Rotation | Enclosure | Common Types | National Electric Code Hazardous Location Classifications | Thermal Protection | Mounting | Bearings | Shaft Type
Rotation
The direction in which shaft rotates: CW-Clockwise; CCW-Counterclockwise; CW/CCW(Reversible), rotation can be changed by electrical reconnection. Unless stated otherwise inSpecial Features column, rotation is viewed facing shaft end on single-shaft motors, and lead endon double-shaft models.
Enclosure
Open motors are designed for use in areas that are dry, clean, well ventilated and non-hazardous.Dusty or dirty conditions require totally enclosed, fan-cooled construction. If installed outside,motor must be protected with a cover that does not restrict air flow. Wet or washdownenvironments, where motor is exposed to high humidity, require a washdown motor. Explosiveconditions, no matter how slight, require a hazardous location motor. Be sure class and grouprating(s) of motor conform to that required by the particular hazardous location. Check theNational Electric Code and local codes to ensure proper selection.
Common Types
Open has ventilation holes in shell and/or endshield. OpAO Open, Air-Over. Depends on air flowfrom driven device for cooling. OpDpf Open Dripproof. Has openings in housing that are placed sodrops of liquid falling within an angle 15 degrees from vertical will not affect performance. OpFC- Open, Fan-cooled. Has external cooling fan.
- Totally Enclosed has no ventilation in shell or endshield.
- TEAO Totally Enclosed, Air-Over. Depends on air flow from driven device for cooling.
- TEFC Totally Enclosed, Fan-Cooled. Has external cooling fan.
- TENV Totally Enclosed, Nonventilated. Depends on convection for air cooling.
- TEVF Totally Enclosed with Vented Flange.
- WD Washdown (TEAO, TEFC, TENV). Designed to withstand high pressure washdowns orother high humidity or wet environments.
- HAZ Hazardous Location (TEFC or TENV). Designed to withstand an internal explosion ofspecified gases or vapors, and not allow the internal flame or explosion to escape. (See tablebelow for Classifications.)
National Electric Code Hazardous Location Classifications
Certain locations are hazardous because the atmosphere does or may contain gas, vapor or dustin explosive quantities. The National Electrical Code (NEC) divides these locations into Classesand Groups according to the type of explosive agent which may be present. Listed are some ofthe agents in each classification. For complete list, see NFPA (National Fire ProtectionAssociation) publication 497M.
Underwriter's Laboratories tests motor and other devices for safety in hazardous locations, andpublishes a list of those meeting its standards for each Class and Group. Use of UL Listed devicesdoes not necessarily make an installation conform to the NEC or local codes. Consult Chapter 5of the NEC, local building codes, OSHA requirements and insurance inspectors for detailed dataas to proper procedures. This guide does not contain any motors designed for Class I, Group A, B,and C atmospheres.
CLASS I- Group A: Acetylene
- Group B: Butadiene, ethylene oxide, hydrogen, propylene oxide, manufactured gases containingmore than 30ydrogen by volume.
- Group C: Acetaldehyde, cyclopropane, diethyl ether, ethylene.
- Group D: Acetone, acrylonitrile, ammonia, benzene, butane, ethanol, ethylene dichloride,gasoline, hexane, isoprene, methane (natural gas), methanol, naphtha, propane, propylene,styrene, toluene, vinyl acetate, vinyl chloride, xylene.
CLASS II- Group E: Aluminum, magnesium, and other metal dusts with similar characteristics.
- Group F: Carbon black, coke or coal dust.
- Group G: Flour, starch or grain dust.
CLASS III
Easily ignitable fibers, such as rayon, cotton, sisal, hemp, cocoa fiber, oakum, excelsior and othermaterials of similar nature.
Thermal Protection
Motors that start automatically (i.e., thermostat controlled) and are located out of operator sightmust be protected against dangerous overheating due to failure-to-start or overloading. Thisprotection may be a separate overcurrent device (i.e., motor starter) complying with Article 430 ofthe National Electric Code (NEC), a thermally protected motor (internal motor protection), or animpedance protected motor.
