CLASS II LOCATIONS

502-1. General. The general rules of this Code shall apply to the electric wiring and equipment in locations classified as Class II locations in Section 500-6. Exception: As modified by this article. "Dust-ignitionproof," as used in this article, shall mean enclosed in a manner that will exclude dusts and, where installed and protected in accordance with this Code, will not permit arcs, sparks, or heat otherwise generated or liberated inside of the enclosure to cause ignition of exterior accumulations or atmospheric suspensions of a specified dust on or in the vicinity of the enclosure. (FPN:) For further information on dust-ignitionproof enclosures, see Type 9 enclosure in Enclosures for Electrical Equipment, ANSI/NEMA 250-1985, and Explosionproof and Dust-Ignitionproof Electrical Equipment for Hazardous (Classified) Locations, ANSI/UL 1203-1988. Equipment installed in Class II locations shall be able to function at full rating without developing surface temperatures high enough to cause excessive dehydration or gradual carbonization of any organic dust deposits that may occur. (FPN): Dust that is carbonized or excessively dry is highly susceptible to spontaneous ignition. Equipment and wiring of the type defined in Article 100 as explosionproof shall not be required and shall not be acceptable in Class II locations unless approved for such locations. Where Class II, Group E dusts are present in hazardous quantities, there are only Division 1 locations. 502-2. Transformers and Capacitors. (a) Class II, Division 1. In Class II, Division 1 locations, transformers and capacitors shall comply with the following: (1) Containing Liquid that Will Burn. Transformers and capacitors containing a liquid that will burn shall be installed only in approved vaults complying with Sections 450-41 through 450-48, and, in addition, (1) doors or other openings communicating with the Division 1 location shall have self-closing fire doors on both sides of the wall, and the doors shall be carefully fitted and provided with suitable seals (such as weather stripping) to minimize the entrance of dust into the vault; (2) vent openings and ducts shall communicate only with the outside air; and (3) suitable pressure-relief openings communicating with the outside air shall be provided. (2) Not Containing Liquid that Will Burn. Transformers and capacitors that do not contain a liquid that will burn shall (1) be installed in vaults complying with Sections 450-41 through 450-48 or (2) be approved as a complete assembly, including terminal connections for Class II locations. (3) Metal Dusts. No transformer or capacitor shall be installed in a location where dust from magnesium, aluminum, aluminum bronze powders, or other metals of similarly hazardous characteristics may be present. (b) Class II, Division 2. In Class II, Division 2 locations, transformers and capacitors shall comply with the following: ARTICLE 502 - CLASS II LOCATIONS 70-487 (1) Containing Liquid that Will Burn. Transformers and capacitors containing a liquid that will burn shall be installed in vaults complying with Sections 450-41 through 450-48. (2) Containing Askarel. Transformers containing askarel and rated in excess of 25 kVA shall (1) be provided with pressure-relief vents; (2) be provided with a means for absorbing any gases generated by arcing inside the case, or the pressure-relief vents shall be connected to a chimney or flue that will carry such gases outside the building; and (3) have an air space of not less than 6 inches (152 mm) between the transformer cases and any adjacent combustible material. (3) Dry-type Transformers. Dry-type transformers shall be installed in vaults or shall (1) have their windings and terminal connections enclosed in tight metal housings without ventilating or other openings and (2) operate at not over 600 volts, nominal. 502-4. Wiring Methods. Wiring methods shall comply with (a) and (b) below. (a) Class II, Division 1. In Class II, Division 1 locations, threaded rigid metal conduit, threaded steel intermediate metal conduit, or Type MI cable with termination fittings approved for the location shall be the wiring method employed. Type MI cable shall be installed and supported in a manner to avoid tensile stress at the termination fittings. (1) Fittings and Boxes. Fittings and boxes shall be provided with threaded bosses for connection to conduit or cable terminations, shall have close-fitting covers, and shall have no openings (such as holes for attachment screws) through which dust might enter or through which sparks or burning material might escape. Fittings and boxes in which taps, joints, or terminal connections are made, or that are used in locations where dusts are of a combustible, electrically conductive