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Do you know IEC Duty Cycle Ratings?

Posted by on 21 August 2010 | 0 Comments

There is various standards exist which specify various operating and constructional parameters of a motor.  The International Electrotechnical Commission (IEC) is one main standard in the world.

The International Electrotechnical Commission (IEC) is a European-based organization that publishes and promotes worldwide, the mechanical and electrical standards for motors. It's the international counterpart of the National Electrical Manufacturers Association (NEMA).

Usually, IEC Duty Cycle Ratings are different from NEMA's. Where NEMA specifies continuous, intermittent, or special duty (typically expressed in minutes), yet IEC uses 8 different duty cycle designations to describe an electrical motors operating conditions.
Below are the eight - (S1 - S8 ) IEC duty cycles of operating electrical motors:

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, and 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, electric braking, and rest. Temperature equilibrium is not reached.

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 of start, run at constant load and given speed, then run at other constant loads and speeds. No rest periods.