Key Difference: The main difference between single phase and three phase motors is that a single phase motor runs on a single phase power source, whereas a three-phase motor runs on a three-phase power source. A three-phase motor may run on a single power source, but it will not self-start.

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Single Phase and Three Phase Motors are two different types of AC motors. An AC motor is a type of motor that runs on alternating current (AC). The main difference between single phase and three phase motors is that a single phase motor runs on a single phase power source, whereas a three-phase motor runs on a three-phase power source. A three-phase motor may run on a single power source, but it will not self-start.

Also see: Synchronous Vs. Induction Motor 

In single-phase, electric power, the voltages of the supply vary in unison. However, in three-phase electric power, the function alternates between electricity generation, transmission, and distribution. The three-phase electric power is the most commonly used method by electrical grids worldwide to transfer power. In comparison, single-phase electric power is rarely used for large areas or projects. This is also due to the fact that single-phase electric power is generally more expensive and less reliable than three-phase electrical power. Three phases of electrical power are more economical because it uses less conductor material to transmit electrical power.

However, single-phase electric power and its corresponding single-phase motors are used on smaller scales such as in homes, offices, shops, and small factories. The main reason for this is that the power requirement in most of these places can be easily met by the single-phase motors. The three-phase motors and electric power is more commonly used in large scale industries or projects, as it is capable of creating more power.

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Both single phase and three phase motors are made up of two parts: the Stator and the Rotor. The rotor, as the name suggests, is the rotating part of the induction motor. It is connected to the mechanical load through the shaft. The stator is the stationary par, i.e. it does not move. It acts as the field magnet and helps create power by interacting with the motion created by the rotor.

 A single phase motor does not have a rotating field, but one that reverses 180 degrees. Hence, it usually is not self-starting; however, at times it does have some provisions for it, usually by switching out the start winding or with the help of a capacitor. A three-phase motor usually has a self-starting mechanism. Also, in a three-phase motor, the phases are 120 degrees apart, so that a proper rotating field can be produced.

In comparison, three-phase motors tend to be cheaper and more efficient than single phase motors. However, single-phase motors are usually cheaper and economical for smaller power requirement. They are also easier to construct and more reliable in their function.

Comparison between Single Phase and Three Phase Motor:

Image Courtesy: acpd.co.uk, allaboutcircuits.com