Rating of Enclosed Motors

Author: E.E. Kimberly

Motors having no restriction to ventilation other than that necessitated by good mechanical construction are called open motors. When the ventilating openings in the frame of a motor are covered with wire screen, expanded metal, or perforated plates, the openings in which do not exceed 1/2 sq in. in area and are of such shape as not to permit the passage of a rod larger than I in. in diameter (except in special cases), the motor is called a semi-enclosed motor.

Fig. 12-1. Semi-Enclosed Motor

A semi-enclosed motor is illustrated in Fig. 12-1. Motors so enclosed as to prevent circulation of air between the inside and the outside of the case, but not covered sufficiently to be termed air-tight, are called totally enclosed motors.1 Semi-enclosed motors are used where it is necessary to protect the internal parts against injury from foreign objects or to prevent personal injury to workmen. Totally enclosed motors are used where it is necessary to protect the internal parts completely against dust or corrosive vapors.