I agree with Jraef, and would like to add just a couple things. First, the protection device is most likely a Eaton-CH HMCP, not AB. As AB does not physicallt make them, even if their name is on it.
Second, the current in question is the asymmetrical current. I plotted the motor curve with the 250A HMCP, and if the asymmetrical factor is greater than 2, it is likely the MCP is going to trip, especially if it has been doing this often, there can be some weakening of the device, i.e. tripping below setting.
Also, in this case, a higher voltage is actually working against you. Motor starting is the oddball when it comes to voltage and current relationship. We typically think of the steady state relationship of V=I*Z, so as V goes up, I goes down. But during starting Z is transient, and therefore as V goes up, so does I, and vice versa (softstarter).
If the motor nameplate is 460V, and the motor bus voltage is stiff at 480V or even slightly above that, then the assymetrical factor may not even need to be 2 for it to trip.
"Just because you're paranoid, doesn't mean they're not out to get you"