Multimeter - Live Wire Test

[dk1uk]

Hi there - I have a small junction box in my garden - inside is a cable with a choc block on the end. I need to find out if it's live.

I think it was once for an outdoor garden light.

Anyhow, I have a multi-meter but I've only every used it for continuity testing. I just want to safely test whether the cable is live or not - it has a black/red/earth.

My multi-meter has two controls. Do I set it to "V with a squiggly line above it"; and to 500V?

many thanks.

 

[Johnmelad]

 

[ericmark]

Yes
However testing for dead also means you first test something you know is live then the item you think is dead then again the thing you know is live.

Also a meter has to measure against something so if the earth and neutral is open circuit then even if it is line it will not show. So I would also use a neon screwdriver as well or stick one probe into the ground to test.

Note line and neutral are both considered live which is why we use the word line to mean phase wire.

 

[dk1uk]

OK, thank you - as a first step though - should I leave the power on at the consumer board and test black probe on black; and red probe on red - does it matter which order I touch the probes in?

If I get no reading, then as a further test, which probe do I stick in the ground?

Sorry - had a shock a couple of years back (stupidly forgot to isolate mains in between changing/testing light-switches) - don't want to repeat the experience! So I've become probably over-cautious!

 

[ericmark]

It does not matter which way around for an AC circuit. However trying to prove dead never easy.

I was required to remove some cables at work and used all the correct methods proving units the lot. However some plant was still running and during the removal it became live.

Also had where two people working on same item of plant without knowing each other were there. One guy using an insulation tester gave other guy a shock. Foreman had to leg it quick.

So you can never be 100%. Borrowed neutrals are another source of shocks where the wires only become live as they are disconnected.

What I do is prove dead then handle as if they are still live. I have even had a socket connected to next doors supply. Which is why I would use a neon screwdriver not to prove dead in first place but in case something unforeseen like a borrowed neutral exists.

Yes I know one can find borrowed neutrals with a clamp on ammeter but I would not expect most DIY guys to own one.

 

[dk1uk]

Thanks a lot for this. I'll test it and hope that it's live.

Hopefully I can then trace it back to a light-switch - there are two switches (one in the kitchen and one in the dining room) that appear to do nothing, so I'm guessing that one of them powered what was once a garden light.

Thanks again.

 

[JohnW2]

Yes. However testing for dead also means you first test something you know is live then the item you think is dead then again the thing you know is live.

Very true - but in this case it may be that what he's testing is live - and if he detects it as live, then that means what it says, without any need to 'prove' the meter.

Also a meter has to measure against something so if the earth and neutral is open circuit then even if it is line it will not show. So I would also use a neon screwdriver as well or stick one probe into the ground to test.

Good point - although if he's got both 'earth' and neutral conductors at the connector block (and tests L against both of them), he'd be extremely unlucky if both of them (but not the L) were open circuit.

Kind Regards, John