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Article 502

Class II Locations

Part I. General

502.1 Scope. Article 502 covers the requirements for electri‐ cal and electronic equipment and wiring for all voltages in Class II, Division 1 and 2 locations where fire or explosion hazards may exist due to combustible dust.

  1. Explosionproof Equipment. Explosionproof equipment and wiring shall not be required and shall not be acceptable in Class II locations unless also identified for such locations.
  2. Zone Equipment. Equipment listed and marked in accordance with 506.9(C)(2) for Zone 20 locations shall be permitted in Class II, Division 1 locations for the same dust atmosphere; and with a suitable temperature class.

Equipment listed and marked in accordance with 506.9(C)

(2) for Zone 20, 21, or 22 locations shall be permitted in Class II, Division 2 locations for the same dust atmosphere and with a suitable temperature class.

Part II. Wiring

502.10 Wiring Methods. Wiring methods shall comply with 502.10(A) or (B).

  1. Class II, Division 1.
    1. General. In Class II, Division 1 locations, the wiring meth‐ ods in (1) through (5) shall be permitted:
      1. Threaded rigid metal conduit, or threaded steel inter‐ mediate metal conduit.
      2. Type MI cable with termination fittings listed for the loca‐ tion. Type MI cable shall be installed and supported in a manner to avoid tensile stress at the termination fittings.
      3. In industrial establishments with limited public access, where the conditions of maintenance and supervision ensure that only qualified persons service the installation, Type MC-HL cable, listed for use in Class II, Division 1 locations, with a gas/vaportight continuous corrugated metallic sheath, an overall jacket of suitable polymeric material, a separate equipment grounding conductor(s) in accordance with 250.122, and provided with termina‐ tion fittings listed for the location, shall be permitted.
      4. Optical fiber cable Types OFNP, OFCP, OFNR, OFCR, OFNG, OFCG, OFN, and OFC shall be permitted to be installed in raceways in accordance with 502.10(A). Opti‐ cal fiber cables shall be sealed in accordance with 502.15.


      (5) In industrial establishments with restricted public access,where the conditions of maintenance and supervision ensure that only qualified persons service the installation, listed Type ITC-HL cable with a gas/vaportight continu‐ ous corrugated metallic sheath and an overall jacket of suitable polymeric material, and terminated with fittings listed for the application, and installed in accordance with the provisions of Article 727.(2) Flexible Connections. Where necessary to employ flexible connections, one or more of the following shall also be permit‐ ted:
      1. Dusttight flexible connectors.
      2. Liquidtight flexible metal conduit with listed fittings.
      3. Liquidtight flexible nonmetallic conduit with listed fittings.
      4. Interlocked armor Type MC cable having an overall jacket of suitable polymeric material and provided with termina‐ tion fittings listed for Class II, Division 1 locations.
      5. Flexible cord listed for extra-hard usage and terminated with listed dusttight cord connectors. Where flexible cords are used, they shall comply with 502.140.
      6. For elevator use, an identified elevator cable of Type EO, ETP, or ETT, shown under the “use” column in Table
      400.4 for “hazardous (classified) locations” and termina‐ ted with listed dusttight fittings.Informational Note: See 502.30(B) for grounding requirements where flexible conduit is used.(3) Boxes and Fittings. Boxes and fittings shall be provided with threaded bosses for connection to conduit or cable termi‐ nations and shall be dusttight. Boxes and fittings in which taps, joints, or terminal connections are made, or that are used in Group E locations, shall be identified for Class II locations.Informational Note: For entry into enclosures required to be dust-ignitionproof, see the information on construction, testing, and marking of cables, dust-ignitionproof cable fittings, and dust-ignitionproof cord connectors in ANSI/UL 2225-2011, Cables and Cable-Fittings for Use in Hazardous (Classified) Locations.
  2. Class II, Division 2.
    1. General. In Class II, Division 2 locations, the following wiring methods shall be permitted:
  1. All wiring methods permitted in 502.10(A).
  2. Rigid metal conduit, intermediate metal conduit, electri‐ cal metallic tubing, dusttight wireways.
  3. Type MC or MI cable with listed termination fittings.
  4. Type PLTC and Type PLTC-ER cable in accordance with the provisions of Article 725, including installation in cable tray systems. The cable shall be terminated with listed fittings.
  5. Type ITC and Type ITC-ER cable as permitted in 727.4 and terminated with listed fittings.
  6. Type MC, MI, MV, TC, or TC-ER 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.Exception to (6): Type MC cable listed for use in Class II, Division 1 locations shall be permitted to be installed without the spacings required by (6).
  7. In industrial establishments with restricted public access, where the conditions of maintenance and supervisionensure that only qualified persons service the installation and where metallic conduit does not provide sufficient corrosion resistance, reinforced thermosetting resin conduit (RTRC) factory elbows, and associated fittings, all marked with suffix -XW, and Schedule 80 PVC conduit, factory elbows and associated fittings shall be permitted.
  8. Optical fiber cable Types OFNP, OFCP, OFNR, OFCR, OFNG, OFCG, OFN, and OFC shall be permitted to be installed in cable trays or any other raceway in accord‐ ance with 502.10(B). Optical fiber cables shall be sealed in accordance with 502.15.
  9. Cablebus.
  1. Flexible Connections. Where provision must be made for flexibility, 502.10(A)(2) shall apply.
  2. Nonincendive Field Wiring. Nonincendive field wiring shall be permitted using any of the wiring methods permitted for unclassified locations. Nonincendive field wiring systems shall be installed in accordance with the control drawing(s). Simple apparatus, not shown on the control drawing, shall be permitted in a nonincendive field wiring circuit, provided the simple apparatus does not interconnect the nonincendive field wiring circuit to any other circuit.

