D - Terms
A special end shield with holes for through bolts in the flange and is primarily used for mounting the motor on gear boxes or bulkheads. Standardized for frames 143T through 445T. "D" flanges are not threaded and the bolt holes extend beyond the motor frame.
D.C. (DIRECT CURRENT)
A current that flows only in one direction in an electric circuit. It may be continuous or discontinuous and it may be constant or varying.
A motor using either generated or rectified D.C. power (see Motor definition) . A DC motor is usually used when variable speed operation is required.
DEFINITE PURPOSE MOTOR
A definite purpose motor is any motor design, listed and offered in standard ratings with standard operating characteristics with special mechanical features for use under service conditions other than usual or for use on a particular type of application. (NEMA)
DESIGN A, B, C, D - for AC MOTORS
NEMA has standard NEMA motor designs of various torque characteristics to meet the various requirements posed by different application loads. The design "B" is the most common design. (See chart for characteristics of each design.)