To the right is an illustrated schematic animation that contains a three phase motor starter with a hand off auto switch.

MS1 is the motor starter.

The Hand Off Auto Switch is a three position switch with two sets of contacts. one set is made in hand and the other is made in auto.

The remote relay can be any relay controlled by any other circuit or PLC.

The Switch is the heart of the circuit's path.

When the switch is in the off position there is no path to the coil and the starter can't run.

When in the hand position the path is directly connected to the coil and the starter is running the motor.

When in auto the remote relay controls the motor starter if the relay is on so is the starter.

Replace the remote relay with any type of isolated switch contact such as a pressure switch or so on.