Informational Note: Simple apparatus is defined in 504.2.

Separate nonincendive field wiring circuits shall be installed in accordance with one of the following:

  1. In separate cables
  2. In multiconductor cables where the conductors of each circuit are within a grounded metal shield
  3. In multiconductor cables or in raceways where the conductors of each circuit have insulation with a mini‐ mum thickness of 0.25 mm (0.01 in.)
  4. Boxes and Fittings. All boxes and fittings shall be dust‐ tight.

502.15 Sealing, Class II, Divisions 1 and 2. Where a raceway provides communication between an enclosure that is required to be dust-ignitionproof 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 3.05 m (10 ft) long
  3. A vertical raceway not less than 1.5 m (5 ft) long and extending downward from the dust-ignitionproof enclo‐ sure
  4. A raceway installed in a manner equivalent to (2) or (3) that extends only horizontally and downward from the dust-ignition proof enclosures

Where a raceway provides communication between an enclo‐ sure that is required to be dust-ignitionproof and an enclosure in an unclassified location, seals shall not be required.

Sealing fittings shall be accessible.

Seals shall not be required to be explosionproof.

Informational Note: Electrical sealing putty is a method of seal‐ ing.

502.25 Uninsulated Exposed Parts, Class II, Divisions 1 and 2. There shall be no uninsulated exposed parts, such as electrical conductors, buses, terminals, or components, that operate at more than 30 volts (15 volts in wet locations). These parts shall

additionally be protected by a protection technique according to 500.7(E), (F), or (G) that is suitable for the location.

502.30 Grounding and Bonding, Class II, Divisions 1 and 2. Regardless of the voltage of the electrical system, wiring and equipment in Class II, Division 1 and 2 locations shall be grounded as specified in Article 250 and in accordance with the requirements of 502.30(A) and (B).

  1. Bonding. The locknut-bushing and double-locknut types of contact shall not be depended on 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, and so forth, between Class II locations and the point of grounding for service equipment or point of grounding of a separately derived system.Exception: The specific bonding means shall only be required to the nearest point where the grounded circuit conductor and the grounding electrode conductor are connected together on the line side of the build‐ ing or structure disconnecting means as specified in 250.32(B) if the branch-circuit overcurrent protection is located on the load side of the disconnecting means.
  2. Types of Equipment Grounding Conductors. Liquidtight flexible metal conduit shall include an equipment bonding jumper of the wire type in compliance with 250.102.

Exception: In Class II, Division 2 locations, the bonding jumper shall be permitted to be deleted where all of the following conditions are met:

(1) Listed liquidtight flexible metal conduit 1.8 m (6 ft) or less in

installed in vaults complying with 450.41 through 450.48 or be identified as a complete assembly, including terminal connec‐ tions.

