I have an electrical current detector that is beeping positive on the 2/6 studs that the 12/3 romex three way wire runs through. The door header that the wires run over at one point also continuously beep positive if I touch the southward current/voltage detector to it. If I turn off the breaker for the light switch, cutting power to the wire, the studs are no longer beeping positive for current. I pulled the wire myself. I also installed the breaker box in this new construction shop. 1/2 I have spray foam insulation in the wall some of which is on the wires. My studs are open so I can see most of the wire and don't detect any breaks. Could this be a ground issue? or perhaps the spray foam is conducting the field? Of do I need to pull the wire and rerun it because this means my have a leak into the stud. And most importantly, is this a fire issue. Any suggestions.

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    I seriously doubt it's a current detector. Though such a thing is buildable, it would be useless because it would not work reliably. It must surely be a voltage detector, and that is vulnerable to induction or capacitive coupling. Are these steel 2x4s? Dec 8, 2019 at 16:55
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    It sounds like phantom voltage in the stud, is this new construction with wet studs since you said 2x6 , is there metal siding? I have not seen spray foam act as an antenna most are insulators. Hid lighting, fluorescent, and LED Lighting all generate high harmonics and would be noisy electrically than an electric heater.
    – Ed Beal
    Dec 8, 2019 at 18:12
  • those little detectors have a lot of false-positives, which is ok. false-negatives are more concerning...
    – dandavis
    Dec 9, 2019 at 22:25

2 Answers 2


It sounds to me like you're using a (Southwire?) non contact voltage detector (NCVD), and it's sounding off when the switch has the wire energized, but it's not when it's not. That would be normal - some of the NCVDs that will pick up low voltages will pick up 120VAC through the wall.


Unless you detect high voltage on the stud, which could be possible if there is a open-ground, or a open-wire from the source or from a control box, to your junction box or electrical outlet, (and these studs I assume are metal since it's commercial area)

I would look for open-wire, bad ground in the electrical outlet or bad electrical detector. Most of recent study have demonstrated that spray-foam can be applied directly on wire (I personally worked many times with this in new or renovated place).

Where it could be bad, is on small wire; Phone lines, fire alarm line, small wire gage since there is gas in spray-foam and could eat the plastic around the wire.

You said this wire is 12/3, there is no way spray-foam could have damaged the wire. But using that kind of electrical detector, can lead to hazardous results and not accurate ones.

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