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Ralph Mowery

In article , says...

It just seems odd not to have it 220 instead of 277 (not far different numbers). But I guess you have three phase completely seperate from your domestic stuff. Our 3 phase is also used for domestic supplies, we get one leg per house, so commercial stuff just takes all three phases, and still has the standard 220 to run
computers and lights.

Large consumers of electricity will have 480 v 3 phase. As stated, the
lights are usually mercury vapor (or similar) or flouresent. The
ballast are set for 277 as that is from the center of the Y winding to
one of the 480 legs. The lights are often split so some go to each leg
of the 480 and center of the Y. That way if something hapens to one
section of lights, the others stay on.

Lots of differences in large companies and small offices and homes in
the US.

Almost no standard homes will have 3 phase. They usually have a
transformer at the power pole that supplies 240 volts with the center
tap to give 120 volts for most of the recepticals and smaller loads and
240 for water heaters, AC or electric heat, stoves, and well pumps if
not on a water system.