Induction Motor Types: What You Need to Know

Induction motors are a staple of the electric motor industry. Although motor technology continues to evolve, we still heavily rely on induction motors around the world. These motors are typically thought of in terms of their winding type, start/run, and the torque they’re capable of operating at. Some of these specific induction motors include:

• Shaded Pole;
• PSC (Permanent Split Capacitor);
• Split Phase;
• Capacitor Start;
• Induction Run;
• Capacitor Start/Capacitor Run; and
• Polyphase (three-phase).

This differentiation is especially important for users such as maintenance technicians and customer service representatives who directly support customers in replacing existing motors. It’s important to understand different induction motor types in order to properly match your application and motor.

Types of Induction Motors by Definition

Shaded Pole Motors

Shaded Pole motors have low starting torque, low cost, low efficiency, no capacitors, and no start switch. These motors are commonly found in small direct drive fan and blower residential applications. Shaded pole motors should not be used to replace other types of single-phase motors.

Permanent Split Capacitor (PSC) Motors

PSC have applications similar to shaded pole except operate at a higher efficiency, possess a lower current (50 - 60 percent less), and deliver higher horsepower capability. PSC motors have a run capacitor in the circuit at all times and can be used to replace shaded pole motors in direct drive fan applications, but not for belted drive fans due to their lower starting.

Split Phase Motors

Split Phase motors produce a higher starting torque (typically 100 - 125 percent of full load torque), high starting current, possess no capacitor, and a utilizes a starting switch to drop out the start winding when the motor reaches approximately 75 percent of its operating speed. These motors are used on easy-to-start belt drive fans and blowers, as well as light-start pump applications.

Capacitor Start Motors

Capacitor Start motors produce the best starting torque with a moderate starting current and high breakdown torque. Moderate-torque cap start motors are used on applications in which starting requires torques of 175 percent or less on light loads such as fans, blowers, and light start pumps. High-torque cap start motors have starting torques in excess of 300 percent of the full load and are used on compressors, industrial, commercial and farm equipment. These motors use a start capacitor and a start switch, which takes the capacitor and start winding out of the circuit when the motor reaches approximately 75 percent of its operating speed.

Capacitor Start/Capacitor Run Motors

Capacitor Start/Capacitor Run motors have applications and 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, capacitor start/capacitor run motors are used for 3 HP and larger single-phase applications..

AC Polyphase

AC Polyphase (Three-Phase) induction motors have a high starting torque, power factor, higher efficiency, and lower current. They do not use a switch, capacitor, or relays 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 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, foot-mounted motors from 1-200 HP.

For more information related to Commercial or Industrial electric motors, contact a member of the Regal Rexnord sales team below.