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ltaneous presence of the specific materials shall be considered when determining the safe operating temperature of the electrical equipment. ENHANCED CONTENT Collapse Examples of where flammable liquid and dust might be simultaneously present are at a coal-handling facility, where there is methane g...

ltaneous presence of the specific materials shall be considered when determining the safe operating temperature of the electrical equipment. ENHANCED CONTENT Collapse Examples of where flammable liquid and dust might be simultaneously present are at a coal-handling facility, where there is methane gas and coal dust, and in an automotive paint spray shop, where flammable paint and powdered metal flecks are sprayed. In the presence of such a combination of simultaneous hazards, less energy may be needed, and the accumulation of gas need not be in the flammable range for an ignition to occur. Marking. Equipment shall be marked to show the environment for which it has been evaluated. Unless otherwise specified or allowed in 500.8(C)(6), the marking shall include the information specified in 500.8(C)(1) through (C)(5). Class. The marking shall specify the class(es) for which the equipment is suitable. Division. The marking shall specify the division if the equipment is suitable for Division 2 only. Equipment suitable for Division 1 shall be permitted to omit the division marking. Informational Note: See 500.8(B)(2). Equipment not marked to indicate a division, or marked “Division 1” or “Div. 1,” is suitable for both Division 1 and Division 2 locations. Equipment marked “Division 2” or “Div. 2” is suitable for Division 2 locations only. (3) Material Classification Group. The marking shall specify the applicable material classification group(s) or specific gas, vapor, dust, or fiber/flying in accordance with 500.6. Exception: Fixed luminaires marked for use only in Class I, Division 2 or Class II, Division 2 locations shall not be required to indicate the group. Informational Note: A specific gas, vapor, dust, or fiber/flying is typically identified by the generic name, chemical formula, CAS number, or combination thereof. (4) Equipment Temperature. The marking shall specify the temperature class or operating temperature at a 40°C ambient temperature, or at the higher ambient temperature if the equipment is rated and marked for an ambient temperature of greater than 40°C. For equipment installed in a Class II, Division 1 location, the temperature class or operating temperature shall be based on operation of the equipment when blanketed with the maximum amount of dust that can accumulate on the equipment. The temperature class, if provided, shall be indicated using the temperature class (T codes) shown in Table 500.8(C)(4). Equipment for Class I and Class II shall be marked with the maximum safe operating temperature, as determined by simultaneous exposure to the combinations of Class I and Class II conditions. Table 500.8(C)(4) Classification of Maximum Surface Temperature Maximum Temperature Temperature Class (T Code) °C °F 450 842 T1 300 572 T2 280 536 T2A 260 500 T2B 230 446 T2C 215 419 T2D 200 392 T3 180 356 T3A 165 329 T3B 160 320 T3C 135 275 T4 120 248 T4A 100 212 T5 85 185 T6 Exception: Equipment of the non–heat-producing type, such as junction boxes, conduit, and fittings, and equipment of the heat-producing type having a maximum temperature not more than 100°C shall not be required to have a marked operating temperature or temperature class. Informational Note: More than one marked temperature class or operating temperature, for gases and vapors, dusts, and different ambient temperatures, may appear. (5) Ambient Temperature Range. Electrical equipment designed for use in the ambient temperature range between –⁠25°C to +40°C shall require no ambient temperature marking. For equipment rated for a temperature range other than –25°C to +40°C, the marking shall specify the special range of ambient temperatures in degrees Celsius. The marking shall include either the symbol “Ta” or “Tamb.” Informational Note: As an example, such a marking might be “–⁠30°C ≤ Ta ≤ +40°C.” (6) Special Allowances. (a) General-Purpose Equipment. Fixed general-purpose equipment in Class I locations, other than fixed luminaires, that is acceptable for use in Class I, Division 2 locations shall not be required to be marked with the class, division, group, temperature class, or ambient temperature range. Dusttight Equipment. Fixed dusttight equipment, other than fixed luminaires, that is acceptable for use in Class II, Division 2 and Class III locations shall not be required to be marked with the class, division, group, temperature class, or ambient temperature range. Associated Apparatus. Associated intrinsically safe apparatus and associated nonincendive field wiring apparatus that are not protected by an alternative type of protection shall not be marked with the class, division, group, or temperature class. Associated intrinsically safe apparatus and associated nonincendive field wiring apparatus shall be marked with the class, division, and group of the apparatus to which it is to be connected. Simple Apparatus. “Simple apparatus” as defined in Article 100 Part III, shall not be required to be marked with class, division, group, temperature class, or ambient temperature range. Temperature. Class I Temperature. The temperature marking specified in 500.8(C) shall not exceed the autoignition temperature of the specific gas or vapor to be encountered. Informational