Motor Frames by the Numbers

Two standards organizations publish motor frame standards: National Electrical Manufacturers  Association (NEMA) and the International Electrotechnical Commission  (IEC). Do you know why a NEMA Frame 56 motor is a 56 motor? I admit, until recently I did not. I just knew that if two motors have the same frame, they will mount in the same place. That does not necessarily mean that they are interchangeable, just that you can physically interchange them. However, I did not know what the 56 stood for in a 56 frame motor. It is really pretty simple. The number in a NEMA Motor frame designation describes the distance from the center of the shaft to the bottom of the mounting base in eighths of an inch. So a 56 frame has a distance from the center of the shaft to the bottom of the base of 56/8, or 7 inches. Of course, there are other dimensions that are set by frame size, but that particular dimension gives the frame its name. Maybe your machines use motors with IEC fame designations. The frame number still describes the distance from the shaft center to the base, but in millimeters. So an IEC 112 Frame motor has a distance from the shaft center to the bottom of the base of 112 millimeters. If you are measuring in centimeters that is 11.2 centimeters. As in the NEMA frame size, the IEC frame size standardizes many dimensions. Both standards have many dimensions that are described but not standardized. This means that manufacturer will report these dimensions, but they will not necessarily be identical from one motor to another. Baldor has a couple of good pdf reference pages which show the dimensions for each type of frame. You can find these at

NEMA  
IEC