UK Light wiring issue - Looking for advice

NotALeccy- · Apr 24, 2023

Hi all,

Replaced a ceiling light yesterday (I'm a novice but confident with basic electrical work). All was well and working, so I turned off the lights and only at night realised the lighting circuit had tripped. Removed the new light today, assuming there was some issue with the wiring - some of the wires did look fairly worked. I cut it back and rewired exactly as it was before, but still the same issue - MCB for the lighting circuit is tripping.

It's an unusual set up, to my eyes at least, so I can't make heads nor tails of what's going on. Three twin and earth cables: lives going into a wago connector, 3 earths combined, 2 neutrals combined, and one neutral sheathed as a live going into live. This is the original set up before I trimmed it back:

[ElectriciansForums.net] Light wiring issue - Looking for advice

The previous owner was a competent electrician as I understand it, so would assume all is in order - but would like to see what you all think, and any suggestions on what the issue might be?

Another picture of the original wires which I cut off:

Thanks!

brianmoooore · Apr 24, 2023

This has been an extremely common way for ceiling lights to be wired in the UK, from the mid 60s, and is still often used in houses with 'basic' wiring. Recently there has been a move away from it, with the rise of electronic switches and badly designed imported light fittings.
What makes you think the tripping MCB is anything to do with the wiring at this fitting?
Does the MCB trip if the switch associated with this wiring is off?

NotALeccy- · Apr 24, 2023

brianmoooore said:
This has been an extremely common way for ceiling lights to be wired in the UK, from the mid 60s, and is still often used in houses with 'basic' wiring. Recently there has been a move away from it, with the rise of electronic switches and badly designed imported light fittings.
What makes you think the tripping MCB is anything to do with the wiring at this fitting?
Does the MCB trip if the switch associated with this wiring is off?

Thanks, that's useful to know.

I guess I'm thinking it's that light because everything was working fine until I replaced it...or at least until shortly after. Hadn't touched anything else on that circuit. It is still tripping the lighting circuit MCB when the light switch is off.

bryanh · Apr 24, 2023

The 3 reds need conecting togeather, the black with red tape is the switch wire and it and the blacks go to the new light SL&N&E

NotALeccy- · Apr 24, 2023

bryanh said:
The 3 reds need conecting togeather, the black with red tape is the switch wire and it and the blacks go to the new light SL&N&E

Thanks Bryan, but I think this is how I currently have it set up? 3 reds connected via wago connector, black with red going to live terminal, two blacks to neutral terminal, earth wires to earth terminal.

bryanh · Apr 24, 2023

So tell me is it still tripping with out the light connected? And if the answer is yes it's not tripping, are you sure you didn't mix up the switch wire? As that is the main reason for it tripping if you did

NotALeccy- · Apr 24, 2023

bryanh said:
So tell me is it still tripping with out the light connected? And if the answer is no it's not tripping, are you sure you didn't mix up the switch wire? As that is the main reason for it tripping if you did

Yep still tripping when I've put wire caps on instead of connecting the light, light switch is off too (not sure if this makes a difference). Definitely the same wiring set up as before I put the new light in.

It was working for a while after I first installed the new light so it might not even be this wiring causing the problem, but the fact it's tripping when I've not touched anything on the circuit seems suspect.

bryanh · Apr 24, 2023

OK Trace the red that's in the same cable as the black with red tape and cover with caps separately and then reconnect the other 2 reds together & the 2 blacks together,see if that stops the tripping

NotALeccy- · Apr 24, 2023

bryanh said:
OK Trace the red that's in the same cable as the black with red tape and cover with caps separately and then reconnect the other 2 reds together & the 2 blacks together,see if that stops the tripping

That did it, cheers Bryan!

What does this mean then? It wasn't set up like this before I took the light off...but was working? Do I keep it capped when I put the light on, or can I combine it with the red tape live to go into the live terminal on the light?

bryanh · Apr 24, 2023

OK so did you turn the switch on ? Did it trip? Are all the others rooms still working? Have you got any means of testing continuity ie an avo meter?

brianmoooore · Apr 24, 2023

If it's not tripping with the switch off, then there's nothing in your pic that is likely to be the problem.
If it's a MCB that's tripping, rather than a RCD, then it's quite a serious fault that needs investigating as soon as possible. MCBs don't appreciate being tripped repeatedly and there's a not insignificant fire risk.
I strongly suggest it's time to involve a professional.

NotALeccy- · Apr 25, 2023

bryanh said:
OK so did you turn the switch on ? Did it trip? Are all the others rooms still working? Have you got any means of testing continuity ie an avo meter?

It's not tripping anymore in that room with your suggestions, switch on or off. However I went round the rest of the lights on the circuit and found that a mains wired lamp in another room is tripping it when switched on...When I took that box off, two earth cables were loose. I reconnected them, and it's still tripping when I switch the lamp on.

I think it's time to call in a professional, this is becoming a can of worms.

Cheers for all your help mate, really appreciate it.

NotALeccy- · Apr 25, 2023

brianmoooore said:
If it's not tripping with the switch off, then there's nothing in your pic that is likely to be the problem.
If it's a MCB that's tripping, rather than a RCD, then it's quite a serious fault that needs investigating as soon as possible. MCBs don't appreciate being tripped repeatedly and there's a not insignificant fire risk.
I strongly suggest it's time to involve a professional.

After Bryan's suggestion to isolate that live wire from the wago, it's not tripping whether the switch is on or off. I'm taking your advice though, I've gone as far as I can with it.

Cheers for the replies.

bryanh · Apr 25, 2023

Hi M8 its always best to ask before as it might have been something simple like mixing up the switch wire (happens alot)which is what I was thinking, but yes its the right time to call in someone

UK Light wiring issue - Looking for advice

NotALeccy-

brianmoooore

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NotALeccy-

bryanh

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NotALeccy-

bryanh

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NotALeccy-

bryanh

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NotALeccy-

bryanh

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brianmoooore

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NotALeccy-

NotALeccy-

bryanh

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