EGC measured 39 volts to Neutral

[Thom Sun]

Unknown building supply / Commercial tenant space has 3 phase 4 wire 120/208 Y Sub-Panel.

Review of the circuits and grounding means for a new tenant showed 39 volts EGC to isolated NEUTRAL. Strange enough was the voltage test from circuits line 1, 2, or 3 showed a normal 120 volts to neutral, but when tested the circuits to EGC, the test showed 147 volts.

My first thought was a loose EGC at the distribution point allowing the EGC to pick up inductance outside of the tenant space.

My second thought was a fault on the EGC somewhere else in the building that is not "tripping"a breaker somewhere outside of the tenant space.

Would my thoughts seem accurate? Any other thoughts?

 

[zbang]

My first thought is the neutral isn't properly bonded to the GES, it has to be connected somewhere. (And if the N and EGC aren't connected, a voltage reading is pretty meaningless.)

 

[LarryFine]

Review of the circuits and grounding means for a new tenant showed 39 volts EGC to isolated NEUTRAL. Strange enough was the voltage test from circuits line 1, 2, or 3 showed a normal 120 volts to neutral, but when tested the circuits to EGC, the test showed 147 volts.

A textbook example of a missing main bonding jumper. In other words, your neutral is not tied to the EGC/GEC system.

There is nothing strange about having normal line-to-neutral voltages. You're used to seeing solidly-grounded neutrals.

 

[infinity]

Since there is a transformer involved it sounds like a missing system bonding jumper in the transformer. I've seen this several times over the years, my guess is that some electricians think that the neutral is factory bonded so they do not install a SBJ.

 

[Thom Sun]

Thank you guys. I appreciate your input(s), and I agree completely about the Neutral not being bonded to the GEC at the transformer. Tomorrows search will discover more.
Thanks

 

[Thom Sun]

Thanks for the help. Just as expected the BOND was missing. Solved the problem. Thanks for your support.