TABLE OF CONTENTS NEMA offers many ways of classifying motors. Most important of these are classifications according to:
Application
Electrical type
Environmental protection and method of cooling
Given below are brief descriptions of these classifications. For more complete information, see NEMA MG1-1993, Fourth Revision.
Three motor classes are recognized:
General-purpose motor
Definite-purpose motor
Special-purpose motor.
A general-purpose motor is a motor with an open or enclosed construction, and is rated for continuous duty. This motor is designed with standard ratings, standard operating characteristics, and mechanical construction for use in usual service conditions and without restriction to a particular application or type of application. Depending on whether the motor is a small, medium or large motor, and whether it is an AC motor or a DC motor, it may have some additional characteristics defined in sections applicable to the particular motor type. Usual service conditions include an altitude no higher than 1000 m and an ambient temperature of 40 C or lower.
A definite-purpose motor is any motor designed in standard ratings with standard operating characteristics or mechanical construction for use in service conditions other than usual, or for use in a particular type of application.
A special-purpose motor is a motor with special operating characteristics or special mechanical construction, or both, designed for a particular application, and not falling within the definition of a general-purpose or definite-purpose motor.
