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How precise are motor nameplate ratings?

Electrical Construction & Maintenance
Publication date: 
June 2013
Tom Bishop, P.E., EASA Senior Technical Support Specialist

A common assumption about induction motor nameplates is that you can use the information at face value. That applies to some but not all of the nameplate data. The power rating (hp or kW) and frame size, for example, are specific to the motor, whereas other ratings may have tolerances associated with them. The focus of this article is to explain how to correctly interpret and apply NEMA and IEC nameplate ratings for each of five operating parameters: voltage, frequency, current, speed, and efficiency.