Air compressor motors are wired directly to an air-operated pressure switch. The pressure switch energises the electric motor circuit when the accumulated air in the storage tank reaches a low, preset amount of air pressure. The motor continues to operate the compressor until the high pressure setting of the switch is reached. Wiring the air compressor to the pressure switch is a task you can perform in 30 minutes or less with a few tools and materials and basic electrical wiring knowledge.
Turn off electrical power to the air compressor switch at the main electrical panel. Tag or otherwise mark the circuit breaker or switch to prevent inadvertent restoration of power.
Remove air compressor pressure switch cover. The cover may have screws near the base or a crown nut depending on the manufacturer. Remove retaining nuts with an adjustable wrench; remove screws with the appropriate tip screwdriver.
Perform a voltage test to verify the absence of power at the switch. The wires from the main electrical panel are connected to the L1 and L2 terminals of the pressure switch. Place one probe of the voltage tester on L1 and the other probe on L2.
Insert the threaded end of the cable clamp into the open slot of the switch body. Attach the retaining nut from the inside of the switch. Tighten the nut in a clockwise direction with the slip joint pliers.
Measure the cable length required to connect the air compressor motor with the pressure switch using a measuring tape. Take into consideration the routing of the cable for a proper measurement.
Cut the cable at the proper length for installation with the wire cutters.
Remove 4 inches of sheathing at the switch end and motor end of the required cable using a utility knife. Take care not to cut into the insulated conductors or nick the bare copper ground wire when removing sheath.
Strip 1/2 inch from each of the insulated wires from both ends of the cable.
Pull the cable through the clamp at the switch and tighten the clamp strap screws. Be sure that the strap is over sheathing and not the insulated wires.
Connect the black wire to the T1 terminal on the pressure switch and tighten in a clockwise direction with a screwdriver.
Connect the white wire to the T2 terminal. Tighten with the screwdriver.
Connect the bare copper ground wire to the green grounding post with the screwdriver.
Replace the pressure switch cover.
Remove terminal access panel screws on the compressor motor with a screwdriver and remove the panel as applicable. Some models of motors have a dimple placed at the lower part of the access panel that serves as a cable clamp. Check the manufacturer's specifications for securing cable to motor.
Connect the black wire to the T1 terminal on the motor. Check the manufacturer's specifications for the type of terminal connections required.
Connect the white wire to the T2 terminal.
Connect the bare copper ground wire to the grounding terminal of the motor according to specifications.
Replace the access panel on the compressor motor.
Restore electrical power and remove tag or markings from the main panel.
There are many electric motor types, styles and horsepower ratings. Be sure you are familiar with the type of motor you are wiring and adhere to the manufacturer's specifications. Always work safely with electricity.