nature, shall be approved for Class II locations. (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 approved for extra-hard usage and provided with bushed fittings shall be used. Where flexible cords are used, they shall comply with Section 502-12. Where flexible connections are subject to oil or other corrosive conditions, the insulation of the conductors shall be of a type approved for the condition or shall be protected by means of a suitable sheath. (FPN): See Section 502-16(b) for grounding requirements where flexible conduit is used. (b) Class II, Division 2. In Class II, Division 2 locations, rigid metal conduit, intermediate metal conduit, electrical metallic tubing, dusttight wireways, or Type MC, MI, or SNM cable with approved termination fittings, or Type PLTC in cable trays, or Type MC or TC cable installed in ladder, ventilated trough, or ventilated channel cable trays in a single layer, with a space not less than the larger cable diameter between the two adjacent cables, shall be the wiring method employed. 70-488 NATIONAL ELECTRICAL CODE Exception: Wiring in nonincendive circuits shall be permitted using any of the methods suitable for wiring in ordinary locations. (1) Wireways, Fittings, and Boxes. Wireways, fittings, and boxes in which taps, joints, or terminal connections are made shall be designed to minimize the entrance of dust and (1) shall be provided with telescoping or close-fitting covers or other effective means to prevent the escape of sparks or burning material and (2) shall have no openings (such as holes for attachment screws) through which, after installation, sparks or burning material might escape or through which adjacent combustible material might be ignited. (2) Flexible Connections. Where flexible connections are necessary, (a)(2) above shall apply. 502-5. Sealing, Class II, Divisions 1 and 2. Where a raceway provides communication between an enclosure that is required to be dustignitionproof and one that is not, suitable means shall be provided to prevent the entrance of dust into the dust-ignitionproof enclosure through the raceway. One of the following means shall be permitted: (1) a permanent and effective seal; (2) a horizontal raceway not less than 10 feet (3.05 m) long; or (3) a vertical raceway not less than 5 feet (1.52 m) long and extending downward from the dust-ignitionproof enclosure. Where a raceway provides communication between an enclosure that is required to be dust-ignitionproof and an enclosure in an unclassified location, seals shall not be required. Sealing fittings shall be accessible. 502-6. Switches, Circuit Breakers, Motor Controllers, and Fuses. (a) Class II, Division 1. In Class II, Division 1 locations, switches, circuit breakers, motor controllers, and fuses shall comply with the following: (1) Type Required. Switches, circuit breakers, motor controllers, and fuses, including pushbuttons, relays, and similar devices that are intended to interrupt current during normal operation, or that are installed where combustible dusts of an electrically conductive nature may be present, shall be provided with dust-ignitionproof enclosures, which, together with the enclosed equipment in each case, shall be approved as a complete assembly for Class II locations. (2) Isolating Switches. Disconnecting and isolating switches containing no fuses and not intended to interrupt current and not installed where dusts may be of an electrically conductive nature shall be provided with tight metal enclosures that shall be designed to minimize the entrance of dust and that shall (1) be equipped with telescoping or close-fitting covers or with other effective means to prevent the escape of sparks or burning material and (2) have no openings (such as holes for attachment screws) through which, after installation, sparks or burning material might escape or through which exterior accumulations of dust or adjacent combustible material might be ignited. ARTICLE 502 - CLASS II LOCATIONS 70-489 (3) Metal Dusts. In locations where dust from magnesium, aluminum, aluminum bronze powders, or other metals of similarly hazardous characteristics may be present, fuses, switches, motor controllers, and circuit breakers shall have enclosures specifically approved for such locations. (b) Class II, Division 2. In Class II, Division 2 locations, enclosures for fuses, switches, circuit breakers, and motor controllers, including pushbuttons, relays, and similar devices, shall be dusttight. 