(3) Group E. No transformer or capacitor shall be installed in a Class II, Division 1, Group E location.

  1. Class II, Division 2. In Class II, Division 2 locations, trans‐ formers and capacitors shall comply with 502.100(B)(1) through (B)(3).
    1. Containing Liquid That Will Burn. Transformers and capacitors containing a liquid that will burn shall be installed in vaults that comply with 450.41 through 450.48.
    2. Containing Askarel. Transformers containing askarel and rated in excess of 25 kVA shall be as follows:
  1. Provided with pressure-relief vents
  2. 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
  3. Have an airspace of not less than 150 mm (6 in.) between the transformer cases and any adjacent combustible mate‐ rial

(3) Dry-Type Transformers. Dry-type transformers shall be installed in vaults or shall have their windings and terminal connections enclosed in tight metal housings without ventilat‐ ing or other openings and shall operate at not over 600 volts, nominal.

502.115 Switches, Circuit Breakers, Motor Controllers, and

(2)

length, with fittings listed for grounding, is used.

Overcurrent protection in the circuit is limited to 10 amperes or less.

Fuses.

(A) Class II, Division 1. In Class II, Division 1 locations,

(3) The load is not a power utilization load.

502.35 Surge Protection — Class II, Divisions 1 and 2. Surge arresters and surge-protective devices 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.

Part III. Equipment

502.100 Transformers and Capacitors.

  1. Class II, Division 1. In Class II, Division 1 locations, trans‐ formers and capacitors shall comply with 502.100(A)(1) through (A)(3).
    1. Containing Liquid That Will Burn. Transformers and capacitors containing a liquid that will burn shall be installed only in vaults complying with 450.41 through 450.48, and, in addition, (1), (2), and (3) shall apply.
      1. Doors or other openings communicating with the Divi‐ sion 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 strip‐ ping) to minimize the entrance of dust into the vault.
      2. Vent openings and ducts shall communicate only with the outside air.
      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 beswitches, circuit breakers, motor controllers, fuses, push- buttons, relays, and similar devices shall be provided with enclosures identified for the location.
  2. Class II, Division 2. In Class II, Division 2 locations, enclo‐ sures for fuses, switches, circuit breakers, and motor control‐ lers, including push buttons, relays, and similar devices, shall be dusttight or otherwise identified for the location.

502.120 Control Transformers and Resistors.

  1. 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 be provided with enclosures identified for the location.
  2. Class II, Division 2. In Class II, Division 2 locations, trans‐ formers and resistors shall comply with 502.120(B)(1) through (B)(3).
    1. Switching Mechanisms. Switching mechanisms (including overcurrent devices) associated with control transformers, sole‐ noids, impedance coils, and resistors shall be provided with enclosures that are dusttight or otherwise identified for the location.
    2. Coils and Windings. Where not located in the same enclo‐ sure with switching mechanisms, control transformers, sole‐ noids, and impedance coils shall be provided with enclosures that are dusttight or otherwise identified for the location.
    3. Resistors. Resistors and resistance devices shall have dust- ignitionproof enclosures that are dusttight or otherwise identi‐ fied for the location.

502.125 Motors and Generators.

  1. Class II, Division 1. In Class II, Division 1 locations, motors, generators, and other rotating electrical machinery shall be in conformance with either of the following:
    1. Identified for the location
    2. Totally enclosed pipe-ventilated
  2. 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 water-air-cooled, totally enclosed fan-cooled, or dust-ignitionproof, for which maximum full-load external temperature shall be in accordance with 500.8(D)(2) 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 follow‐ ing shall be permitted to be installed:

  1. Standard open-type machines without sliding contacts, centrifu‐ gal or other types of switching mechanism (including motor over‐ current, overloading, and overtemperature devices), or integral resistance devices
  2. Standard open-type machines with such contacts, switching mechanisms, or resistance devices enclosed within dusttight hous‐ ings without ventilating or other openings
  3. Self-cleaning textile motors of the squirrel-cage type
  4. Machines with sealed bearings, bearing isolators, and seals

502.128 Ventilating Piping. Ventilating pipes for motors, generators, or other rotating electrical machinery, or for enclo‐ sures for electrical equipment, shall be of metal not less than

0.53 mm (0.021 in.) in thickness or of equally substantial noncombustible material and shall comply with all of 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
  3. Be protected against physical damage and against rusting or other corrosive influences

Ventilating pipes shall also comply with 502.128(A) and (B).

