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I've tried to find where the AC cables are in a brick wall in my house, as I need to drill into it.

The Stud/AC Finder is showing the whole wall as AC Live. I also used the Volt Stick on the wall and its also glowing Red. I've turn off the mains breaker by the fuse box to disconnect the power from the entire house and the wall is still showing up as Live!

The wall I am testing is a party/common wall that is adjoining to the house next door.

I've used 2 different detectors and 2 different Volt Sticks.

Does anyone have any advice on what the issue could be?

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    Does this answer your question? Stud sensor finds current on large wall area
    – Kris
    Feb 1, 2021 at 14:42
  • Thanks @Kris it actually doesn't as I have turned the power off to my house and it still is detecting and also so is the volt stick.
    – Rickstar
    Feb 1, 2021 at 15:09
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    I think the question is a duplicate but no answer is satisfactory One of our electrical experts will weigh in soon I hope!
    – Kris
    Feb 1, 2021 at 15:24
  • The wall's plain (unreinforced) masonry, right? Feb 2, 2021 at 1:42

1 Answer 1

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The stud finder and the volt stick operate on changing electrical field strength levels, and they perform measurements by means of capacitive coupling.

It is possible that the fire & sound insulation in the parting wall is statically charged due to your or the neighbour's electrical wiring through or against the insulation. Even with circuits disconnected at the breaker, there can still be a small enough field capacitively coupled-in to trigger your devices.

With a bit of luck you may be able to reduce the sensitivity of your detector by placing a non-metallic spacer, like several sheets of paper, between the device and the wall, as you skim the wall.

Have you asked the neighbour to disconnect their power?

Alternatively, if you have outlets or wiring in that wall, you might be able to neutralize the field by grounding all conductors in the cables. This can be done by connecting a load but with the circuit power off. The load must preferably be "dumb" or "old fashioned" without control circuits, so no LED light, but a simple incandescent bulb, fan, or kettle would work.

Another trick that might work is grounding the wall itself: while grounding yourself place your hand on the wall to dissipate and keep dissipating any coupled charges. The important thing is to make sure you are well grounded, and so it depends on the flooring and your footwear.

It may be safer and more effective if you grounded the wall by placing a large and bare grounded metal object against it (e.g. pressing/leaning some HVAC sheet metal), or smaller objects at several spots on the wall. Then you have free hands and a clear path to ground without placing yourself in the circuit path. You could also ground the insulation by piercing nails or screws at several locations into it, and grounding them.

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  • Thanks, This really help and you have gone into a-lot of detail when I put my hand on the wall and ground myself by where trainers it stops giving false readings.
    – Rickstar
    Feb 2, 2021 at 15:28
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    @Rickstar good to know it works: will help other readers too!
    – P2000
    Feb 2, 2021 at 16:57

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