How to use a Multimeter to test if wires are live

[RedQueenie]

Hiya could someone please tell me how to use a multi-meter to see if some wires are live?
When the house was rewired the electricians left in all the old wires so we keep finding the odd wire that we have no idea if are safe. I've attached photos of the recent wires we have found and our multi-meter

 

[Fred Blogs]

Those wires could possibly have 240 volts across the live and the neutral. This is could well be a fatal voltage if you happen to touch a live wire with any part of your body. I'm afraid that if you do not know how to use a multimeter safely, and there is no way to actually be 100% safe when testing potentially life threatening wiring, then I would suggest you get a qualified electrician in to test them.

 

[RedQueenie]

Thank you for your reply and your concern. I thought there would be a safe way to test the wires.

 

[thomp1983]

Those wires look like there in a block connector.

Turn off your consumer unit and carefully remove the tape and take a photo of what's under it, if it's a 'chocolate block' then it's fairly easy to safely check it

 

[ETAF]

well that depends also on what the wire is doing - you are showing 3 wire and earth - which is often used for 2 way lighting - but can be used for anything - like controlling 2 different lights - from a double switch - which i have just found doing some DIY in utility room

and so any of the 3 colour wires maybe live - as i say often on a switch and so no neutral + you dont know if the earth is connected at the other end - so testing with a multimeter for 240V AC
may not actually reveal anything - But if you touched the wire - you are connected to earth and so may/will get an electric shock

the yellow 750 at the bottom between 6&7 oclock - V~ is the AC Voltage measure setting

Also you need to make sure the cables are OK and do not give you a shock - no idea where the meter came from and if cheap unsafe rubbish often sold on ebay from china

 

[bernardgreen]

The most important thing to do is to use a known Earth as the reference point when testing whether a wire is Live. This can require the use of a long lead from the Earth bar in the consumer unit.

One meter probe on the known Earth and the other meter probe on the wire to be tested.

To be safe one should verify that the meter is working.

 

[SUNRAY]

The most important thing to do is to use a known Earth as the reference point when testing whether a wire is Live. This can require the use of a long lead from the Earth bar in the consumer unit.

One meter probe on the known Earth and the other meter probe on the wire to be tested.

To be safe one should verify that the meter is working.

VFC or neon/LED screwdriver would be my very first test.

 

[RedQueenie]

I've attached another photo. It looks like it is in a block. Fairly certain it is one of the old wires left as it was behind a false wall we have just taken down, but would like to be certain before we put another wall back up.

 

[ericmark]

My multi-meter has a non contact voltage (NCV) setting, so placed near live wires it will show one to four bars to help direct you to where is live. The multi-meter you show seems to be for automobile use, to test it needs a reference point. My meter uses my body as the reference point.

If the cable is always live, then great, but what if it comes from say a extractor fan isolator, then you may find it shows dead, then some one switches on the isolator and it becomes live. There are many non contact voltage testers and some are quite cheap, I see one for £8:00 in Screwfix, since built into my meter, I have not tried using them.

 

[RedQueenie]

View attachment 382028 My multi-meter has a non contact voltage (NCV) setting, so placed near live wires it will show one to four bars to help direct you to where is live. The multi-meter you show seems to be for automobile use, to test it needs a reference point. My meter uses my body as the reference point.

If the cable is always live, then great, but what if it comes from say a extractor fan isolator, then you may find it shows dead, then some one switches on the isolator and it becomes live. There are many non contact voltage testers View attachment 382034 and some are quite cheap, I see one for £8:00 in Screwfix, since built into my meter, I have not tried using them.

Thank you. You are right the multi-meter we have is for cars. I'll have a look for the non contact tester.

 

[RedQueenie]

Just had a quick look at the non contact pen and they look like just the ticket for what we need (and also could be good when working on an old mini). Is there anything specific I should look for? As Ericmark said you can get them for £8 up but are the cheaper ones just as good?

 

[ericmark]

I wanted a multi-meter, able to do things my old meter could not do, one was measure DC amps, another to measure amps down to 1 mA, and I got the new clamp-on for £35. the UT210E does seem to have gone up in price, but I still use it as a bench mark, why would anyone pay £45 for a volt stick, which only does one of the many functions of the multi-meter, and does not do that function as well, being only on/off rather than four stages?

My wife has got me a few over the years

with many extra features, pity really, as I just use the one. They all seem to work OK, until the batteries bust, and it does not matter how expensive, once that happens, they are junk.

 

[ETAF]

are any of the wires connected on the other end of the block
it maybe a 2 way swich has now changed to 1 way and still in use
My brother had a 2 way switch which he nolonger needed and rather than sort out the wiring (which i would have done - he just switched it so the other switch was off - "UP" and then when they had a mate in to add a false wall / board-up / plaster - he boarded it in....... so same as you -

as it was behind a false wall we have just taken down,

 

[Harry Bloomfield]

Thank you. You are right the multi-meter we have is for cars. I'll have a look for the non contact tester.

The non contact testers, should never be absolutely relied upon, they can be fooled. If they light up, you can be reasonably sure something is live, if they don't light up, you cannot be certain it is dead. Additional testing is needed....

 

[RedQueenie]

I think it may be the old wires that were replaced when we had the house rewired as the switch in the utility has a two way switch to the kitchen. They didn't remove any one the old wiring when they did the new.