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2: See ANSI/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 const...

2: See ANSI/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. 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 or more of the following shall be permitted: Listed flexible metal fittings Flexible metal conduit with listed fittings and bonded in accordance with 501.30(B) Interlocked armor Type MC cable with listed fittings Liquidtight flexible metal conduit with listed fittings and bonded in accordance with 501.30(B) Liquidtight flexible nonmetallic conduit with listed fittings Flexible cord listed for extra-hard usage and terminated with listed fittings, with a conductor for use as an equipment grounding conductor 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 fittings In restricted industrial establishments, listed Type P cable with or without metal braid armor, with an overall jacket, terminated with listed fittings and installed in accordance with Part II of Article 337 ENHANCED CONTENT Collapse Where necessary, limited flexibility is provided through use of wiring methods with listed fittings such as flexible metal conduit (FMC), liquidtight flexible metal conduit (LFMC), and extra-hard-usage flexible cord. However, the fittings are not required to be specifically identified for Class I locations. See also 501.10(A)(2) and its enhanced content for more information on flexible connections. 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.) ENHANCED CONTENT Collapse Although many low-voltage, low-energy circuits, including some communications circuits and thermocouple circuits, are of the nonincendive type, a Class 2 or Class 3 circuit, as defined in Article 725, is not necessarily nonincendive. See also Article 100 for the definitions of the terms nonincendive circuit and nonincendive field wiring. Boxes and Fittings. Boxes and fittings shall be explosionproof if required by 501.105(B)(2), 501.115(B)(1), or 501.150(B)(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 cable 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 In Class I, Division 2 locations, boxes, fittings, and joints are not required to be explosionproof if they contain no arcing devices. They also are not required to be explosionproof for lighting outlets or enclosures containing nonarcing devices (such as solid-state relays, solenoids, and control transformers), if the maximum operating temperature of any exposed surface does not exceed 80 percent of the ignition temperature. 501.15 Sealing and Drainage. Seals in conduit and cable systems shall comply with 501.15(A) through (F). Sealing compound shall be used in Type MI cable termination fittings to exclude moisture and other fluids from the cable insulation. Informational Note No. 1: Seals are provided in conduit and cable systems to minimize the passage of gases and vapors and prevent the passage of flames from one portion of the electrical installation to another through the conduit. Such communication through Type MI cable is inherently prevented by construction of the cable. Unless specifically designed and tested for the purpose, conduit and cable seals are not intended to prevent the passage of liquids, gases, or vapors at a continuous pressure differential across the seal. Even at differences in pressure across the seal equivalent to a few inches of water, there may be a slow passage of gas or vapor through a seal and through conductors passing through the seal. Temperature extremes and highly corrosive liquids and vapors can affect the ability of seals to perform their intended function. Informational Note No. 2: Gas or vapor leakage and propagation of flames may occur through the interstices between the strands of standard stranded conductors larger than 2 AWG. Special conductor constructions, such as compacted strands or sealing of the individual strands, are means of reducing leakage and preventing the propagation of flames. ENHANCED CONTENT Collapse Because the sealing compound used in conduit seal fittings is typically somewhat porous, gases, particularly those under slight pressure and those with small molecules such as hydrogen, could pass slowly through the compound. Because the seal is around the insulation on the conductor, gases can be transmitted slowly through the air spaces (the interstices) between strands of stranded conductors. Under normal conditions for smaller conductors with only normal atmospheric pressure differentials across the seal, the passage of gas through a seal is not sufficient to result in a hazard. For larger conductors, gas or vapor leakage and flame propagation can occur through the interstices. Special conductor constructions, such as compacted strands or sealing individual strands, may reduce leakage and prevent flame propagation. Different sealing compounds have different rates of expansion and contraction that can affect their performance within a given fitting. Tapes or compounds on conduit threads can weaken the seal fitting and interrupt the equipment grounding path. Tabular summaries of the conduit and cable sealing requirements in this section can be found in the Related Resources section below. Related Resources Cable Sealing Requirements (Class 1 locations) DOCUMENT Conduit Sealing Requirements (Class 1 locations) DOCUMENT (A) Conduit Seals, Class I, Division 1. In Class I, Division 1 locations, conduit seals shall be located in accordance with 501.15(A)(1) through (A)(4). Entering Enclosures. Each conduit entry into an explosionproof enclosure shall have