NEMA frame size used for stepper motors and brushless DC motors

Step motors are categorized by frame size, such as "size 11" or "size 23".  Ever wonder how that came to be or what it means?  The National Electrical Manufacturers Association sets standards for many electrical products, including step motors.  Generally speaking, "size 11" mean the mounting face of the motor is 1.1 inches square.  So a Size 23 step motor is, wait for it, 2.3 inches square.  Or 56.4 mm as shown below.

This photo includes NEMA size 34, 23, 24, 17, 11 and 08 step motors.  Size 24 is somewhat of an outlier - there is no formal NEMA  definition for size 24.  It mounts like a size 23, but is slightly wider (about 4 mm), allowing for a larger rotor and stator and thus about 30% more torque.

The NEMA frame size of motors is used for both stepper motors and brushless DC motors but it is used most commonly with stepper motors as a useful shorthand for the size of the motor (and hence the power and torque).

Always remember that (within the NEMA sizing system) the length of the motor will vary but the NEMA frame size simply refers to the diameter of the motor face.

Most commonly these faces are square (for example the ZDN2319 which is a square faced 1.9Nm NEMA 23 stepper motor) but in some cases they may be circular (as with the ZDBLM57600 brushless DC motor for example)

Frame sizes are split up into NEMA (National Electronic Manufacturers Association) ratings.

Equally the stepper motor controller that you use will have a major impact on the mechanical performance you are able to achieve using the motor. If the controller is not able to deliver more power than the motor can handle then it is unlikely that you will be able to achieve the maximum possible mechanical performance from the motor. 

One of the key reasons for this is that a certain controller may be able to deliver full power from one motor but, as the motor stack length is increased that particular motor controller may struggle to get the power into the larger motor coils to deliver the required torque. There are other reasons that can affect this. Why not have a look at our support section for more information on these factors.

As an example of this, our stepper motors with integrated controllers have higher powered controllers the bigger the motors get.

If your interest in motor sizes was purely academic then we hope we have helped. If you have any questions about this please do not hesitate to get in touch and we will do our best to help.

Alternatively if you are looking for a motor and aren’t sure which is best for your application then you could start by having a quick look at our standard range.

We offer a range of stepper motors of different sizes which are available in geared or standard format.

As always, if you have any questions about choosing the right motor or the pros and cons of a long stack NEMA 17 versus a short stack NEMA 23 (for example) then you can get in touch with us via online chat, phone or email.

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