ENCLOSURES AND COOLING METHODS
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 nonventilated, fan-cooled, or dual-cooled, depending on the horsepower.
Totally enclosed, nonventilated. Motors are not equipped for cooling by means exter- nal to the enclosing parts, generally limited to low horsepower ratings or short-time rated machines.
Totally enclosed, fan-cooled. Motors with exterior surfaces are cooled by an external fan on the motor shaft. Cooling is dependent upon motor speed.
Totally enclosed air-over in-line. Motors with an external fan are driven by a constant- speed ac motor flange mounted to the motor fan shroud. These provide cooling inde- pendent of motor speeds. Brakes and tachometers cannot be mounted on the motor end bracket, except for specific small tachometers which can be nested between the motor bracket and fan.
Totally enclosed air-over piggyback. Motors have a top-mounted, ac motor-driven blower with shroud to direct ventilating air over the motor frame.
Totally enclosed dual-cooled air-to-air heat exchanger. Motors are cooled by circulating internal air through the heat exchanger by an ac motor-driven blower. External air circulated through the heat exchanger by another ac motor-driven blower removes heat from the circulating internal air. No free exchange of air occurs between the inside and outside of the motor.
Totally enclosed dual-cooled with air-to-water heat exchanger. This is similar to the previous description except that external circulating airflow is replaced by user-supplied water to remove heat from the heat exchanger.
Totally enclosed pipe-ventilated or totally enclosed separately ventilated. Motors are cooled by user-supplied air which is piped into the machines and ducted out of the machines by user-supplied ducts.
Explosion-proof. The enclosures of these motors are designed and constructed to withstand an explosion of a specified gas or vapor which may occur within them. It prevents the ignition of the specified gas or vapor surrounding the machines by sparks, flashes, or explosions of the specified gas or vapor which may occur within the machine casing.
Dust-ignition-proof. The enclosures of these motors are designed and constructed so as to exclude ignitable amounts of dust or amounts which might affect performance or rating. It will not permit arcs, sparks, or heat otherwise generated or liberated inside the enclosure to cause ignition of exterior accumulations or atmosphere-suspended dust on or in the vicinity of the enclosure.
Weather-protected. These motors are divided into two types, I and II. A type I motor is open, with ventilating passages constructed to minimize the ability of rain, snow, and airborne particles to come in contact with the electric parts. A type II motor includes ventilating passages at both intake and discharge in an arrangement so that high-velocity air and particles blown into the machine by storms or winds can be discharged without entering the internal ventilating passages leading directly to the motor’s electric parts.
Totally enclosed, pipe-ventilated. These motors are totally enclosed except for openings so arranged that inlet and outlet pipes are connected to them for the admission and dis- charge of ventilating air. The air may be circulated by means integral with the motor or external to and not a part of the motor, or separately forced ventilation.
Totally enclosed water, air-cooled. A totally enclosed motor is cooled by circulating air, which, in turn, is cooled by circulating water. The motor is provided with a water- cooled heat exchanger for cooling ventilating air and with a fan or fans, integral with or separate from the rotor shaft, for circulating ventilating air.
Totally enclosed air-to-air cooled. This totally enclosed motor is cooled by circulating internal air through a heat exchanger, which is cooled by circulating external air.
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