What Are All These NEMA Motor Numbers?

When you review the data sheets for small motors you’ll run into specifications such as “NEMA 11,” NEMA 23,” and so on. Unfortunately for design engineers, few data sheets refer to the original motor standards promulgated by NEMA, The Association of Electrical and Medical Imaging Equipment Manufacturers. Although data sheets may provide motor dimensions and information about mechanical mounts, designers might want to refer to the original source of that information. But a search for “NEMA 11,” for example, simply leads to more motor suppliers and not to the standard.

Engineers who want to rely on more than manufacturer’s specifications can find motor and generator standards in “Motors and Generators,” NEMA MG 1-2006 Rev 1 2007. Although NEMA makes some standards available as free downloads, the MG1 document sells for $255 in hardcopy or $255 for a download. Visit: www.nema.org. When you search the NEMA site, use MG1 rather than MG-1 or MG 1.

The MG in the standard name abbreviates “motors and generators,” so you can search the NEMA Web site for “MG” in the standard’s title to locate other motor-and-generator documents such as:

• Energy Management Guide for Selection and Use of Fixed Frequency Medium AC Squirrel-Cage Polyphase Induction Motors, NEMA MG 10-2001 (R2007), a free download.
• Energy Management Guide for Selection and Use of Single-Phase Motors, NEMA MG 11-1977 (R1997, R2001, R2007), a free download.
• Safety Standard for Construction and Guide for Selection, Installation and Use of Electric Motors and Generators, NEMA MG 2-2007, a free download.

NEMA also publishes “General Specification for Consultants, Industrial and Municipal: NEMA Premium Efficiency Electric Motors (600 V or Less),” which covers motor-efficiency standards and test conditions. You can download a free copy of the 6-page document at: www.nema.org/stds/nemapremium.cfm.

For handy charts of NEMA frame sizes, do a Google search for nema motor frame size chart. (No quotes.)

For a NEMA frame-size chart for stepper motors, visit: www.steppermotors.us.

Do you have a helpful motor reference to share? Leave a comment for your colleagues. –Jon Titus