a conduit seal where either of the following conditions apply: The enclosure contains apparatus, such as switches, circuit breakers, fuses, relays, or resistors that may produce arcs, sparks, or temperatures that exceed 80 percent of the autoignition temperature, in degrees Celsius, of the gas or vapor involved in normal operation. Exception: Seals shall not be required for conduit entering an enclosure under any one of the following conditions: The switch, circuit breaker, fuse, relay, or resistor is enclosed within a chamber hermetically sealed against the entrance of gases or vapors. The switch, circuit breaker, fuse, relay, or resistor is immersed in oil in accordance with 501.115(B)(1)(2). The switch, circuit breaker, fuse, relay, or resistor is enclosed within an enclosure, identified for the location, and marked “Leads Factory Sealed,” or “Factory Sealed,” “Seal not Required,” or equivalent. The switch, circuit breaker, fuse, relay, or resistor is part of a nonincendive circuit. The entry is metric designator 53 (trade size 2) or larger, and the enclosure contains terminals, splices, or taps. An enclosure, identified for the location, and marked “Leads Factory Sealed”, or “Factory Sealed,” or “Seal not Required,” or equivalent shall not be considered to serve as a seal for another adjacent enclosure that is required to have a conduit seal. Conduit seals shall be installed within 450 mm (18 in.) from the enclosure or as required by the enclosure marking. Only threaded couplings, or explosionproof fittings such as unions, reducers, elbows, and capped elbows that are not larger than the trade size of the conduit, shall be permitted between the sealing fitting and the explosionproof enclosure. ENHANCED CONTENT Collapse A seal fitting must be placed within 18 inches of the entrance of trade size 2 or larger conduit into any explosionproof enclosure, regardless of whether the enclosure contains arcing or sparking equipment or only splices, taps, or terminals. Conduit seals are to prevent an explosion from traveling through the conduit to another enclosure and to minimize the passage of gases or vapors from hazardous locations to nonhazardous locations. Pressurized Enclosures. Conduit seals shall be installed within 450 mm (18 in.) of the enclosure in each conduit entry into a pressurized enclosure where the conduit is not pressurized as part of the protection system. Informational Note No. 1: Installing the seal as close as possible to the enclosure will reduce problems with purging the dead airspace in the pressurized conduit. Informational Note No. 2: See NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equipment, for information regarding pressurized enclosures. (3) Two or More Explosionproof Enclosures. Where two or more explosionproof enclosures that require conduit seals are connected by nipples or runs of conduit not more than 900 mm (36 in.) long, a single conduit seal in each such nipple connection or run of conduit shall be considered sufficient if the seal is located not more than 450 mm (18 in.) from either enclosure. ENHANCED CONTENT Collapse If two enclosures are spaced within 36 inches of each other, as illustrated by Enclosures No. 1 and No. 2 below, a single seal may be placed between two connecting nipples if the seal is located not more than 18 inches from either enclosure and if no additional conduit fittings exist between the enclosures, such as a “T” fitting. If such a “T”, or other conduit body, fitting exists, then a seal between each enclosure and the “T”, or conduit body fitting, is necessary. Class I, Division 1 Boundary. A conduit seal shall be required in each conduit run leaving a Division 1 location. The sealing fitting shall be permitted to be installed on either side of the boundary within 3.05 m (10 ft) of the boundary, and it shall be designed and installed to minimize the amount of gas or vapor within the portion of the conduit installed in the Division 1 location that can be communicated beyond the seal. The conduit run between the conduit seal and the point at which the conduit leaves the Division 1 location shall contain no union, coupling, box, or other fitting except for a listed explosionproof reducer installed at the conduit seal. Where the seal is located on the Division 2 side of the boundary, the Division 1 wiring method shall extend into the Division 2 area to the seal. Exception No. 1: Metal conduit that contains no unions, couplings, boxes, or fittings, that passes completely through a Division 1 location with no fittings installed within 300 mm (12 in.) of either side of the boundary, shall not require a conduit seal if the termination points of the unbroken conduit are located in unclassified locations. Exception No. 2: For underground conduit installed in accordance with 300.5 where the boundary is below grade, the sealing fitting shall be permitted to be installed after the conduit emerges from below grade, but there shall be no union, coupling, box, or fitting, other than listed explosionproof reducers at the sealing fitting, in the conduit between the sealing fitting and the point at which the conduit emerges from below grade. ENHANCED CONTENT Collapse A seal fitting is required at the boundary where the conduit leaves a Division 1 location or passes from a Division 2 location to an unclassified location per 501.15(B)(2). The seal is permitted on either side of the boundary, and no union, coupling, box, or similar fitting is permitted between the seal and the boundary. However, listed explosionproof reducers are permitted