Voltage on the Ground

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  #1  
Old 05-08-11, 09:50 AM
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Voltage on the Ground

I am working on a house in Bucks County PA. I have come across a problem with a few circuits in the house. The most direct problem I seem to have is that I am measuring a voltage (~32V) on the ground wire in a few areas throughout a circuit but not back at the panel or most other circuits. In one location on that same circuit, I have measured a ~149V hot to ground, ~125V h-n, and ~32V n-g. I have been slowly trying to isolate the issue, but I have run out of exposed options to disconnect (it seems that I have one or more covered junction boxes, very frustrating ).

The voltage (32V n-g) on the ground remains when the breaker is turned off, but decreases to ~16V when an additional breaker is turned off and is 0V when a third circuit is turned off.

In one box where there is a switch (that controlled an outlet, the switch is removed) the measured voltage hot is 35V h-n, 56V h-g, and 26V n-g. The switched outlet measures 80V h-n, 54V n-g, and 24V h-g. When the switch was closed, the outlet read 125V.

The receptacles on the circuits seem to have a few dangling grounds, but as I started to connect them, it propagated the problem to more devices on the same circuit.

No other circuits in the house, or the panel seem to have an issue.

What on earth could be causing this issue?
 
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Old 05-08-11, 10:26 AM
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Are you using a digital meter? DVMs are prone to ghost voltages. If you are using a DVM I would suggest buying an analog multimeter to verify your findings.
 
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Old 05-08-11, 11:35 AM
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Also check your meters battery. We just had another poster that was getting some odd readings and it turned out to be a bad battery.
 
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Old 05-08-11, 12:53 PM
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It sounds like the ground wire is open on the way back to the panel. With a high impedence voltmeter, you will measure capacitively coupled voltage to that isolated line. You can see that 2 or 3 circuits are contributing to that 32 or 16v reading. The only issue is a ground open, somewhere. Check the areas(outlets) closest to the panel that feeds that circuit.
 
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Old 05-08-11, 01:09 PM
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The batteries are band new. I am using an Ideal 61-312. I have heard about ghost voltages, but I could feel the voltage, and sense it with a non-contact voltage sensor.

I have tracked back to the connections that I can find. I cannot determine the absolute first device on the circuit and fear that the there may be two or more parallel sub-branches from a covered J-box.

How could I be getting non-120V readings from h-n at the switch and the switched outlet?
 
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Old 05-08-11, 04:44 PM
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I think I'd be opening device boxes and checking all connections, especially neutral and ground connections.
 
  #7  
Old 05-08-11, 05:49 PM
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It sounds like some voltage being introduced into the line whether it be an improperly wired pilot light, mov's or a ground indicator, combined with an open ground. I would not doubt a buried splice as there are alot in my area, and the wiring seems just as bad around the state.
 
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Old 05-09-11, 05:39 AM
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I had a similar problem

I had two similar situations recently.

One circuit I found that the 'apparent' voltage of ~30V on my digital failed to read at all on my analog meter. We were doing a full gut and rehab, so down came the walls. This particular line ran from the junction box I was metering along two other lines to another junction box and terminated. No connections, but still read ~30V on the digital...

Another circuit was a line that ran to a detached garage. Three conductor armored cable. Checked the lines with an ohm meter and they all read good, no shorts. Hooked up a single circuit and got funny voltages at the other end, 85V b-g, 25v r-g, etc. Turned out the cable was crimped and voltage was leaking across moist paper insulators.

Just ideas.
 
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Old 05-09-11, 08:59 AM
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Because the integrity of your ground is suspected to be bad you can't trust the readings you're getting. You'll need to get a long extension cord and plug it into a known good grounded receptacle. Drag the other end of the cord around with you and measure voltage between the round ground hole on the extension cord and the suspect terminal in your circuit. It is also best to have a table lamp plugged in to the target receptacle and turned on while you are taking measurements.

Extension cord ground to box ground should be 0V.
Extension cord ground to box neutral should be close to 0V within maybe 2-3V.
Extension cord ground to box hot should be close to 120V.

I believe your ground wire is broken or not connected somewhere in this circuit. You also might have a bootleg ground (ground connected to neutral) somewhere in the circuit.
 
  #10  
Old 05-09-11, 10:19 AM
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My own house had voltage to ground on two circuits...first one had overtightened romex clamps that spliced into the cable...other was a crushed romex behind a garage shelf.... And I too have had meters with suspect leads that gave false readings...
 
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