HELP - any Sparky's please!

[Glynne]

A bit of background in case it helps.
About 7 weeks ago I came home to find I had a leak in the loft which was dripping through the bathroom ceiling in which I have 4 of the lights below.

2 of the lights weren't working despite changing the bulbs but the other 2 were so as I probably need to replace the ceiling, I left things until it gets a bit warmer.

Separately, last week I changed the fluorescent tube in the loft to sort out some rubbish and everything was fine.

Today I went in the loft and the strip light worked for about 10 minutes and then one of my lighting RCDs tripped. As the only light on in the house was the strip light I thought that had to be the problem so: -
I took out the whole strip light assembly and tried the RCD - it wouldn't reset?
Tested the light in my workshop and it was fine so I re-installed it.

Then I thought that perhaps some water from the leak had go into the cables leading to the bulbs and had rusted causing a short.
So I've taken all of the lights out and tested them - all fine.
I then thought that perhaps it was one of the transformers and took them out. A couple were heat damaged but the other 2 were fine. Rather than mess about II've left them all out thinking that if they are not there then there is nothing to short.
Tried the RCD, it still wouldn't reset.

Tested every single light bulb on the circuit that trips - all absolutely fine.
Then remembered I have small extractor over the shower. Took that out and tested it, fine but again left it out.

As a final resort, I took the switch for the strip light apart, again fine.

I've just about run out of ideas so before I have to get someone in, does anyone have any suggestions please?

 

[Dee J]

Is it an MCB (miniature circuit breaker) - normally a 6amp rated item that is tripping... or is it an RCD that is tripping? (wider unit with a test button). Just asking because you state 'lighting rcd' and most domestic setups use an RCD to feed several circuits - generally a mix of lighting and sockets - so it's unusual to have a
dedicated lighting RCD. So the fault may well not be in the lighting circuit. Indeed it may not even be lighting related or even water leak related. Working in the loft you may well have disturbed/crushed wires in another circuit. Sadly, at this point you really need an electrician equipped with an RCD tester and an Insulation meter (megger) - who can then logically test eazch part of your installation in a logical order. Random swapping parts can work, but ultimately logic and analysis needs to be applied.
Dee.

 

[Glynne]

Thanks Dee.
I've posted a picture of the board in case that helps: -

The lighting circuits are on the left hand side and I think you're right re the MCB as the RCD to the right operates both of the switches.
You can see the one that doesn't reset.

 

[Dee J]

Yes that is an MCB which is an overcurrent device. And yes it is restricted to a lighting circuit. If that won't reset when all the lights are switched off then its a fault in the wiring or junction boxes. There is a slim chance that the fault is water related, but there is a far greater chance that it is related to your activities in the loft - wire trapped under a loft floorboard, disturbed junction box etc even a rodent damaged cable - all rodents are very fond of pvc cable insulation - so you may well have just knocked a previously damaged cable. You might be able to spot the fault by careful examination of the cables - best done with all the power off and a good torch - just in case there are other damaged circuits which haven't shorted yet. If you cant spot it visually they its back to you local electrician with suitable test gear.
Hope that helps.
Dee

 

[porker]

I agree with Dee J's assessment but I have had an MCB go faulty after a trip (actually a Wylex one like those shown). Might be worth swapping the lighting one over to the other one and see if it is the actual MCB.

 

[Dee J]

I agree with Dee J's assessment but I have had an MCB go faulty after a trip (actually a Wylex one like those shown). Might be worth swapping the lighting one over to the other one and see if it is the actual MCB.

True. good point, wouldn't discount that. Simple test, just disconnect the circuit at the MCB and see if it will reset with nothing connected.

 

[Lons]

I agree with Dee J's assessment but I have had an MCB go faulty after a trip (actually a Wylex one like those shown). Might be worth swapping the lighting one over to the other one and see if it is the actual MCB.

True. good point, wouldn't discount that. Simple test, just disconnect the circuit at the MCB and see if it will reset with nothing connected.

Or swap the 2 mcbs around will show if it's faulty.

 

[Glynne]

Huge thanks guys, it's now sorted without needing an electrician.
As per the advice, I swapped the MCBs around and the same circuit wouldn't reset so it had to be the wiring as predicted.
Therefore it had to me stomping around the loft yesterday so I retraced my steps, literally.

Now when I retired 5 years ago, I used my retirement collection money to buy some air dried oak planks from Pugh's and these have been stored in the loft since then. I thought I had carefully made sure that there were no trapped wires but obviously sometime over the years a plank had moved and trapped just a tiny bit of wire against a roof joist. The wire wasn't broken but just showed a tell tale pale stretch mark on the PVC sheathing. Cut a piece out and carefully took off the sheathing to show: -

Rejoined the wire and "voila", the MCB resets! So whilst it was an electrical problem, it was woodwork connected!
I just have to re-install my bathroom lights and extractor fan back now.
Thanks again guys, your help is really appreciated.
Glynne

 

[Lons]

OOPS :lol: glad it's sorted =D>