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ave enclosures identified for Class I, Division 1 locations in accordance with 501.105(A). Exception: General-purpose enclosures shall be permitted if current-interrupting contacts are one of the following: (1) Immersed in oil (2) Enclosed within a chamber hermetically sealed against the entrance of...

ave enclosures identified for Class I, Division 1 locations in accordance with 501.105(A). Exception: General-purpose enclosures shall be permitted if current-interrupting contacts are one of the following: (1) Immersed in oil (2) Enclosed within a chamber hermetically sealed against the entrance of gases or vapors (3) In nonincendive circuits (4) Part of a listed nonincendive component ENHANCED CONTENT Collapse See also 501.105(B)(2) and its enhanced content regarding arcing contacts and the use of general-purpose enclosures in Class I, Division 2 locations. Resistors and Similar Equipment. Resistors, resistance devices, thermionic tubes, rectifiers, and similar equipment shall comply with 501.105(B)(3). Protectors. Enclosures shall be provided for lightning protective devices and for fuses. Such enclosures shall be permitted to be of the general-purpose type. Wiring and Sealing. All wiring shall comply with 501.10(B), 501.15(B), and 501.15(C). ENHANCED CONTENT Collapse Some audible signaling devices may contain make-and-break contacts that are capable of producing a spark of sufficient energy to cause ignition of a hazardous atmospheric mixture. If used in Class I locations, this type of equipment must be contained in explosionproof or purged and pressurized enclosures, wiring methods must comply with 501.10, and seal fittings must be provided in accordance with 501.15. An example of an audible signaling device for use in hazardous locations is pictured below. Electronic signal devices without make-and-break contacts usually do not require explosionproof enclosures in Division 2 locations. (Courtesy of Eaton, Crouse-Hinds Division) Article 502 Class II Locations Part I. General 502.1 Scope. This article covers the requirements for electrical 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. ENHANCED CONTENT Collapse Class II, Division 1 and 2 locations are defined in 500.5(C) as “hazardous because of the presence of combustible dust.” Two different types of dust environments typically warrant a Class II, Division 1 area classification. The first is where a cloud of combustible dust is likely to be present continuously or intermittently under normal operating conditions or because of repair or maintenance operations or leakage. The other environment is one in which a dust layer is likely to accumulate to a depth greater than â…› inch on major horizontal surfaces over a defined period of time, usually 24 hours. A Class II, Division 2 location is typically one where these conditions exist infrequently or under abnormal conditions. NFPA 484, Standard for Combustible Metals, provides methods to minimize the occurrence of, and resulting damage from, fire or explosion in areas where combustible metals or metal dusts are produced, processed, finished, handled, stored, and used. 502.5 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. ENHANCED CONTENT Collapse The electrical equipment required in Class II locations is different from that required for Class I locations. Class II equipment is designed to prevent the ignition of layers of dust, which can also cause an increase in equipment operating temperature, while Class I equipment does not address this concern. To protect against explosions in hazardous locations, all electrical equipment exposed to the hazardous atmosphere must be suitable for the location. Equipment suitable for one class and group is not necessarily suitable for any other class and group. Class I equipment is not necessarily suitable for a Class II location because the hazard contemplated in the equipment design is different. Grain dust, for example, ignites at a temperature lower than that of most flammable vapors. Motors listed for use in Class I locations might not have dust shields on the bearings to prevent entrance of dust into the bearing race, thereby causing overheating of the bearing and resulting in ignition of dust on the motor. Class I equipment is not designed for dust layering. Dust-ignitionproof enclosures are not required to be explosionproof. Explosionproof enclosures are not necessarily dust-ignitionproof. 