More and more multi-speed and variable-speed motors are being incorporated into HVACR systems to increase the efficiency of the equipment. Variable-speed motors go by several names. You may hear a variable-speed motor referred to as a “brushless permanent magnet” (BPM) device, as an “electronic commutated motor” (ECM), or as an “integrated controlled motor” (ICM). All of these motors work on the same basic principle. Changes in a variable— air flow or static pressure, for example—are monitored by a sensor. By responding to changes in the variable, the motor has the ability to adjust the speed of a blower or fan, and thus maintain a predetermined setpoint. The motor’s electronic controls can be pre-programmed, and are contained in a package or module mounted on the rear of the motor housing. This figure shows the difference between a “standard” 56 frame and a BPM 56 frame motor.