  1. Class II, Division 1. In Class II, Division 1 locations, venti‐ lating 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
    4. Be rendered dusttight by some other equally effective means
  2. Class II, Division 2. In Class II, Division 2 locations, venti‐ lating 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 accu‐ mulations or combustible material in the vicinity. For metal

pipes, lock seams and riveted or welded joints shall be permit‐ ted; and tight-fitting slip joints shall be permitted where some flexibility is necessary, as at connections to motors.

502.130 Luminaires.

  1. Class II, Division 1. In Class II, Division 1 locations, luminaires for fixed and portable lighting shall comply with 502.130(A)(1) through (A)(4).
    1. Marking. Each luminaire shall be identified for the loca‐ tion and shall be clearly marked to indicate the type and maxi‐ mum wattage of the lamp for which it is designed.
    2. Physical Damage. Each luminaire shall be protected against physical damage by a suitable guard or by location.
    3. Pendant Luminaires. Pendant luminaires shall be suspen‐ ded by threaded rigid metal conduit stems, by threaded steel intermediate metal conduit stems, by chains with approved fittings, or by other approved means. For rigid stems longer than 300 mm (12 in.), permanent and effective bracing against lateral displacement shall be provided at a level not more than 300 mm (12 in.) above the lower end of the stem, or flexibility in the form of a fitting or a flexible connector listed for the location shall be provided not more than 300 mm (12 in.) from the point of attachment to the supporting box or fitting. Threa‐ ded joints shall be provided with set screws or other effective means to prevent loosening. Where wiring between an outlet box or fitting and a pendant luminaire is not enclosed in conduit, flexible cord listed for hard usage shall be permitted to be used in accordance with 502.10(A)(2)(5). Flexible cord shall not serve as the supporting means for a luminaire.
    4. Supports. Boxes, box assemblies, or fittings used for the support of luminaires shall be identified for Class II locations.
  2. Class II, Division 2. In Class II, Division 2 locations, luminaires shall comply with 502.130(B)(1) through (B)(5).
    1. Portable Lighting Equipment. Portable lighting equip‐ ment shall be identified for the location. They shall be clearly marked to indicate the maximum wattage of lamps for which they are designed.
    2. Fixed Lighting. Luminaires for fixed lighting shall be provided with enclosures that are dusttight or otherwise identi‐ fied for the location. Each luminaire 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 500.8(D)(2) under normal conditions of use.
    3. Physical Damage. Luminaires for fixed lighting shall be protected from physical damage by suitable guards or by loca‐ tion.
    4. Pendant Luminaires. Pendant luminaires shall be suspen‐ ded by threaded rigid metal conduit stems, by threaded steel intermediate metal conduit stems, by chains with approved fittings, or by other approved means. For rigid stems longer than 300 mm (12 in.), permanent and effective bracing against lateral displacement shall be provided at a level not more than 300 mm (12 in.) above the lower end of the stem, or flexibility in the form of an identified fitting or a flexible connector shall be provided not more than 300 mm (12 in.) from the point of attachment to the supporting box or fitting. Where wiring between an outlet box or fitting and a pendant luminaire is not enclosed in conduit, flexible cord listed for hard usage shall be
      permitted if terminated with a listed cord connector that main‐ tains the protection technique. Flexible cord shall not serve as the supporting means for a luminaire.
    5. Electric-Discharge Lamps. Starting and control equip‐ ment for electric-discharge lamps shall comply with the requirements of 502.120(B).

502.135 Utilization Equipment.

  1. Class II, Division 1. In Class II, Division 1 locations, all utilization equipment shall be identified for the location.
  2. Class II, Division 2. In Class II, Division 2 locations, all utilization equipment shall comply with 502.135(B)(1) through (B)(4).
    1. Heaters. Electrically heated utilization equipment shall be identified for the location.Exception: Metal-enclosed radiant heating panel equipment shall be permitted to be dusttight and marked in accordance with 500.8(C).
    2. Motors. Motors of motor-driven utilization equipment shall comply with 502.125(B).
    3. Switches, Circuit Breakers, and Fuses. Enclosures for switches, circuit breakers, and fuses shall comply with 502.115(B).
    4. Transformers, Solenoids, Impedance Coils, and Resistors. Transformers, solenoids, impedance coils, and resistors shall comply with 502.120(B).