502-7. Control Transformers and Resistors. (a) Class II, Division 1. In Class II, Division 1 locations, control transformers, solenoids, impedance coils, resistors, and any overcurrent devices or switching mechanisms associated with them shall have dustignitionproof enclosures approved for Class II locations. No control transformer, impedance coil, or resistor shall be installed in a location where dust from magnesium, aluminum, aluminum bronze powders, or other metals of similarly hazardous characteristics may be present unless provided with an enclosure approved for the specific location. (b) Class II, Division 2. In Class II, Division 2 locations, transformers and resistors shall comply with the following: (1) Switching Mechanisms. Switching mechanisms (including overcurrent devices) associated with control transformers, solenoids, impedance coils, and resistors shall be provided with dusttight enclosures. (2) Coils and Windings. Where not located in the same enclosure with switching mechanisms, control transformers, solenoids, and impedance coils shall be provided with tight metal housings without ventilating openings. (3) Resistors. Resistors and resistance devices shall have dustignition-proof enclosures approved for Class II locations. Exception: Where the maximum normal operating temperature of the resistor will not exceed 120°C (248°F), nonadjustable resistors or resistors that are part of an automatically timed starting sequence shall be permitted to have enclosures complying with (b)(2) above. 502-8. Motors and Generators. (a) Class II, Division 1. In Class II, Division 1 locations, motors, generators, and other rotating electrical machinery shall be: (1) Approved for Class II, Division 1 locations, or (2) Totally enclosed pipe-ventilated, meeting temperature limitations in Section 502-1. (b) Class II, Division 2. In Class II, Division 2 locations, motors, generators, and other rotating electrical equipment shall be totally enclosed nonventilated, totally enclosed pipe-ventilated, totally enclosed fan-cooled or dust-ignitionproof for which maximum full-load external temperature shall 70-490 NATIONAL ELECTRICAL CODE I be in accordance with Section 500-3(f) for normal operation when operating in free air (not dust blanketed) and shall have no external openings. Exception: If the authority having jurisdiction believes accumulations of nonconductive, nonabrasive dust will be moderate and if machines can be easily reached for routine cleaning and maintenance, the following shall be permitted to be installed: a. Standard open-type machines without sliding contacts, centrifugal or other types of switching mechanism (including motor overcurrent, overloading, and overtemperature devices), or integral resistance devices. b. Standard open-type machines with such contacts, switching mechanisms, or resistance devices enclosed within dusttight housings without ventilating or other openings. c. Self-cleaning textile motors of the squirrel-cage type. 502-9. Ventilating Piping. 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 also comply with (a) and (b) below. (a) Class II, Division 1. In Class II, Division 1 locations, ventilating pipes, including their connections to motors or to the dust-ignitionproof enclosures for other equipment, shall be dusttight throughout their length. For metal pipes, seams and joints shall comply with one of the following: (1) be riveted and soldered; (2) be bolted and soldered; (3) be welded; or (4) be rendered dusttight by some other equally effective means. (b) Class II, Division 2. In Class II, Division 2 locations, ventilating pipes and their connections shall be sufficiently tight to prevent the entrance of appreciable quantities of dust into the ventilated equipment or enclosure and to prevent the escape of sparks, flame, or burning material that might ignite dust accumulations 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. 502-10. Utilization Equipment. (a) Class II, Division 1. In Class II, Division 1 locations, all utilization equipment shall be approved for Class II locations. Where dust from magnesium, aluminum, aluminum bronze powders, or other metals of similarly hazardous characteristics may be present, such equipment shall be approved for the specific location. (b) Class II, Division 2. In Class II, Division 2 locations, all utilization equipment shall comply with the following: (1) Heaters. Electrically heated utilization equipment shall be approved for Class II locations. ARTICLE 502 - CLASS II LOCATIONS 70-491 Exception: Metal-enclosed radiant heating panel equipment shall be dusttight and marked in accordance with Section 500-3(d). (2) Motors. Motors of motor-driven utilization equipment shall comply with Section 502-8(b). (3) Switches, Circuit Breakers, and Fuses. Enclosures for switches, circuit breakers, and fuses shall be dusttight. (4) Transformers, Impedance Coils, and Resistors. Transformers, solenoids, impedance coils, and resistors shall comply with Section 502-7(b). 