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. Regardless of the voltage of the electrical system, wiring systems and equipment shall comply with 503.30(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...

. Regardless of the voltage of the electrical system, wiring systems and equipment shall comply with 503.30(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 503.30(B)(1) and (B)(2). Specific Bonding Means. Bonding shall comply with 503.30(B)(1)(a) and (B)(2)(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 III locations are the same as those for Class I and Class II locations. See also 501.30(B)(1) and its enhanced content for more information on grounding and bonding requirements. See 250.100 for additional requirements applying to bonding in hazardous locations. Liquidtight Flexible Metal Conduit. Liquidtight flexible metal conduit shall comply with 503.30(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 III 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. Part III. Equipment 503.100 Transformers and Capacitors — Class III, Divisions 1 and 2. Transformers and capacitors shall comply with 502.100(B). 503.115 Switches, Circuit Breakers, Motor Controllers, and Fuses — Class III, Divisions 1 and 2. Switches, circuit breakers, motor controllers, and fuses, including pushbuttons, relays, and similar devices, shall be provided with dusttight enclosures. 503.120 Control Transformers and Resistors — Class III, Divisions 1 and 2. Transformers, impedance coils, and resistors used as, or in conjunction with, control equipment for motors, generators, and appliances shall be provided with dusttight enclosures complying with the temperature limitations in 503.5. 503.125 Motors and Generators — Class III, Division 1 and Division 2. In Class III, Division 1 and Division 2 locations, motors, generators, and other rotating machinery shall be totally enclosed nonventilated, totally enclosed pipe ventilated, or totally enclosed fan cooled. Exception: In locations where, in the judgment of the authority having jurisdiction, only moderate accumulations of ignitible fibers/flyings are likely to collect on, in, or in the vicinity of a rotating electrical machine and where such machine is readily accessible for routine cleaning and maintenance, one of the following shall be permitted: (1) Self-cleaning textile motors of the squirrel-cage type (2) Standard open-type machines without sliding contactsor centrifugal or other types of switching mechanisms, including motor overload devices (3) Standard open-type machines having such contacts, switching mechanisms, or resistance devices enclosed within tight housings without ventilating or other openings 503.128 Ventilating Piping — Class III, Divisions 1 and 2. Ventilating pipes for motors, generators, or other rotating electrical machinery, or for enclosures for electric 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 the following: (1) Lead directly to a source of clean air outside of buildings Be screened at the outer ends to prevent the entrance of small animals or birds Be protected against physical damage and against rusting or other corrosive influences Ventilating pipes shall be sufficiently tight, including their connections, to prevent the entrance of appreciable quantities of fibers/flyings into the ventilated equipment or enclosure and to prevent the escape of sparks, flame, or burning material that might ignite accumulations of fibers/flyings or combustible material in the vicinity. For metal pipes, lock seams and riveted or welded joints shall be permitted; and tight-fitting slip joints shall be permitted where some flexibility is necessary, as at connections to motors. 503.130 Luminaires — Class III, Divisions 1 and 2. (A) Fixed Lighting. Luminaires for fixed lighting shall provide enclosures for lamps and lampholders that are designed to minimize entrance of fibers/flyings and to prevent the escape of sparks, burning material, or hot metal. Each luminaire shall be clearly marked to show the maximum wattage of the lamps that shall be permitted without exceeding an exposed surface temperature of 165°C (329°F) under normal conditions of use. Physical Damage. A luminaire that may be exposed to physical damage shall be protected by a suitable guard. Pendant Luminaires. Pendant luminaires shall be suspended by stems of threaded rigid metal conduit, threaded intermediate metal conduit, threaded metal tubing of equivalent thickness, or by chains with approved fittings. For 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. Portable Lighting Equipment. Portable lighting equipment shall be equipped with handles and protected with substantial guards. Lampholders shall be of the unswitched type with no provision for receiving attachment plugs. There shall be no exposed current-carrying metal parts, and all exposed non–current-carrying metal parts shall be grounded. In all other respects, portable lighting equipment shall comply with 503.130(A). 503.135 Utilization Equipment — Class III, Divisions 1 and 2. (A) Heaters. Electrically heated utilization equipment shall be identified for Class III locations. Motors. Motors of motor-driven utilization equipment shall comply with 503.125. Switches, Circuit Breakers, Motor Controllers, and Fuses. Switches, circuit breakers, motor controllers, and fuses shall comply with 503.115. 