmer and replaced the GU10 with dimmable LEDs ... and the problem is still present.

Any ideas what this could be and how to test the fault ?

Could there be water somewhere in the ceiling cavity ?

Any advice is appreciated !

Many thanks !

Harpoon

 

[Octopus]

Has anyone come across this before ? ... i.e. RCD only trips after the circuit has been switched on for a while ... does it make sense ?

Not unusual at all.....

 

[Ian1981]

Has anyone come across this before ? ... i.e. RCD only trips after the circuit has been switched on for a while ... does it make sense ?

Yes as conductors gently begin to heat up from draw of current (even low temperature)a low insulation problem in the wiring can operate the protective device or rcd

 

[static zap]

... does it make sense ?

Opposite of dampness , carbon build-up ,WORST case .
Firebrigade next !
( you may be creating semi-conductor condition-heat sensitive)

 

[harpoon]

Opposite of dampness , carbon build-up ,WORST case .
Firebrigade next !
( you may be creating semi-conductor condition-heat sensitive)

This makes absolutely no sense ...

 

[davesparks]

Opposite of dampness , carbon build-up ,WORST case .
Firebrigade next !
( you may be creating semi-conductor condition-heat sensitive)

What is going to cause this carbon build up, and where's the carbon coming from?

 

[Deleted member 9648]

Yep, I agree with Will, the reason I asked if low voltage or mains voltage was because if they had been low voltage, the transformer would have come into play and may have been faulty, but as they are mains this does not apply.
How old is your wiring?

It's the RCD tripping, as transformers are generally class 11 how are they going to trip the RCD?

 

[Deleted member 9648]

Its been a fairly wet week across Britain so damp on that part of the lighting circuit might be an issue. Seeing as you have changed the switch and lamps its pointing towards the wiring instead. Basic Insulation Resistance testing would find the fault but remember to disconnect your brand new accessories. This is simple fault finding for any decent Electrician, call one.

Why disconnect the accessories?
If the RCD is tripping there is no point in L-N tests, therefore no point in disconnecting accessories and potentially removing causes of the tripping during testing resulting in wrong conclusions.

 

[Deleted member 9648]

I got out of bed wrong side this morning but ffs, doesn't anyone understand fault finding?

 

[onions1066]

I got out of bed wrong side this morning but ffs, doesn't anyone understand fault finding?

I'm guessing this is your one week in every four.

 

[Andy-1960]

It's the RCD tripping, as transformers are generally class 11 how are they going to trip the RCD?

I agree under normal circumstances a class II device should not trip an RCD but we have a fault situation and possible dampness, if a transformer is sitting in a puddle of water in the ceiling void would this not cause the RCD to trip?
As the OP had changed the lights and the fault still existed, I was thinking what else could there be, it has been eliminated anyway as they are mains powered.

 

[davesparks]

Why disconnect the accessories?
If the RCD is tripping there is no point in L-N tests, therefore no point in disconnecting accessories and potentially removing causes of the tripping during testing resulting in wrong conclusions.

The point would be to separate L and N so that you can establish whether the fault is L-E or N-E, which may (or may not) assist in the fault finding process.

 

[davesparks]

I agree under normal circumstances a class II device should not trip an RCD but we have a fault situation and possible dampness, if a transformer is sitting in a puddle of water in the ceiling void would this not cause the RCD to trip?
As the OP had changed the lights and the fault still existed, I was thinking what else could there be, it has been eliminated anyway as they are mains powered.

It would hopefully cause something to trip if it's sitting in a puddle of water but then you'd expect the ceiling to be noticeably wet and discoloured. This wouldn't be unique to transformers though as that much water would likely have got in to joint boxes etc.
Also I wouldn't expect connections sitting in water to present such a delayed tripping action.

 

[Specialist]

I got out of bed wrong side this morning but ffs, doesn't anyone understand fault finding?

Not many.

 

[LankyWill]

Why disconnect the accessories?
If the RCD is tripping there is no point in L-N tests, therefore no point in disconnecting accessories and potentially removing causes of the tripping during testing resulting in wrong conclusions.

OP said he had already swapped the dimmer and lamps and the fault is still occurring. He has then ruled out that the aceesories are not at fault. He should remove them anyway to properly carry out insulation resistance testing.

 

[telectrix]

an earth leakage clamp meter might come in useful.