[Al Skierkiewicz]

OK,
The 120 amp main breaker and all the other breakers have basically the same construction. The only difference is the main breaker is not auto resettable. All the breakers are capable of over current up to 600% of rated current for a few seconds.

Changing to smaller breakers does not limit the current supplied to the motors. CIMs will still pull 129 amps in stall even if you feed them with 5 amp breakers. The main breaker occasionally trips but more often this is due to external forces rather than an over current condition.