True motor efficiency may differ from nameplate rating.

RALEIGH - More and more industries are switching to energy-efficient motors because these motors lower production costs. A motor can cost thousands of dollars a year to operate, so savings of even a few percent add up quickly. An energy-efficient motor can generate savings whenever it is running and as long as it lasts, which could be 20 years or more.

Motors and Their Efficiencies

There are many ways to specify motor efficiency. Nameplate efficiency numbers are specific, allowable values defined by the National Electrical Manufacturers Association (NEMA) that have a minimum efficiency associated with them. Most other efficiency values are trade-fined. What level of efficiency is actually achieved when a motor is in operation? The conventional wisdom of many motor purchasers is the expectation that motors should operate at the efficiency indicated on the nameplate at full load.

Industrial Electrotechnology Laboratory (IEL) testing suggests that motor manufacturers use different strategies and considerations in labeling their products. The majority of motors tested at IEL perform below their nameplate efficiency, and the measured efficiency of a significant number of motors falls below the NEMA minimum efficiency. The test data …