DIY Question - false positive from non-contact live wire detector

pturo · Mar 17, 2015

Hi,

I was going to post this in the DIY forum, but I can't seem to view or post anything there...

Pulling up some floorboards in my old victorian house, which previous owner had re-wired recently, I found a cable which has been cut off. When I passed my non-contact live wire detector over this cable, it gave the warning signal for presence of a live wire.

I haven't managed to trace this cable back more than a few metres, as it'll involve pulling more floorboards, but it does run alongside some of the new wiring for a few metres; could the current detected be induced by these other cables?

And how can I test to be 100% sure there is no current? I might pop out and buy a multimeter. If I strip the ends of the wires (with the power off!) and then put the multimeter across live and neutral (on the correct setting), would that tell me whether or not this wire is live? I've seen a video of someone doing that with a socket, but it sounds a bit dangerous to me...

I just want to be 100% sure this wire is safe, as I am wary of working in that area of this room in case I brush against it accidentally...

I'd really appreciate any advice here, so I can get on with things!

Deleted member 9648 · Mar 18, 2015

It's likely to be simply induced voltage lighting up your volt stick. You can check for voltage with a suitable tester (2 probe voltage tester) if you feel competant to do so. Alternatively isolate all circuits via the main switch and blank off the cable by terminatiing it into a joint box. You do need to be absolutely certain the cable is dead before working though.

pturo · Mar 18, 2015

Thanks a lot for your reply, Wirepuller. I will attempt to measure the voltage in the cable with a multimeter. Then either cut it back further, or cap it off into a junction box.

telectrix · Mar 18, 2015

isolate by turning off the main switch for the installation. don't rely on guessing which fuse/breaker it is. then strip end of cable after proving dead. terminate into junction box, making sure the outer sheath is inside the box. then, with power restored, carefully check terminals L-N, L-E, and N-E with meter set on AC volts. if in doubt, get a local spark round.