johnjohnls.js
Member
- Location
- US
How could a sub pannel show 50v netween neutral and ground?
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50v between neutral and ground
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
One or both not properly terminated at the source.
Adamjamma
Senior Member
- Location
- Jamaica and london
Like He Said.
Unless you are looking at a 110 panel in Europe, then it is on a site transformer and has a voltage drop because 110 circuits here in Europe are 55 volts to ground on what the USA considers line and neutral, and 110 volts line to neutral. Safety regulation for working at all building sites.
But not applicable in USA, usually.
Unless you are looking at a 110 panel in Europe, then it is on a site transformer and has a voltage drop because 110 circuits here in Europe are 55 volts to ground on what the USA considers line and neutral, and 110 volts line to neutral. Safety regulation for working at all building sites.
But not applicable in USA, usually.
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
Or discontinuous somewhere between the source and the subpanel.
Or a radical amount of voltage drop. (which would likely be accompanied by a radical amount of smoke, and ultimately result in one of the two conditions above)
- Location
- Tennessee NEC:2017
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- Semi-Retired Electrician
Or "phantom voltage" read from a high impedance meter.
drcampbell
Senior Member
- Location
- The Motor City, Michigan USA
- Occupation
- Registered Professional Engineer
Phantom voltage can only exist on conductors that are not connected to each other.
In a properly-installed subpanel, the ground & white wires will be connected to each other in the main panel. There should be no more than ~3 volts difference (voltage drop on white wire), regardless of voltmeter impedance.
In a properly-installed subpanel, the ground & white wires will be connected to each other in the main panel. There should be no more than ~3 volts difference (voltage drop on white wire), regardless of voltmeter impedance.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
190110-0913 EST
johnjohnls.js:
At your main panel measure the voltage between the EGC bus and the neutral bus. Should not be very large, just millivolts. If this voltage is large, then the problem is before the main panel.
Assuming that the main panel measurement is good, then connect a long test lead to the main panel neutral bar, an extension cord will work.
At the subpanel measure the voltage of the neutral and EGC buses relative to neutral at the main panel. This will tell you which or both of the wires from the main is the problem. Further probing along the problem wire may identify where the problem is. Could be an open wire buried somewhere, or more likely a termination point at either the main or sub.
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johnjohnls.js:
At your main panel measure the voltage between the EGC bus and the neutral bus. Should not be very large, just millivolts. If this voltage is large, then the problem is before the main panel.
Assuming that the main panel measurement is good, then connect a long test lead to the main panel neutral bar, an extension cord will work.
At the subpanel measure the voltage of the neutral and EGC buses relative to neutral at the main panel. This will tell you which or both of the wires from the main is the problem. Further probing along the problem wire may identify where the problem is. Could be an open wire buried somewhere, or more likely a termination point at either the main or sub.
.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
are you measuring between neutral and dirt?
if between neutral and the EGC it likely means the neutral-ground bond is missing.
If they were using the ground as the neutral on one of the circuits in the sub-panel, could we see 50 volts?
The first thing I would do is turn off all the circuits in the subpanel and see if the voltage is still there. Does this make sense or do I need more coffee to wake up?
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
You can also simply measure voltage between each hot and neutral and each hot and EGC. One should measure ~120v and ~120v, and the other should measure ~170v and ~70v. The problem will be on the one, neutral or EGC, with the gross imbalance.
It should be the EGC, because, presuming the sub-panel is in use, because if it was the neutral, you would be observing a great amount of open-neutral symptoms, which you did not mention.
It should be the EGC, because, presuming the sub-panel is in use, because if it was the neutral, you would be observing a great amount of open-neutral symptoms, which you did not mention.
- Location
- Illinois
- Occupation
- retired electrician
Is the power source for the panel a transformer? If so, I would suspect a missing system bonding jumper. I have seen that happen many times.
johnjohnls.js
Member
- Location
- US
Yes it is. Ill check there
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