To satisfy consumers’ desires for quieter motors, manufacturers have developed eight-pole motors. All can come in either totally open, totally enclosed, or combination models, adding to their versatility. They are often used for air-handling equipment, direct-drive applications, window fans, furnace blowers, room air conditioners, heat pumps, and other equipment where the relatively slower motor speed makes for quieter operation. 6) and between 1,050 and 1,175 rpm loaded.Six-pole motors run at 1,200 rpm unloaded (7,200 Ã It is beneficial to become aware of the different speed-related sounds motors make. One thing for the service technician to keep in mind in the field is that the higher the rpm, the noisier a motor may sound to the untrained ear. Two-pole motors often are found in pump applications, such as sump pumps, swimming pool pumps, and water recirculating equipment. 2) unloaded, and approximately 3,450 under load.Motors of this speed are commonly found in belted applications such as blowers, fans, air-handling equipment, compressors, and some conveyors.Ī two-pole motor operates at 3,600 rpm (7,200 rpm Ã Motor Speeds, Both Loaded and Unloaded Our spinning four-pole motor, then, operates at 1,800 rpm in this example under no-load conditions and approximately 1,725 rpm under load. The difference between the field speed of 1,800 rpm in this example and the rotor speed of approximately 1,725 rpm is called the “slip.” Slip varies with the load over a narrow operating range for each motor design. Instead, the rotor or moving part of the motor is restrained by the load from “catching up” to the field speed. Note that when an ac motor is loaded, the spinning magnetic field in the stator does not change speed. Using this formula, you can see that a four-pole motor operating on the bench under no-load conditions runs at 1,800 rpm (7,200 Ã Therefore, for a 60-Hz system, the formula would be:įor a 50-Hz system, the formula would be: The mathematical formula to remember in helping make this calculation is the number of cycles (Hz) times 60 (for seconds in a minute) times two (for the positive and negative pulses in the cycle) divided by the number of poles. So, all four-pole motors will run at the same speed under no-load conditions, all six-pole motors will run at the same speed, and so on. The number of poles, combined with the ac line frequency (Hertz, Hz), are all that determine the no-load revolutions per minute (rpm) of the motor.

Induction motor rewinding calculation