>Several years ago, the U.S. Department of Energy (DOE) conducted a technical study as to what could be done to raise the efficiency levels of “small” motors. After years of study and litigation, the Small Motor Rule was passed that covers two-digit NEMA frame single- and three-phase 1/3 through 3 horsepower motors in Open enclosures.

Although the Small Motor Rule seems simple, it has the effect of creating motors with much larger footprints, particularly on single phase designs where capacitor start/induction run motors may largely be discontinued in Open enclosures. In some cases, a TEFC motor may be more cost effective and smaller than an Open motor.

The DOE is presently conducting another technical study on “medium” AC induction motors of 1- to 500-hp. In their study, DOE is evaluating a possible increase in nominal motor efficiency of 1 – 3 NEMA bands (approximately 0.4 to 1.5%) above NEMA Premium Efficiency levels as defined in MG 1-2011 table 12-12. Although this sounds simple to do, such a motor redesign could entail new laminations, winding equipment and in many cases, new frames to fit the extra material. Some designs may not fit where existing motor designs of the same ratings fit today. This means that OEMs would need to redesign their machine if that is an issue and end users may have trouble fitting the new higher efficiency replacement motor into their equipment or existing envelope.<