Out in the oil patch in west Texas they have many remote spots running 480 volt three phase pumps. This is a disconnect for one such application, (sorry could'nt figure out how to get the picture rotated) I'm trying to figure out how this works. The 'B' phase has a copper bar to ground yet they can run a three phase motor. This site had some other problem, the power was reported as down. when I got there I checked the voltages and currents. Here are the findings:
Voltage Phase to Phase
A-B 481 - 485
B-C 377 - 425
A -C 409 - 430
The voltages were fluctuating between those values, the voltages to ground were 0 on 'B' of course and I forgot to record A and C. What really threw me was the load. It was a 20 HP motor running a PD pump at 1179 rpm and it was running fine. The load currents were 25A on 'A', 26A on 'B' and 'C' was 1.5A and would jump up to 8A. I wanted to investigate further but it was running fine and we had other site issues to get to so we had to leave. No one reported any other problems. How can that work? What was going on? Thanks

Comments rated to be Good Answers:
Comments rated to be "almost" Good Answers: