NEMA is short for "National Electrical Manufacturers Association". NEMA is a US based association that attempts to set standards for manufacturing. These standards are developed by the manufacturers through a voluntary consensus. Essentially, it is the manufacturers all agreeing on the proposed standard. For stepper motors, they have chosen a label that lists the size first. This gives manufacturers more flexibility with their designs since they know ahead of time that one NEMA 17 motor will fit into the mounts of another NEMA 17 without having to redesign anything; especially if they choose to change motor suppliers.
The full NEMA stepper motor naming includes diameter DD (inches x 10), mount type MM (inches x 10), length LLL (inches x 10), phase current CCC (amps x 10), insulation class I, phase voltage VVV (rating x 10), steps SSS, and winding code W. The quantities are written without a decimal point and the dash (-) separates mounting characteristics from other data.
So the full NEMA description of a stepper motor would be written as:
On our website, we show the truncated version of the NEMA standards i.e:
NEMA 8 is 0.79 inches (20 mm)
NEMA 11 is 1.10 inches (28 mm)
NEMA 17 is 1.65 inches (42 mm)
NEMA 24 is 2.36 inches (60 mm)
NEMA 34 is 3.35 inches (85 mm)
It is important to note that NEMA is a USA standard and our company is a Japanese company. As can be seen by the list of our products, the motor is not perfectly “NEMA,” however our bolt hole pattern will closely match that of the NEMA standard.
Since most companies use the basic frame size classification: NEMA DD, not all of the information is provided. This means that there can still be differences between one NEMA motor and another NEMA motor. It is, therefore, important to compare all motor specifications (speed, torque, inertia) as well as dimensions (mounting hole location and size, output shaft diameter and length, overall motor length, etc.) before attempting to swap out any one NEMA motor for another.
As you can see in the example below, when comparing the NEMA 17 motors of the RK2 series and PKP series, the RK2 will have a larger 6 mm output shaft compared to the 5 mm output shaft of the PKP. Another thing to note is the overall length (L1 dimension) as this could also be different depending on the motor part number.
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