Small electric motors are defined as general-purpose, alternating-current, single-speed induction motors, built in a two-digit frame-number series in accordance with NEMA Standards Publication MG1-1987, “Motors and Generators”. Such motors include single-phase, capacitor-start induction-run (CSIR), capacitor-start capacitor-run (CSCR), and polyphase motors. The two-digit frame series encompasses NEMA frame sizes 42, 48, and 56. The horsepower ratings for the two-digit frame series range from 1/4 to 3 horsepower (hp). These motors operate at 60 Hertz and have either a single-phase or a three-phase (also known as “polyphase”) electrical design. Typical applications for small electric motors include pumps, fans and blowers, woodworking machinery, conveyors, air compressors, commercial laundry equipment, service industry machines, food processing machines, farm machinery, machine tools, packaging machinery, and major residential and commercial equipment.
The energy efficiency of small electric motors, expressed as a percentage, is the ratio of useful power output to total power input. DOE published a final rule in March 2010 establishing the first energy conservation standards for small electric motors, which went into effect in 2015. The minimum efficiency standards depend on the motor horsepower and the number of poles (number of sets of electromagnetic windings). DOE estimated that the standards will save approximately 2.2 quads of energy over 30 years, which is equivalent to about 2.2% of total annual U.S. energy consumption.
Small electric motors are primarily purchased by original equipment manufacturers (OEM) for use in equipment that they produce. The three categories (polyphase, CSIR, and CSCR), three pole configurations (2, 4, and 6 poles), and eight horsepower ratings (1/4 hp to 3 hp) affect the energy consumption or efficiency. The efficiency of small motors is improved by minimizing various losses, which are grouped into four categories: electrical resistance losses (I2R losses), core losses, friction and windage losses, and stray load losses. These losses can be minimized in a variety of ways, such as changing the conductor material (copper versus aluminum wire), adjusting the quantity or quality of the steel in the steel components, improving the bearings, or improving the cooling system. The biggest savings opportunity is to change from inefficient types of motors such as shaded pole to more efficient types such as permanent split capacitor.