BUYING AN ENERGY-EFFICIENT ELECTRIC MOTOR (3)

3. What efficiency values should I use when comparing motors?

When comparing motor efficiencies, be sure to use a consistent measure of efficiency. Nominal efficiency is best. Nominal efficiency is an average value obtained through standardized testing of a population of motors. Minimum guaranteed efficiency, which is based on nominal efficiency, is slightly lower to take into account typical population variations. Minimum guaranteed efficiency is also less accurate, because the value is rounded. Other efficiency ratings, including apparent and calculated, should not be used.

In the United States, the recognized motor efficiency testing protocol is the Institute of Electrical and Electronics Engineers (IEEE ) 112 Method B, which uses a dynamometer to measure motor output under load.
Different testing methods yielding significantly different results are used in other countries. The NEMA nameplate labeling system for design A and B motors in the 1- to 500-hp range uses bands of efficiency values based on IEEE 112 testing.
to be continued…………..

Source : Fact Sheet – US Department of Energy

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