502-11. Lighting Fixtures. Lighting fixtures shall comply with (a) and (b) below. (a) Class II, Division 1. In Class II, Division 1 locations, lighting fixtures for fixed and portable lighting shall comply with the following: (1) Approved Fixtures. Each fixture shall be approved for Class II locations and shall be clearly marked to indicate the maximum wattage of the lamp for which it is approved. In locations where dust from magnesium, aluminum, aluminum bronze powders, or other metals of similarly hazardous characteristics may be present, fixtures for fixed or portable lighting and all auxiliary equipment shall be approved for the specific location. (2) Physical Damage. Each fixture shall be protected against physical damage by a suitable guard or by location. (3) Pendant Fixtures. Pendant fixtures shall be suspended by threaded rigid metal conduit stems, threaded steel intermediate metal conduit stems, by chains with approved fittings, or by other approved means. For rigid 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 a fitting or a flexible connector approved for the location shall be provided not more than 12 inches (305 mm) from the point of attachment to the supporting box or fitting. Threaded joints shall be provided with setscrews or other effective means to prevent loosening. Where wiring between an outlet box or fitting and a pendant fixture is not enclosed in conduit, flexible cord approved for hard usage shall be used, and suitable seals shall be provided where the cord enters the fixture and the outlet box or fitting. Flexible cord shall not serve as the supporting means for a fixture. (4) Supports. Boxes, box assemblies, or fittings used for the support of lighting fixtures shall be approved for Class II locations. (b) Class II, Division 2. In Class II, Division 2 locations, lighting fixtures shall comply with the following: (1) Portable Lighting Equipment. Portable lighting equipment shall be approved for Class II locations. They shall be clearly marked to indicate the maximum wattage of lamps for which they are approved. (2) Fixed Lighting. Lighting fixtures for fixed lighting, where not of a type approved for Class II locations, shall provide enclosures for lamps and lampholders that shall be designed to minimize the deposit of dust on 70-492 NATIONAL ELECTRICAL CODE lamps and to prevent the escape of sparks, burning material, or hot metal. Each fixture shall be clearly marked to indicate the maximum wattage of the lamp that shall be permitted without exceeding an exposed surface temperature in accordance with Section 500-3(f) under normal conditions of use. (3) Physical Damage. Lighting fixtures for fixed lighting shall be protected from physical damage by suitable guards or by location. (4) Pendant Fixtures. Pendant fixtures shall be suspended by threaded rigid metal conduit stems, threaded steel intermediate metal conduit stems, by chains with approved fittings, or by other approved means. For rigid 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. Where wiring between an outlet box or fitting and a pendant fixture is not enclosed in conduit, flexible cord approved for hard usage shall be used. Flexible cord shall not serve as the supporting means for a fixture. (5) Electric-Discharge Lamps. Starting and control equipment for electric-discharge lamps shall comply with the requirements of Section 502-7(b). 502-12. Flexible Cords, Class II, Divisions 1 and 2. Flexible cords used in Class II locations 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 by other suitable means in such a manner that there will be no tension on the terminal connections; and (5) be provided with suitable seals to prevent the entrance of dust where the flexible cord enters boxes or fittings that are required to be dust-ignitionproof. 502-13. Receptacles and Attachment Plugs. (a) Class II, Division 1. In Class II, Division 1 locations, receptacles and attachment plugs shall be of the type providing for connection to the grounding conductor of the flexible cord and shall be approved for Class II locations. (b) Class II, Division 2. In Class II, Division 2 locations, receptacles and attachment plugs shall be of the type providing for connection to the grounding conductor of the flexible cord and shall be so designed that connection to the supply circuit cannot be made or broken while live parts are exposed. 