to be installed at the conduit seal. The seal is best located on the nonhazardous side of the boundary, where it serves two purposes: completion of the explosionproof wiring method and completion of the explosionproof enclosure system. For example, even though a conduit seal is not required for ½-inch conduit connected to an explosionproof box that contains only splices, the required seal at the boundary of the Division 1 location serves to complete the explosionproof system. The seal at the boundary also prevents the conduit system from serving as a pipe to transmit flammable mixtures from either a Division 1 or a Division 2 location to an unclassified location. The following exhibit illustrates a Class I, Division 1 location where the enclosures for the disconnecting means and motor controller for the motor (right portion of the drawing) are placed on the other side of the wall in a nonhazardous location and are not required to be explosionproof. Each of the three conduits shown is sealed on the nonhazardous side before it enters the hazardous location, in accordance with 501.15(A)(4). The pigtail leads of both motors are factory sealed at the motor-terminal housing, and, unless the size of the flexible fitting entering the motor-terminal housing is trade size 2 or larger, no other seals are needed at that point. Because the pushbutton control station and the combination switch and starter are considered arc-producing devices, conduits are sealed within 18 inches of the entrance to those enclosures. Seals are required even if the contacts are immersed in oil if the conduit is trade size 2 or larger. Additionally, the exhibit shows a seal provided within 18 inches of the switch controlling the lighting. Because the explosionproof luminaire has an explosionproof chamber for the wiring that is separated or sealed from the lamp compartment, a separate seal is not required adjacent to this luminaire. Conduit Seals, Class I, Division 2. In Class I, Division 2 locations, conduit seals shall be located in accordance with 501.15(B)(1) and (B)(2). Entering Enclosures. For connections to enclosures that are required to be explosionproof, a conduit seal shall be provided in accordance with 501.15(A)(1)(1) and (A)(3). All portions of the conduit run or nipple between the seal and enclosure shall comply with 501.10(A). ENHANCED CONTENT Collapse An enclosure will not be explosionproof if the necessary conduit seals are not provided. Seals complete the explosionproof enclosure. Class I, Division 2 Boundary. A conduit seal shall be required in each conduit run leaving a Class I, Division 2 location. The sealing fitting shall be permitted to be installed on either side of the boundary within 3.05 m (10 ft) of the boundary and it shall be designed and installed to minimize the amount of gas or vapor within the portion of the conduit instal⁠led in the Division 2 location that can be communicated beyond the seal. Wiring methods permitted in 501.10(B)(1)(1) or (B)(1)(6) shall be used between the sealing fitting and the point at which the conduit leaves the Division 2 location, and a threaded connection shall be used at the sealing fitting. The conduit run between the conduit seal and the point at which the conduit leaves the Division 2 location shall contain no union, coupling, box, or other fitting except for a listed explosionproof reducer installed at the conduit seal. Such seals shall not be required to be explosionproof but shall be identified for the purpose of minimizing the passage of gases permitted under normal operating conditions and shall be accessible. Informational Note No. 1: See ANSI/UL 514B, Conduit, Tubing, and Cable Fittings, for additional information. Exception No. 1: Metal conduit that contains no unions, couplings, boxes, or fittings and that passes completely through a Division 2 location with no fittings installed within 300 mm (12 in.) of either side of the boundary shall not require a seal if the termination points of the unbroken conduit are located in unclassified locations. Exception No. 2: Conduit terminating in an unclassified location where the metal conduit transitions to cable tray, cablebus, ventilated busway, or Type MI cable, or to cable not installed in any cable tray or raceway system, shall not require a seal where passing from the Division 2 location into the unclassified location under the following conditions: (1) The unclassified location is outdoors, or the unclassified location is indoors and the conduit system is entirely in one room. (2) The conduits do not terminate at an enclosure containing an ignition source in normal operation. Exception No. 3: Conduit passing from an enclosure or a room permitted to use general-purpose equipment as a result of pressurization into a Division 2 location shall not require a seal at the boundary. Informational Note No. 2: See NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equipment, for further information. Exception No. 4: Aboveground conduit shall not require a seal where passing from a Division 2 location into an unclassified location if all of the following conditions are met: (1) No part of the conduit passes through a Division 1 location where the conduit contains unions, couplings, boxes, or fittings that are located within 300 mm (12 in.) of the Division 1 location. (2) The conduit is located entirely outdoors. (3) The conduit is not directly connected to canned pumps, process or service connections for flow, pressure, or analysis measurement, and so forth, that depend on a single compression seal, diaphragm, or