Box fans provide a convenient way to circulate air in areas where the air from a fixed-location fan will not reach. Many box fans take advantage of a three-speed motor. Adjusting a fan's speed allows the fan to circulate the air in different-sized rooms without producing an overpowering blast of air. Upgrading a single-speed fan to a three-speed fan requires a new switch and motor. Single-speed box fans use parts with two wires, while a three-speed box fan needs a four-wire switch and motor.
Identify the three-speed switch's and fan motor's wires, using their wiring diagrams as a guide. The switch contains one input wire, often called "Line", and three-speed wires. The motor contains three-speed wires and a neutral wire. Each wire uses its own colour-coded insulation, and the colours vary between manufacturers.
Strip one half-inch from the end of each wire with wire strippers. This includes the wire set that enters the fan. It has a wall plug on the other end.
Twist the end of the motor's neutral wire to one of the wires from the wire set that enters the box fan. Secure them with a wire nut. The wire set that enters the fan contains two wires.
Twist the second wire from the wire set that enters the fan to the switch's input wire. Secure them with a wire nut.
Twist the fan's low-speed wire to the switch's low-speed wire. Use the wiring diagrams on the motor and switch as a guide. Secure these wires with a wire nut.
Twist the fan's medium-speed wire to the switch's medium-speed wire. Use the wiring diagrams on the motor and switch as a guide. Secure the wires with a wire nut.
Twist the fan's high-speed wire to the switch's high-speed wire. Use the wiring diagrams on the motor and switch as a guide. Secure the wires with a wire nut.
Route the wires away from the fan blades. Secure the wires to the box fan's frame with plastic wire ties.