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#190748 - 12/02/09 08:55 PM 60V on ground!!
Up2code Offline
Member

Registered: 05/15/07
Posts: 55
Loc: Missouri
Hope all had a great Thanxgiving! Weather was great! Went on service call to a retail store, customer claims she was "shocked" when plugging in surge strip to a metal handybox plug. Plug tested 120V HOT to NEUTRAL, 120V HOT to GROUND, 60V GROUND to NEUTRAL, 60V GROUND to METAL HANDY BOX. Junction box feeding plug (above ceiling grid) tested exactly same. Everything is EMT & MC w/ metal strip inside. All conduit & boxes are bonded as should be, as far as I could tell. I did not recieve any sort of shock from handy box in question, but turned off until I could return. Any Ideas?

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#190752 - 12/03/09 12:46 AM Re: 60V on ground!! [Re: Up2code]
Trumpy Offline

Member

Registered: 07/05/02
Posts: 8540
Loc: SI,New Zealand
Time to get your Megger out.
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#190753 - 12/03/09 12:48 AM Re: 60V on ground!! [Re: Up2code]
frenchelectrican Offline

Member

Registered: 02/06/03
Posts: 938
Loc: Wi/ Paris France { France for ...
the 60 volts I have a feeling is this circuit is on isolating transfomer ?

Did you check if this is on MWBC as well ?

The other time I ran into like this if someone ran a isolated transfomer which the secondary is little odd set up but something like L1 - N - L2 = 60v 0V 60 V and L1 to L2 is 120 volts

the reason for using the isolated transfomer to keep the electrical noise out.

any chance do you have B/B in there as well?

Merci,Marc

As soon I got done typing the reply here Trumpy came up a simple solution get the megger to find the curpit.


Edited by frenchelectrican (12/03/09 12:53 AM)
Edit Reason: add info after Trumpy got done reply
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#190754 - 12/03/09 01:10 AM Re: 60V on ground!! [Re: Up2code]
sparkyinak Online   content
Member

Registered: 07/08/07
Posts: 1297
Loc: Alaska
Sounds like a main bonding or an open neutral issue. First ensure that the main bond is intact. If that checks out, if you can attach a solenoid type voltage meter to a point of bad voltage. Shut off the main to verify the problem is on sight. If the voltage is gone, the problem is on the premise. You can isolate the circuit by shutting off panel feeders then shutting off each circuit. Keep us posted
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#190755 - 12/03/09 07:27 AM Re: 60V on ground!! [Re: sparkyinak]
Up2code Offline
Member

Registered: 05/15/07
Posts: 55
Loc: Missouri
Thanks for all the tips. Will try all. Yes, it is a MWBC. My first thought was problem w/ main bonding. It seems as though I have ran across this before. Since they are open all day & weekends, I will have to go in after hours to start shutting things off & tracking the culprit. Another long day, but at least I have work! Stay tuned. smile

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#190757 - 12/03/09 11:24 AM Re: 60V on ground!! [Re: Up2code]
LarryC Offline
Member

Registered: 07/05/04
Posts: 776
Loc: Winchester, NH, US
Any IG recepticles in the building? I would suspect cash registers and other point of sale equipment and networks. Possibly somebody decided to create a SDS and decided not to bond the neutral.

Good Luck.

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#190758 - 12/03/09 11:33 AM Re: 60V on ground!! [Re: LarryC]
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
60v really sounds like what happens when you have an open ground and a PC or other equipment with RF filters on them. They have an LC network on the hot and neutral, tied to ground at the center point ... hence 60v or half of line voltage if the ground floats. Since the box is OK I agree with the IG receptacle idea. It might be as simple as an installer who thinks "Isolated Ground" means isolated FROM ground. Believe me, I have seen it.
A wiggy will probably "ground" this so don't be surprised if the problem goes away when you use it to test this "ground to box".
If you wiggy from hot to equipment ground you might see 120v on the ground referenced to the box.
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#190759 - 12/03/09 12:07 PM Re: 60V on ground!! [Re: gfretwell]
wa2ise Offline
Member

Registered: 11/29/02
Posts: 771
Loc: Oradell NJ USA
If the neutral is being shared between 2 of 3 phases, and the neutral goes open, and if the loads on the two hots are roughly equal, you could see a reading of 60V on the bad neutral to ground. You can visualize this by drawing a Y, 120/208 system, and draw a line between 2 of the hots. The midpoint of that line will be about 60V from true ground (center of the Y). If the loads were resistive, and identical, a hot to the bad neutral would read 104V (half of 208V). A slight imbalance could give you 120V. Computer and similar power supplies are usually rated to accept 100VAC (so they can be used in Japan, a 100V country), and if enough are on the bad circuits, they may behave normally.

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#190803 - 12/05/09 11:08 AM Re: 60V on ground!! [Re: wa2ise]
Up2code Offline
Member

Registered: 05/15/07
Posts: 55
Loc: Missouri
Found IT!! gretwell was right on. Open ground. Circuit goes thru 5 j-boxes between service panel & plug. Previous "electrician" used romex between j-box #3 & #4, and did not bond either end to a grounding conductor(EMT or wire). I only checked box #1 & #2, where grounding conductor was present & properly bonded, so assumed rest were fine. Explains why store clerk was shocked by metal handy box. Originally posted I was getting 120V HOT to GROUND, but was getting 60V HOT to GROUND, as well.(Sorry for that misinformation.) Grounded plug to grounding conductor & bonded handy box; now everything test & works fine. Thanks to ALL!

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