502.6 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). Informational Note: See Article 100 for the definition of restricted industrial establishment [as applied to hazardous (classified) locations]. (A) Class II, Division 1. General. In Class II, Division 1 locations, the following wiring methods shall be permitted: Threaded rigid metal conduit (RMC) or threaded intermediate metal conduit (IMC), including conduit systems with supplemental corrosion protection coatings. Type MI cable with termination fittings listed for the location. Type MI cable shall be installed and supported in a manner to avoid tensile stress at the termination fittings. In restricted industrial establishments, 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 termination fittings listed for the location, shall be permitted. Optical fiber cable Type OFNP, Type OFCP, Type OFNR, Type OFCR, Type OFNG, Type OFCG, Type OFN, or Type OFC shall be permitted to be installed in raceways in accordance with 502.10(A). Optical fiber cables shall be sealed in accordance with 502.15. In restricted industrial establishments, listed Type ITC-HL cable with a gas/vaportight continuous corrugated metallic sheath and an overall jacket of suitable polymeric material, and terminated with fittings listed for the application, and installed in accordance with 335.4. In restricted industrial establishments, for applications limited to 600 volts nominal or less, where the cable is not subject to physical damage and is terminated with fittings listed for the location, listed Type TC-ER-HL cable. When installed in ladder, ventilated trough, or ventilated channel cable trays, cables shall be installed in a single layer, with a space not less than the larger cable diameter between the two adjacent cables unless otherwise protected against dust buildup resulting in increased heat, Type TC-ER-HL cable shall be installed in accordance with 336.10. Informational Note No. 1: See ANSI/UL 2225, Cables and Cable-Fittings for Use in Hazardous (Classified) Locations, for construction, testing, and marking of cables and cable fittings. In restricted industrial establishments, listed Type P cable with metal braid armor, with an overall jacket, that is terminated with fittings listed for the location and installed in accordance with 337.10. When installed in ladder, ventilated trough, or ventilated channel cable trays, cables shall be installed in a single layer, with a space not less than the larger cable diameter between the two adjacent cables, unless otherwise protected against dust buildup resulting in increased heat. Informational Note No. 2: See ANSI/UL 1309, Marine Shipboard Cable, for information on construction, testing, and marking of Type P cable. Informational Note No. 3: See ANSI/UL 2225, Cables and Cable-Fittings for Use in Hazardous (Classified) Locations, for information on construction, testing, and marking of cable fittings. Flexible Connections. Where flexible connections are necessary, one or more of the following shall also be permitted: Dusttight flexible connectors. Liquidtight flexible metal conduit (LFMC) with listed fittings and bonded in accordance with 502.30(B). Liquidtight flexible nonmetallic conduit (LFNC) with listed fittings. Interlocked armor Type MC cable having an overall jacket of suitable polymeric material and provided with termination fittings listed for Class II, Division 1 locations. Flexible cord listed for extra-hard usage and terminated with listed dusttight cord connectors. Where used, flexible cords shall comply with 502.140. For elevator use, an identified elevator cable of Type EO, Type ETP, or Type ETT, shown under the “use” column in Table 400.4 for “hazardous (classified) locations” and terminated with listed dusttight fittings. In restricted industrial establishments, for applications limited to 600 volts nominal or less, and where the cable is not subject to physical damage and is terminated with fittings listed for the location, listed Type TC-ER-HL cable. Type TC-ER-HL cable shall be installed in accordance with 336.10. Informational Note No. 1: See ANSI/UL 2225, Cables and Cable-Fittings for Use in Hazardous (Classified) Locations, for construction, testing, and marking of cables and cable fittings. In restricted industrial establishments, listed Type P cable with metal braid armor, with an overall jacket, terminated with fittings listed for the location, and installed in accordance with 337.10. Informational Note No. 2: See UL 1309A, Outline of Investigation for Cable for Use in Mobile Installations, for information on construction, testing, and marking of Type P cable. Informational Note No. 3: See ANSI/UL 2225, Cables and Cable-Fittings for Use in Hazardous (Classified) Locations, for information on construction, testing, and marking of cable fittings. ENHANCED CONTENT Collapse See also 501.10(A)(2) and its enhanced content for information on the use of a flexible fitting. Boxes and Fittings. Boxes and fittings shall be provided with threaded bosses for connection to conduit or cable terminations 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: See ANSI/UL 2225, Cables and Cable-Fittings for Use in Hazardous (Classified) Locations, for information on construction, testing, and marking of cables, dust-ignitionproof cable fittings, and dust-ignitionproof cord connectors for entry into enclosures required to be dust-ignitionproof. (B) Class II, Division 2. Wiring methods installed in Class II, Division 2 locations shall be in accordance with 502.10(B)(1)through (B)(4). General. In Class II, Division 2 locations, the following wiring methods shall be permitted: All wiring methods permitted in 502.10(A). Rigid metal conduit (RMC)or intermediate metal conduit (IMC) with listed threaded or threadless fittings, including conduit systems with supplemental corrosion protection coatings. Dusttight wireways or electrical metallic tubing (EMT) with listed compression-type