In the United States, the National Electric Manufacturers Association (NEMA) establishes standard dimensions for electric motors. The rating plate of a motor will give a “frame size,” consisting of a number which may be followed by a letter. In purchasing a replacement motor, it is only necessary to get the same frame size to be sure of a physical fit (horsepower, voltage, type of enclosure, bearings, etc. are another matter). In the home, the most commonly encountered frame sizes are 48 and 56.
The NEMA standards also describe the way the motor shaft is modified so that pulleys and gears can be securely fastened to it.
|Size||Key on shaft|
|56||3/16″ wide, 3/16″ deep, 1 3/8″ long slot|
|8,000 horsepower electric locomotive.|
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Last revised: 3 June 2002.