Multi-Speed Motors

Author: E.E. Kimberly

Some constant-speed motors are provided with leads from the pole groups brought out to an external switch by which the number of poles and hence the synchronous speed may be changed quickly even while the motor is running. Such a motor is defined as a multi-speed motor. For example, the pole leads may be so arranged as to provide quick changes from 4 to 6 to 8 poles with corresponding synchronous speeds of 1800, 1200, and 900 rpm, respectively, on 60-cycle supply. At each speed the motor will run as a constant-speed motor, and no intermediate speeds are available. Two-speed motors are sometimes built with two separate windings to accomplish the change in speed.