CLASS III LOCATIONS

70-495 ARTICLE 503 - CLASS III LOCATIONS 503-1. General. The general rules of this Code shall apply to electric wiring and equipment in locations classified as Class III locations in Section 500-7. Exception: As modified by this article. Equipment installed in Class III locations shall be able to function at full rating without developing surface temperatures high enough to cause excessive dehydration or gradual carbonization of accumulated fibers or flyings. Organic material that is carbonized or excessively dry is highly susceptible to spontaneous ignition. The maximum surface temperatures under operating conditions shall not exceed 165°C (329°F) for equipment that is not subject to overloading, and 120°C (248°F) for equipment (such as motors or power transformers) that may be overloaded. (FPN): For electric trucks, see Powered Industrial Trucks Including Type Designations, Areas of Use, Maintenance, and Operation, NFPA 505-1992 (ANSI). 503-2. Transformers and Capacitors, Class III, Divisions 1 and 2. Transformers and capacitors shall comply with Section 502-2(b). 503-3. Wiring Methods. Wiring methods shall comply with (a) and (b) below. (a) Class III, Division 1. In Class III, Division 1 locations, the wiring method shall be rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, electrical metallic tubing, dusttight wireways, or Type MC, MI, or SNM cable with approved termination fittings. (1) Boxes and Fittings. All boxes and fittings shall be dusttight. (2) Flexible Connections. Where necessary to employ flexible connections, dusttight flexible connectors, liquidtight flexible metal conduit with approved fittings, liquidtight flexible nonmetallic conduit with approved fittings, or flexible cord in conformance with Section 503-10 shall be used. (FPN): See Section 503-16(b) for grounding requirements where flexible conduit is used. (b) Class III, Division 2. In Class III, Division 2 locations, the wiring method shall comply with (a) above. Exception: In sections, compartments, or areas used solely for storage and containing no machinery, open wiring on insulators shall be permitted where installed in accordance with Article 320, but only on condition that protection as required by Section 320-14 be provided where conductors are not run in roof spaces and are well out of reach of sources of physical damage. 503-4. Switches, Circuit Breakers, Motor Controllers, and Fuses, Class III, Divisions 1 and 2. Switches, circuit breakers, motor controllers, and fuses, including pushbuttons, relays, and similar devices, shall be provided with dusttight enclosures. 70-496 NATIONAL ELECTRICAL CODE 503-5. Control Transformers and Resistors, Class III, Divisions 1 and 2. Transformers, impedance coils, and resistors used as or in conjunction with. control equipment for motors, generators, and appliances shall be provided with dusttight enclosures complying with the temperature limitations in Section 503-1. 503-6. Motors and Generators, Class III, Divisions 1 and 2. In Class III, Division 1 and 2 locations, motors, generators, and other rotating machinery shall be totally enclosed nonventilated, totally enclosed pipeventilated, or totally enclosed fan-cooled. Exception: In locations where, in the judgment of the authority having jurisdiction, only moderate accumulations of lint or flyings will be likely to collect on, in, or in the vicinity of a rotating electric machine and where such machine is readily accessible for routine cleaning and maintenance, one of the following shall be permitted: a. Self-cleaning textile motors of the squirrel-cage types; b. Standard open-type machines without sliding contacts, centrifugal or other types of switching mechanism, including motor overload devices; or c. Standard open-type machines having such contacts, switching mechanisms, or resistance devices enclosed within tight housings without ventilating or other openings. 503-7. Ventilating Piping, Class III, Divisions 1 and 2. Ventilating pipes for motors, generators, or other rotating electric machinery, or for enclosures for electric equipment, shall be of metal not less than 0.021 inch (533 micrometers) in thickness, or of equally substantial noncombustible material, and shall comply with the following: (1) lead directly to a source of clean air outside of buildings; (2) be screened at the outer ends to prevent the entrance of small animals or birds; and (3) be protected against physical damage and against rusting or other corrosive influences. Ventilating pipes shall be sufficiently tight, including their connections, to prevent the entrance of appreciable quantities of fibers or flyings into the ventilated equipment or enclosure and to prevent the escape of sparks, flame, or burning material that might ignite accumulations of fibers or flyings or combustible material in the vicinity. For metal pipes, lock seams and riveted or welded joints shall be permitted; and tight-fitting slip joints shall be permitted where some flexibility is necessary, as at connections to motors. 