How to Wire an AO Smith Air Compressor Motor


There are many electric motors in use on air compressors; some are smaller than your fingernail and others large enough to shoot a nail 100 yards. Air compressors run on an induction motor. An air compressor has no brushes in its motor and it runs on alternating current. A. O. Smith manufactures fractional compressor motors designed to work with all compressor technologies. The company's air compressor motors range from 1/100th to 5 horsepower.

Things You'll Need

  • Volt meter
  • 8/2 cable
  • Screwdriver set
  • 60-amp disconnect switch
  • Double 50-amp circuit breaker
  • Shut the power off to the breaker panel. Test the termination of the power supply with a volt meter. Touch the meter tip to the wires of the circuit breaker. If there is no movement of the needle then power is off.

  • Read the compressor motor's information plate. You will see the motor's operating amperage. You need to know how much operating power the air compressor takes, so that you can select the appropriate wiring material and right size circuit breaker for the job.

  • Calculate how much power the air compressor will actually take to start. The rule of thumb is that motors take three times more operating current to start than to run. An example is 1/2-horsepower motor wired for 110 volts can run on less than 7 amps, but in order to start the air compressor the motor requires 22 amps.

  • Take the 8/2 cable and wire the air compressor for 240 volts. The AO Smith Air Compressor runs on a 240-volt line. The ground wire is not counted in an 8/2 cable, but the A.O. Air Compressor still needs grounding.

  • Connect the ground wire in the cable to the green wire on the circuit breaker. Use a screwdriver to loosen and then tighten the screws in the switch. Repeat this process for the black wire and the red wire. Run the whole cable to a 60-amp disconnect in the breaker panel. This disconnect is not the same as the circuit breaker.

  • Run the cable to the air compressor motor for the bottom terminals. Connect the black with the black and the red with the red, leaving the two ground wires. Connect the outgoing and incoming grounds together. Use a screwdriver to connect the wires.

  • Complete the wiring by moving to the top terminals and connecting the cable to the circuit in the breaker box. Attach the ground wire to the ground bar in the breaker box. Run the black and red wire from the motor terminals to the double 50-amp breaker in the breaker box. The circuit is complete for the air compressor.

Tips & Warnings

  • Purchase all necessary materials prior to project beginning. This saves time and you can stay focused on the job at hand.
  • Any time you work with electricity make sure you shut the supply of power completely off.

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