TrueRMS
Member
- Location
- Windsor Colorado
So gents lets see if someone can help with this one.
480v 400 amp molded case breaker (1950's vintage) feeding a motor with a FLA of 219 and operating at a current level of 187 amps steadily has been tripping after 8 or so hours. The contactor has overloads on each phase and are sized appropriately and are not taking the motor out. Motor and cable have been meggered and are good. voltage drop from line side of the breaker and the bottom of the contactor is in the range of .578 volts and contacts have been cleaned and filed. No current difference measured from the same points. Other than heating or a weak breaker I am scratching my head. Using a thermo camera we see a slight temp difference on the center phase in the 50degF range. Breaker holding during starting currents of 1600+ amps with no issue.
480v 400 amp molded case breaker (1950's vintage) feeding a motor with a FLA of 219 and operating at a current level of 187 amps steadily has been tripping after 8 or so hours. The contactor has overloads on each phase and are sized appropriately and are not taking the motor out. Motor and cable have been meggered and are good. voltage drop from line side of the breaker and the bottom of the contactor is in the range of .578 volts and contacts have been cleaned and filed. No current difference measured from the same points. Other than heating or a weak breaker I am scratching my head. Using a thermo camera we see a slight temp difference on the center phase in the 50degF range. Breaker holding during starting currents of 1600+ amps with no issue.