connectors or listed compression-type couplings. Type MC, Type MV, Type TC, or Type TC-ER cable, including installation in cable tray systems. Type TC-ER cable shall include an equipment grounding conductor in addition to a drain wire that might be present. The cable shall be terminated with listed fittings. Type PLTC cable or Type PLTC-ER cable used in Class 2 or Class 3 circuits, including installation in cable tray systems. The cable shall be terminated with listed fittings. Type PLTC-ER cable shall include an equipment grounding conductor in addition to a drain wire that might be present. Type ITC cable or Type ITC-ER cable as permitted in 335.4 and terminated with listed fittings. Type ITC-ER cable shall include an equipment grounding conductor in addition to a drain wire. In restricted industrial establishments where wiring methods in 502.10(B)(1)(1)(2) will not provide the corrosion resistance required for the installation environment, either of the following: Listed reinforced thermosetting resin conduit (RTRC), factory elbows, and associated fittings, all marked with suffix -XW Schedule 80 PVC conduit, factory elbows, and associated fittings Optical fiber cable Type OFNP, Type OFCP, Type OFNR, Type OFCR, Type OFNG, Type OFCG, Type OFN, or Type OFC, installed in cable trays or any other raceway in accordance with 502.10(B). Optical fiber cables shall be sealed in accordance with 502.15. Cablebus. In restricted industrial establishments, listed Type P cable with or without metal braid armor, with an overall jacket, that is terminated with listed fittings and installed in accordance with 337.10. Informational Note: See UL 1309A, Outline of Investigation for Cable for Use in Mobile Installations, for information on construction, testing, and marking of Type P cable. Flexible Connections. If flexibility is necessary, 502.10(A)(2) shall apply. 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 if the simple apparatus does not interconnect the nonincendive field wiring circuit to any other circuit. Informational Note: See Article 100 for the definition of simple apparatus. Separate nonincendive field wiring circuits shall be installed in accordance with one of the following: (1) In separate cables In multiconductor cables where the conductors of each circuit are within a grounded metal shield In multiconductor cables or in raceways where the conductors of each circuit have insulation with a minimum thickness of 0.25 mm (0.01 in.) Boxes and Fittings. All boxes and fittings shall be dusttight. ENHANCED CONTENT Collapse Boxes and fittings in a Class II, Division 2 location need only be dusttight. In Division 1 locations, however, boxes containing taps, joints, or terminal connections, in addition to being dusttight, must be provided with threaded hubs and must be identified for use in Class II locations. Pictured below is dusttight-covered junction box with threaded hubs, suitable for use in Class II, Group E hazardous atmospheres. (Courtesy of AppletonTM, Emerson Electric Co.) 502.15 Sealing, Class II, Divisions 1 and 2. If 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 A horizontal raceway not less than 3.05 m (10 ft) long A vertical raceway not less than 1.5 m (5 ft) long and extending downward from the dust-ignitionproof enclosure A raceway installed in a manner equivalent to 502.15(2) or (3) that extends only horizontally and downward from the dust-ignition proof enclosures Electrical sealing putty If 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 and shall not be required to be explosionproof. ENHANCED CONTENT Collapse Four suitable ways are provided in 502.15 to prevent dust from entering dust-ignitionproof enclosures through the raceway. Three of these methods for Class II locations are shown in the exhibit below. The requirement to provide a seal applies if a raceway connects two enclosures in a hazardous location — from one enclosure that is required to be dust-ignitionproof to one that is not required to be dust-ignitionproof. Dust could enter the system through the other enclosure that is not dust-ignitionproof. If a raceway extends from a dust-ignitionproof enclosure to an enclosure in an unclassified location, a seal in that raceway is not required since dust will not enter through the conduit system. Seal fittings designed for use in Class I locations are acceptable for Class II locations. However, because the Class I location pressure-piling considerations are not inherent in Class II locations, conduit seals are not required to be explosionproof. Conduit seals are expected only to prevent the migration of dust into dust-ignitionproof enclosures. 