Yeah I replaced a lot of 277 volt ballasts back in the early 70s.
That 277 can be wicked if you get across it.
One time I lifted a drop in fixture to get to something else and fire shot past my head to the drop in celling frame.
Then the light went out.
Seems the fixture was operating grounded to the ceiling frame using a 120 ballast on 277.
Really nice modification by some one.