It is difficult to image the world without electric motors. From smaller versions (like tiny motors found in quartz watches) to a million-plus horsepower ones found in ships, motors are used in a variety of applications. As many know, an electric motor is a device that converts electrical energy into Kinetic energy, for example motion. It can be either alternating current (AC) or direct current (DC), and there are some models that can operate on both. Below we will talk about the most common types of AC motors that are used today. AC motors are divided into single phase and 3-phase types.

AC Motor

3-phase AC Induction Motors

This type of AC induction motor is the most common type used in commercial and industrial applications. It is divided into two sub-categories:

  • Wound rotor motors
  • Squirrel cage motors

An AC induction motor uses electromagnetic induction to power a rotating device which is usually the shaft. Its rotor typically turns slower than the frequency that is supplied to it and the induced current is what leads the magnetic field that protects the rotor of this motor.

Single Phase Induction Motors

This type is applied where 3-phase power is not available – typically in agricultural, residential and commercial applications. It is also used in applications that require power below 1 horsepower. Its sub-categories include:

  • Universal motors
  • Shaded pole
  • Capacitor start
  • Capacitor run
  • Split phase


A common feature of all AC motors is a rotating magnetic field, which is produced by the stator windings and can be illustrated for three phase motors – each coil is connected to one phase of a three phase power supply. The current that passes through each coil varies sinusoidally with time. This means that the current from one coil runs faster 1/3 of a period of time that in the other coil. The rotor then creates the torque on the motor drive shaft. The rotating magnetic field can rotate either clockwise or counter clockwise. This will depend on the order of the phases connected to the motor.


To ensure great performance and long term reliability of an AC motor, proper maintenance is essential. Motor efficiency is extremely important, for that reason, check this guide to learn how to keep your AC motor well maintained.

When purchasing an AC motor, keep in mind that lifetime energy costs for intense usage of the motor will exceed the original purchase price in time. For some models, the extra cost to buy a more energy efficient motor is totally worthy. Take into consideration simple decision factors and you will realize whether it is better to replace or to repair a failed motor.