we just had a 3 phase 120 hp motor go out on us last week. It melted the breaker contacts together and tripped a main upstream breaker. Sucks, have you ran inductance and resistance checks on the compressor motor? Might want to order 2 breakers if you haven't. Ours fried the new breaker during current load checks and we had to go get another one. It lasted about 3 trips and 20 minutes of run time before the long time delay over-currents fried.