We have a 3 phase 208V Machine(connected to overhead bus) with a 220v/110v step down transformer inside the cabinet that powers a 110v receptacle outside the cabinet.(Very old Machine and no electrical Prints).
Today... Someone decided to plug another machine into that receptacle with a Defective Start Capacitor (Currently they hand turn the motor to get the motor going, and I tested the Cap.). As they turned on the machine all 3 phases seemed to drop out. As all the lights and machines turned off in the building. Has anyone ever heard of this? I am reluctant to test it out again to see if it's just a coincidence. Because, it created a lot of problems for us with the servers and Fire Suppression system as they are ran on two different legs.
No Breakers, fuses, tripped anywhere in the building and No reported power outage in the area(That I know of). Weather was calm. Power was down for about 15 seconds and came back on its own.
I looked in the machine cabinet, it does have 40 amp fuses on the Machine Disconnect and 15 amp fuse on the secondary side of the step down transformer.
Has Anyone heard of this happening before is this just a Coincidence? I won't be able to get back to that machine for at least a couple of weeks to create an electrical diagram for it. But if anyone had this happen to them before would be helpful. As in my 15 years I have never had this happen to me before. (For now I just slapped a do not use tag on the receptacle).
Most of these machines are built in the 80's and 90's with some modifications. I have found Lead side switched and Neutral side Switched and same goes for fuses. Any wiring mistakes you can think of, is very likely at this point.