How do you calculate wattage for 277v's?
Is it the same as 277(15A)=4155 watts (If the amps is 15)
If so, does this mean if I wanted to supply 150w (output) HID light fixtures that are 277v, I could supply 28 lights using a 15 amp circuit?

Just learning, not thinking of doing 3phase, but curious.

Also, where does 277 come from?
What with all the voltages (120, 240, 208, 240, 277, 480... I even seen 380?? )

Sorry for all the questions. My main question is the first one.