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How to Wire a 3 Phase Air Compressor


By Dave Rongey - Summary:

Wiring a 3 Phase Motor for an Air Compressor: The Basic Requirements for Wiring Electric Motors, 3 Phase Motor Circuits


Air Compressor Electric Motor

Electrical Question: We have a Saylor Beall air compressor we are trying to get wired up. It ran fine at the previous shop and then we moved it to this shop. The motor is 3 phase and it appears to be wired according to the diagram for the low voltage 220. The label shows that it can be wired for 220 or 460. It is all wired and hooked up to the controller, but here is where we are having problems, we cant get it to start, it only hums. The motor starter is a Cutler Hammer # A10CNO. The wires from our shop circuit breaker has 2 yellow hot wires at 120 volts each, 1 white neutral wire and 1 green ground wire. Is it possible to wire the compressor with this combination of wires and where do they go? When the compressor was moved it was simply unplugged from the wall and moved, all pressure switches and motor wires are in their same locations as before.

This electrical wiring question came from Cody, in Enid, Oklahoma.

Dave’s Reply:
Thanks for your electrical wiring question Cody.

Wiring a 3 Phase Motor for an Air Compressor

air compressor

The Basic Requirements for Wiring Electric Motors

  • Every motor should have a name plate which is typically attached on the side or end of the motor. The information found on the label tells all about the motor size and electrical requirements. To stay on track with this question, the shop where the motor is to be installed must have an electrical service which supplies either 3 phase 230 volts, or 3 phase 460 volts.

Electrical Service Panels

  • Just like electric motors, an electrical service panel should be equipped with a label which is attached either on the cover or inside the door. The information on this label will be specific to the make and model of the electrical panel along with the voltage and amperage rating. Here in the USA, a typical home electrical panel may be 120/240 volts 125 amps. The actual amperage capacity of the panel is best known by examining the Main Disconnect or Main Circuit Breaker, which will have the amperage rating identified, such as on the breaker handle.

Electrical Power for 3 Phase Motors

  • ¬†Without getting too technical, a 3 phase electrical service panel will produce 3 separate lines of electrical power. A 120/240 volt single phase panel found at a home¬† or shop can only provide up to two separate lines of power, therefore this type of electrical service could not provide the necessary power for a 3 phase motor.

3 Phase Motor Circuits

  • As described above, a typical 3 phase motor circuit will have 3 separate insulated wire conductors for the power and the ground wire. A neutral wire is not required for a 3 phase motor.

A Summary of Wiring 3 Phase Motors

  • Identify the required voltage and amperage.
  • Determine if the electrical service panel has the same voltage and available amperage capacity.
  • Electric motors are typically wired to a motor controller or motor starter which is sized appropriately to the horsepower of the motor and has thermal overload protection.

 

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