When you’re preparing to swap out an electric motor, timeliness and accuracy are needed to minimize your process downtime and related expenses. Imagine shutting down your line and disconnecting the old motor only to realize that the replacement isn’t correctly sized for your needs.
NEMA standards help eliminate these issues by defining how motors are designed, built, and referenced on their respective nameplates. Having a thorough understanding of existing NEMA standards, in addition to working with an experienced vendor, will ensure the replacement motor you order is a true form, fit, and functional match.
What Is NEMA?
NEMA stands for National Electrical Manufacturers Association, which is the United States’ largest trade association for electrical equipment manufacturers. The association provides advocacy, offers business analytics, and develops industry standards.
These standards relate to “products that have been commercially standardized and are subject to repetitive manufacture,” such as electric motors. At HECO, our knowledge of NEMA MG-1’s standards for motors and generators allows us to provide consistent and reliable customer service.
Motor Nameplates And Labels
To source a replacement, you’ll need to find your motor’s NEMA frame number on its label or nameplate.
In the example above, the NEMA frame size is 286T, but what does that mean? Read on to find out!
Frame Sizes
A lot of important dimensional information can be gathered by knowing the frame size of your motor. With a NEMA frame chart in hand, one can reference the most critical mounting dimensions such as D, 2F, 2E, U, etc.
It should be noted that the frame size does not have a direct bearing on the diameter or overall length of the motor body.
NEMA frame sizes include two or three numbers.
Two-digit numbers are assigned to fractional frames which generally designate a motor with a rated output of 1 hp or smaller and sometimes are followed by a letter. Three-digit numbers are followed by the letter “T” for modern NEMA frames and sometimes extra letters that define a special characteristic of the motor. Three-digit numbers are assigned to integral frames and generally have a rated output of 1 hp or greater.
When looking at a frame chart, the D Dimension, which is the distance from the bottom of the motor mount to the centerline of the shaft, is represented by the first number in a two-digit format and the first two numbers in a three-digit format.
Any letters or numbers appearing in front of a NEMA frame number are usually manufacturer specific.
Once you know a frame size, you can obtain dimensions D, E, F, BA, N-W, U, and V. These dimensions are standardized across all manufacturers unless a suffix at the end of the frame size indicates otherwise.
All Systems Go
When it comes time to replace a motor in your facility, a Knower member can help ensure that the replacement motor will fit and operate the same way, or better, than the old motor. If you need assistance or just want to confirm your conclusion with an expert, Knower can help!
More information about NEMA frame sizes and replacing electric motors is available in HECO’s free NEMA Electric Motor Frame Standards e-book. You can also contact us to learn how we can help you understand your electric motor systems better and, in turn, increase their reliability.
Future posts in the complete NEMA Standards blog series will include:
- Part 2 – Interpreting Frame Sizes.
- Part 3 – Understanding Frame Number Suffixes.
