In NEMA world,typically duty cycle is referred to in one of two terms:
Continuous or intermittent
SI - Continuous duty
The motor works at constant load for enough time to reach temperature equilibrium
The motor works at constant load,but not long enough to reach temperature equilibrium,and 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 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 breaking.
Sequential identical cycles of starting,running at constant load.Temperature equilibrium is not reached.