Dulwich wrote:
We had major work done on the house a couple of years ago. This
included, amongst other things, a loft conversion. When the electrical
wiring was being done we had a new consumer unit installed. The
builder used various sub-contractors including an electrician - in
whom we did not have a lot of confidence. This scepticism has been
borne out by a legacy of problems.

A new electrical problem surfaced yesterday and I wanted to air it
here to get your views before I take issue.

A light bulb in a ceiling fitting in the loft blew. This is in one of
two light fittings on the same circuit. I replaced the bad bulb and
switched on the wall switch. The was slight click and neither fitting
lit up. I went to the consumer unit and turned off the supply on the
circuit for the lights in the loft. I came back up and to be safe, I
put a voltage detector to the fitting and was surprised to hear it
beep. I toggled the light switch and in both positions and the
detector still registered voltage.

That isn't necessarily an indication of anything wrong/faulty. It depends
how the voltage detector works. Many such devices will 'detect voltage'
due to capacitive coupling between wires.


I thought then that maybe the circuit was mis-labeled. I then turned
off various circuits and found that the voltage disappeared only when
the circuit for the 13 amp sockets in the loft and the loft lighting
circuit were both turned off at the same time.

That fits with the above diagnosis, remove *all* power from adjacent
wiring and the voltage detector 'sees' nothing.


I kept the circuit for the sockets off then put two new bulbs in the
light fittings. I switched on the wall switch. Only one came on. The
original bad one was still not working.

I'm not an expert in electrics but something here just isn't right -
to put it mildly.

What should I do next to check things and to try to get to the bottom
of the mystery?

I suspect that things may actually be alright (in that the lights are
on the right circuit etc.) and what has happened is that the light
bulb that has failed also has a faulty/worn out holder and that the
new bulb is not working for that reason.


First get a reliable way of detecting the presence of mains, an
analogue meter is pretty good. Then check out the lamp holder
where the non-working lamp is.

--
Chris Green