503.140 Flexible Cords — Class III, Divisions 1 and 2. Flexible cords shall comply with the following: (1) Be of a type listed for extra-hard usage Contain, in addition to the conductors of the circuit, an equipment grounding conductor complying with 400.23 Be supported by clamps or other suitable means in such a manner that there will be no tension on the terminal connections Be terminated with a listed dusttight cord connector 503.145 Receptacles and Attachment Plugs — Class III, Division 1 and Division 2. Receptacles and attachment plugs shall be of the grounding type, shall be designed to minimize the accumulation or the entry of fibers/flyings, and shall prevent the escape of sparks or molten particles. Exception: In locations where, in the judgment of the authority having jurisdiction, only moderate accumulations of ignitible fibers/flyings are likely to collect in the vicinity of a receptacle, and where such receptacle is readily accessible for routine cleaning and mounted to minimize the entry of fibers/flyings, general-purpose grounding-type receptacles shall be permitted. 503.150 Signaling, Alarm, Remote-Control, and Local Loudspeaker Intercommunications Systems — Class III, Division 1 and Division 2. Signaling, alarm, remote-control, and local loudspeaker intercommunications systems shall comply with the requirements of this article regarding wiring methods, switches, transformers, resistors, motors, luminaires, and related components. 503.155 Electric Cranes, Hoists, and Similar Equipment — Class III, Divisions 1 and 2. Where installed for operation over combustible fibers or accumulations of flyings, traveling cranes and hoists for material handling, traveling cleaners for textile machinery, and similar equipment shall comply with 503.155(A) through (D). ENHANCED CONTENT Collapse In Class III locations, two hazards can be introduced by cranes, equipped with rolling or sliding collectors that contact with bare conductors, that are installed over accumulations of fibers/flyings. The first hazard results from arcing between a conductor and a collector rail igniting combustible fibers or lint that has accumulated on or near the bare conductor. This hazard can be prevented by maintaining the proper alignment of the bare conductor, by using a collector designed so that proper contact is always maintained, and by using guards or shields to confine hot metal particles that result from arcing. The second hazard occurs if enough moisture is present and fibers/flyings accumulating on the insulating supports of the bare conductors form a conductive path between the conductors or from one conductor to ground, permitting enough current to flow to ignite the fibers. If the system is ungrounded, a current flow to ground is unlikely to start a fire. A suitable recording ground detector sounds an alarm and automatically de-energizes contact conductors when the insulation resistance is lowered by an accumulation of fibers on the insulators or in case of a fault to ground. A ground-fault indicator that maintains an alarm until the system is de-energized or the ground fault is cleared is permitted. Power Supply. The power supply to contact conductors shall be electrically isolated from all other systems, ungrounded, and shall be equipped with an acceptable ground detector that gives an alarm and automatically de-energizes the contact conductors in case of a fault to ground or gives a visual and audible alarm as long as power is supplied to the contact conductors and the ground fault remains. Contact Conductors. Contact conductors shall be located or guarded so as to be inaccessible to other than authorized persons and shall be protected against accidental contact with foreign objects. Current Collectors. Current collectors shall be arranged or guarded so as to confine normal sparking and prevent escape of sparks or hot particles. To reduce sparking, two or more separate surfaces of contact shall be provided for each contact conductor. Reliable means shall be provided to keep contact conductors and current collectors free of accumulations of lint or flyings. Control Equipment. Control equipment shall comply with 503.115 and 503.120. 503.160 Storage Battery Charging Equipment — Class III, Divisions 1 and 2. Storage battery charging equipment shall be located in separate rooms built or lined with substantial noncombustible materials. The rooms shall be constructed to prevent the entrance of ignitible amounts of flyings or lint and shall be well ventilated.Article 504 Intrinsically Safe Systems 504.1 Scope. This article covers the installation of intrinsically safe (I.S.) apparatus, wiring, and systems for hazardous (classified) locations. Informational Note: See ANSI/ISARP 12.06.01, Recommended Practice for Wiring Methods for Hazardous (Classified) Locations Instrumentation — Part 1: Intrinsic Safety, for additional information. ENHANCED CONTENT Collapse There are two standards used in the United States for construction and performance requirements for intrinsically safe (IS) systems: ANSI/UL 913, Standard for Intrinsically Safe Apparatus and Associated Apparatus for Use in Class I, II, and III, Division 1, Hazardous (Classified) Locations, and ANSI/UL 60079-11, Electrical Apparatus for Explosive Gas Atmospheres — Part 11: Intrinsic Safety “I,” which is based on the IEC 60079-11 standard. The NEC offers the choice of designating hazardous locations as two divisions (1 and 2) or three zones (0, 1, and 2). Equipment certified by a testing laboratory