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voltage tester


Jerry Lozier
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I use a noncontact AC voltage detector to test for live wires, ( knob and tube etc) however seems to go nuts in high static area, sometimes within a foot or two.... so can be unreliable at times

any voltage tester out there that is not as suseptible to static or other suggestions??

thanks Jerry

All non-contact voltage detectors are highly unreliable. They'll give both false positives and false negatives. Never rely on one in a life-threatening situation. They're not really voltage detectors anyway, there're electric field detectors and, as you've discovered, they'll react to any electric field. Worse, if the wire you're testing is shielded, the tester won't tell you that the wire is hot.

If you want something reliable, use a multimeter, a wiggy, or a simple neon light tester. Only use the non-contact sticks when the results really don't matter.

- Jim Katen, Oregon

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any voltage tester out there that is not as suseptible to static or other suggestions??

I had one once, a GreenLee I believe, that was overly sensitive to the point that I couldn't even use it to determine polarity in a 2-prong, ungrounded outlet. Anywhere in the vicinity of the receptacle and it would light up. It may have to do with the voltage sensing range(...?). Anyway, I've been using Flukes for a while that don't have that issue.

I do think they have their uses as long as you understand their limitations. Besides KT wiring, I also find them very handy for quick checks of AFCI & GFCI protected receptacles (basically to make sure they are off) and checking that ceiling fans are grounded. A fridge plugged into a hidden ungrounded receptacle (via one of those damn "adaptors") will also light up the tester touched to a metal part, like the hinge, if the compressor is running.

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Has anyone here ever seen a false negative on K&T if you are able to get the tip in actual contact with the insulator/conductor - that's all I ever use them for.

Well, sort of. It depends on what's on the circuit and how much current it's drawing. If there's no load, you'll get a nice strong reading with the non-contact stick. If there's a heavy load, the reading will be much weaker and might even be intermittent with some brands of tester. The same thing happens with radiant heating cables.

- Jim Katen, Oregon

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