peoplehouse
Member
I need some help understanding why this happened. We have an MCC that was blowing a fuse on the primary side of a transformer (480v.x120v.) The root cause was a mechanical bind on a conveyor, the OL device and fuse protection for this motor starter did not trip or open. Also, the circuit breaker for the 120v. control did not trip, instead one of the primary side (480 single phase)blew due to the OL device being destroyed. Replaced OL and the primary fuse blew again. I started checking for mechanical issues.
This was a bear to troubleshoot, it looked like a ground fault/dead short everywhere I put my meter (0.4 ohms). I isolated the transformer and pulled each 120v. control conductor one by one from the terminal block until the apparent short to ground changed from .4 to 135 ohms. then traced the problem to the OL on the motor starter.
Hopefully someone can explain this, Monday I will verify motor size and OL are correct.
Thank you for any insite to this
Jeff
This was a bear to troubleshoot, it looked like a ground fault/dead short everywhere I put my meter (0.4 ohms). I isolated the transformer and pulled each 120v. control conductor one by one from the terminal block until the apparent short to ground changed from .4 to 135 ohms. then traced the problem to the OL on the motor starter.
Hopefully someone can explain this, Monday I will verify motor size and OL are correct.
Thank you for any insite to this
Jeff