If you had a delta system with a neutral tap on one of the secondaries, and a corner ground, then you would get a pretty dangerous situation that would _work_ with most loads. For 3 phase loads you would have 240-240-0, just like a normal corner grounded system. But for single phase loads you would have 240-120-0 instead of the normal 120-0-120 (all voltages relative to ground). Standard 120V lamps would function in sockets, but the socket would _always_ be energized. Add anything with a ground-neutral bond and _bang_.
-Jon
