We have a 480V 150hp motor that keeps tripping a mag only circuit breaker in a combination starter. The circuit breaker is an AB HMCP breaker rated at 250A with the dials set to 2500A. The motor has a FLA of 175A with a Locked rotor code of G.
Figuring the locked rotor code I come up with a maximum of about 1136A starting current or locked rotor current. This value is certainly under the 2500A setting on the breaker. Also I know that there may be an inrush factor assosciated with the motor, and I have seen this previously to be about 1.6 x LRC so using this I get about 1817A. This is still under the 2500A setting on the breaker.
All the voltages on the starter look o.k. and are about 480V. The breaker tripping is internitent. The application is a water pump that is running as a backup to another similar pump. We had problems starting when other pump was causing this pump to freespin backwards, but we have since solved that problem and pump is not spinning at all when we go to start and get the intermitent trips.
Any ideas on what could be causing the breaker trip?
Figuring the locked rotor code I come up with a maximum of about 1136A starting current or locked rotor current. This value is certainly under the 2500A setting on the breaker. Also I know that there may be an inrush factor assosciated with the motor, and I have seen this previously to be about 1.6 x LRC so using this I get about 1817A. This is still under the 2500A setting on the breaker.
All the voltages on the starter look o.k. and are about 480V. The breaker tripping is internitent. The application is a water pump that is running as a backup to another similar pump. We had problems starting when other pump was causing this pump to freespin backwards, but we have since solved that problem and pump is not spinning at all when we go to start and get the intermitent trips.
Any ideas on what could be causing the breaker trip?