Cord plug amperage rating for 3-phase machine
3 Phase NEMA cord caps jump from 30 amps to 50 amps so you would need a 50.
 What is the voltage? this will define the style of outlet and cord cap.
480 V would use a NEMA L16-50 this is a true 3 phase with ground (4 wire). If you are using a system that also requires a neutral you will need the 5 wire.