Reed Electric

Size Matters !

When it comes to new or replacement motors, a common mistake that creates a lot of headaches is OVERALL SIZE of the motor. Such a basic common-sense factor as available space for where the motor is installed gets overlooked routinely.

Our own industry may be the cause for this mistake of assuming a motor will fit.


One Frame Fits All – Nope!

Decades ago, our industry did both a good and bad thing. The industry group (NEMA) set up a size standard called "Frame Size". As can be seen in the dimension drawings from all manufacturers, this standardization was very specific in MOST dimensions. The output shaft diameter (U), the shaft height (D), the mounting feet bolt-hole pattern are all standard no matter which manufacturer. These are standardized by the NEMA frame call-out. This accomplished the very good goal of making motors from many different manufacturers very interchangeable. The standard also helped keep the various manufacturers competitive with each other and helped improve ready availability.

The inadvertent bad result was the general assumption that ALL the dimensions for the same frame size were standardized; if you specified the same frame for a motor you were replacing, it would fit.... Wrong!

One of the primary means to increase electrical usage efficiency, service factor, operating temperature, overall quality and longevity is to design a motor with more active materials. A bigger cast iron frame can help a motor run cooler and increase life and service factor. Longer rotors and stator cores may help increase efficiency. Conversely, in applications where the motor runs only occasionally and the above issues are not a concern, but initial motor cost is, then a smaller overall dimension may fit the bill.

Final Notes on Overall Space

  •     Allow for extra space around the motor:
    •    Helps with cooling – longer life
    •    Helps with maintenance
    •    Helps with removal and installation
    •    Ensures you will have many options (price, availability, efficiency, brands)
  •     Don’t forget about the size of the Terminal Box (Conn. Box, Peckerhead). They are not all the same size either. Some manufacturers try to give big terminal boxes for ease of connection and safety – but that makes for a larger overall width.
  •     Dimension Drawing Tips:
    •    "C" is the overall length of motor
    •    "P" is the overall width of motor but does not include the terminal box
    •    "O" is the overall height of motor but does not include the lifting eye.

Overall Size Matters! Take a few minutes with a measuring tape.

New Customer?
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Reed Electric - LA
5503 S. Boyle Avenue, Los Angeles, CA 90058
Ph: 323-587-2284 / Fax: 323-587-2142

Reed Electric - Reno
5375 Louie Lane, Reno, NV 89511
Phone: 775-824-7333 / Fax: 775-824-7344