Which is the switched live wire?

[markandmich]

Took an old light fitting down on a loop in system.

There are the usual three cables and L(red)/N(black)/E(copper) for all three.

One of the three blacks is the live feed from the switch but it was not noted when the fitting was removed.

What is the easiest and safest way to find out which is the live black wire?

Thanks

 

[JohnD]

Have you got a multimeter?

If not, pop up to the High Street with £8 in your pocket and get one, then report back. It will then be very easy.

Buy some red sticky tape (or, better, red sleeving) while you are up there.

 

[Chivers7]

Thought it was brown now

 

[JohnD]

...There are the usual three cables and L(red)/N(black)/E(copper) for all three...

p.s. better buy some Green&Yellow sleeving too.

 

[Spark123]

tbh I'd prefer to see the same colour scheme used as what is existing to minimise confusion.

 

[markandmich]

Thanks all

Got myself a multimeter.

Haven't seen one of these since physics lessons at school.

Please advise on the best way to use multimeter to find the live wire

Thanks again.

 

[JohnD]

You are looking for the switch cable. It will have a red core, connected to the other reds, and a black core, which is the switched live.

Turn off the power to the circuit, and verify (by testing from every red to every black) that there is no voltage across them.

Now turn your meter to "continuity" or "low ohms" (it might have a bleeper) and test by touching the probes together.

Put the light switch in the "on" position.

Now test from the bunch of reds to each of the blacks in turn. One of them will have continuity with a very low voltage.

Now put the light switch in the "off" position and test again. The continuity will have gone and it will be open circuit with a resistance so high that your meter will be unable to measure it. This shows that you have found the switch cable.

Now tag the switched-live black core with your red tape (at both ends) and sleeve the bare copper earths with G&Y.

 

[CallEdsFirst]

and not an RCBO in sight!

 

[gas4you]

Thought it was brown now

I was instructed that from the start of this year gone, that red sleeving was not allowed and has to be brown.

 

[Spark123]

In which case I'd advise all the phase conductors to be sleeved brown or use alphanumerics. Still think it is a bit daft not to be able to use red sleeve on an old system from a safety point of view, but I don't make the rules!!

 

[RF Lighting]

I use red sleeving if I'm working on old wiring, and brown if it's new colours

 

[securespark]

I use red sleeving if I'm working on old wiring, and brown if it's new colours

Thanks for that, Rob! So do I, and I thought I was the only one...

 

[gas4you]

I use red sleeving if I'm working on old wiring, and brown if it's new colours

Thanks for that, Rob! So do I, and I thought I was the only one...

Sounds more sensible to me listening to you guys, pity I threw out 1/2 a reel of red sleeving last xmas

 

[markandmich]

Many thanks for all the advice.

All is working and I have quite literally seen the light.