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Hi
I have 2 wall lights and one ceiling light connected together controlled from one wall switch, they've been working fine for years.
I changed ceiling light today, worked after install but stopped working when tried few hours later. I checked voltages at each light and they show 150-170V but 240 between live and CPC. The junction box is in the loft easy access, went there and same thing the voltage at the line feed (black sleeve cable in photos) reads 190V between Live red and N black, but 240 between L and PC. I tried different light switch, still same.
I tested wall wall lights and ceiling light individually on wall socket and all work fine.

Shall I short switch wires L and common and try? What else can I check?
There is a socket in the loft used for antenna booster and one flourescent loft light, I am thinking removing light live feed (black cable) and generate live feed from loft socket, is this a good plan?
Is it possible the neutral wire in the line feed (black cable) may be broken somewhere but why today when I changed light ceiling?
Or is there something else???

Photo attached
Thanks

If it did work, and now it doesn't work after you changed lights, it is something you have done. From what you have said, it does sound like lost neutral. It could be a broken wire, but more likely a loose/bad connection.
You could remake all connections (not just tighten them) or replace the JBs with wago connectors.
It maybe one of the wires has no connection, but the screw has squashed through the insulation, that doesn't happen with wagos.

Someone-Else wrote: ↑Sun Apr 28, 2024 5:59 pm If it did work, and now it doesn't work after you changed lights, it is something you have done. From what you have said, it does sound like lost neutral. It could be a broken wire, but more likely a loose/bad connection.
You could remake all connections (not just tighten them) or replace the JBs with wago connectors.
It maybe one of the wires has no connection, but the screw has squashed through the insulation, that doesn't happen with wagos.

Yes this is my thinking, lost neutral but I didn't go to the loft to change the ceiling light and the cable for it is long even if pulled won't affect the junction box. I will check the neutrals in the junction box, take them off and reconnect or just a wago for neutral only for testing.

Someone-Else wrote: ↑Sun Apr 28, 2024 5:59 pm If it did work, and now it doesn't work after you changed lights, it is something you have done. From what you have said, it does sound like lost neutral. It could be a broken wire, but more likely a loose/bad connection.
You could remake all connections (not just tighten them) or replace the JBs with wago connectors.
It maybe one of the wires has no connection, but the screw has squashed through the insulation, that doesn't happen with wagos.

I used on wago on all except on CPCs, same
This is weird, I just changed ceiling light and dimmer to on off switch, it worked straight away, 4 hours later and this prob

All other lights on same RCD working fine

Picture?

Someone-Else wrote: ↑Sun Apr 28, 2024 5:59 pm If it did work, and now it doesn't work after you changed lights, it is something you have done. From what you have said, it does sound like lost neutral. It could be a broken wire, but more likely a loose/bad connection.
You could remake all connections (not just tighten them) or replace the JBs with wago connectors.
It maybe one of the wires has no connection, but the screw has squashed through the insulation, that doesn't happen with wagos.

I removed black live feed cable, replace with new cable powered from socket in loft and it did work. As we thought Neutral buggered somehow somewhere. Wires in live feed cable are black and red but not massively old, could be broken somewhere or loose at the RCD. I will leave like this for now, opening CU is something I haven't done before, not doing it now.

Someone-Else wrote: ↑Sun Apr 28, 2024 7:10 pm Picture?

Pics attached, I tidied all wagos into JB, put old live feed in another JB, lights working not the best option but will do for now.