How to Wire a Window Unit to a Breaker Box

Locate the electrical terminal box on the window unit and remove the cover with a screwdriver. Near the terminals, either on the box cover or elsewhere on the machine, locate the plate specifying the electrical requirements of the unit. You need these specifications to determine the size of electrical cable and breaker you need to hardwire the unit.

Use 10-gauge, 4-strand cable if the unit requires 240 volts and draws 30 amps or less. Use 8-gauge cable if it draws 30 to 50 amps, and 6-gauge if it draws more than 50. 240-volt circuits require a double-pole circuit breaker. If the unit requires 120-volt electricity, use 12-gauge, 3-strand cable and a single-pole breaker. The breaker rating should match the current rating on the specifications plate.

Run the cable between the unit and the breaker box. The most efficient way to do this so that most of the cable is hidden depends on the configuration of your house and the location of the breaker box relative to the unit. If the breaker box is in the basement, the best option is usually to run it vertically down from the unit through the floor and pull it to the breaker box through the basement, stapling it to the bottoms of the floor joists with wire staples.

Strip both ends of the cable with a utility knife after you have run it and expose the ends of the insulated wires with a wire stripper. Crimp ring lugs onto the ends of the wires that attach to the window unit with a pair of pliers and remove the terminal screws with a screwdriver.

Feed the brass screw through the lug on the black wire of 3-strand cable and tighten the screw into the brass terminal if your window unit runs on 120-volt power. If it runs on 240-volt power and you're using 4-strand cable, connect the red wire to the other brass terminal. Connect the white wire to the silver terminal and the ground wire to the green terminal.

Reattach the terminal cover. It should have a notch in it that allows the wire to pass through, and it may also have an attached wire clamp to hold the cable in place. If it has a clamp, tighten the clamp with a screwdriver.

Turn off the main breaker in the breaker box and remove the cover with a screwdriver. Pull the other end of the cable into the box through a hole in the side or bottom. You can feed it through a pre-existing hole that has other wires in it if there is room. Otherwise, punch a new hole with a screwdriver and screw on a wire clamp.

Feed the end of the white wire into a vacant slot on the silver bus and the ground wire into one on the ground bus. Tighten the screws with a screwdriver to hold the wires. Keep your tools and hands away from the brass bus bars while you are doing this. They are still energized even when the main breaker is off, and you can get a shock if you touch them.

Feed the black wire into the slot on the bottom of an appropriately sized single-pole breaker and tighten the screw. Snap the breaker into a single slot on the front of the panel and label the circuit.

Use a double-pole breaker, which is a set of two identical breakers coupled together, if you are wiring a 240-volt unit. Feed the black wire into one of the breakers and the red wire into the other. Snap the breakers into a slot large enough to accommodate both of them and label the circuit.

Replace the cover of the breaker box, turn on the main breaker, then turn on the breaker you just installed. The window unit is now energized.