The power factor of a fully loaded motor will run about 85%. The power factor of a lightly loaded motor may be as low as 20%. The wattage draw at lighter loads is not excessive. A lightly loaded motor may be drawing a high amperage, but there is an issue called power factor that comes into play. The overloads are designed so they will not trip out on startup. The motor starter for the 10 HP motor should have properly sized motor overloads to trip out if there is a prolonged overcurrent situation. The minimum wire size would be #6 AWG for a 10 HP motor, and larger if the length of feeder is long. The wire size does not need to match the amperage of the supply breaker for motor applications. I don't have my old reference materials close at hand, but I recall that the supply breaker can be as much as 250% of full load amps. The NEC allows for the supply breaker to be sized large enough to withstand the inrush current with the assumption that the motor overloads in the motor starter are protecting the motor and supply wires from damage due to overcurrent. In motor circuits, the breaker needs to be large enough to avoid tripping on startup. That works out to about 57 amps, so the bare minimum is a 60 amp breaker in those cases.

In typical, non-motor, applications, a breaker needs to be sized such that it is not loaded to more than 80% of the full load amps of the load being served.

(I am assuming that a 480 volt supply is not being considered here.) The supply breaker needs to handle the inrush current to the motor which will be quite severe. An entry to this post stated the following: 'If you go with the 10 hp motor, it will require a 50 amp breaker.' According to my Grainger catalog, a 10 HP, 230 volt, single phase, motor will draw 46 amps.

10 hp single phase motor used