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

 

[HandySparks]

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

Quite possibly.

I was thinking of the modern electronic double insulated lighting 'transformers'.

 

[plugsandsparks]

https://www.google.co.uk/imgres?img...d=0ahUKEwjptc3E8v_KAhWJ1ywKHeOdCH8QMwgdKAEwAQ

 

[martinh89]

Hi guys bit late but thought I'd follow upi found the fault on a switch feed for an outside light, but on investigation there were no nails that had pierced the cable, so just for my own satisfaction what could of caused the cable to burn out so far down the cable?
Cheers

 

[telectrix]

cable could have been trapped and squashed or damaged on installation. good to hear you found the fault.

 

[Leclanche]

Any sign of mice droppings in the roof space? looks to me like the cable could have been nibbled or friction burn from rubbing cables.

 

[mache]

Nice find, what was the location in the house where that section of cable came from ?? over joist in loft, under sofit to the outside light ?? It's interesting because it looks like a quite well defined area of damage but can't tell from the photo if there are any nibble marks.

 

[martinh89]

Nice find, what was the location in the house where that section of cable came from ?? over joist in loft, under sofit to the outside light ?? It's interesting because it looks like a quite well defined area of damage but can't tell from the photo if there are any nibble marks.

It was in a small section on trunking leading down from the loft to a switch in the kitchen, I first thought it may have been rats so I went from one end of the loft to the other and the installation appears to be in very good order, new cables but the damaged cable I found were the old colours so I can only assume it were the age of the cable?? When I pulled the new cable in, it flew down so there wasn't any nails snagging it, still a bit of a mystery to me

 

[Octopus]

Good feedback. Its nice to find the fault - did you show the client?

 

[mache]

It was in a small section on trunking leading down from the loft to a switch in the kitchen, I first thought it may have been rats so I went from one end of the loft to the other and the installation appears to be in very good order, new cables but the damaged cable I found were the old colours so I can only assume it were the age of the cable?? When I pulled the new cable in, it flew down so there wasn't any nails snagging it, still a bit of a mystery to me

Definite a mystery that one. Inside trunking but with paint mark on it. I would hate to think that a previous installer might have used it in a partially damaged condition, but thinking that as it was in trunking it would be OK and not a hazard. But over time the PVC has embrittled and eventually a fault developed. That's a wild guess by the way....
Another wild guess... when the circuit was changed and new colours were installed, the change in the circuit left excess cable on the switch feed which was just then feed through the trunking and excess trimmed off at the switch. Maybe this cable was damaged during the issue that warranted the new circuit wires going in in the first place but damaged notice to other cables and not this one. ??

 

[martinh89]

Yes I did show the client the cable and tried to explain the best I could about how I thought the cable failed I think they were just happy that the outside light were working.

 

[Integrity]

Hi, I would suggest completing your dead tests and seeing what arises from that and then if neccesary find the mid point of the circuit and see which side the problems on. best guess I would use the IR test to determin falt location.

 

[martinh89]

I found the fault location, I managed to gauge the route of the lighting cables and because the test wasn't clear from the c/u I went in the loft and tested legs from the junction boxes and manged to find it that way