tube to prevent flammable or combustible fluids from entering the conduit system. (4) The conduit contains only threaded metal conduit, unions, couplings, conduit bodies, and fittings in the unclassified location. (5) The conduit is sealed at its entry to each enclosure or fitting located in the Division 2 location that contains terminals, splices, or taps. (C) Class I, Divisions 1 and 2. Seals installed in Class I, Division 1 and Division 2 locations shall comply with 501.15(C)(1) through (C)(6). Exception: Seals that are not required to be explosionproof by 501.15(B)(2) or 504.70 shall not be required to comply with 501.15(C). (1) Fittings. Enclosures that contain connections or equipment shall be provided with an integral sealing means, or sealing fittings listed for the location shall be used. Sealing fittings shall be listed for use with one or more specific compounds and shall be accessible. ENHANCED CONTENT Collapse Fittings should be sealed with only the sealing compound or compounds specified by the manufacturer’s instructions furnished with the fitting. Compound. The compound shall provide a seal to minimize the passage of gas and/or vapors through the sealing fitting and shall not be affected by the surrounding atmosphere or liquids. The melting point of the compound shall not be less than 93°C (200°F). Thickness of Compounds. The thickness of the sealing compound installed in completed seals, other than listed cable sealing fittings, shall not be less than the metric designator (trade size) of the sealing fitting expressed in the units of measurement employed; however, in no case shall the thickness of the compound be less than 16 mm (5⁄8 in.). ENHANCED CONTENT Collapse Below is a cutaway of a seal fitting containing sealing compound and conductors. All conductors must be separated to permit the compound to run between them. The compound must have a minimum thickness of not less than the trade size of the conduit and never less than ⅝ inch. To eliminate the time-consuming task of field-poured seals, a factory-sealed device with the seal designed into the device is permissible. (Courtesy of AppletonTM, Emerson Electric Co.) Splices and Taps. Splices and taps shall not be made in fittings intended only for sealing with compound; nor shall other fittings in which splices or taps are made be filled with compound. Assemblies. An entire assembly shall be identified for the location where the equipment that may produce arcs, sparks, or high temperatures is located in a compartment that is separate from the compartment containing splices or taps, and an integral seal is provided where conductors pass from one compartment to the other. In Division 1 locations, seals shall be provided in conduit connecting to the compartment containing splices or taps where required by 501.15(A)(1)(2). Conductor or Optical Fiber Fill. The cross-sectional area of the conductors or optical fiber tubes (metallic or nonmetallic) permitted in a seal shall not exceed 25 percent of the cross-sectional area of a rigid metal conduit of the same trade size unless the seal is specifically identified for a higher percentage of fill. ENHANCED CONTENT Collapse The maximum permitted fill for most conduit seals is 25 percent, which is less than permitted for most conduit applications. If the conduit fill exceeds 25 percent of the cross-sectional area of the seal fitting, a larger trade size or expanded seal might be required. Reducers are allowed for connection of a larger trade size seal fitting to the conduit per 501.15(A)(1). Cable Seals, Class I, Division 1. In Division 1 locations, cable seals shall be located according to 501.15(D)(1) through (D)(3). At Terminations. Cables shall be sealed at all terminations with sealing fittings. The seals at all terminations shall be in accordance with 501.15(C) and shall be installed within 450 mm (18 in.) of the enclosure or as required by the enclosure marking. Only threaded couplings or explosionproof fittings such as unions, reducers, elbows, and capped elbows not larger than the trade size of the conduit shall be permitted between the sealing fitting and the enclosure. Type MC-HL cable with a gas/vaportight continuous corrugated metallic sheath and an overall jacket of suitable polymeric material, Type TC-ER-HL cable, and Type P cable shall be sealed with a listed fitting after the jacket and any other covering have been removed so that the sealing compound can surround each individual insulated conductor to minimize the passage of gases and vapors. Shielded cables and twisted pair cables that have their conductors sealed in accordance with the instructions provided with their listed fitting to minimize the entrance of gases or vapors and prevent propagation of flame into the cable core shall not be required to have the shielding material removed or the twisted pairs separated. ENHANCED CONTENT Collapse The sealing requirements for cables installed in Class I, Division 1 locations differ from the requirements for sealing conduits. Unlike 501.15(A) for conduits, 501.15(D)(1) requires cables to be sealed at all terminations regardless of the type of equipment contained in the enclosure or the cable diameter. Type MC-HL cable is specifically listed for use as a wiring method in Class I, Division 1 locations. An example of a cable seal fitting for Type MC-HL cable is pictured below. (Courtesy of Eaton, Crouse-Hinds Division) Cables Capable of Transmitting Gases or Vapors. Cables with a gas/vaportight continuous sheath capable of transmitting gases or vapors through