Motor oversizing

The most common reasons for oversizing electric motors are:

  • unawareness of the load itself;
  • ignorance of methods for a more adequate dimensioning;
  • application of successive safety factors;
  • expectation of increased load;
  • non-specification of motors with service factor greater than 1.0;
  • replacement of a damaged motor with a larger motor when a suitable motor is missing;
  • reduction of production.

In the oversizing of the induction motors we find several disadvantages like elevation of the cost, greater weight and volume of the engine, as well as the reduction of the power factor, reduction of the efficiency, although some motors have their maximum efficiency to 75% of their nominal load.

Another disadvantage is a higher starting current, resulting in higher installation cost and protection.

In times when it is necessary to use energy efficiently, the aspect of oversizing should take into account technical and economic analysis. Studies show that oversizing does not always correspond to greater energy losses.

A 15-hp engine driving a 10-hp load will have a better performance and lower power demand than a 10-hp rated-horsepower engine.