How do you wire from an on-off 3 phase switch to a 3 phase motor?

Answer 1

To wire a three phase compressor, you will need a motor starter( three pole contactor) with a motor overload device sized for the motor run current. A single or double pole pressure switch. This example is for 208 volts, coil on starter should be rated for 208 volts. Bring the three phase conductors to the top of the starter from the disconnect and land them in the wire terminals. Bring the three motor leads to the bottom of the starter and land them in the wire terminals. Go back to the top of the starter, land a wire in A phase terminal ( left Hand phase) with the wire that is already there(some starters have provisions for two wires) take this wire to the pressure switch and land on one side of the contact. Land another wire on the other side of the contact and go back to the starter and go the "coil" terminal on the starter. Go back to the top of the starter B phase terminal(center phase) land another wire there and go to the starter overload device terminal. When the pressure switch closes you should have 208 volts present on the starter coil and it should pull in. Once the pressure switch is satisfied the contacts will open and the starter will drop out.

Answer 2

Very much depends on the motor. Most have very large surge currents (compared to running) when switched on and large back EMF's when switched off. But, a home is littered with motors that are swtiched on normal mains switches - washing machine, vacuum cleaner, food mixer, coffee grinder, various fans, etc etc. etc.