*I have found that the actual voltage varies by power company. One
company in NJ supplies 460/265 volts while another supplies 480/277. ...

More than likely it's owing to variations in distribution or even local
voltage drops rather than a difference in system generation setpoints
between utilities.


*Many years ago I had an issue with the voltage at a hospital that I was
working at. It seemed that there was low voltage everywhere. I had the
power company come in and monitor the building for a week, but they assured
me that they only supply 460/265 and that is what we were getting. The
ballasts for the fluorescent lighting were rated for 277 volts. I had to go
to every transformer in the building and change the taps so that we could
get 120 volts out of an outlet instead of the 102-105. I also had to
install a few buck and boost transformers on some A/C equipment.

Of course variation in distribution, voltage drop and distance from
transformers does have an effect.