Lighting circuit issue

[martinh89]

Hi guys, just after some advice. Went to a job today with the description that one rcd on a dual board has tripped and when closed trips instantly, the customer was watching TV at night and all of a sudden the lights and sockets went under normal running conditions. I arrived today and the rcd, the lights(whole house as it's a bungalow) and the sockets had tripped. I flicked the sockets and the light back on and the rcd tripped I left the lighting circuit off and now the sockets and the rcd are working. I Removed all the bulbs and the rcd still tripped. Normally I would assume a borrowed neutral but as this was working perfectly fine up until last night I'm a little stumped, could this be a possible transformer fault on the spotlights? I have been in the loft and the wiring actually looks pretty good.
Cheers for any advice

 

[Leesparkykent]

Have you carried out any tests such as insulation resistance?

 

[plugsandsparks]

I guess rats, is there a funny smell

 

[martinh89]

No tests at all yet Lee, as my tester is being calibrated, I'm back Friday morning, tester an all. Just thought I'd ask the question and get a point in the right direction.

 

[martinh89]

I though rats as well but I did a good visual inspection and the cables and the routes seem to be clear and good, no smells either

 

[Octopus]

If there are 12v down lights my money is on burnt cables and/or transformers!

what you describe is a classic sign of this


or DIYer putting nails, screws or holes through cables!

 

[martinh89]

Yes in the bathroom there 12v down lights Murdock, I've never come across a transformer failing could this cause a live to earth fault? And is it a common fault?
Cheers for the reply

 

[HandySparks]

Yes in the bathroom there 12v down lights Murdock, I've never come across a transformer failing could this cause a live to earth fault? And is it a common fault?
Cheers for the reply

It would be unusual for a lighting transformer to cause a live to earth fault (and therefore RCD tripping) as they're not normally earthed.

 

[ipf]

Try locating the switch circuit to narrow the fault down.....for starters, of course.

 

[Octopus]

Yes in the bathroom there 12v down lights Murdock, I've never come across a transformer failing could this cause a live to earth fault? And is it a common fault?
Cheers for the reply

Really??



This one, the cable was so damaged by the heat, the live was in contact with the earth!

 

[Dave OCD]

I'd also look around for any outside lights with signs of water ingress, we've had so much rain lately !

 

[ipf]

Really??

View attachment 31550

This one, the cable was so damaged by the heat, the live was in contact with the earth!

Protection did it's job and saved a fire then :wink_smile:

 

[Octopus]

Protection did it's job and saved a fire then :wink_smile:

Yup. big flash and the MCB switched off.

No RCD protection, bathroom lights, fitted last year "to European standards" by an NICEIC spark. cough, cough.

 

[martinh89]

It would be unusual for a lighting transformer to cause a live to earth fault (and therefore RCD tripping) as they're not normally earthed.

I thought they were centre tapped and the metal enclosure would be earthed.
Cheers for the advice I'm back on Friday so I'll reply back Friday with a picture

 

[telectrix]

if the rcd holds with just the lighting mcb off, then it looks like a l-e fault on the lights. look for a picture hung above a switch for starters.