HECO provides tips on NEMA standards and frame number suffixes
HECO's latest blog entry offers useful assistance for understanding and interpreting NEMA standards. This latest blog is specifically about frame number suffixes. By defining how motors are designed, built, and referred to on their respective nameplates, standards from the National Electrical Manufacturers Association apply to all electric motor manufacturers to ensure that all manufacturers follow identical dimension data and naming conventions.
Known as NEMA frame sizes or electric motor frame sizes, these electric motor dimensions assist operators, manufacturers, and electric motor repair shops in identifying and swapping out electric motors.
Standards & Potential Surprises
Letters included after a NEMA frame size are very important. If misunderstood, problems can come up when replacing one NEMA motor with another NEMA motor.
While T means all manufacturers of a given motor use the same 2F and 2E mounting holes, the motors may come in different ratings. For example, a 256T could be a 20 HP @ 1,800 RPM, 15 HP @ 1,200 RPM, or 25HP @ 3,600 RPM.
NEMA also does not regulate the C dimension, which is the overall length of the motor from the end of the shaft to the back of the motor. As a result, this dimension varies by manufacturer. This is very important when trying to install a replacement motor in a tight space.
The most common frame number suffixes and meanings on the NEMA frame size chart include:
C – Type C face mounting on DE
CH – The type C face-mounting dimensions are different from those for the frame designation having just the suffix letter C
D – Type D flange mounting on DE
H – Designated 56H motors have two sets of 2F mounting holes (3 and 5”)
J – Face mount for jet pumps
JM – Face-mounted, close-coupled pump motors
JP – Type C face-mounted, close-coupled pump motors
K – Has hub for sump pump mounting
LP or LPH – Type P flange-mounted, vertical solid-shaft motors
M or N – Flange mount for oil-burner motors
P or PH – Type P flange-mounted vertical hollow shaft motors
R – Drive end tapered shaft extension
S – Short shaft for direct connection
T – Included as part of a frame designation for which standard dimensions have been established
U – Previously used as part of a frame designation for which standard dimensions have been established
V – Vertical mounting only
VP – Type-P flange-mounted, vertical solid shaft motors
X – Double shaft extension
Y – Special mounting dimensions (contact manufacturer for the dimensions)
Z – All mounting dimensions are standard except the shaft extensions; can also be used to designate double shaft extensions (contact manufacturer for dimensions)
Electric Motor Replacements
Finding a replacement motor with the same NEMA frame size does not necessarily mean it will work as a drop-in replacement. To be safe, it is imperative to check with the motor supplier to find out if the non-standardized physical dimensions will work for your application.
The Y suffix after a NEMA frame size means that the motor has special mounting dimensions, and you will have to contact the motor supplier to find out what they are. Installation will be very challenging if you don’t notice the Y suffix and do your research.
The Z suffix also requires extra attention. It means that the shaft has dimensions that deviate from the standard. Finding a match without factoring in the original motor’s shaft deviations could present a challenge.
All Systems Go
The timing and need for a motor replacement can be stressful enough. Contact HECO for assistance in understanding the exact dimensions and capabilities of your motor and any potential motors you plan to install in its place.
To learn more about NEMA frame sizes and the role they play in replacing electric motors, download HECO’s NEMA Electrical Motor Frame Standards e-book.
The complete NEMA Standards blog series includes: