Motor Enclosures

Electric motors are manufactured with a variety of mechanical enclosure features to provide protection to the working parts for specific environmental conditions. Although these

FIGURE 16 Power control circuit for (4) phase SR motor, (6) transistors, (6) diodes, (3) current sensors, (1) capacitor, and (6) motor lead connections

special enclosures are classified, they are not, for reasons of economy, available for all size motors. The electric motor industry has incorporated a number of specific enclosure classifications on standard designs of small- and medium-size motors.

The following list describes the motor enclosure specifications available for polyphase ac induction motors used with pumps. This availability depends on demand. Furthermore, the PM brushless and SR brushless motors might not be available in some of the enclosures listed. In general, totally enclosed motors are required for most integral horsepower (kilowatt) pump applications regardless of the motor type. In some instances, such as highspeed centrifugal pumps with integral motors, the motor is furnished to the pump manufacturer as a rotor and stator parts kit. The motor is then included in the pump enclosure.

open This enclosure permits passage of external cooling air over and around the windings and rotor of a motor and normally includes no special restrictions to ventilation other than those that are inherent in the mechanical parts of the motor. Most designs include openings at each end of the motor frame either in the bearing end frame or openings around each end of the frame.

open dripproof This is an open machine with ventilating openings designed to permit satisfactory operation when liquids or solids fall on the machine at any angle up to 15° from the vertical. openings are normally in the bottom portions of the frame assembly. This construction includes mechanical baffling to prevent materials from entering the machine within these limits.

splashproof This is an open machine with ventilating openings designed to permit satisfactory operation when liquids or solids fall directly on the machine or come toward the machine in a straight line at any angle up to 100° from the vertical.

guarded enclosure This provision limits the size of the ventilating opening to prevent accidental contact with the operating parts of the motor other than the shaft.

semiguarded This is an open construction where some of the ventilating openings are guarded and the remaining openings are left open.

open, externally ventilated This motor is ventilated by a separate motor-driven blower mounted on the motor enclosure (piggyback construction).

open, pipe-ventilated This motor is equipped to accommodate an air-inlet duct or pipe for accepting cooling air from a location remote from the motor. Air is circulated in the motor either by its own internal blower parts or by an external blower, in which case the motor is said to be forced-ventilated.

weather-protected type I This is an open-construction motor with ventilating openings to minimize the entrance of rain, snow, and airborne particles to the motor's electrical parts, and with the openings arranged to prevent the passage of a 33 -in (19-mm) round rod.

weather-protected type II This construction has the same features as the type I machine, but in addition the intake and discharge ventilating passages are designed so high-velocity air and airborne particles blown into the machine by storms can be discharged without entering the internal ventilating passages of the motor leading to the electrical parts. The ventilating passages leading to the electrical parts of the motor are provided with baffles or other features to allow at least three abrupt changes of at least 90° for the ventilating air. The intake air path and openings are proportioned to maintain a maximum of 600 ft/mm (3 m/s) velocity of the entering air.

totally enclosed This motor is designed without air openings, so there is no free exchange of air between the inside and outside of the motor frame; the construction is not liquid- or airtight. Normally the rotor has die-cast air circulating fins at each end to circulate the trapped inside air and improve convection cooling to the frame.

totally enclosed, FAN-COOLED This totally enclosed motor is equipped with an external fan operating on the motor shaft to circulate external air over the outside of the motor. Most motors have cast fins the length of the frame to increase surface area and take advantage of the fan cooling.

explosionproof This totally enclosed motor is designed to withstand an internal explosion of gas or vapor and constructed to prevent ignition by the internal explosion of gases or vapors outside the motor.

totally enclosed, pipe-Ventilated This motor enclosure is similar to the open, pipe-ventilated motor except that it is equipped to accept outlet ducts or pipes in addition to inlet ducts or pipes.

totally enclosed, WATER-COOLED This is a totally enclosed motor cooled by water passages or conductors internal to the motor frame.

totally enclosed, WATER-TO-AIR heat exchange This is a totally enclosed motor equipped with a water-to-air heat exchanger in a closed, recirculating air loop through the motor. Air is circulated through the heat exchanger and motor by integral fans or fans separate from the rotor shaft and powered by a separate motor.

totally enclosed, AIR-TO-AIR heat exchange This motor is similar to the water-to-air heat exchanger motor, except external air is used to remove the heat from the heat exchanger instead of water.

submersible This totally enclosed motor is equipped with sealing features to permit operation while submerged in a specified medium at a specified depth.

Environmental Factors The environmental conditions of the pump application dictate the type of motor enclosures to be used. A brief set of rules for selecting motor enclosures follows.

dripproof For installation in nonhazardous, reasonably clean surroundings free of any abrasive or conducting dust and chemical fumes. Moderate amounts of moisture or dust and falling particles or liquids can be tolerated.

mill AND CHEMICAL MOTOR (TO nema frame 449T) For installation in nonhazardous, high-humidity, or chemical applications free of clogging materials, metal dust, or chips, or where hosing down or severe splashing is encountered.

totally enclosed, NONVENTILATED OR FAN-COOLED For installation in nonhazardous atmospheres containing abrasive or conducting dusts, high concentrations of chemical or oil vapors, where hosing down or severe splashing is encountered.

totally enclosed, EXPLOSIONPROOF For installation in hazardous atmospheres containing:

Class I, Group D

Class II Group G Class II, Group E

Class II, Group F

Acetone, acrylonitrile, alcohol, ammonia, benzine, benzol, butane, dichloride, ethylene, gasoline, hexane, lacquer-solvent vapors, naphtha, natural gas, propane, propylene, styrene, vinyl acetate, vinyl chloride, or xylenes

Flour, starch, or grain dust

Metal dust including magnesium and aluminum or their commercial alloys.

Carbon black, coal, or coke dust

NOTE: Under Class 1 only, there are two divisions that allow some latitude on motor selection. Generally, Class 1, Division 1 locations are those in which the atmosphere is or may be hazardous under normal operating conditions, including locations which can become hazardous during normal maintenance. An explosionproof motor is mandatory for Division 1 locations. Class 1, Division 2 refers to locations where the atmosphere may become hazardous only under abnormal or unusual conditions (breaking of a pipe, for example). In general, a motor in a standard enclosure can be installed in Division 2 locations if the motor has no normally sparking parts. Thus, open or standard totally enclosed squirrel-cage motors are acceptable, but motors with open slip rings or commutators (wound rotor, synchronous or dc) are not allowed unless the commutators or slip rings are in an explo-sionproof enclosure.

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