Ceiling Rose Oddity With new Light and now not Working


Postby Pendelfin » Fri Jun 09, 2017 7:50 pm

I thought I'd put up my new light fitting today - I've done this several times in the past, but never this particular light - an electrician put up this light fitting several years ago. As always, I took a photo (attached) of the wiring before I removed the old fitting and was surprised to see a blue wire (I'm assuming it's neutral) from the ceiling, attached to the earth terminal of the fitting. I've never had any issues with this light since it was fitted.

I've wired up the new fitting in exactly the same way - and (of course) it's not working. On a happier note - at least it's not tripping the fuse and all the other lights on the same loop circuit are still working too.

Is this wiring acceptable? Is it likely the wiring or the fitting that's the reason for it not working?

Thanks in advance
Al
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Postby kbrownie » Sun Jun 11, 2017 1:53 pm

It is very likely that the blue core cable attached to the earth terminal on the light is acting as an earth and the original installer was too lazy to attach an earth coloured core. It is much better and safer to have class 1 fittings connected to earth, but it is unexceptionable not to identify the core by the correct colour.

Have you any test equipment to test that the core is indeed connected to earth?

The reason that the light does not work could be down to a loose conductor or that the insulation of the neutral or live conductor are trapped in the terminal, thus not making contact with the terminal. Or maybe even the lamp/bulb is faulty or not making good contact.
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Postby Pendelfin » Sun Jun 11, 2017 2:42 pm

Thanks for that. My suspicion is that the new light fitting is faulty. If I test the blue (possible earth) from the ceiling, what should expect to see on the test meter?

Thanks
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Postby kbrownie » Sun Jun 11, 2017 6:16 pm

The best method to ID the cables, would be to do continuity test for the earth (AKA CPC). This is dead test, So you would require to isolate the system and join up the CPC and the live conductor at the fuse board of this circuit, then test for low ohms continuity between the live and suspected earth at the light fitting with the switch in the on position. There are other methods but this is the best way to achieve it. I would also recommend that the main isolator at the fuse board was put in the off position

You would be looking for a low ohms reading generally not bigger that 2 ohms often much less.
Once this has been proven, then you can test continuity of the neutral by doing a similar test between either live or the earth and neutral.
If you get continuity you know that the circuit is not broken anywhere before that fitting. If you do not, then you have a broken circuit. If you do not get a reading for the earth, you cannot install Class 1 metallic fittings.
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