Polyphase (three-phase) induction motors have a high starting torque, power factor, high efficiency, and low current.
They do not use a switch, capacitor, relays, etc., and are suitable for larger commercial and industrial applications.
Polyphase induction motors are specified by their electrical design type: A, B, C, D or E, as defined by the National Electrical Manufacturers
Association (NEMA). These designs are suited to particular classes of applications based upon the load requirements typical of each class.
Because of their widespread use throughout industry and because their characteristics lend themselves to high efficiencies, many types of general purpose three-phase motors are required to meet mandated efficiency levels under the U.S. Energy Policy Act. Included in the mandates are NEMA Design B, T frame, and foot-mounted motors from 1-200 HP.
