Sizing Wires and circuit breakers for 3HP and 5HP shop motor circuits
3HP motor on 690 must use 17A from NEC tables for FLC. Continuous duty must be used, so you must multiply it by 125%, thus calculations must all be made with 21.25A. 12ga wire will flow 21.25A at 60C for wire termination critieria using NM (and of course 75C for connections to CB and motor itself will be met). 90C THHN wire or NM strands will carry the continuous duty FLC of 21.25A, so 12 AWG is fine. However, your circuit breaker should be sized above 21.25A, so 30A (I think that's the next standard up) should be used. 30A is fine on 12AWG wiring on a dedicated motor circuit as the "small conductors" rule is excepted for motors.
If you're already going to run a 30A breaker, you should just use 10AWG and thus be set for both machines. Both machines protect the load/motor as well as the wires via internal overload thermal protection on the motor, the function of the breaker is to protect from ground fault or short circuit in this case. I think Stephen above mentioned you may not trust that overload protection, but in this case 30A CB will protect the circuit/wire perfectly anyways, and is very likely to work acceptably on startup surges.
With a 30A circuit, you should use approved 30A receptacles and plugs. There is no reason you can't wire your 690 with a 30A plug, and considering the NEC mandates you plan for 21.25A on it, I think there's more reason to use the 30A plug than not. Certainly the intent of safe connections for expected amperage is met, and there is no downside--again, everything drives you to ensuring you don't run TOO SMALL in your wire and connections--larger is safer, particularly in that you're actually planning on protecting with the normal and expected 30A CB for the 10AWG already.
The answer is "Yes", you can and should run both on a 10AWG circuit protected by a 30A breaker. Probably the most accurately acceptable thing you can do via the NEC. Absolutely nothing wrong with running larger size AWG than the load NORMALLY demands, most of the complexities of NEC motor calculations revolve around ensuring you DO have a larger conductor to act as a heat sink for the load and ensure temps stay low.
Read my thread linked above for more details.
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