What Electric Motor Frame Sizes Tell You - HECO

It is standard to see the “frame” size on every electric motor nameplate, but do you understand what that frame means in regard to the mounting of the motor? Many have been in the situation where you needed a specific frame only to realize it was made with a special shaft or has a mounting flange, but no one knew how to find this information!

There is a letter suffix after the frame number that has been standardized by NEMA (National Electrical Manufacturer Association) regulations. These are commonly noted as a “T” on the nameplate. For example, if you have a 324T frame motor, every manufacture of motor will have the same shaft diameter, shaft length and bolt hole mounting dimensions, but be warned, your physical size of the motor may differ.

There are other common letter suffixes that are also standard. “C” or “D” let you know that there is a flange on the drive end of the motor, or the “S” indicates that the motor has a short shaft. The rest of the letter designations get a little more difficult and can mean anything from how the motor is mounted to special non-NEMA regulated shaft dimensions. Take “Z” for example, this means there was special machining done to the shaft to make it different from the standard stocked motor. You should also be aware of motor repair shops modifying a shaft and not stamping the “Z” on the frame. If they don’t do that, you will find out at 2am that the standard “T” frame you thought you had in your spares won’t work!

Another suffix that may cause some issues is “Y”. This indicates that the motor has special mounting dimensions, which must come from the manufacture of the motor. You have probably also seen “JP” and “JM” indicating a closed pump motor, LP or LPH lets you know the motor is a vertical solid shaft unit. There are many other designations out there but these are some of the heavy hitters.

Now you do have to be careful in regard to medium voltage or high voltage motor frame sizes as these are not regulated like the NEMA frames. For this type of frame, you will have to get clarification on dimensions from the motor OEM. These motors are many times referred to as Above-NEMA or ANEMA Motors since there isn’t a NEMA frame to match to.

No matter what your frame designates, your motor supplier should be able to help you better understand what these letters designate and make sure you are getting a motor that will fit into the original one’s location.

This is a chart we constructed to reference the different suffixes.

Posted in Equipment Management, Predictive