502.140 Flexible Cords — Class II, Divisions 1 and 2.

  1. Permitted Uses. Flexible cords used in Class II locations shall comply with all of the following:
    1. For connection between portable lighting equipment or other portable utilization equipment and the fixed portion of its supply circuit. The flexible cord shall be attached to the utilization equipment with a cord connec‐ tor listed for the protection technique of the equipment wiring compartment. An attachment plug in accordance with 502.145 shall be employed.
    2. Where flexible cord is permitted by 502.10(A)(2) for fixed and mobile electrical utilization equipment; where the flexible cord is protected by location or by a suitable guard from damage; and only in an industrial establish‐ ment where conditions of maintenance and engineering supervision ensure that only qualified persons install and service the installation.
    3. For electric submersible pumps with means for removal without entering the wet-pit. The extension of the flexible cord within a suitable raceway between the wet-pit and the power source shall be permitted.
    4. For electric mixers intended for travel into and out of open-type mixing tanks or vats.
    5. For temporary portable assemblies consisting of recepta‐ cles, switches, and other devices that are not considered portable utilization equipment but are individually listed for the location.
  2. Installation. Where flexible cords are used, the cords shall comply with all of the following:
  1. Be of a type listed for extra-hard usage.Exception: Flexible cord listed for hard usage as permitted by 502.130(A)(3) and (B)(4).
  2. Contain, in addition to the conductors of the circuit, an equipment grounding conductor complying with 400.23.
  3. Be supported by clamps or by other suitable means in such a manner that there will be no tension on the termi‐ nal connections.
  4. In Division 1 locations, the cord shall be terminated with a cord connector listed for the location or a listed cord connector installed with a seal listed for the location. In Division 2 locations, the cord shall be terminated with a listed dusttight cord connector.
  5. Be of continuous length. Where 502.140(A)(5) is applied, cords shall be of continuous length from the power source to the temporary portable assembly and from the temporary portable assembly to the utilization equip‐ ment.

502.145 Receptacles and Attachment Plugs. Receptacles and attachment plugs shall be identified for the location.

  1. Class II, Division 1.
    1. Receptacles. In Class II, Division 1 locations, receptacles shall be part of the premises wiring.
    2. Attachment Plugs. Attachment plugs shall be of the type that provides for connection to the equipment grounding conductor of the flexible cord.
  2. Class II, Division 2.
    1. Receptacles. In Class II, Division 2 locations, receptacles shall be part of the premises wiring.
    2. Attachment Plugs. Attachment plugs shall be of the type that provides for connection to the equipment grounding conductor of the flexible cord.

502.150 Signaling, Alarm, Remote-Control, and Communica‐ tions Systems; and Meters, Instruments, and Relays.

Informational Note: See Article 800 for rules governing the installation of communications circuits.

  1. Class II, Division 1. In Class II, Division 1 locations, signaling, alarm, remote-control, and communications systems; and meters, instruments, and relays shall comply with 502.150(A)(1) through (A)(3).
    1. 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 identified for the 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 general- purpose type.
    2. Resistors and Similar Equipment. Resistors, transformers, choke coils, rectifiers, thermionic tubes, and other heat- generating equipment shall be provided with enclosures identi‐ fied for the location.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.ARTICLE 503 — CLASS III LOCATIONS 503.10
    3. Rotating Machinery. Motors, generators, and other rotat‐ ing electrical machinery shall comply with 502.125(A).
  2. Class II, Division 2. In Class II, Division 2 locations, signaling, alarm, remote-control, and communications systems; and meters, instruments, and relays shall comply with 502.150(B)(1) through (B)(4).
    1. Contacts. Contacts shall comply with 502.150(A)(1) or shall be installed in enclosures that are dusttight or otherwise identified for the location.Exception: In nonincendive circuits, 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 comply with 502.120(B)(2).
    3. Resistors and Similar Equipment. Resistors, resistance devices, thermionic tubes, rectifiers, and similar equipment shall comply with 502.120(B)(3).
    4. Rotating Machinery. Motors, generators, and other rotat‐ ing electrical machinery shall comply with 502.125(B).

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