We likewise recommend against labeling motors with minimum efficiency. It is a confusing term with little basis in reality. It implies that the real population of motors follows somewhat of a truncated Gaussian distribution with the peak at the mean efficiency and nothing below minimum efficiency. Our review of actual motor efficiency from motor testing laboratories shows real distributions to be far less idealized. There are no sharp delineations at the minimum efficiency level.
Many individual motors fall below the nominal and significant numbers below the minimum.
However customers have no practical way of determining if the minimum is exceeded so it would be a meaningless guarantee. We believe that rigorous verification of compliance with the nominal efficiency will greatly reduce the occurrences of motors below minimum. Some manufacturers have advocated for alternative efficiency determinations methods as discussed on page 60448. The Department proposes to permit manufacturers to determine efficiency through predictive mathematical calculations. Simplified predictive methods tend to operate by fortifying certain known quantities with assumptions about unknown ones.