IEC (the International Electrotechnical Commission) uses eight duty cycle designations to describe electrical motors operating conditions:
|S1||Continuous duty||The motor works at a constant load for enough time to reach temperature equilibrium.|
|S2||Short-time duty||The 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.|
|S3||Intermittent periodic duty||Sequential, identical run and rest cycles with constant load. Temperature equilibrium is never reached. Starting current has little effect on temperature rise.|
|S4||Intermittent periodic duty with starting||Sequential, identical start, run and rest cycles with constant load. Temperature equilibrium is not reached, but starting current affects temperature rise.|
|S5||Intermittent periodic duty with electric braking||Sequential, identical cycles of starting, running at constant load and running with no load. No rest periods.|
|S6||Continuous operation with intermittent load||Sequential, identical cycles of running with constant load and running with no load. No rest periods.|
|S7||Continuous operation with electric braking||Sequential identical cycles of starting, running at constant load and electric braking. No rest periods.|
|S8||Continuous operation with periodic changes in load and speed||Sequential, identical duty cycles run at constant load and given speed, then run at other constant loads and speeds. No rest periods.|
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