Super Weird Voltage on Offline Generator

[Sean98]

I'm running two 400V generators in parallel, but one is currently offline, the circuit breaker to switchgear is disconnected.
the problem is with the offline generator. I measure 279V between Neutral and Ground, and I measure 279V between Phase and Ground
But 0V between Phase to Phase and Phase to Neutral. How can I get 279V to ground when the machine is completely disconnected? Any ideas for troubleshooting this phantom voltage?

 

[Alan]

That’s definitely a head scratcher when the unit is offline but still showing voltage to ground. Phantom readings like that can make you question everything.

Are you seeing that 279V with a high impedance meter, or have you checked it with a different tester too?

 

[PGB1]

The best troubleshooting, to rule out problems with the generator's regulator or other is to completely disconnect it- neutral and all if present. (You can leave the equipment grounding conductor if everything is solidly bonded.)

Be absolutely sure to also disconnect the control wiring that keeps the parallel generators in frequency sync at the off line unit. Sometimes one unit is disconnected at the switch and gives odd voltages because the syncing control is trying to get phasing correct. I've had this service call more than once from electricians. When the control is removed, suddenly the off line generator behaves perfectly. Putting the offline one back on line and it stays perfect.

Hope This Helps,
Paul