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. Regardless of the voltage of the electrical system, wiring systems and equipment shall comply with 502.30(A) and (B). Grounding. Wiring systems and equipment shall be grounded in accordance with Part I and Part VI of Article 250, as applicable. Bonding. Bonding shall comply with Part I and Part V of Article 250, as applicable, and 502.30(B)(1) and (B)(2). Specific Bonding Means. Bonding shall comply with 502.30(B)(1)(a) and (B)(1)(b). The locknut-bushing and double-locknut types of contacts shall not be depended on for bonding purposes, but bonding jumpers with identified fittings or other approved means of bonding shall be used. These bonding means shall apply to all metal raceways, fittings, boxes, cable trays, and enclosures, and other parts of raceway systems between hazardous (classified) locations and the point of grounding for service equipment or point of grounding for a separately derived system. Metal struts, angles, or channels provided for support and mechanical or physical protection as permitted in 335.4(5), 336.10(7)(c), or 722.135(C) shall be bonded in accordance with 250.102. Where the branch-circuit overcurrent protection is located on the load side of the disconnecting means, the specific bonding means shall be permitted to end at the nearest point where the grounded circuit conductor and the grounding electrode conductor are connected together on the line side of the building or structure disconnecting means as specified in 250.32(B). ENHANCED CONTENT Collapse The requirements for enhanced bonding in Class II locations are the same as those given in 501.30(A) for Class I locations. See also 501.30(B)(1) and its enhanced content for more information on specific bonding methods. See 250.100 for additional requirements applying to bonding in hazardous locations. Liquidtight Flexible Metal Conduit. Liquidtight flexible metal conduit shall comply with 502.30(B)(2)(a) and (B)(2)(b). Liquidtight flexible metal conduit shall include an equipment bonding jumper of the wire type in accordance with 250.102. In Class II, Division 2 locations, the bonding jumper shall not be required where all of the following conditions are met: Listed liquidtight flexible metal conduit 1.8 m (6 ft) or less in length, with fittings listed for grounding, is used. Overcurrent protection in the circuit is limited to 10 amperes or less. The load is part of a meter, instrument, or relay circuit. 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. ENHANCED CONTENT Collapse When designing an electrical installation for hazardous locations, the preferred location of service equipment, switchboards, panelboards, and much of the electrical equipment is in less hazardous areas, usually in a separate room. The use of pressurized rooms, as described in NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equipment, is a common method of protecting panelboards and switchboards in grain elevators and similar locations. Class II, Division 1. In Class II, Division 1 locations, transformers and capacitors shall comply with 502.100(A)(1) through (A)(3). 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. 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. Vent openings and ducts shall communicate only with the outside air. Suitable pressure-relief openings communicating with the outside air shall be provided. Not Containing Liquid That Will Burn. Transformers and capacitors that do not contain a liquid that will burn shall be installed in vaults complying with 450.41 through 450.48 or be identified as a complete assembly, including terminal connections. Group E. No transformer or capacitor shall be installed in a Class II, Division 1, Group E location. Class II, Division 2. In Class II, Division 2 locations, transformers and capacitors shall comply with 502.100(B)(1) through (B)(3). 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. Containing Askarel. Transformers containing askarel and rated in excess of 25 kVA shall be as follows: Provided with pressure-relief vents 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 Have an airspace of not less than 150 mm (6 in.) between the transformer cases and any adjacent combustible material 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 ventilating or other openings and shall operate at not over 600 volts, nominal. 502.115 Switches, Circuit Breakers, Motor Controllers, and Fuses. (A) Class II, Division 1. In Class II, Division 1 locations, switches, circuit breakers, motor controllers, fuses, push-buttons, relays, and similar devices shall be provided with enclosures identified for the location. Class II, Division 2. In Class II, Division 2 locations, enclosures for fuses, switches, circuit breakers, and motor controllers, including push buttons, relays, and similar devices, shall be dusttight or otherwise identified for the location. ENHANCED CONTENT Collapse Dust-ignitionproof equipment enclosures can be used in Class II, Division 2 locations, but because of the reduced level of hazard associated with Division 2, dusttight equipment enclosures also are permitted. In addition to being suitable for Class II and the specific division, the equipment also must be suitable for the dust group(s) (i.e., Groups E, F, and G) present in a specific hazardous location. Pictured below is a dust-ignitionproof pushbutton control station suitable for use in Class II, Group E, F, and G locations. (Courtesy of AppletonTM, Emerson Electric Co.) Next is a dust-ignitionproof panelboard for use in Class II, Division 2, Group F and G locations. (Courtesy of Eaton, Crouse-Hinds Division) 502.120 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 be provided with enclosures identified for the location. (