HotLine's post brings up another point.
When testing (always)
disconnects and breakers, be sure to not only test line to ground, but line to line as well, lest you run into an ungrounded delta system that will show no voltage to ground (but might be hot 480).
Some of the younger folks have worked just on Y systems, and the delta never even seems to enter their minds.
Just the thought of it makes me ill