Basic types include:- Automatic-Reset (Auto.)After motor cools, thermal protector automatically restores power. Motorswith automatic reset thermal protection MUST NOT be used where automatic or otherwiseunexpected starting of the motor could be hazardous. Applications where automatic restartingcould be hazardous include compressors, conveyors, power tools, farm equipment, and somefans and blowers. Where such a hazard exists, always use a Manual-Reset thermally protectedmotor.
- Manual-Reset (Man.) An external button must be pushed to restore power to a motor. Preferredwhere unexpected restarting would be hazardous, as on compressors, conveyors, power tools,etc.
- Impedance or Impedance Protected(Imp.) Motor is designed so that it will not burn out in lessthan 15 days under locked rotor (stalled) conditions, in accordance with UL standard No. 519.
Mounting
Basic types include:- Face, Flange (C-face, Flange). Shaft-end endshield has a flat mounting surface, machined tostandard dimension, with holes to allow easy, secure mounting to driven equipment. Commonlyused on jet pumps, oil burners and gear reducers. The mounting dimensions are based onindustry (NEMA) standards.
- Brkt, Lug, Halo. Mounting bracket is secured to motor. Bracket's mounting holes have positionswhich do not relate to an industry standard, but specific applications will usually have the samehole mounting patterns. When replacing a motor, the on-center dimensions of holes should bechecked.
- Holes. Threaded holes are machined into motor and are usually located on shaft end. Holepositions do not relate to an industry standard, but motors intended for specific applications willusually have the same hole patterns. When replacing a motor, the on-center dimensions of holesshould be checked.
- Cradle (Resilient cradle). Motor is provided with a base which is isolated from motor shell withvibration-absorbing material, such as rubber rings. Mounting dimensions are based on industry(NEMA) standards.
- Rigid (Rigid base). Motor is provided with base which is either welded or bolted to motor shell.Mounting dimensions are based on industry (NEMA) standards.
- Ring (Resilient ring). Vibration-absorbing material such as rubber rings are provided on eachendshield. Base or bracket (not provided) is usually clamped to these rings. When replacingmotor, on-center distance of rings should be checked.
- Stud (Stud, Bolt, Thrubolt). Motor has bolts or welded studs extending from front and/or rearendshield. Positioning of studs or bolts do not relate to an industry standard, but will usually becommon for a given motor diameter. When replacing motor, on-center distance of studs or boltsshould be checked.
- Yoke. Tabs are welded to bottom of motor shell for bolting to a fan column or bracket. Used onfan-duty motors only.
- Hub. A mounting ring on shaft end of motor. Designed to fit specific applications, such ascarbonator pumps and pedestal sump pumps.
Bearings
Basic types include:- Sleeve (Slv.) Preferred where low noise level is important, as on fan and blower motors. Unlessotherwise stated, sleeve bearing motors listed herein can be mounted in any position, includingshaft-up or shaft-down (all position mounting).
- Ball. Used where higher load capacity is required or periodic lubrication is impractical.
- Ball-SS (Ball, Single-Shielded). Same as Ball, except metal (shields) rings with close runningclearance on one side of bearing.
- Ball-DS (Ball, Double-Shielded). Same as Ball, except metal (shields) rings with both runningclearance on both sides of bearing.
- Ball-SLD (Ball, Sealed). Same as Ball and similar to Shielded, except have rubber (seals) lipsthat press against inner face, more effectively excluding dirt, etc.
- Unit. Motors are constructed with a long, single sleeve bearing. For fan duty only. All positioningmounting unless otherwise stated.
Shaft Type
Basic types include:
- Flat. Usually found on motors with up to 1/2" diameter shaft. Lengths of flat is governed byNEMA standards. Balance of shaft is round.
- Key. Primarily used on motors with 5/8" and larger shaft diameter. Key size is determined byNEMA standards.
- Round. Used on small C-frame shaded pole motors. Full length of shaft is round.
- Thd (Threaded). Used on uni-directional motors for special applications such as driving impellerof jet pumps. Threaded in opposite direction to shaft rotation so driven device tightens on shaft.
NOTE: Other shaft types are also in this guide that are not included in this list. They are for veryspecific applications. See Special Features column for additional information.
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