The larger the motor, or the more mismatched the motor and load are, the larger the potential savings in energy that a power control device will acheive. If the load never varies, it is more efficient to always match the motor closely to the expected load than to add one of these devices. Motor loads that do vary can benefit most from these controlling devices. Because the controller continuously applies the correct power to the motor, the motor operates consistently at its peak efficiency and cooler. As a consequence of this, manufacturers of these devices claim they will improve the efficiency and life expectancy of electric appliance motors.
Power controlling devices come in a wide variety of voltage and amperage ratings.
There are also three-phase controllers for very large motors available. In most new home appliances that have electric motors, such as a refrigerator, the factory-installed motor is already closely matched to the load. So an electronic controlling device will have little effect on electrical consumption. Appliances newer than 1990 may see no energy savings at all, due to their existing energy-saving features. In some cases, the controller slightly increased the appliance's electrical consumption.