Home wiring - changed light fitting, now no power

[Rodd Nock]

Hiya, hoping for some help here. I just took an old fitting down and replaced it, now that circuit on the fuseboard goes back on OK (no short that's making it trip immediately) but there is no power to anything on that circuit (upper floor lighting - none of the bedrooms or the hallway switch on).

The old fitting had about 15W of led bulbs in it, the new one is similar. I have actually removed the new fitting completely now in case that was causing the problem but it's made no difference.

The wiring was exactly as I expected to find - three 1.5mm T+E going to the fitting which were wired as per lighting ring in, lighting ring out, and a T+E to the switch which was clearly labelled using red sleeving over the black cable. I have double and triple checked and everything is put back together exactly as it should be. The old fitting had a screw-down connector block, I've switched to Wago connectors (and then switched back again to connector block!) so I am sure the connections are good. I've even tried putting the old fitting back on in case there was something magical about it!

I've dug out a bit of the plasterboard to make sure that I didn't put a screw through a wire - all good. I have tried turning the master breaker on and off to see if that made any difference, and even gone as far as turning every breaker in the consumer unit on and off individually to see if that helped at all.

I'm mystified now - what kind of fault stops any power going through a lighting circuit, but doesn't cause an RCD breaker to trip??

Thanks in advance for any help!!

[Rushjob]

Rodd Nock said:

I'm mystified now - what kind of fault stops any power going through a lighting circuit, but doesn't cause an RCD breaker to trip??

Thanks in advance for any help!!

A broken / disconnected live or neutral will create that scenario

[Belle427]

There will be a mass of connector blocks tucked up in the ceiling and one or more of the wires will have snapped off in all probability.

[Rodd Nock]

I've just cut a hole off to one side of the fitting and pulled all three cables through. I've got half a meter of the three T&Es having out of the ceiling, no sign of damage to any of them, no other connectors or junction boxes. New clean connections in the normal in/out/switch configuration, and the problem persists!!

[Road2Ruin]

Rodd Nock said:

I've just cut a hole off to one side of the fitting and pulled all three cables through. I've got half a meter of the three T&Es having out of the ceiling, no sign of damage to any of them, no other connectors or junction boxes. New clean connections in the normal in/out/switch configuration, and the problem persists!!

Take a picture of how you have wired it and post it here, just in case a mistake has been made.

[Rodd Nock]

I've identified which of the three wires is the switch wire by checking continuity with my multimeter, left that wire out of the equation and used some two way wagos to join red to red, earth to earth and black to black on the other two wires. Which should compete the ring and get all the other lights working. But nothing happens!

[Road2Ruin]

Have you turned the supply back on and checked the 'ring' wires for current?

[netherfield]

Unless you've managed to tug on one of the cables and broken the connection at the next ceiling rose along.

As above you've got to keep moving from one to the next fitting looking initially for live power, voltmeter would be handy.

Edited by netherfield on Wednesday 3rd December 17:04

[Rodd Nock]

Yes, I've checked for current and there is nothing there. I don't think that there's any risk that I've damaged anything upstream, I got lucky when I cut my ceiling holes and was able to unclip the cables rather than having to yank them out.

I am now asking around my mates for an electrician as I'm all out of ideas, if it was a complicated task that had gone wrong I could think of a lot more things to check!

[Road2Ruin]

If none of the other lights in the circuit are not working, have you tried swapping out the mcb with another. There is only a limited number of reasons why none of them won't work. Is there a rcd somewhere, that might have tripped.

[Richard-D]

Rodd Nock said:

Yes, I've checked for current and there is nothing there. I don't think that there's any risk that I've damaged anything upstream, I got lucky when I cut my ceiling holes and was able to unclip the cables rather than having to yank them out.

I am now asking around my mates for an electrician as I'm all out of ideas, if it was a complicated task that had gone wrong I could think of a lot more things to check!

Not to be picky but have you checked for current or voltage (just out of interest)?

In your position, if I was confident I'd not broken a connection near where I was working (seemed most likely to me also) I'd be removing the CU cover and checking for voltage on the output of the MCB.

[Rodd Nock]

I've used one of those light up volt sticks - works on the TV flex but not on the problematic wiring. I've also used a multimeter set to 250v ac.

Think I will have to try the CU tomorrow, it's amazing how fast things escalate!!

[Mr Pointy]

Rodd Nock said:

I've just cut a hole off to one side of the fitting and pulled all three cables through. I've got half a meter of the three T&Es having out of the ceiling, no sign of damage to any of them, no other connectors or junction boxes. New clean connections in the normal in/out/switch configuration, and the problem persists!!

Have you got a test meter? If so put a Wago or connector block on each cable for safety (don't join them together yet) & see if you can measure 240v on the loop in cable - measure L-N, L-E & N-E. If you get 240/240/0v then try connecting the loop in to the loop out & see if the downstram lights come on.

[Watchthis]

Trip the full consumer unit, switch all mcb/rcbo/rcd to off positions, re engage each one ensuring it's not tripping and see how you go.

My best guess is your mcb is likely the root cause

[Russet Grange]

I reckon you might be dealing with the first light on the radial and you've disturbed a connection on the feed from the CU.

Is it possible that someone moved the light in the past, and in doing so extended the feed from the consumer unit to do it?

So a case of :

1.5mm T&E >>> ------------------/ connector you don't know about /------------------->>> T&E into your ceiling rose

Just a thought.

[Rodd Nock]

Watchthis said:

Trip the full consumer unit, switch all mcb/rcbo/rcd to off positions, re engage each one ensuring it's not tripping and see how you go.

My best guess is your mcb is likely the root cause

I've tried that process a couple of times - none of the breakers trip, but still no power on that circuit.

Mr Pointy said:

Have you got a test meter? If so put a Wago or connector block on each cable for safety (don't join them together yet) & see if you can measure 240v on the loop in cable - measure L-N, L-E & N-E. If you get 240/240/0v then try connecting the loop in to the loop out & see if the downstram lights come on.

I've just done that test. no voltage on either cable in any combination, HOWEVER I do have continuity between earth and neutral on one of the cables. That definitely doesn't seem right! This circuit feeds lights in 13 rooms across two floors, some of which have multiple downlighters . . . where do I start looking for the problem?!

[finlo]

Unless you disconnect them from the board you will have continuity between N and E because they are connected together further downstream unless you are on a TT/earth rod system.

[Rodd Nock]

Thanks finlo, that saved me a wood goose chase! I've just checked the CU, there is no voltage between the output of the breaker for this circuit and the neutral bus bar. Does that indicate that I need a new breaker module? (It is turned on when I am doing this check!!)

[Richard-D]

I think you've found your problem.

[Rodd Nock]

Sorted it!! I've never known one of those to fall before but I've just replaced it with a new 6a b curve breaker and everything works again. Well, apart from the room I changed that fitting in originally, which now has several holes in the ceiling to patch....