502-14. Signaling, Alarm, Remote-Control, and Communication Systems, Meters, Instruments, and Relays. (FPN): See Article 800 for rules governing the installation of communication circuits. (a) Class II, Division 1. In Class II, Division 1 locations, signaling, alarm, remote-control, and communication systems; and meters, instruments, and relays shall comply with the following: ARTICLE 502 - CLASS II LOCATIONS 70-493 (1) Wiring Methods. The wiring method shall comply with Section 502-4(a). (2) Contacts. Switches, circuit breakers, relays, contactors, fuses and current-breaking contacts for bells, horns, howlers, sirens, and other devices in which sparks or arcs may be produced shall be provided with enclosures approved for a Class II location. Exception: Where current-breaking contacts are immersed in oil or where the interruption of current occurs within a chamber sealed against the entrance of dust, enclosures shall be permitted to be of the generalpurpose type. (3) Resistors and Similar Equipment. Resistors, transformers, choke coils, rectifiers, thermionic tubes, and other heat-generating equipment shall be provided with enclosures approved for Class II locations. Exception: Where resistors or similar equipment are immersed in oil or enclosed in a chamber sealed against the entrance of dust, enclosures shall be permitted to be of the general-purpose type. (4) Rotating Machinery. Motors, generators, and other rotating electric machinery shall comply with Section 502-8(a). (5) Combustible, Electrically Conductive Dusts. Where dusts are of a combustible, electrically conductive nature, all wiring and equipment shall be approved for Class II locations. (6) Metal Dusts. Where dust from magnesium, aluminum, aluminum bronze powders, or other metals of similarly hazardous characteristics may be present, all apparatus and equipment shall be approved for the specific conditions. (b) Class II, Division 2. In Class II, Division 2 locations, signaling, alarm, remote-control, and communication systems; and meters, instruments, and relays shall comply with the following: (1) Contacts. Enclosures shall comply with (a)(2) above; or contacts shall have tight metal enclosures designed to minimize the entrance of dust and shall have telescoping or tight-fitting covers and no openings through which, after installation, sparks or burning material might escape. Exception: In nonincendive circuits that under normal conditions do not release sufficient energy to ignite a dust layer, enclosures shall be permitted to be of the general-purpose type. (2) Transformers and Similar Equipment. The windings and terminal connections of transformers, choke coils, and similar equipment shall be provided with tight metal enclosures without ventilating openings. (3) Resistors and Similar Equipment. Resistors, resistance devices, thermionic tubes, rectifiers, and similar equipment shall comply with (a)(3) above. Exception: Enclosures for thermionic tubes, nonadjustable resistors, or rectifiers for which maximum operating temperature will not exceed 120°C (248°F) shall be permitted to be of the general-purpose type. (4) Rotating Machinery. Motors, generators, and other rotating electric machinery shall comply with Section 502-8(b). 70-494 NATIONAL ELECTRICAL CODE (5) Wiring Methods. The wiring method shall comply with Section 502-4(b). 502-15. Live Parts, Class II, Divisions 1 and 2. Live parts shall not be exposed. 502-16. Grounding, Class II, Divisions 1 and 2. Wiring and equipment in Class II, Division 1 and 2 locations shall be grounded as specified in Article 250 and with the following additional requirements: (a) Bonding. The locknut-bushing and double-locknut types of contact 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 II 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 protection is located on the load side of the disconnecting means. (FPN): See Section 250-78 for additional bonding requirements in hazardous (classified) locations. (b) Types of Equipment Grounding Conductors. Where flexible conduit is used as permitted in Section 502-4, it shall be installed with internal or external bonding jumpers in parallel with each conduit and complying with Section 250-79. Exception: In Class II, Division 2 areas, the bonding jumper shall be permitted to be deleted where all the following conditions are met: a. Approved liquidtight flexible metal conduit 6 feet (1.83 m) or less in length, with approved fittings, is used; b. Overcurrent protection in the circuit is limited to 10 amperes or less; c. The load is not a power utilization load. 502-17. Surge Protection, Class II, Divisions 1 and 2. Surge arresters, including their installation and connection, shall comply with Article 280. In addition, surge arresters, if installed in a Class II, Division 1 location, shall be in suitable enclosures. Surge-protective capacitors shall be of a type designed for specific duty. 502-18. Multiwire Branch Circuits. In a Class II, Division 1 location, a separate grounded conductor shall be installed in each single-phase branch circuit that is part of a multiwire branch circuit. Exception: Where the disconnect device(s) for the circuit opens all ungrounded conductors of the multiwire circuit simultaneously.