Many motors today are designed to be as flexible as possible when it comes to speed. A three-speed motor has three field windings and a rotor, all in one housing. Each field winding is designed to spin the rotor at a different speed. This enables one motor to be used for a number of different applications. A three-speed motor usually has four wires, the three speed wires and the common wire. Power is supplied to the common wire and any one of the speed wires for a certain speed.
Check the motor wiring diagram and documentation for how the motor should be wired. Some manufacturers use different names for the terminals on their motors. Locate the ground terminal on the motor. Connect the ground wire of the circuit to the ground terminal of the motor. The ground should always be the first thing you connect for safety reasons.
Locate the common terminal on the motor. The common wire is the one wire that is shared by all of the field coils. This wire should be connected to the white common wire of the feeder circuit.
Connect the hot wire to the terminal that has the speed you want. You can also connect the hot wire to a multi-speed switch. A multi-speed switch allows you to connect one hot wire to all three speed terminals. This allows you to change the speed of the motor by changing the speed setting on the switch. This is how a window box fan works.