IEC (the International Electrotechnical Commission) uses eight duty cycle designations to describe electrical motor operating conditions:

 

S1Continuous dutyThe motor works at a constant load for enough time to reach temperature equilibrium.
S2Short-time dutyThe motor works at a constant load, but not long enough to reach temperature equilibrium. The rest periods are long enough for the motor to reach ambient temperature.
S3Intermittent periodic dutySequential, identical run and rest cycles with constant load. Temperature equilibrium is never reached. Starting current has little effect on temperature rise.
S4Intermittent periodic duty with startingSequential, identical start, run and rest cycles with constant load. Temperature equilibrium is not reached, but starting current affects temperature rise.
S5Intermittent periodic duty with electric brakingSequential, identical cycles of starting, running at constant load and running with no load. No rest periods.
S6Continuous operation with intermittent loadSequential, identical cycles of running with constant load and running with no load. No rest periods.
S7Continuous operation with electric brakingSequential identical cycles of starting, running at constant load and electric braking. No rest periods.
S8Continuous operation with periodic changes in load and speedSequential, identical duty cycles run at constant load and given speed, then run at other constant loads and speeds. No rest periods.