Voltage on device screws?

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I have a customer who is complaining of getting shocked at times from several locations throughout his house when he touches the plate screw. I did find in one location a nicked wire that likely was energizing the metal box.It read 120v to neautral when i used my tester. Fixed it,all is well in that location.The house is an old two wire system without ground so the box was not grounded and breaker never tripped.
Now here is where I am confused several of the switches through the house cause my ideal"tick tester" to beep when I touch the screws. When I use my Ideal digital voltmeter I read 31 or so volts from the plate screw to a nearby outlet neutral( no ground in the house to put meter lead to). I checked one box and there where no visible nicks in the wire.Though I have yet to pull all of them apart and look for hot wires touching the boxes I have a feeling there aren't any nicked wires. I know from experience that the digital meter will read voltage when there isn't necessarily any voltage on the wire. Is there actually voltage on the screw? Is this a phantom reading? Should I stick to my Wiggy which shows no voltage there?Do I tell the customer that there is nothing to worry about or do I start tearing the switches apart looking for faults?

As a side note this house has plenty of handyman work in it. Most of the switches are digital timers or "insteon" switches. And i have found at least one new 12/2 wire ground tied into and old wire neutral to create a grounded light.


Please excuse If the subject has been covered before I had no luck with the search engine.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Mr. Bubbles, welcome to the forum! :)

Is this a phantom reading? Should I stick to my Wiggy which shows no voltage there?
Yes, and yes.

As a side note this house has plenty of handyman work in it. Most of the switches are digital timers or "insteon" switches.
Many home-automation devices won't work without a ground/neutral, and 2-wire switch loops have none, so they often connect the wire that should be grounded to the device mounting strap.

And i have found at least one new 12/2 wire ground tied into and old wire neutral to create a grounded light.
Dangerous, and there's never an excuse to do that.
 
Thanks for the welcome and the advice. I have been creeping for a while on this forum and finally decided to throw out some questions.But alas I have more. Is there anyway to explain why, in laymans terms, a digital meter shows voltage when there is none? Throughout the years I have found that my "tick tester" goes off at times and my meter reads voltage around water pipes and devices that I know( a least I think I do arent connected to a hot wire.

The customer in this case always demands a full theory explanation of what went wrong and why and I don't want to be caught slippin. So any explanations would be great.
 

dmagyar

Senior Member
Location
Rocklin, Ca.
Trust only a tester you know is working

Trust only a tester you know is working

If you've got a tester showing 31 volts its my guess it's right. Tick tracers although having their uses are only a first line defense against getting yourself electrocuted in any situation. Anyway that's my $.02 on that.

With regard to the mess this particular house seems to be in, one thing to check is three way switches and associated connections. With these it's really common for neutrals to be tied in at the junction boxes with the switchlegs leaving the 3 ways. Then add in anything thats plugged in to receptacles downstream and it can get complicated fast.

With an owner that's looking over your shoulder at every turn, he may be responsible for most of what's wrong anyway. He's possibly "learned" only portions of what a qualified electrician should know by watching and asking alot of questions from whomever has been working in the house over the years. Ask him from day one in the house what he's installed or worked on and start there.

With one customer where I ran into low voltage, the wife had replaced the receptacles in the kitchen after a counter top replacement. Every screw was loose and one of the neutrals had come off the silver screw.

The reason that the circuit in question didn't trip was that it had resistance and wasn't a direct short. Sounds like you got plenty to do straigthing out this problem house.
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Is there anyway to explain why, in laymans terms, a digital meter shows voltage when there is none?
Sure. The voltage the meter is reading is real, but because the voltage is induced, and not from a direct connection, it's not capable of supplying any useable current.

That's why the wiggy doesn't read "phantom" voltage, is a better troubleshooting tool than a voltmeter, and is what I save for when I need to know the exact voltage.
 

mull982

Senior Member
Sure. The voltage the meter is reading is real, but because the voltage is induced, and not from a direct connection, it's not capable of supplying any useable current.

That's why the wiggy doesn't read "phantom" voltage, is a better troubleshooting tool than a voltmeter, and is what I save for when I need to know the exact voltage.

Voltage on the secondary of a transformer is also "induced" but is indeed capable of supplying large amounts of current.

I think it may be better to say that the "induced" or "phantom" voltage has a very large impedance (source impedance) and therefore is not capable of supplying current or voltage to any load which will typically have a lower impedance.
 

Article 90.1

Senior Member
What kind of two wire system, NM or AC? If AC there could be a fault to the AC jacket somewhere, but the jacket may not have a good path back to ground at the panel.
 
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