Electrical issue (kitchen light - wiring fault?)

pendulum

Hi,

Mum turned her kitchen light on yesterday (4-bulb strip light) and it blew the fusewire for the downstairs light circuit. I replaced the fuse, and now all the other lights work, but this kitchen light still won't work.

We suspected it was the light, as it was old... so we bought a new one. I fitted it, and the new light wouldn't work either.

I got a cable and plug and hooked up the new and old light directly to the mains to test them - they both work fine! So it's not the lights.

I got my multimeter out and sure enough it showed roughly 250V AC between the neutral and positive connection blocks. I hooked the light up directly to this (bypassing the switched live) and it works fine, but obviously its permanently on regardless of what the switch is doing

I tested the voltage between the positive (Red wire) and switched live (single black wire) with the switch on and it is only 150V for some reason...? I'm thinking this is probably the reason why the light isn't lighting?

I opened the switch and bypassed it by connecting the two wires together in a terminal block but still got the same issue, so it can't be the switch.

I'm out of ideas now, and I think it's about time for an electrician, but welcome any suggestions on what else I could try. I've just thought about measuring the resistance in the switch cable (I'd measure from the start of the positive cable near the light, to the end of the neutral (switched live) - so effectively down and back up the cable. Does anyone know what a healthy figure would be approximately?

Ideas welcome
Thanks

GordonIsA

I opened the switch and bypassed it by connecting the two wires together in a terminal block but still got the same issue, so it can't be the switch.

Explain how you work that out then I am confused?

The only explanation I can think of is a break in the switch live cable or a temperamental termination problem if your account is correct.

I would just get an electrician in

pendulum

My reasoning is, if the switch was causing the problem, then by connecting the two wires up manually (bypassing the switch), it would then work. As it doesn't work, the cause of the fault is elsewhere?

molerat

Are you sure you are connecting it up correctly, have you connected the old light back up, what wires have you got in the ceiling, pictures may help.

Ectophile

I would suspect a broken wire or failed joint somewhere along the switch drop.

A reading of around half mains voltage is often just an induced voltage in an open-circuit conductor, caused by it running in parallel with a live one.

I would expect the resistance of mains wiring to be very low when measured with a normal multimeter. Anything more than a few ohms is a problem.

I do hope you're isolating the circuit each time you try out some new configuration.

ormus

for 2.5mm twin and earth cable, the resistance should be about 7-8 mohms/per m.
for 1.5mm, itll be about 12 mohms per m.

DVardysShadow

I would measure voltages across the live and switched live [there is no positive in an ac system] at the switch and at the ceiling with the switch on and off