TABLE OF CONTENTS An electric motor that has been properly maintained will contribute greatly to the continuous operation and success of a plant. Since the cost of unscheduled downtime is high, regular maintenance of motors has become one of the highest priorities in plants. A loss of a motor could result in reduction in reliability of a system, impairment of a system, or shutdown of a plant.
The nameplate data include the rated horsepower, speed, voltage, and service factor if different from 1.0. The service factor is a multiplier that can be applied to the horsepower of motors that are designed to handle periodic overloading.
The National Electric Manufacturers Association (NEMA) classifies motors according to environmental protection and methods of cooling. The available categories include the following:
Open dripproof. Motor has ventilating openings constructed so that operation will not be affected by solid or liquid particles that strike or enter the enclosure at any angle up to 15 downward from the vertical.
Dripproof guarded. These self-ventilating motors feature louvered covers on the sides with grilles on bottom openings to prevent accidental exposure to live metal or rotating parts.
Dripproof forced ventilated. Dripproof guarded motors with forced ventilation are provided by a motor-mounted blower driven by a three-phase ac motor.
Dripproof separately ventilated. These motors provide high horsepower ratings with separate ventilation supplied by the customer.
Totally enclosed. Motors that operate in severe environments require a totally enclosed frame. These motors are...