503-8. Utilization Equipment, Class III, Divisions 1 and 2. (a) Heaters. Electrically heated utilization equipment shall be approved for Class III locations. (b) Motors. Motors of motor-driven utilization equipment shall comply with Section 503-6. (c) Switches, Circuit Breakers, Motor Controllers, and Fuses. Switches, circuit breakers, motor controllers, and fuses shall comply with Section 503-4. ARTICLE 503 - CLASS III LOCATIONS 70-497 503-9. Lighting Fixtures, Class III, Divisions 1 and 2. (a) Fixed Lighting. Lighting fixtures for fixed lighting shall provide enclosures for lamps and lampholders that are designed to minimize entrance of fibers and flyings and to prevent the escape of sparks, burning material, or hot metal. Each fixture shall be clearly marked to show the maximum wattage of the lamps that shall be permitted without exceeding an exposed surface temperature of 165°C (329°F) under normal conditions of use. (b) Physical Damage. A fixture that may be exposed to physical damage shall be protected by a suitable guard. (c) Pendant Fixtures. Pendant fixtures shall be suspended by stems of threaded rigid metal conduit, threaded intermediate metal conduit, threaded metal tubing of equivalent thickness, or by chains with approved fittings. For stems longer than 12 inches (305 mm), permanent and effective bracing against lateral displacement shall be provided at a level not more than 12 inches (305 mm) above the lower end of the stem, or flexibility in the form of an approved fitting or a flexible connector shall be provided not more than 12 inches (305 mm) from the point of attachment to the supporting box or fitting. (d) Portable Lighting Equipment. Portable lighting equipment shall be equipped with handles and protected with substantial guards. Lampholders shall be of the unswitched type with no provision for receiving attachment plugs. There shall be no exposed current-carrying metal parts, and all exposed noncurrent-carrying metal parts shall be grounded. In all other respects, portable lighting equipment shall comply with (a) above. 503-10. Flexible Cords, Class III, Divisions 1 and 2. Flexible cords shall comply with the following: (1) be of a type approved for extra-hard usage; (2) contain, in addition to the conductors of the circuit, a grounding conductor complying with Section 400-23; (3) be connected to terminals or to supply conductors in an approved manner; (4) be supported by clamps or other suitable means in such a manner that there will be no tension on the terminal connections; and (5) be provided with suitable means to prevent the entrance of fibers or flyings where the cord enters boxes or fittings. 503-11. Receptacles and Attachment Plugs, Class III, Divisions 1 and 2. Receptacles and attachment plugs shall be of the grounding type and shall be so designed to minimize the accumulation or the entry of fibers or flyings, and shall prevent the escape of sparks or molten particles. Exception: In locations where, in the judgment of the authority having jurisdiction, only moderate accumulations of lint or flyings will be likely to collect in the vicinity of a receptacle, and where such receptacle is readily accessible for routine cleaning, general-purpose grounding-type receptacles mounted so as to minimize the entry of fibers or flyings shall be permitted. 503-12. Signaling, Alarm, Remote-Control, and Local Loudspeaker Intercommunication Systems, Class III, Divisions 1 and 2. Signaling, alarm, remote-control, and local loudspeaker intercommunication systems shall 70-498 NATIONAL ELECTRICAL CODE comply with the requirements of Article 503 regarding wiring methods, switches, transformers, resistors, motors, lighting fixtures, and related components. 503-13. Electric Cranes, Hoists, and Similar Equipment, Class III, Divisions 1 and 2. Where installed for operation over combustible fibers or accumulations of flyings, traveling cranes and hoists for material handling, traveling cleaners for textile machinery, and similar equipment shall comply with (a) through (d) below. (a) Power Supply. Power supply to contact conductors shall be isolated from all other systems and shall be equipped with an acceptable ground detector that will give an alarm and automatically deenergize the contact conductors in case of a fault to ground or will give a visual and audible alarm as long as power is supplied to the contact conductors and the ground fault remains. (b) Contact Conductors. Contact conductors shall be so located or guarded as to be inaccessible to other than authorized persons and shall be protected against accidental contact with foreign objects. (c) Current Collectors. Current collectors shall be so arranged or guarded as to confine normal sparking and prevent escape of sparks or hot particles. To reduce sparking, two or more separate surfaces of contact shall be provided for each contact conductor. Reliable means shall be provided to keep contact conductors and current collectors free of accumulations of lint or flyings. (d) Control Equipment. Control equipment shall comply with Sections 503-4 and 503-5. 503-14. Storage-Battery Charging Equipment, Class III, Divisions 1 and 2. Storage-battery charging equipment shall be located in separate rooms built or lined with substantial noncombustible materials so constructed as to adequately exclude flyings or lint and shall be well ventilated. 503-15. Live Parts, Class III, Divisions 1 and 2. Live parts shall not be exposed. Exception: As provided in Section 503-13. 503-16. Grounding, Class III, Divisions 1 and 2. Wiring and equipment in Class III, Divisions 1 and 2 shall be grounded as specified in Article 250 and with the following additional requirements: (a) Bonding. The locknut-bushing and double-locknut types of contacts shall not be depended upon for bonding purposes, but bonding jumpers with proper fittings or other approved means of bonding shall be used. Such means of bonding shall apply to all intervening raceways, fittings, boxes, enclosures, etc., between Class III locations and the point of grounding for service equipment or point of grounding of a separately derived system. Exception: The specified bonding means shall only be required to the point of grounding of a building disconnecting means as specified in Sections 250-24(a), (b), and (c), provided that branch-circuit overcurrent protection is located on the load side of the disconnecting means.