False reading from non-contact electrical tester

[jussi]

I sometimes get a false positive reading from my non-contact electrical tester. This is the one I have. Live-Wire It lights up even when I turn off every single breaker in the house. I almost always do that as the house is old and the breakers weren't properly labeled. Plus electricity freaks me out. It's gone off when testing wire going through metal conduit and from the older wiring wrapped in a black plastic tube (not sure what they're called).

[Uncle Cracker]

It's probably keying on the RF emissions from the neutral wire. Some of those things are pretty non-discriminatory. Try unhooking the neutral wire on the circuit you are testing. (BE CAREFUL!)

[MilDoc]

Good point. My electrician buddy said the same.

[Tom Slick]

Is it coming on and staying on when testing or jsut giving you a flash and a beep?

I used to have a gardner bender tester and pitched it in the garbage because it gave annoying false signals. I now only use Fluke or Greenlee, they don't give false indications like the GB unit did.

[Hellrazor]

A lot of those testers also detect static electricity from your clothes. They are nice to have, but if I have to bet my $%^ on the power being off, I'll use my Fluke 322.

[Anna]

I used to have a gardner bender tester and pitched it in the garbage because it gave annoying false signals. I now only use Fluke or Greenlee, they don't give false indications like the GB unit did.

Oh, darn, I just got a Gardner. Spent a few minutes last night going around the house testing it. It beeps near my firewire cables connected to the computer, beeps close to my laptop, etc. Haven't seen a false positive so far that I should be concerned with, but if it's that bad, I'll get a Fluke instead.

[jussi]

Is it coming on and staying on when testing or jsut giving you a flash and a beep?

I used to have a gardner bender tester and pitched it in the garbage because it gave annoying false signals. I now only use Fluke or Greenlee, they don't give false indications like the GB unit did.

It stays on. But when I lower the sensitivity it turns off. If I test another wire that's still live with that same lowered sensitivity it lights up. So should I just always use it on a very low sensitivity setting?

With a fluke do you an actual terminal to touch the leads right? I like the non-contact tester to 1. use before drilling (or breaking) through a wall. 2. Sometimes with a cramped gang box it's hard to get the leads to the terminals. 3. Testing lines not inside walls (like ones in counduits).

I'm no electrician so if you have a better and more importantly safer method, I'm all ears.


Also I initially bought a Greenlee to use use on spots I wanted to drill into but found it wouldn't light up in spots where I knew for sure there was an line behind the wall. I exhanged it for the GB and it worked better. Hmm maybe the Greenlee was just more accurate.

[Uncle Cracker]

It stays on. But when I lower the sensitivity it turns off. If I test another wire that's still live with that same lowered sensitivity it lights up. So should I just always use it on a very low sensitivity setting?

Yes. Why else would there be a sensitivity setting? You've got it turned up so high, it would ring out on a bucket of grits...

[Tom Slick]

Your old wiring could have odd things going on. homeowners and handymen are known for all sorts of wiring shenanigans.

My fluke and greenlee are both the exact same type of tool as your GB non-contact (NC). I like the fluke a little better but the greenlee works fine, neither have a sensitivity adjustment and I haven't found a need for one. Ideal also makes a nice NC sensor.

Just to clear things up on the safety of these tools:
this type of tool is only an indicator that the line is ON, to be "absolutely safe" you need to double check that it is OFF with a voltmeter. no indication means that you need to follow up with a voltmeter to ensure zero volts. I work with my NC testers often enough and use safe electrical handling practices that I trust mine. I always test it on a known live circuit, especially if it has an on off switch, before using it.

[jussi]

Your old wiring could have odd things going on. homeowners and handymen are known for all sorts of wiring shenanigans.

My fluke and greenlee are both the exact same type of tool as your GB non-contact (NC). I like the fluke a little better but the greenlee works fine, neither have a sensitivity adjustment and I haven't found a need for one. Ideal also makes a nice NC sensor.

Just to clear things up on the safety of these tools:
this type of tool is only an indicator that the line is ON, to be "absolutely safe" you need to double check that it is OFF with a voltmeter. no indication means that you need to follow up with a voltmeter to ensure zero volts. I work with my NC testers often enough and use safe electrical handling practices that I trust mine. I always test it on a known live circuit, especially if it has an on off switch, before using it.

good tips Tom. thanks