Motor Classifications

There are three major classes of commonly used motors. Classification depends on the type of power supply the motor will use; DC, single-phase AC, or polyphase AC. The design of individual motors varies within each classification. Different types of construction produce specific starting and running characteristics more or less suited to particular applications.

DC motors appear in small power applications where precisely adjustable speed control is desirable. These motors are battery operated and their power requirements are small. DC speed control is simpler, less costly, and offers more control over a greater range of speeds than AC speed control systems.

Single phase induction motors are used in residential and commercial applications where three phase power is not available.

Eighty percent of operating motors in the United States are AC single phase induction motors. They're used in applications with power requirements of 10 horsepower or less.

AC single phase induction motors are further classified by their start and run characteristics. These characteristics are covered in more detail in this section.

Three phase induction motors are widely used in industrial and commercial applications, classified either as squirrel cage or wound rotor motors.

Three phase induction motors self-start and use no capacitor, start winding, centrifugal switch, or other starting device.

Power ratings range from one third to several hundred horsepower in three phase motors. Motors of this type rated one horsepower or more cost less and can start heavier loads than their single phase counterparts.

And Furthermore . . .