60v nuetral to ground

[Blaine25168]

Working on a 120/240 residential sub panel today I noticed a few EGCs that had some discoloration.
- the refrigerator ciruit
- one kitchen small appliance circuit
- a dedicated garage gfci circuit
I took the EGC for the dedicated garage circuit off the bus and noticed there was 25v from the nuetal bus to that ground. Upon checking the others they had 37v(refrigerator) and 56v(kitchen small appliance) from the EGC to the nuetral bus. The kitchen is right next to the garage. Both the dedicated garage circuit and the fridge circuit are right next to each other and approximately 30-40' in length. The kitchen small appliances covers 6 outlets and my best guess would the length is around 70-80'.
I couldn't find anything wrong in either the service panel or the circuits themselves. So I started to think it may just be induction? That seemed like extremely high voltage for induction though.
For a test I ran a straight 40' run of 12/2 romex out on the ground and hooked it to one of the breakers without landing the EGC and sure enough 40v from that EGC to the nuetral bus.
What could this be?

 

[zbang]

Is the feed to the sub-panel 3 wire or 4? If it's 3, how does the EGC arrive? Are there other circuits in the panel or just those?

Have you checked that there's a proper N-G bond at the service panel and that both of those make it to the sub-panel (assuming it's 4-wire)? I'd bet there's a problem with that. (Things like this are almost always a bad neutral or disconnected grounding lead somewhere.)

Also, are you using a low- or high-impedance meter? The standard multimeter (high) can read phantom voltages that the low won't; use something like a Fluke T-pro for this. (I highly recommend those meters)

 

[GoldDigger]

You are apparently using a voltmeter with a very high input impedance. Since is draws very little current from the circuit you are measuring, it does not take much capacitive coupling between two wires to create a measurable voltage. Since the EGC wire in a piece of NM (TM Romex) is equidistant between the hot and the neutral, it is not surprising to measure 60 volts between the EGC and either one of them. You have a voltage divider made up of two equal capacitors.
If you measure with a low impedance meter, you will read close to zero volts instead.

 

[LarryFine]

Welcome to the forum.

Try a connecting a small 120v bulb in parallel with your meter.

 

[Blaine25168]

Thank you both for your replies.

What a simple and genius idea! I will definitely try with a small 10w 120v led in parallel with my meter.

If it does turn out to be "ghost voltage" from capacitive coupling, any ideas on the EGC discoloration? It was throughout the entire circuit. I wish I would have taken a picture, but it looked as though it had maintained a high temperature for a extended period of time.

I'm starting to believe the 12/2 romex just came with a discolored ground as the sheathing of the phase conductor and nuetral showed no signs of overheating.

 

[retirede]

Exposed copper will discolor over time. If what you are seeing is from heating, I’d expect insulation damage.

 

[ptonsparky]

I think a small incandescent lamp was his thought, but let us know how the LED works out.

 

[ptonsparky]

About 20' of 10/2G NMB. 120v applied to one end(black & white). EG floating. Fluke 87, white to EG and black to EG. Both about 55 volts. Add load of 4.2 watt LED between white & EG voltage White to EG dropped to about 2.5 volts. 60W incandescent lamp dropped voltage White & EG to about 2mV. I didn't take a measurement between Black & EG....forgot to.

Now back to work...

 

[LarryFine]

I think a small incandescent lamp was his thought, but let us know how the LED works out.

Yes, it was. Even a night-light bulb would suffice. I wouldn't trust an LED lamp for this purpose.

An extension cord and a table lamp makes using a tester and a bulb in parallel an easy thing to do.

 

[Blaine25168]

So yall were 100% correct. The led bulb was not enough of a load to test this. I ended up testing with a small vacuum as a load and there was no voltage. I definitely believe at this point the EGC came discolored and the voltage is just induction.

Follow up question being, why do other circuits in the sub panel not have any induction on the EGC when disconnected from the bus.

 

[Blaine25168]

So yall were 100% correct. The led bulb was not enough of a load to test this. I ended up testing with a small vacuum as a load and there was no voltage. I definitely believe at this point the EGC came discolored and the voltage is just induction.

Follow up question being, why do other circuits in the sub panel not have any induction on the EGC when disconnected from the bus.

 

[don_resqcapt19]

Working on a 120/240 residential sub panel today I noticed a few EGCs that had some discoloration.
- the refrigerator ciruit
- one kitchen small appliance circuit
- a dedicated garage gfci circuit
I took the EGC for the dedicated garage circuit off the bus and noticed there was 25v from the nuetal bus to that ground. Upon checking the others they had 37v(refrigerator) and 56v(kitchen small appliance) from the EGC to the nuetral bus. The kitchen is right next to the garage. Both the dedicated garage circuit and the fridge circuit are right next to each other and approximately 30-40' in length. The kitchen small appliances covers 6 outlets and my best guess would the length is around 70-80'.
I couldn't find anything wrong in either the service panel or the circuits themselves. So I started to think it may just be induction? That seemed like extremely high voltage for induction though.
For a test I ran a straight 40' run of 12/2 romex out on the ground and hooked it to one of the breakers without landing the EGC and sure enough 40v from that EGC to the nuetral bus.
What could this be?

Yes, but EGCs on any installed circuit should be connected to the equipment grounding bar and then via the main bonding jumper to the neutral and that won't happen.

If you have voltages like that on a working system where the line to neutral voltages are both the same under loaded conditions, the EGCs with the voltages are not connected to the system.

 

[tthh]

use something like a Fluke T-pro for this. (I highly recommend those meters)

My wife already thinks I have a tool collection problem