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Motor nameplate ratings: How precise are they?

Publication date: 
December 2012
Tom Bishop, P.E., EASA Senior Technical Support Specialist
Type of media: 

Correct interpretation of five operating parameters for NEMA, IEC induction motors When someone reads an electric motor nameplate, the normal assumption is that the information can be used at face value. That applies to some but not all of the nameplate information. For example, the power rating (hp or kW) and frame size are specific to the motor. However, ratings such as voltage, frequency, current, speed (rpm) and efficiency have tolerances associated with them. Our focus in this article will be to discuss the correct interpretation of each of these five operating parameters for induction motors of both NEMA and IEC design. Topics discussed include:

  • Voltage and frequency - NEMA MG1-12.44 and IEC 60034-1.7.3
  • Current - NEMA MG1-12.47 and IEC 60034-1
  • Speed (rpm) - NEMA MG1-12.46 and IEC 60034-1-12.1
  • Efficiency - NEMA MG1-12.58 and IEC 60034-1 Note: The letter codes for insulation class, design and kVA code that appear on NEMA motor nameplates are addressed in "Motor Nameplate Letter Code Designations" in the March 2009 issue of Currents.