Proper use of voltage detector.

[1991Syclone]

During my garage reorganization I found an outlet box in the attic where the wires were terminated with nuts (white, black, red) and not connected to anything. I couldn't find my old voltage detector so I went out and bought a new Greenlee kit to see if the wires were live or not.

I get up in the attic and touch the covered wires with the tester and it will light up and beep on the black and red 99% of the time indicating they're hot. If it touch the white wire immediately after one of the live wires, 50% of the time it will signal it as hot. If I tap the tip of the detector on a non conductive surface like plywood and then touch the white wire, 99% of the time it will not indicate it's live.

So, am I doing something wrong here? I am sure that everything is wired right with the white being ground, etc, but if I'm getting a false positive 50% of the time it doesn't make me warm and fuzzy when I try to work with the wiring. Any tips on which methods provide the most accurate way to test if a wire is live?

It got to the point where the copper line coming into the A/C handler was acting like it was live. I also have a clamp on voltage meter I can use to test if that would be better?

 

[luvit]

i think you'll have to use your tongue.

 

[MrMark]

Maybe they are really hot? What you have there is a capacitively coupled device and that's what it detects. Capacitively coupled voltage levels. As for the white wire showing hot, that is what can happen with those devices when the circuit is not connected to anything. The white is being capacitively coupled to the red and black by being so close in proximity in a parallel run. I imagine the light is not showing as bright on the white wire. The electricians would call this ghost voltage.

The white isn't ground either. It is ultimately tied to the power company's neutral at the panel. It has nothing to do with equipment ground.

As far as the copper line coming into the AC handler, it probably is live. The only way to tell for sure is with a current clamp.

 

[1991Syclone]

i think you'll have to use your tongue.

I tried that first. Each time my pecker rose I figured the wire was hot. I used the voltage detector as a way to confirm.

 

[ishiboo]

During my garage reorganization I found an outlet box in the attic where the wires were terminated with nuts (white, black, red) and not connected to anything. I couldn't find my old voltage detector so I went out and bought a new Greenlee kit to see if the wires were live or not.

I get up in the attic and touch the covered wires with the tester and it will light up and beep on the black and red 99% of the time indicating they're hot. If it touch the white wire immediately after one of the live wires, 50% of the time it will signal it as hot. If I tap the tip of the detector on a non conductive surface like plywood and then touch the white wire, 99% of the time it will not indicate it's live.

So, am I doing something wrong here? I am sure that everything is wired right with the white being ground, etc, but if I'm getting a false positive 50% of the time it doesn't make me warm and fuzzy when I try to work with the wiring. Any tips on which methods provide the most accurate way to test if a wire is live?

It got to the point where the copper line coming into the A/C handler was acting like it was live. I also have a clamp on voltage meter I can use to test if that would be better?

A non-contact voltage detector is a nice tool, but it has its limitations. It is like a metal detector, it's not a "live" or "not live" light you can just use without thought. Neutral has no AC waveform (mostly) on it when there is no load, so as MrMark said you will not receive a reading from a white wire unless you are quite close and the AC waveform is appearing somewhat on the neutral as well, or there is a load on the circuit.

Do not touch it to plywood/etc., turn it on and bring it in to the potentially live conductor. A live wire generates a continuous tone, a quick beep/blip of the lamp does not indicate anything, you can get that from just touching it to an object.

AC is a wave, and the sensor is quite sensitive so it can pick up transients on the copper AC line, probably from the running motor or some bleed over from the 24VAC thermostat.

A clamp on meter only works if you have access to the individual conductors, as you have to get the clamp over only the hot. I use the non-contact for identifying circuits, then before I work on them I use a DMM to verify the wires are off. Clamp is only used when I have to measure current, what it's designed for.

 

[ishiboo]

I tried that first. Each time my pecker rose I figured the wire was hot. I used the voltage detector as a way to confirm.

Bahahaha. Best line in Lighting & Electrical ever.

 

[ddawg16]

Connect the wires to a load such as an incandescent bulb. It if lights....it's 'alive'.

As noted above, even though wires are not hooked up....if they run any lenght next to live wires, they will read voltage....it's a common problem for Controls guys....in the old days they would install relays or lights to suppress the voltage.

 

[egdede]

I still prefer the Wiggy I inherited from my dad 30 years ago.

 

[kngelv]

Get a proper meter and if you have the room carefully undo the wire nuts. Test for voltage with the meter. Make sure you are checking for AC. You should return the Greenlee. Do not trust it one bit. In the trade we use them for certain things but never trust them. They have many nicknames like cricket or chirper but most tradesman call them death sticks. The average person should steer well away. I'm an Electrical Journeyman BTW. If you are uncomfortable with any of this find a reputable electrician to handle it.

James