I had a unique situation happen recently that has me puzzled. I have a location that has a 480 ungrounded delta bank that runs some water pumps,conveyors,and other equipment. When I arrived on site, I found a fuse blown on a primary phase conductor feeding this bank. However, one pump was running. Other 480 3-phase equipment on this service was also started with the primary fuse blown prior to noticing the fuse blown.
Now I understand that a motor will run on 2 phases but not start......right. But how did the other equipment start on only 2 phases? When I metered the voltage, I read 480 volts across all three phase. Does the running motor cause a "false" phase allowing other motors to start? Similar to a phase converter?
Thanks for the info.