I was talking to a guy from Massachusetts (electronic engineer) and he says 480 delta is common up there for industrial applications. How is that generally grounded? He didn't know but he says he thought it was ungrounded. That did not sound right. I have seen plenty of 480/277 wye but I have never seen a 480 delta down here.
We have several mission critical facilities that use an ungrounded delta system. In the event of a ground fault the system stays energized until it can be corrected. The only time that the system goes down is when there is a second ground fault before the first one gets cleared.
An ungrounded delta is kinda capacitively coupled to the Earth, so a ground detector device is used. There are 3 lights wired from phase to a ground rod and all glow continuously at the same brightness. If one of the phases has a ground fault that light will go out and the other 2 get much brighter.
That tells you which phase the ground fault is on...but finding where it is becomes very challenging. One of our facilities has had a ground fault on one of the phases for several years...and the maintenance folks are still trying to chase it down. I think there may be a ground in 2 places on the same phase; which is like trying to find the 2 bad bulbs in an old string of Christmas lights.