A separately powered fan is driven at constant speed by its own small motor instead of the fan on the motor shaft. Whatever the speed of the main motor, the cooling airflow does not change; the cooling method changes from IC411 to IC416.

It usually comes up when:

  • A constant-torque load (conveyor, mixer, screw feeder) will run at low speed for long periods,
  • The motor has to hold torque at near-zero speed,
  • The ambient temperature is high or the motor is inside an enclosed cabinet.

In applications where the load falls with speed, such as fans and centrifugal pumps, it is mostly not needed.

Because the forced fan has its own supply, a separate supply and protection circuit is set up in the panel. An interlock that prevents the main motor from starting while the fan is not running is advisable. The fan unit may change the rear construction and overall length of the motor; mounting clearance and dimensions should be confirmed in the order.

For the difference between cooling types, see the article on electric motor cooling methods (IC411, IC416).