for Zone 1 would not necessarily meet UL 913 requirements for Division 1. Due to its physical and electrical characteristics, an IS circuit does not develop sufficient electrical energy (millijoules) in an arc or spark to cause ignition or sufficient thermal energy resulting from an overload condition to cause the temperature of the installed circuit to exceed the ignition temperature of a specified gas or vapor under normal or abnormal operating conditions. An abnormal condition may occur due to damage, failure of electrical components, excessive voltage, or improper adjustment or maintenance of the equipment. Abnormal conditions are mitigated by associated apparatus such as the IS barrier shown below, which limits the energy available to the hazardous location. (Courtesy of Pepperl+Fuchs, Inc.) 504.3 Application of Other Articles. Except as modified by this article, all applicable articles of this Code shall apply. ENHANCED CONTENT Collapse Because IS wiring must be low energy, the wiring itself is most likely to be a Class 2 or a power-limited fire-protective signaling circuit. See Article 725 or 760, as appropriate, for the requirements for such wiring. The installation may also fall under the scope of Article 800. The associated apparatus, on the other hand, may be supplied by ordinary power circuits, in which case other NEC requirements may apply. The associated apparatus is not normally suitable for a hazardous location. Therefore, another protection technique, such as installing the associated apparatus in an explosionproof enclosure, is commonly used if it must be installed in a hazardous location. IS systems are not exempt from the grounding and bonding requirements of 501.30, 502.30, 503.30, and 505.30. 504.4 Equipment. All intrinsically safe apparatus and associated apparatus shall be listed. Exception: Simple apparatus, as described on the control drawing, shall not be required to be listed. 504.10 Equipment Installation. (A) Control Drawing. Intrinsically safe apparatus, associated apparatus, and other equipment shall be installed in accordance with the control drawing(s). A simple apparatus, whether or not shown on the control drawing(s), shall be permitted to be installed provided the simple apparatus does not interconnect intrinsically safe circuits. Informational Note No. 1: The control drawing identification is marked on the apparatus. Informational Note No. 2: Associated apparatus with a marked Um of less than 250 V may require additional overvoltage protection at the inputs to limit any possible fault voltages to less than the Um marked on the product. ENHANCED CONTENT Collapse A sample zener carrier control drawing is shown below, as an example of the control drawing required to be followed to correctly install an IS system. This drawing is normally provided by the associated equipment manufacturer. A similar drawing is provided by the IS equipment manufacturer. Compliance with the requirements of both drawings is required to properly install an IS system. An IS system is required to be installed according to the control drawings, which may put limitations on cables and on the separation of circuits in the system. Control drawings also illustrate what is permitted to be connected in the system. Compliance with all the conditions in the control drawings is essential if intrinsic safety is to be maintained. The investigation of the equipment by third-party testing laboratories is based on installation in accordance with the control drawing. Location. Intrinsically safe apparatus shall be permitted to be installed in any hazardous (classified) location for which it has been identified. Associated apparatus shall be permitted to be installed in any hazardous (classified) location for which it has been identified. Simple apparatus shall be permitted to be installed in any hazardous (classified) location in accordance with 504.10(D). Enclosures. General-purpose enclosures shall be permitted for intrinsically safe apparatus and associated apparatus unless otherwise specified in the manufacturer’s documentation. Simple Apparatus. Simple apparatus shall be permitted to be installed in any hazardous (classified) location in which the maximum surface temperature of the simple apparatus does not exceed the ignition temperature of the flammable gases or vapors, flammable liquids, combustible dusts, or ignitible fibers/flyings present. The maximum surface temperature can be determined from the values of the output power from the associated apparatus or apparatus to which it is connected to obtain the temperature class. The temperature class can be determined by: Reference to Table 504.10(D) Calculation using the following equation: [504.10(D)] code book image: 9a5b088b-aa9c-11ec-a46d-e9dd887336cb where: T = surface temperature Po = output power marked on the associated apparatus or intrinsically safe apparatus Rth = thermal resistance of the simple apparatus Tamb = ambient temperature (normally 40°C) and reference Table 500.8(C)(4) In addition, components with a surface area smaller than 10 cm2 (excluding lead wires) may be classified as T5 if their surface temperature does not exceed 150°C. Table 504.10(D) Assessment for T4 Classification According to Component Size and Temperature Total Surface Area Excluding Lead Wires Requirement for T4 Classification <20 mm2 Surface temperature ≤275°C ≥20 mm2 ≤10 cm2 Surface temperature ≤200°C ≥20 mm2 Power not exceeding 1.3 W Based on 40°C ambient temperature. Reduce to 1.2 W with an ambient of 60°C or 1.0 W with 80°C ambient temperature. ENHANCED CONTENT Collapse Simple apparatus stores little or no energy. Simple apparatus is permitted to be used without requiring the apparatus to be listed or to be specifically mentioned on the control drawing. See the first informational note following the definition of simple apparatus in Article 100 for examples of simple apparatus. 