[Al Skierkiewicz]

Circuit breakers are chosen for the wiring used to feed a motor. A 40 amp breaker is used for #12 or larger wire. A 30 for #14 or larger and a 20amp for #18 or larger. Since the van door motor has a stall current of 40 amps you will likely be designing for much less run current (you don't want to stall the motor do you?). A #14 wire and a 30 amp breaker should be sufficient.