Neutral to ground on sub panel

[PowerdT]

when you measure N-G on the sub panel, voltage should be zero or maybe very small below .5V. When you measure the ohms, if the meter is bouncing around, what does it mean?

 

[synchro]

when you measure N-G on the sub panel, voltage should be zero or maybe very small below .5V.

That will be the voltage drop on the neutral conductor of the feeder, since the EGC would not have a voltage drop because it should'nt be conducting any current. And so the N-G voltage will obviously depend on the amount of neutral current being drawn, which can vary substantially as the loads on the opposing phases change and depart from a balanced condition.

when you measure N-G on the sub panel, voltage should be zero or maybe very small below .5V. When you measure the ohms, if the meter is bouncing around, what does it mean?

It means that the AC voltage is interfering with the resistance measurement, which uses a DC current as a test signal. You would need to shut off the main breaker to eliminate this.

 

[augie47]

If "the meter is bouncing around" it means you are on a rough road or in high winds"
(sorry, the devil made me )

 

[PowerdT]

That will be the voltage drop on the neutral conductor of the feeder, since the EGC would not have a voltage drop because it should'nt be conducting any current. And so the N-G voltage will obviously depend on the amount of neutral current being drawn, which can vary substantially as the loads on the opposing phases change and depart from a balanced condition.


It means that the AC voltage is interfering with the resistance measurement, which uses a DC current as a test signal. You would need to shut off the main breaker to eliminate this.

Actually the panel does not have ground wire, they used conduits as EGC.

It’s lug panel, I may have to shut all the breakers to measure N-G off load

 

[Strathead]

Actually the panel does not have ground wire, they used conduits as EGC.

It’s lug panel, I may have to shut all the breakers to measure N-G off load

a metal conduit is a conductor as in EGConductor.

 

[LarryFine]

Also keep in mind that an ohmmeter on a low setting will vary with contact pressure.

 

[LarryFine]

It’s lug panel, I may have to shut all the breakers to measure N-G off load

Or just the feeder breaker.

 

[jaggedben]

It could be voltage drop on the neutral, or it could be that the EGC to the sub is no good somehow, or it could be that the main bonding jumper at the service is missing or no good somehow.