Note: See NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, for information on autoignition temperatures of gases and vapors. ENHANCED CONTENT Collapse Electrical equipment intended for installation in a hazardous location is evaluated for maximum temperatures regardless of the type of protection afforded the equipment. Gases and vapors are qualified with an autoignition temperature, and dusts are qualified with a layer or cloud ignition temperature, each of which is the temperature at which the material ignites. The equipment temperature is compared to these material temperatures to determine if a potential for a thermal ignition exists. The autoignition temperature of a solid, liquid, or gaseous substance is the minimum temperature required to initiate or cause self-sustained combustion independent of the heating or heated element. The flash point is the minimum temperature at which a liquid gives off enough vapor to form an ignitible mixture with air. The ignition temperature and the flash point are unrelated properties, except that the flash point is always lower than the ignition temperature. Class II Temperature. The temperature marking specified in 500.8(C) shall be less than the ignition temperature of the specific dust or metal fiber/flying to be encountered. For organic dusts that might dehydrate or carbonize, the temperature marking shall not exceed the lower of either the ignition temperature or 165°C (329°F). Informational Note: See NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, for minimum ignition temperatures of specific dusts. (3) Class III Temperature. The temperature marking specified in 500.8(C) shall be less than the ignition temperature of the specific fiber/flying to be encountered, except as specified in 500.8(D)(3)(a) or (D)(3)(b). (a) For nonmetal combustible fibers/flyings that might dehydrate or carbonize, the temperature marking shall not exceed the lower of either the ignition temperature or 165°C (329°F). When ignitible fibers/flyings are present, 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 might be overloaded. Threading. The supply connection entry thread form shall be NPT or metric. Conduit and fittings shall be made wrenchtight to prevent sparking when fault current flows through the conduit system, and to ensure the explosionproof integrity of the conduit system where applicable. Equipment provided with threaded entries for field wiring connections shall be installed in accordance with 500.8(E)(1) or (E)(2) and with (E)(3). ENHANCED CONTENT Collapse To ensure the integrity of the ground-fault current path of the conduit system, all conduit joints must be made up wrenchtight to prevent ignition-capable arcing between the conduit and the coupling, fitting, or enclosure under ground-fault conditions. The use of a bonding jumper in lieu of a wrenchtight connection is not permitted. Equipment Provided with Threaded Entries for NPT-Threaded Conduit or Fittings. For equipment provided with threaded entries for NPT-threaded conduit or fittings, listed conduit, listed conduit fittings, or listed cable fittings shall be used. All NPT-threaded conduit and fittings shall be threaded with a National (American) Standard Pipe Taper (NPT) thread. NPT-threaded entries into explosionproof equipment shall be made up with at least five threads fully engaged. Exception: For listed explosionproof equipment, joints with factory-threaded NPT entries shall be made up with at least four and one-half threads fully engaged. Informational Note No. 1: See ASME B1.20.1, Pipe Threads, General Purpose (Inch), for thread specifications for male NPT threads. Informational Note No. 2: See ASME B1.20.1, Pipe Threads, General Purpose (Inch), and ANSI/UL 1203, Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Hazardous (Classified) Locations, for information on female NPT-threaded entries using modified National Standard Pipe Taper (NPT) threads. Equipment Provided with Threaded Entries for Metric-Threaded Fittings. For equipment with metric-threaded entries, listed conduit fittings or listed cable fittings shall be used. Such entries shall be identified as being metric, or listed adapters to permit connection to conduit or NPT-threaded fittings shall be provided with the equipment and shall be used for connection to conduit or NPT-threaded fittings. Metric-threaded fittings installed into explosionproof equipment shall have a class of fit of at least 6g/6H and shall be made up with at least five threads fully engaged. Informational Note: See ISO 965-1, ISO general purpose metric screw threads — Tolerances — Part 1: Principles and basic data, and ISO 965-3, ISO general purpose metric screw threads — Tolerances — Part 3: Deviations for constructional screw threads, for threading specifications for metric-threaded entries. (3) Unused Openings. All unused openings shall be closed with blanking elements or close-up plugs that are listed for the location. The thread engagement shall comply with the requirements of 500.8(E)(1) or (E)(2). Optical Fiber Cables. An optical fiber cable, with or without current-carrying conductors (hybrid optical fiber cable), shall be installed to address the associated fire hazard and sealed to address the associated explosion hazard in accordance with Part II of Articles 501, 502, or 503, as applicable. Equipment Involving Optical Radiation. The risk of ignition from optical radiation shall be evaluated for laser equipment,optical fiber equipment, and any other convergent light sources or beams where light is focused in