We’re excited to introduce Motor Talk Monday! Each Monday, we’ll be posting something we find interesting or educational about motors. This week’s topic: the mystery of motor frame sizes.
Electric motors have evolved significantly over the past century, notably in the ability to deliver more horsepower in smaller physical sizes. A key factor in motor interchangeability has been the standardization of frame sizes by the National Electric Manufacturers Association (NEMA). This ensures that motors from different manufacturers with the same horsepower, speed, and enclosure can be easily replaced as long as they share the same frame size. The standardization spans three generations of frame sizes—original, U frames (introduced in 1952), and T frames (introduced in 1964), the latter being the current standard.
The advancement of motor frame technology is largely due to improved insulating materials, which allow motors to run at higher temperatures, thereby accommodating more horsepower in compact frames. This has led to changes in shaft and bearing sizes to handle higher loads. For easy reference, tables outlining frame size assignments across different eras, horsepower ratings, and speeds are available, providing a useful guide for replacing older motors still in operation today.
You can find these tables and more information about motor size on pages 12-15 (digital pages 14-17) in the Cowern Papers.
