3-Phase Electric Motor Specifications


Three-phase electric motors are used for a wide variety of applications, for everything from operating woodworking tools to powering electric cars and other vehicles. Many types of 3-phase motors are available, and it can be a little confusing for the novice to tell the difference between all the models. However, most 3-phase motors come with specifications to help the prospective buyer understand what the motor does and what it will be useful for. Often, these specifications can be found on a metal plate connected to the motor. Understanding what these specifications are and what they mean is a good first step in choosing the 3-phase electric motor that best suits your needs.


  • Horsepower (hp) is one of the most important specifications you will encounter for your 3-phase electric motor. Horsepower measures the amount of force that the engine manages to generate. Usually, for 3-phase motors used in the home, you will want a motor specified to run at about 1/4 hp if it is powering small tools and 5 hp if it is powering an air compressor. Horsepower is not always the best way to judge a motor's efficiency, however, as different motors with the same horsepower specifications may require different amounts of power to achieve that level of horsepower.

Revolutions Per Minute

  • Revolutions per minute (rpm) is another important specification for 3-phase electric motors. Revolutions per minute measures the amount of times the shaft on the motor will revolve in a minute. If you are working in a home shop, your motor should be specified to run at either 1725 or 3450 rpm. However, motors come in a wide variety of different rpms, and they are often able to run at many different rpms.


  • Voltage is another important specification for 3-phase motors. Voltage is a measure of the amount of electricity required to run the motor. Most motors run on either 110 or 220 volts. A motor runs at its optimum power usually at 220 volts.

Ambient Temperature

  • Ambient temperature refers to the temperature in the room or environment in which the motor is being used. Maximum ambient temperature is another common specification on 3-phase motors, telling you the maximum temperature in which the motor will operate at full efficiency.

Current Type

  • The type of current the motor uses is also important, especially for vehicle motors. Three-phase electric motors can run off either AC or DC power. Usually, an AC-powered motor will run from the same sort of power source as a DC motor, but it will come equipped with an inverter.

Mounting Method

  • The manner in which the motor is mounted in another important specification. Several mounting methods exist. Among the most popular are rigid bass mounts, resilient base mounts and NEMA C face mounts. Rigid base mounts are cast or welded to their base. Resilient base mounts have rings in between the mounting hubs to absorb the vibration and noise of the motor. Face mounts can be attached and disconnected by bolts that run through threaded holes in the motor's face. Foot-mounted motors have a foot-like piece on their bottom to connect them to a workbench, while flange-mounted motors do not have a foot on the bottom, meaning they can be attached wherever they are needed.

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  • Photo Credit Big electric motor in a marble quarry. Alentejo, Portugal image by mrfotos_fotolia from Fotolia.com
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