504.20 Wiring Methods. Any of the wiring methods suitable for unclassified locations, including those covered by Chapter 7 and Chapter 8, shall be permitted for installing intrinsically safe apparatus. Sealing shall be as provided in 504.70, and separation shall be as provided in 504.30. ENHANCED CONTENT Collapse An IS system evaluation also includes wiring faults and cable parameters (e.g., short circuits and cable capacitance). Any of the wiring methods for unclassified locations may be used for IS systems, as long as the conditions specified in the control drawings are followed. See also 504.3 and its enhanced content for more information on the types of circuits typically used in an IS system. 504.30 Separation of Intrinsically Safe Conductors. ENHANCED CONTENT Collapse It is essential that non-IS circuits and IS circuits be physically and electrically separated to prevent unsafe energy from being introduced into the IS system by a wiring fault. Other low-voltage, low-energy circuits, such as Class 2 and communications circuits, are not IS circuits and must not be installed in the same raceways or cables as IS circuits in either a hazardous or a nonhazardous location. From Nonintrinsically Safe Circuit Conductors. In Raceways, Cable Trays, and Cables. Conductors of intrinsically safe circuits shall not be placed in any raceway, cable tray, or cable with conductors of any nonintrinsically safe circuit, unless they meet the requirements of one of the following methods: Separated from conductors of nonintrinsically safe circuits in accordance with one of the following: By a distance of at least 50 mm (2 in.) and secured By a grounded metal partition that is 0.91 mm (0.0359 in) or thicker An approved insulating partition All of the intrinsically safe circuit conductors or nonintrinsically safe circuit conductors are in Type MC cable, Type MI cable, or other approved grounded metal-sheathed or metal-clad cables where the sheathing or cladding is capable of carrying fault current to ground In a Division 2 or Zone 2 location, installed in a raceway, cable tray, or cable along with nonincendive field wiring circuits when installed in accordance with 504.30(B) Where passing through a Division 2 or Zone 2 location to supply apparatus that is located in a Division 1, Zone 0 or Zone 1 location, installed in a raceway, cable tray, or cable along with nonincendive field wiring circuits when installed in accordance with 504.30(B) ENHANCED CONTENT Collapse Items No. 3 and No. 4 permit IS circuits in a Division 2 or Zone 2 location to be installed with nonincendive field wiring circuits if the circuits are installed as required for two separate IS circuits. Within Enclosures. Conductors of intrinsically safe circuits shall be secured so that any conductor that might come loose from a terminal is unlikely to come into contact with another terminal. The conductors shall be separated from conductors of nonintrinsically safe circuits by one of the following methods: Separation by at least 50 mm (2 in.) from conductors of any nonintrinsically safe circuits, and secured Separation from conductors of nonintrinsically safe circuits by use of a grounded metal partition 0.91 mm (0.0359 in.) or thicker or approved restricted access wiring ducts separated from other wiring ducts by a minimum of 19 mm (3⁄4 in.) Separation from conductors of nonintrinsically safe circuits by use of rigid insulating partition 0.91 mm (0.0359 in,) or thicker that extends to within 1.5 mm (0.0625 in.) of the enclosure walls Use of separate wiring compartments for intrinsically safe and nonintrinsically safe terminals Either all intrinsically safe circuit conductors or all nonintrinsically safe circuit conductors are installed in grounded metal-sheathed or metal-clad cables, where the sheathing or cladding is capable of carrying fault current to ground Other (Not in Raceway or Cable Tray Systems). Conductors and cables of intrinsically safe circuits run in other than raceway or cable tray systems shall be separated by at least 50 mm (2 in.) and secured from conductors and cables of any nonintrinsically safe circuits unless one of the following applies: All of the intrinsically safe circuit conductors are in Type MI or MC cables. All of the nonintrinsically safe circuit conductors are in raceways or Type MI or Type MC cables where the sheathing or cladding is capable of carrying fault current to ground. ENHANCED CONTENT Collapse Even where not installed in an enclosure, raceway, or cable tray, IS circuit conductors are required to be securely separated from other conductors. From Different Intrinsically Safe Circuit Conductors. The clearance between two terminals for connection of field wiring of different intrinsically safe circuits shall be at least 6 mm (0.25 in.), unless this clearance is permitted to be reduced by the control drawing. Different intrinsically safe circuits shall be separated from each other by one of the following means: The c