Induced Voltage????

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A/A Fuel GTX

A/A Fuel GTX

Senior Member
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WI & AZ
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Electrician
Ok, I've got a strange one for you. I had a service call regarding a hot ground on a residential branch circuit. The house was built circa 1970. A builder I often work with used his Fluke proximity voltage tester on a ground wire and received a tone so he called me to further investigate. I found a real mess with a combination of original wiring along with recently added circuitry obviously not done by an electrician. There were many cases of 12-2 W/G where the ground wire was snipped off right at the connector as it entered the box. There were some cases where the ground wires were connected. I tried my Fluke and got the same result that he did. The ground I tried my Fluke on was part of a switch leg where the original installer ran a short 12-2 from a J box to the switch box using the black as the line and the white as the load conductor. The ground wire in this case was snipped off at the J box where the power was being tapped and was left at normal length in the switch box. I put my Amprobe multi meter between the line and the ground wire and showed a reading of 60V. Question......How could I get a reading between a hot wire and a floating ground that is not physically attached to anything? I could possibly see induced voltage causing the Fluke to show hot but the multimeter reading really baffles me.
 
Multimeters are high-impedance devices, so they won't 'load down' the circuit under test. I bet that a wiggy would show no voltage. Try a light bulb in parallel with the multimeter; I'll bet you get no voltage.
 
LarryFine said:
Try a light bulb in parallel with the multimeter; I'll bet you get no voltage.
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Nice trick, Larry.

I imagine using a pigtail lamp holder. Do you recommend a paticular wattage?
 
kingpb said:
Is a neutral and ground connected together somewhere, maybe not where you are working but maybe back in the original install.
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That is certainly a possibility in this poor wiring job. Getting back to the voltage proximity testers, I seem to recall working on some knob & tube a while back where I got a tone on the neutral wire also. I never had that problem with NM-B orother conductors. Maybe insulation is a factor with those stick testers and their accuracy.
 
LarryFine said:
Multimeters are high-impedance devices, so they won't 'load down' the circuit under test. I bet that a wiggy would show no voltage. Try a light bulb in parallel with the multimeter; I'll bet you get no voltage.
Click to expand...


Thanks for the tip Larry, although if it were a legitimate 60V backfeed or something, I doubt that my Wiggy would pick that up.
 
your tick tester is unreliable it can buzz with as little as one volt

I use mine to tell me this may be hot be a little MORE careful before you know how much it is on or off NEVER assume a circuit is off untill you have tested it throughly even if you think you have turned it off.

do you get the same reading with hot to grounded (nuetral) 50 to 60 volts tells me I have an open grounded conductor someplace more times then I care to count.

poor grounding is a real PITA to trace out and fix when you give him your T&M bill maybe he will realize he should have had a licenced and qualified (almost said competant) person do his electrical install.

just spent 60 man/hours fixing the same type of problem loose conections were the main problems we ran into. 6 #14's under a yellow wire nut not twisted wire, nut falls off the end of the wires when you remove the device, plugs and switches installed with no wires attached to them just to name a few (Ya gotta love piece workers or you are liable to kill them)

by the way S.D.N.C. (spelling does not count) can not get spell check to work
 
al hildenbrand said:
I imagine using a pigtail lamp holder. Do you recommend a paticular wattage?
Click to expand...
Not really; I imagine anything from a night-light bulb up to a 60 watter would do. The small round Edison-based bulbs (7.5 watts, I think) are a handy size.

When troubleshooting open circuits, I never assume the ungrounded conductor is the problem; I carry the female end of a cord plugged into a known-properly-wired receptacle as references to measure against.
 
Thanks, Larry,

I like the "known" properties of a long cord, as well.
 
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