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I wanted to install a shelving system into my closet. The stud finder seems to detect live wires over a large area (approximately 4 by 4 feet!) The closet is in the basement, with no power outlets except the light fixture. But the stud finder's signal turns on about 3 feet above ground and continues all the way to the ceiling. I checked it with two different stud finders (same result). Question: is this even possible??? That there is so much going on behind a closet wall? I don't want to drill through any wires, but honestly, a closet like this, without shelves is quite useless...

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Stud finders find studs, not live wires. And they're notoriously inaccurate - it's not uncommon to have them go off in a large area, or nowhere at all. – BlueRaja - Danny Pflughoeft Jan 11 '14 at 6:19
My stud finder has a live wire detector. I've noticed that the live wire detector often goes off on textured walls in places where I know that there are no wires. Is the wall textured? – mikeazo Jan 11 '14 at 12:42
Is there a service panel on the other side of the wall? – Tester101 Jan 11 '14 at 13:14
With some models, once it detects a live wire, it continues to show the warning until you release the button, or perhaps until you pass over another stud. – BMitch Jan 11 '14 at 14:50
1. It found the studs quite accurately and it also has a live wire detector feature. 2. The wall is not textured - simple painted drywall. 3. I tried releasing the button and starting over again at different places of that area. The live wire detector goes off right away. No service panel on the other side of the wall, there the wire detector goes off as well and shows there an even larger area – Irina Jan 11 '14 at 15:21

With most live wire detectors there is an adjustment wheel that sets the sensitivity. If you have this turned up too high it won't give a localised reading.

Usual procedure is to turn the device on, then in free air, adjust the sensitivity up until the detector emits a tone, then turn back until it turns off.

Sensitivity may be affected by metalwork on the other side of the plasterboard/drywall. So you may need to back off the sensitivity further.

Test the detector somewhere else. For example if you have a power outlet and know the cables run vertically from that outlet, use that area to adjust the sensitivity to give a good localised indication of the wire run. Then try it in your closet.

If you have un-insulated hollow interior walls ("stud walls") and can justify buying, renting or borrowing an inspection camera, you may be able to make a small hole in a "safe" area and use that to locate wooden studs.

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Nope. No adjustment wheel on my model. I guess I'll have to find another one with the sensitivity adjustment feature. How precise will it be? – Irina Jan 11 '14 at 15:44
@Irina, the best I would expect would be an inch or so. However these tools are not foolproof. I think they work best where there is only a live wire and everything else is wood air, brick or plaster/drywall. I'm pretty sure that any significant metalwork nearby can make it difficult or impossible to get an accurate indication. – RedGrittyBrick Jan 11 '14 at 15:49
thank you! Will see what I can do. – Irina Jan 11 '14 at 16:04

Here is an easy method to determine the location of live wires, with a stud finder. I have a stud finder on which there is no means to adjust the sensitivity of the live wire detector. However, you may use paper for the same purpose. Stud finder is sensitive to the electric field; electric field depends on the distance (i.e. how far you are from the live wire) and the medium (i.e. the material between you and wire (air or other material). If you put some paper between the stud finder and the wall you decrease the sensitivity of the stud finder. I use phone book pages for this purpose (they are free and you may add as many pages as needed). The thickness of the pages may go from one page to 1 centimeter or more depending on the current in the wire, and the paint used on the wall. You will see that the stud finder sounds for electricity only when it comes on top of the wire; you can pinpoint the location of the wire exactly. I hope this info helps someone. Good luck.

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It's best to do a visible inspection. Just cut a small hole at the level of a normal power outlet and use a flash light and mirror to look up in the cavity wall. After the inspection, either patch the wall/paint or just install a blank plate over the hole. If you don't have a mirror, a camera phone with a flash works pretty well.

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It could be the power lines inducing eddy currents in lead paint, which the detector would interpret as a live cable.

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