one single point within a hazardous area with a wavelength range of 380 nm to 10 μm. This requirement shall include optical equipment that is located outside the explosive atmosphere, but whose emitted optical radiation enters such atmospheres. Informational Note: See ANSI/UL 60079-28, Explosive Atmospheres — Part 28: Protection of Equipment and Transmission Systems Using Optical Radiation, for information on types of protection that can be applied to minimize the risk of ignition in explosive atmospheres from optical radiation.Article 501 Class I Locations Part I. General 501.1 Scope. This article covers the requirements for electrical and electronic equipment and wiring for all voltages in Class I, Division 1 and Division 2 locations where flammable gases, flammable liquid–produced vapors, or combustible liquid–produced vapors are or might be present in the air in quantities sufficient to produce explosive or ignitible mixtures. ENHANCED CONTENT Collapse Where ignitible concentrations (concentrations within flammable or explosive limits) are present, the atmosphere can be ignited by an arc, spark, or high temperature. NFPA 497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, includes information on the flammable limits of liquids and gases. Electrical equipment that can cause ignition-capable arcs or sparks should be kept out of Class I locations, or the equipment must be identified for the appropriate hazardous location. It is practically impossible to make threaded joints gastight. The conduit system and apparatus enclosure “breathe” due to temperature changes, and any flammable gases or vapors in the room may slowly enter the conduit or enclosure, creating an explosive mixture. If an arc occurs, an explosion could also occur. When an explosion occurs within the enclosure or conduit system, the burning mixture or hot gases must be sufficiently confined within the system to prevent ignition of any explosive mixture outside the system. 501.5 Zone Equipment. Equipment listed and marked in accordance with 505.9(C)(2) for use in Zone 0, 1, or 2 locations shall be permitted in Class I, Division 2 locations for the same gas and with a suitable temperature class. Equipment listed and marked in accordance with 505.9(C)(2) for use in Zone 0 locations shall be permitted in Class I, Division 1 or Division 2 locations for the same gas and with a suitable temperature class. Part II. Wiring 501.10 Wiring Methods. Wiring methods shall comply with 501.10(A) or (B). Class I, Division 1. General. In Class I, Division 1 locations, the following wiring methods shall be permitted: Informational Note No. 1: See Article 100 for the definition of restricted industrial establishment [as applied to hazardous (classified) locations]. Threaded rigid metal conduit (RMC) or threaded intermediate metal conduit (IMC), including RMC or IMC conduit systems with supplemental corrosion protection coatings. PVC conduit, RTRC conduit, or HDPE conduit, where encased in a concrete envelope a minimum of 50 mm (2 in.) thick and provided with not less than 600 mm (24 in.) of cover measured from the top of the conduit to grade. The concrete encasement shall be permitted to be omitted where it is in accordance with 514.8(C) or 515.8(A). RMC or IMC conduit shall be used for the last 600 mm (24 in.) of the underground run to emergence or to the point of connection to the aboveground raceway. An equipment grounding conductor shall be included to provide for electrical continuity of the raceway system and for grounding of non–current-carrying metal parts. Type MI cable terminated with fittings listed for the location. Type MI cable shall be installed and supported to avoid tensile stress at the termination fittings. In restricted industrial establishments, Type MC-HL cable listed for use in Class I, Zone 1 or Division 1 locations, with a gas/vaportight continuous corrugated metallic sheath, an overall jacket of suitable polymeric material, and a separate equipment grounding conductor(s) in accordance with 250.122, and terminated with fittings listed for the application. If installed in a ladder, ventilated trough, or ventilated channel cable tray, the cable shall be installed in accordance with 392.22. Type MC-HL cable shall be installed in accordance with Part II of Article 330. In restricted industrial establishments, Type ITC-HL cable listed for use in Class I, Division 1 or Zone 1 locations, with a gas/vaportight continuous corrugated metallic sheath and an overall jacket of suitable polymeric material, terminated with fittings listed for the application, and installed in accordance with 335.4. Optical fiber cable Type OFNP, Type OFCP, Type OFNR, Type OFCR, Type OFNG, Type OFCG, Type OFN, or Type OFC installed in raceways in accordance with 501.10(A). These optical fiber cables shall be sealed in accordance with 501.15. 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, Type TC-ER-HL cable. If installed in a ladder, ventilated trough, or ventilated channel cable tray, the cable shall be installed in accordance with 392.22. Type TC-ER-HL cable shall be listed for use in Class I, Division 1 or Zone 1 locations and shall be installed in accordance with 336.10. Informational Note No. 2: See ANSI/UL 2225, Cables and Cable-Fittings for Use in Hazardous (Classified) Locations, for information on construction, testing, and marking of cables and cable fittings. In restricted industrial establishments, listed Type P cable with metal braid armor and an overall jacket, terminated with fittings listed for the location, and installed in accordance with Part II of Article 337. If installed in a ladder, ventilated trough, or ventilated channel cable tray, the cable shall be installed in accordance with 392.22. Informational Note No. 3: 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. 