IEC Electric Motor Duty Cycles
The eight S1-S8 IEC duty cycles of operating electrical motors. IEC (the International Electrotechnical Commission) uses eight duty cycle designations to describe electrical motor operating conditions and thermal characteristics.
IEC Electric Motor Duty Cycles
The International Electrotechnical Commission (IEC) defines eight duty cycle designations (S1-S8) to describe electrical motor operating conditions:
Duty Cycle Definitions
| Code | Name | Description |
|---|---|---|
| S1 | Continuous Duty | Motor works at constant load long enough to reach thermal equilibrium |
| S2 | Short-Time Duty | Motor works at constant load but not long enough to reach thermal equilibrium; long rest periods allow cooling to ambient temperature |
| S3 | Intermittent Periodic Duty | Sequential, identical run and rest cycles at constant load; thermal equilibrium never reached |
| S4 | Intermittent Periodic Duty with Starting | Sequential, identical start, run and rest cycles at constant load; thermal equilibrium not reached; starting current affects temperature rise |
| S5 | Intermittent Periodic Duty with Electric Braking | Sequential cycles of starting, running at constant load, and running with no load; no rest periods |
| S6 | Continuous Operation with Intermittent Load | Sequential cycles of running at constant load and running with no load; no rest periods |
| S7 | Continuous Operation with Electric Braking | Sequential cycles of starting, running at constant load, and electric braking; no rest periods |
| S8 | Continuous Operation with Periodic Load/Speed Changes | Sequential duty cycles run at different constant loads and speeds; no rest periods |
Key Considerations
- S1 is the baseline continuous duty cycle
- S2-S4 include rest periods for cooling
- S5-S8 are continuous operation cycles with no rest periods
- Thermal characteristics vary significantly between cycles
- Motor selection must match the actual duty cycle requirements