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Part 3: Motors Replacement Selection
By James Piper, P.E.
February 2012 -
Most motors made for use in facilities must meet the high efficiency standards established by the National Electrical Manufacturers Association (NEMA). In reality, many motors available before the energy-efficiency standards went into to place already met or exceeded those standards. While those standards were a starting point, some motor manufacturers felt they could achieve even higher levels of efficiency.
To promote higher efficiencies, NEMA developed the premium-efficiency standard for single-speed, polyphase motors of up to 500 horsepower. For example, a 5 hp, high-efficiency motor operating at 75 percent rated load has an operating efficiency of about 88 percent. A premium-efficiency motor of the same rating and load has an operating efficiency of nearly 91 percent.
This increase in operating efficiency might not seem significant, given the number of hours the average motor operates. But this savings typically translates into a paypack of less than three years.
When seeking a premium-efficiency replacement motor, managers must make certain it is certified by NEMA as premium efficiency. Some manufacturers might offer motors that meet the energy-efficiency requirements to be labeled as premium but fail to meet other requirements of the NEMA specification.
James Piper, P.E., is a national facilities management consultant based in Bowie, Md. He has more than 25 years of experience with facilities maintenance and engineering issues.
Part 1: Improving Motor Efficiency
Part 2: Managing Motors
Part 4: Product Focus: Motors