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Consider motor load requirements, applications

Publication date: 
March 2003
Cyndi Nyberg Esau, Former EASA Technical Support Specialist

Most motors are run continuously with little variation in load. A continuous duty motor is energized and loaded for an extended period of time. When the motor is started, the temperature increases, and then the temperature stabilizes after some time. If the motor was designed with a service factor, it is possible to run the motor at a higher than rated load for short periods of time without significant thermal damage to the windings, rotor or bearings. A motor to be used with a continuous load is sized based on that load rating. There are, however, many applications where a motor is not loaded consistently throughout its duty cycle, or is energized intermittently. Some motors are started and stopped often, while others are loaded lightly for some time, then more heavily for some time, and the applied load can vary greatly. If there are periods of time where the motor is operating at less than full load, then it may be possible to size the motor smaller than the maximum load level.