You need to account for the efficiency when converting from mechanical output to electrical input watts.
Yes and this applies to single phase as well as 3 phase.
You can by high efficiency motors or cheap ones.
My point was the same as your point that going three phase does not necessarily mean energy savings any more than a 480 motor saves over the same HP (and efficiency) motor in 208 volt.
Bob Badger Construction & Maintenance Electrician Massachusetts
