SOLUTION

Intermittent duty Class:- A duty in which the main contacts of a contactor remain closed for periods bearing a finite relationship to the no-load periods, both periods being too short to allow the contractor to reach thermal equilibrium. The intermittent duty above implies a capability of operation at a rate of 12 operating cycles per hour, the on-load period of each cycle being 60% of the whole cycle.

Starting and braking are not taken into account on the assumption that the times taken up by these events are too short in comparison with the on-load period, and therefore do not appreciably affect the heating of the motor.

The load torque during one cycle may be greater than the rated torque of the motor. The load torque during one cycle may be greater than the rated torque of the motor.

When starting the motor power for this form of duty, it is also necessary to state the cyclic duration factor:

Cyclic duration factor = (on time/cycle time) × 100%

The standards specify that the duration of one cycle must b shorter than 10 min. Cases, where the duty cycle is longer than 10 min, must be brought to the attention of the motor manufacturer.