4: See ANSI/UL 2225, Cables and Cable-Fittings for Use in Hazardous (Classified) Locations, for information on construction, testing, and marking of cable. ENHANCED CONTENT Collapse Regarding item (3) of 501.10(A)(1), a termination fitting used in a Division 1 location with Type MI cable must be specifically listed for use in Class I, Division 1 hazardous locations. Shown below is an example of this type of cable and fitting in which the screw-on pot contains field-installed sealing compound to seal the end of the cable. The threaded gland has threads for connection to explosionproof enclosures. (Courtesy of Tyco Thermal Controls) Flexible Connections. If flexibility is necessary to minimize the transmission of vibration from equipment during operation or to allow for movement after installation during maintenance, one of the following shall be permitted: Flexible fittings listed for the location. Flexible cord in accordance with 501.140, terminated with cord connectors listed for the location. 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, Type TC-ER-HL cable. The cable shall be listed for use in Class I, Division 1 or Zone 1 locations and 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 information on construction, testing, and marking of cables and cable fittings. In restricted industrial establishments, listed Type P cable with metal braid armorand an overall jacket where the cable is terminated with fittings listed for the location and installed in accordance with Part II of Article 337. 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 fittings. 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 This section refers to a connection to equipment that requires flexibility, not to a flexible wiring method. For wiring methods where a flexible connection is no longer necessary, refer to 501.10(A)(1). Four options are presented if a length of flexible connection is necessary. Listed flexible fittings commonly used at motor connections can withstand continuous vibration for long periods and provide maximum protection to enclosed conductors. Limited use of flexible cord is permitted in accordance with 501.140 for specific applications where flexibility is made necessary by the type of equipment being supplied. Type TC-ERHL or Type P is permitted in industrial establishments where a flexible connection is necessary. The requirement in 501.15(A)(1) to provide a seal within 18 inches of an explosionproof enclosure applies where flexible connections are used. Boxes and Fittings. All boxes and fittings shall be identified for Class I, Division 1. Informational Note No. 1: See ANSI/UL 2225, Cables and Cable-Fittings for Use in Hazardous (Classified) Locations, for information on construction, testing, and marking of cables, explosionproof cable fittings, and explosionproof cord connectors for entry into enclosures required to be explosionproof. Informational Note No. 2: See ANSI/UL 1203, Explosion-Proof and Dust-Ignition-Proof Electrical Equipment for Use in Hazardous (Classified) Locations, for information on construction, testing, and marking of explosionproof conduit fittings for entry into enclosures required to be explosionproof. ENHANCED CONTENT Collapse An explosionproof junction box with two hubs and a threaded opening for the screw-type cover is pictured below. Unused openings must be effectively closed by inserting threaded metal plugs that engage at least five full threads [4½ permitted in accordance with the exception to 500.8(E)] and afford protection equivalent to that of the box wall. (Courtesy of O-Z/Gedney, Emerson Electric Co.) Class I, Division 2. General. In Class I, Division 2 locations, all wiring methods in accordance with 501.10(A) and the following wiring methods shall be permitted: Informational Note No. 1: See Article 100 for the definition of restricted industrial establishment [as applied to hazardous (classified) locations]. Rigid metal conduit (RMC) or intermediate metal conduit (IMC) with listed threaded or threadless fittings, including RMC or IMC conduit systems with supplemental corrosion protection coatings. Enclosed gasketed busways and enclosed gasketed wireways. Type PLTC cable or Type PLTC-ER cable used for Class 2 and 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. 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. All cable types shall be terminated with listed fittings. Where metal conduit will not provide the corrosion resistance needed for the installation environment, any of the following shall be permitted: Listed reinforced thermosetting resin conduit (RTRC), factory elbows, and associated fittings, all marked with the suffix -XW PVC-coated RMC, factory elbows, and associated fittings PVC-coated IMC, factory elbows, and associated fittings In restricted industrial establishments, 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 501.10(B). Optical fiber cables shall be sealed in accordance with 501.15. Cablebus. In restricted industrial establishments, listed Type P cable with or without metal braid armor, with an overall jacket, and terminated with fittings listed for the location when entering explosionproof, flameproof, or pressurized equipment. The cable shall be installed in accordance with Part II of Article 337. Informational Note No.