On Mon, 30 Apr 2018 12:35:03 -0600, rbowman
wrote:

On 04/30/2018 10:05 AM, Ralph Mowery wrote:
Most places that have equipment that uses lots of power in the US will
have 480 volt 3 phase equipment such as motors. The lights are most
often 277 volts single phase as that is the neutral to one hot leg of
the 480 volt 3 phase circuit.

We leased an old bakery where the freight elevator was 550. After 40
years of home repairs the 550 showed up in the damnedest places. I never
made any assumptions about what I'd find when I opened a panel.

The strangest panel for the uninitiated is 3 p corner grounded delta.
It will look exactly like single phase 120/240 (2 pole breakers, 2
hots and a white grounded conductor) except there will be 240 to
ground and you will have 240v 3 phase equipment hanging off of it.
The first time I saw it I took a minute to figure out what I was
looking at.
The only place you will see it is where there are pretty much all 3
phase loads and maybe some 240v L/L load.