Product Manual

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NEMA Frame/Shaft Sizes
Frame numbers are not intended to indicate electrical characteristics
such as horsepower. However, as a frame number becomes higher so in
general does the physical size of the motor and the horsepower. There
are many motors of the same horsepower built in different frames.
NEMA (National Electrical Manufacturers Association) frame size refers
to mounting only and has no direct bearing on the motor body diameter.
In any standard frame number designation there are either two or three
numbers. Typical examples are frame numbers 48, 56, 145, and 215.
The frame number relates to the “D” dimension (distance from center
of shaft to center bottom of mount). For example, in the two-digit 56
frame, the “D” dimension is 31/2”, 56 divided by 16 = 31/2”. For the
“D” dimension of a three-digit frame number, consider only the first two
digits and use the divisor 4. In frame number 145, for example, the first
two digits divided by the constant 4 is equal to the “D” dimension. 14
divided by 4 = 31/2”. Similarly, the “D” dimension of a 213 frame motor
is 51/4”, 21 divided by 4 = 51/4”.
By NEMA definition, two-digit frame numbers are fractional frames even
though 1 HP or larger motors may be built in them. Three-digit frame
numbers are by definition integral frames. The third numeral indicates
the distance between the mounting holes parallel to the base. It has no
significance in a footless motor.
A summary of NEMA standard dimensions is on the facing page.