The OP question is if one leg to ground provides 120 volts to run a
device like a vacuum cleaner, or pressure washer.

Please ask the power co person if it's possible to run a 120 volt
device.

--
Christopher A. Young
Learn more about Jesus
www.lds.org
..


"John Grabowski" wrote in message
...

What you are describing sounds to me like a 240V "star" system with
high
leg, a variant of Y. Two of the phases are 240V center tap with the
center
tap connected to neutral. That provides four 120V legs. The third
is
240V
with one end rather than the center tap of that transformer's
winding
connected to neutral to provide the "high leg". It is possible to
use the
center tap of that to provide a fifth 120V leg.


*It's been a while since I have worked on three phase, but I seem to
recall
on a three phase 240 volt delta system, the high (Orange) leg is
around 180
volts to ground. I only remember one phase as being center tapped.
Next
time I meet with someone from the power company I will ask them to
refresh
my memory.