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
S2-Short-time duty 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.