"We tried using a 100A thermal-mag breaker and it tripped on motor inrush current."
Then you have some other problem, most likely. a 480V, 3phase, 25hp motor should work fine with a 50 amp thermal-magnetic breaker.
You can also measure these properties with a network analyzer, if you don't have the mfrs specs. Typically, this is done by an RF engineer. (Network analyzer in the RF field is not similar to the network analyzer in the IT field.)
