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Millivolts between N and G

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electro7

Senior Member
Location
Northern CA, US
Occupation
Electrician, Solar and Electrical Contractor
I have a few panelboards at a commercial site. One reads 30 millivolts between ground and nuetral. Another that is further away from the MSB reads 110 millivolts between ground and neutral. At the MSB I read 0V with my Fluke 376FC meter. The two panelboards mentioned above were read using my Fluke Megger- a more sensitive instrument. I did not read voltage at the MSB from neutral to ground with my Megger. It's possible it could be in the millivolts there as well.

Does anybody have any concerns and/or thoughts about this? Is that small voltage normal/acceptable?



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__dan

Senior Member
That's a good reading.

The neutral under load has some Voltage drop, elevating the neutral some millivolts above zero. Usually anything less than 500 milliVolts will not concern me and a reading over that will usually indicate to me there may be a problem. The difference is accounted for by the drop of the neutral under load.
 
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GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
That kind of voltage at the panel where the ground/neutral bond is located, however, would indicate a more substantial current across the lower resistance, and could indicate a serious problem.
Measuring the current in the GEC with a clamp on meter is a useful test in that case.
 
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