What Is Motor Rating?


The rating of the motor is based on the allowable operating limit determined by the temperature rise of the motor and the nature of the load. Rated values include motor output, voltage, frequency, current, torque and speed. The rated output is the motor's output power at the maximum load whose temperature rise does not exceed the standard limit within a specified time, that is, the basic set output power of the motor. The speed and torque produced by the motor at the rated output are rated speed and rated torque. For example, when a 25W electric motor output power reaches 25W, the speed, torque, and current are the set rated output data, that is, the full load data where maximum efficiency is obtained from the electric motor.

Time Rating, Continuous Rating and Short-time Rating

Motor rated time is the period during which the motor can continuously bear a constant load without causing its temperature to exceed the safety limit in an environment with a room temperature of 40°C(104°F). A standard motor is rated for continuous duty at its rated load and maximum ambient temperature. Specialized motor, such as reversible motor, is designed for short-time operate requirement and intermittent duty, which means that the motor can only be used within the specified time range from 5 minutes to 60 minutes. Although the rated time of the reversible motor is 30 minutes, in the case of short-term intermittent operation, the operating time can still be changed depending on the operating conditions. When the motor starts and reverses, it generates heat due to a large current. The "30-minute rating" mainly depends on the temperature rise of the motor. If the installation environment, load conditions, duty cycle, stopping time etc. can be considered, the motor can be prevented from burning due to excessive temperature. The surface temperature of the motor housing should not exceed 90°C (194°F), and it can be operated for a long time.