Major Types Electrical Motor 

Alternating current (AC) induction motors are divided into two electrical

Categories Based on their Power Source – 

single phase and polyphase (three phase).

AC Single Phase Types

Types of single-phase motors are distinguished mostly by the way they

are started and the torque they develop.

Shaded Pole motors have low starting torque, low cost, low efficiency,

and no capacitors. There is no start switch. These motors are used on

small direct drive fans and blowers found in homes. Shaded pole motors

should not be used to replace other types of single-phase motors.

PSC (Permanent Split Capacitor)

motors have applications similar to shaded

pole, except much higher efficiency,

lower current (50% - 60% less), and higher

horsepower capability. PSC motors have a

Run capacitor in the circuit at all times. They

can be used to replace shaded pole motors

for more efficient operation and can be used

for fan-on-shaft fan applications, but not for

belted fans due to the low starting torque.

Split Phase motors have moderate to low

starting torque (100% - 125% of full load),

high starting current, no capacitor, and a

starting switch to drop out the start winding when

the motor reaches approximately 75% of its operating speed. They are used on easy-tostart belt drive fans and blowers, as well as light-start pump applications.

Capacitor Start motors 

are designed in both moderate and high

starting torque types with both having moderate starting current, high breakdown torques.

Moderate-torque motors are used on applications in which starting

requires torques of 175% or less or on light loads such as fans, blowers,

and light-start pumps. High-torque motors have starting torques

in excess of 300% of full load and are used on compressors, industrial, commercial and farm equipment. Capacitor start motors use a

start capacitor and a start switch, which takes the capacitor and start

winding out of the circuit when motor reaches approximately 75% of its operating speed.

Capacitor Start/Capacitor Run motors

Performance similar to capacitor start except for the addition of a run

capacitor (which stays in circuit) for higher efficiency and reduced running amperage. Generally, start/ capacitor run motors are used for 3 HP and larger single-phase applications On industrial duty motors, capacitors are usually protected by metal cases attached to the motor frame. This capacitor start/capacitor run motor has two cases.

AC Polyphase (Three-Phase)

Polyphase 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.

The table on the next page can be used to help guide which design type to select based on application requirements.

Because of their widespread use throughout industry and because their

characteristics lend themselves to high efficiencies, many types of generalpurpose 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, foot-mounted motors from 1-200 HP.