Air compressors use heavy-duty electric motors to run air pumps that force air into a chamber, which is why most air compressors are powered by 240 volts of AC electricity. A pressure switch controls the air compressor electric motor. Wiring a 240-volt air compressor pressure switch involves connecting the two power wires, one ground wire and two electric motor wires to the terminals on the air pressure switch.
Locate the pressure switch on the air tank and remove the switch cover, using a screwdriver. View the four terminal screws on the switch and loosen each screw.
Measure the length of electrical cable needed to run from the pressure switch to the 240-volt wall receptacle, and cut an equivalent length of electrical cable (3 wire). Remove two inches from the outer covering on both ends of the cable, using diagonal pliers. Strip off 1/2 inch of insulation from the tip of each wire on both ends of the cable.
Hook the black wire (hot) and the white wire (hot) clockwise around each outermost terminal screw on the switch. Tighten each screw to secure the connections. Wrap black electrical tape around the white wire to indicate that it is a live wire. Hook the green or bare wire (ground) clockwise to the green screw on the metal frame of the pressure switch.
Unscrew the plug cover of a 240-volt male plug. Hold the other end of the electrical cable, and slip the tip of the cable into the opening on top of a 240-volt male plug. Pull the wires from the opening at the base of the plug and wrap black electrical tape around the exposed part of the white wire to indicate that it is a power wire.
Hook the black wire (hot) and the white wire (hot) clockwise around each brass terminal screw on the plug. Hook the green or bare wire (ground) around the green terminal screw. Tighten each screw to secure the connections. Replace the plug cover, and tighten the clamp screws on the plug handle to secure the cable.
Hold the two power wires coming from the electric motor and hook both wires clockwise around each of the two innermost terminal screws on the pressure switch. In the U.S., power wires are required by local and national electrical codes to be coloured black, but red or blue can also be used for additional power wires. Replace the cover of the pressure switch. Plug the compressor into the 240-volt outlet to test the connection.
The male plug serves as manual disconnect that will allow you to disconnect the compressor from the power supply in case of repairs or emergency. The amperage of the air compressor must be 80 per cent of the circuits amperage. Check the owner's manual to know the amperage of the compressor, and divide the figure by .80 to arrive at the amperage of the wires and plug.
Wiring electrical circuits is a dangerous job and should only be performed by a qualified electrician. Never attempt to perform this task unless you possess prior qualified training and experience. The type of electrical plug must match the type of 240-volt receptacle.