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I am doing things to my walls and can't tell whether I have pierced an electrical cable. My AC wire detecting studfinder seems unreliable.

I have tried continuity tests via my multimeter between some of the holes and different circuits and they have come up negative. I'd like to be able to poke a prong like my multimeter into the hole and see if it whatever it touches is metal.

Is there any kind of an instrument to do this or an attachment to my multimeter?

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    so, for instance, if your probe found the head of a nail you'd want a positive result?
    – Jasen
    Apr 26, 2019 at 0:15
  • exactly!!!!!!!!
    – Walrus the Cat
    Apr 26, 2019 at 2:49
  • Uh, I think you failed to detect sarcasm. "Is there any kind of an instrument to do" ... what you should be doing, which is looking for potential? Yes, it's called an non-contact voltage tester. Which you will have to entirely penetrate the wall with. Did something go "pop" and the lights went out? Otherwise carry on....
    – Mazura
    Apr 26, 2019 at 3:23
  • ... What are you going to do if it's a nail.. or some metal corner bead. Tear the wall open and feel silly? What if it's just a neutral, or an un-powered switch leg? It being made out of metal, or a lack of current, confirms nothing. If I am doing things to my walls and I suspect I've pierced an electrical cable, that wall gets opened up to find out. I'm not going to wave a magic wand at it and hope it doesn't beep...
    – Mazura
    Apr 26, 2019 at 3:31
  • Magnets are great at detecting metal in the wall. Not wires - just ferrous metal.
    – JPhi1618
    Apr 26, 2019 at 14:33

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The only meter that I know of that could detect leakage from a small hole in insulation would be a megger and it would have to be used by a trained operator not to make things worse. You might try and put the circuit on a GFIC breaker and see if you get a trip from some small voltage leakage.

Good luck.

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  • i ended up testing for continuity with every wire in every circuit. thanks for the tip re: gfci
    – Walrus the Cat
    Apr 26, 2019 at 20:22
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The best way to know if it's metal is to open up the hole just enough to slide a magnetic grabber in there; or a borescope. Magnets only stick to iron/steel, so it won't stick to electrical cables. They now make very cheap borescopes that plug into smartphones.

If you can touch it with certainty, you can make two voltmeter measurements (settings on volts AC ranged 240+ volts, do not set to amps unless you want to die).

  • Mystery object to mains power "NEUTRAL"
  • Mystery object to mains power "HOT"

Those will be the two major slots on your receptacles. If there's a third slot that's an oddball, that'll be ground which you will not use for this test.

Know your mains voltage (120V in North America, 230V in Europe).

If both numbers are a small fraction of mains voltage, then the object is electrically isolated from mains voltage and isn't an electrical wire... or you failed to touch it sufficiently - always a risk.

If either number is mains voltage, it is an electrical wire, or it's grounded (e.g. if all your water pipes are metal).

If the "mystery to NEUTRAL" number is approximately your mains voltage, you definitely hit a "hot" wire.

Hitting a neutral or ground wire is also serious. Current flows in loops; all the current comes back on the neutral wire. if you damaged it, it'll get hot there and potentially start a fire.

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