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I'm installing an outlet plate sealers in my home, so I turned off the circuit breaker for all the outlets. However, when I removed the plate cover, and used a Non-contact voltage tester, it detected voltage on the Live (Black) wire. I then used a Receptacle Tester and a phone charger to confirm there's no electricity in the outlet which there wasn't.

How did the voltage tester detect voltage in the live wire if the circuit breaker was off? Is this phantom voltage? Note that I've used the voltage tester on the 70v-1000v mode.

Note that I've checked the other answers in this question, and all the questions it links to. But I'm not sure which one applies to my case?

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  • NCVs are deliberately very sensitive. Sounds like phantom voltage. Though for those sealers why does it matter? Isn't it: remove cover, add sealer, replace cover? Dec 19, 2021 at 3:16
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    You're right, it doesn't matter for sealers. I'm still new to this, so I was just confused why electricity would be detected even though circuit breaker is shut off.
    – Yohanna
    Dec 19, 2021 at 3:21
  • NCVT's are magnetic field detectors. Your de-energized wire has probably run through the magnetic field of an energized circuit creating a field in your de-energized wire. Dec 19, 2021 at 5:05

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We get a lot of reports of wiring problems on this forum, as you can imagine. We see defects all the time which can cause a circuit to be energized even when its breaker is off. And sometimes non-defects - handle-ties weren't required on multi-wire branch circuits until the 2000's.

I got an object lesson in that once, when I cut off a circuit for servicing - I knew for sure I had the right breaker, I watched the lights on that circuit turn off, and it was in conduit so I could visually observe the wiring route! Well, I flashed hot to ground with a screwdriver just to triple-check it was off, and the lights on the circuit turned back on. I would not have expected that.

As such, it's really safest to cut the main breaker (first disconnect point past the meter) when doing home wiring. Then, you don't have to worry about it.

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