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

 

[Andy-1960]

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.

Not quite sure what I have done to deserve the tone of response on this one, fault finding remotely is always difficult at the best of times!
Maybe my statement of a puddle was a bit OTT, but I was trying to make a point. I have been in this game for 40 years and have not failed to find a fault yet!

 

[onions1066]

Not quite sure what I have done to deserve the tone of response on this one, fault finding remotely is always difficult at the best of times!
Maybe my statement of a puddle was a bit OTT, but I was trying to make a point. I have been in this game for 40 years and have not failed to find a fault yet!

If you've been in the game 40 years a bit of confrontation/ banter should be water of a ducks back. I don't think it was meant in the way you have read it

 

[Deleted member 72666]

I'm sure Andy had just over exaggerated when he said " a puddle of water", I assumed he meant it could be damp which could have the effect the op is experiencing, that's how I interpreted it, just saying.

 

[static zap]

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

It's an analogy to burnt cooking , degraded insulation becoming heat sensitive .
Well cooked , brittle , as it warms some of flexibilty is removed , so may be suffering compression . The main effect , insulation failure begins to make its own
heat , causing more degradation, in the same place ,like burnt dinner .
( Chemicals found in damaged PVC / plastics probably more worring to mention)
Regs about low smoke cable , etc ,are for special cases .

 

[Deleted member 9648]

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.

Quite frankly it wouldn't make any difference whatsoever to the process of finding a fault. Disconnecting equipment for no reason will ultimately prolong the process and remove possible causes of the fault leading to false conclusions.

 

[davesparks]

Quite frankly it wouldn't make any difference whatsoever to the process of finding a fault. Disconnecting equipment for no reason will ultimately prolong the process and remove possible causes of the fault leading to false conclusions.

I don't see how you can say that categorically without seeing the job and knowing what the fault is.

 

[harpoon]

ok ... had planned to get an electrician in, but hampered by Sports day ... and my electrician does not do weekends. So I decided to have another look. Turns out it is a N-E fault. Opened up the switch and managed to find the N wire that is causing the problem. Turns out that it is the N wire coming into the switch, shorting with a few E wires. Hope my electrician can find the fault quickly and fix it.

 

[onions1066]

Not connected into the switch though???

 

[harpoon]

No ... Not connected into the switch (only live wires connected to the actual switch) ... But located in the switch box. There are a lot of N wires screwed together using a terminal block. Identified the N connected to the lights and the N coming into the terminal block. The N connected to the lights are ok ... No N-E fault ... But the N coming in has a short to some of the E wires.

 

[onions1066]

What are you testing with?

 

[harpoon]

A multimeter ...

 

[harpoon]

In the end, it was a L-E fault ... One of the lights had too much insulation around it causing the wiring insulation to become brittle and eventually short.

All is good now ...

 

[harpoon]

Congrats to Murdoch and Ian for their educated guess ... We should have a competition on here for fault finding ...

 

[Octopus]

Congrats to Murdoch and Ian for their educated guess ... We should have a competition on here for fault finding ...

Thanks for feedback. Who found the issue?

 

[DPG]

In the end, it was a L-E fault ... One of the lights had too much insulation around it causing the wiring insulation to become brittle and eventually short.

All is good now ...

What about the N-E short you said you had found? Did the L-E short not trip the MCB?