Today we went back to a building where we installed an MCC, transfer switch and some emerg panels and while doing some small finishing work the building electrician told us a phase is showing a ground fault.

Its a delta and phase to phase we get about 600 volts, but one of them shows 0 volts to ground.

I was thinking it looks like a corner grounded delta, but our work was up and running 2 months ago and the problems started last week, coincidently while some major work is being done on another floor.

I still havent learnt enough about delta-wye systems, especially when they have an open or grounded configuration.

What should I be looking at? We arent diagnosing the problem, but I would like to understand it for myself.

No real question here, just looking for some feedback.