Duty cycles of electric motors

The relative duty cycle (previously called ON time) is the percentage of the time with constant load with respect to the total duration of a duty cycle:

Duty cycle of electric motors

The cycle duration, if nothing else has been agreed, is 10 minutes. The relative duty cycle as a % is specified between the code for the rated duty type and the cycle duration in minutes. e.g. S3: 25 %, 12 min. The shorter the relative duty cycle, the more the rated power can be increased with respect to continuous duty, whereby, with the normal version, the breakdown torque should be taken into consideration (according to VDE this is 160 % of the rated torque).

The duty cycle of an electric motor is closely related to the duty type of the electric motor.

Duty types of electric motors

The duty type of an electric motor defines the load cycle of the electric motor and ranges from S1 to S9, where S1 is for continuous duty with the motor running 24/7, and S9 is for converter duty. The remaining duty types are found in Table 1 below:

Duty types of electric motors

Duty types of electric motors_2

Table 1: Duty types of electric motors