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NEMA Frame Size

General

A key part of motor interchangeability has been the standardization of frame sizes. This means that the same power, speed, and enclosure will normally have the same frame size from different motor manufacturers. Thus, a motor from one manufacturer can be replaced with a similar motor from another company provided they are both in standard frame sizes.

The NEMA (National Electrical Manufacturer's Association) standardized the motor frame sizes for the global "inch" markets. Regions using SI units work with IEC standards (see page IEC Frame Size). Therefore most motor series are offered with both standard frame sizes.

Usual NEMA sizes

All dimensions in inch

Figure: Reference graphic for dimensions

NEMA Flange Bolt Circle
(AJ)
Mounting Holes
(TAP)
Register Diameter
(AK)
Shaft Diameter
(U)
Shaft Length
(V)
Keyway width
(S)
remaining shaft thickness
to keyway (R)
8 0,8 0,4455 0,078 0,5906 0,1575 0,53    
11 1,1 0,6435 0,1 0,866 0,1965 0,71    
14 1,4 0,8061 0,118 0,866 0,1965 0,71    
17 1,7 0,8627 0,118 0,866 0,1965 0,86    
23 2,3 1,3152 0,2 1,5 0,25 0,75    
34 3,4 1,9374 0,22 2,875 0,375 1,13    
42 4,2 3,75 0,25 3 0,375 1,125 FLAT 0,3281
48 4,8 3,75 0,25 3 0,5 1,5 FLAT 0,4531
56 5,6 5,875 0,375 4,5 0,625 1,875 0,1875 0,5156
143 14,3 5,875 0,375 4,5 0,875 2,25 0,1875 0,7656

All dimensions in inch

Frame size variants (extract)

In addition to the standard numbering system for frames, there are some standardized variations that are denoted by the following suffixes to the NEMA number.

C Designates a C flange/face mounted motor, e.g., "NEMA 56C frame". This is the most popular type of face mounted motor and has a specific bolt pattern on the shaft end to allow mounting. The critical items on C face motors are the bolt circle (AJ dimension), rabbet diameter (AK dimension) and the shaft size (U dimension). C flange motors always have threaded mounting holes in the face of the motor.

D Designates a D flange/face mounted motor. This motor has a special type of mounting flange installed on the shaft end. In the case of the D flange, the flange diameter is larger than the body of the motor and it has clearance holes suitable for mounting bolts to pass through from the back of the motor into threaded holes in the mating part. D flange motors are not as popular as C flange motors.

S designates that the motor has a short shaft. They are designed to be directly coupled to a load through a flexible coupling (Love-Joy, etc.). They are not designed for use in belt drive applications.

Y indicates that the motor has a special, manufacturer specific mounting configuration.

Z indicates that the motor has a special, manufacturer specific shaft.