Resolución 2535: adopta el Código Eléctrico Nacional, versión 1993. (Sustituye el Anejo A del Reglamento 4435)

(2) Coils and Windings. Enclosures for windings of transformers, solenoids, or impedance coils shall be permitted to be of the generalpurpose type. (3) Resistors. Resistors shall be provided with enclosures; and the assembly shall be approved for Class I locations, unless resistance is nonvariable and maximum operating temperature, in degrees Celsius, will not exceed 80 percent of the ignition temperature of the gas or vapor involved, or has been tested and found incapable of igniting the gas or vapor. 501-8. Motors and Generators. (a) Class I, Division 1. In Class I, Division 1 locations, motors, generators, and other rotating electric machinery shall be (1) approved for Class I, Division 1 locations; or (2) of the totally enclosed type supplied with positive-pressure ventilation from a source of clean air with discharge to a safe area, so arranged to prevent energizing of the machine until ventilation has been established and the enclosure has been purged with at least 10 volumes of air, and also arranged to automatically deenergize the equipment when the air supply fails; or (3) of the totally enclosed inert gas-filled type supplied with a suitable reliable source of inert gas for pressuring the enclosure, with devices provided to ensure a positive pressure in the enclosure and arranged to automatically deenergize the equipment when the gas supply fails; or (4) of a type designed to be submerged in a liquid that is ARTICLE 501 - CLASS I LOCATIONS 70-481 flammable only when vaporized and mixed with air, or in a gas or vapor at a pressure greater than atmospheric and that is flammable only when mixed with air; and the machine is so arranged to prevent energizing it until it has been purged with the liquid or gas to exclude air, and also arranged to automatically deenergize the equipment when the supply of liquid or gas or vapor fails or the pressure is reduced to atmospheric. Totally enclosed motors of Types (2) or (3) shall have no external surface with an operating temperature in degrees Celsius in excess of 80 percent of the ignition temperature of the gas or vapor involved. Appropriate devices shall be provided to detect and automatically deenergize the motor or provide an adequate alarm if there is any increase in temperature of the motor beyond designed limits. Auxiliary equipment shall be of a type approved for the location in which it is installed. (FPN): See ASTM Test Procedure (Designation D 2155-69). (b) Class I, Division 2. In Class I, Division 2 locations, motors, generators, and other rotating electric machinery in which are employed sliding contacts, centrifugal or other types of switching mechanism (including motor overcurrent, overloading, and overtemperature devices), or integral resistance devices, either while starting or while running, shall be approved for Class I, Division 1 locations, unless such sliding contacts, switching mechanisms, and resistance devices are provided with enclosures approved for Class I, Division 2 locations in accordance with Section 501-3(b). The exposed surface of space heaters used to prevent condensation of moisture during shutdown periods shall not exceed 80 percent of the ignition temperature in degrees Celsius of the gas or vapor involved when operated at rated voltage, and the maximum surface temperature [based upon a 40°C (104°F) ambient] shall be permanently marked on a visible nameplate mounted on the motor. Otherwise, space heaters shall be approved for Class I, Division 2 locations. In Class I, Division 2 locations, the installation of open or nonexplosionproof enclosed motors, such as squirrel-cage induction motors without brushes, switching mechanisms, or similar arc-producing devices, shall be permitted. (FPN No. 1): It is important to consider the temperature of internal and external surfaces that may be exposed to the flammable atmosphere. (FPN No. 2): It is important to consider the risk of ignition due to currents arcing across discontinuities and overheating of parts in multisection enclosures of large motors and generators. Such motors and generators may require equipotential bonding jumpers across joints in the enclosures and from enclosure to ground and cleanair purging immediately prior to and during start-up periods. 501-9. Lighting Fixtures. Lighting fixtures shall comply with (a) or (b) below. (a) Class I, Division 1. In Class I, Division 1 locations, lighting fixtures shall comply with the following: (1) Approved Fixtures. Each fixture shall be approved as a complete assembly for the Class I, Division 1 location and shall be clearly marked to indicate the maximum wattage of lamps for which it is approved. Fixtures intended for portable use shall be specifically approved as a complete assembly for that use. 70-482 NATIONAL ELECTRICAL CODE (2) Physical Damage. Each fixture shall be protected against physical damage by a suitable guard or by location. (3) Pendant Fixtures. Pendant fixtures shall be suspended by and supplied through threaded rigid metal conduit stems or threaded steel intermediate conduit stems, and threaded joints shall be provided with set-screws or other effective means to prevent loosening. For stems longer than 12 inches (305 mm), permanent and effective bracing against lateral displacement shall be provided at a level not more than 12 inches (305 mm) above the lower end of the stem, or flexibility in the form of a fitting or flexible connector approved for the Class I, Division 1 location shall be provided not more than 12 inches (305 mm) from the point of attachment to the supporting box or fitting. (4) Supports. Boxes, box assemblies, or fittings used for the support of lighting fixtures shall be approved for Class I locations. (b) Class I, Division 2. In Class I, Division 2 locations, lighting fixtures shall comply with the following: (1) Portable Lighting Equipment. Portable lighting equipment shall comply with (a)(1) above. Exception: Where portable lighting equipment are mounted on movable stands and are connected by flexible cords, as covered in Section 501-11, they shall be permitted, where mounted in any position, provided that they conform to Section 501-9(b)(2) below. (2) Fixed Lighting. Lighting fixtures for fixed lighting shall be protected from physical damage by suitable guards or by location. Where there is danger that falling sparks or hot metal from lamps or fixtures might ignite localized concentrations of flammable vapors or gases, suitable enclosures or other effective protective means shall be provided. Where lamps are of a size or type that may, under normal operating conditions, reach surface temperatures exceeding 80 percent of the ignition temperature in degrees Celsius of the gas or vapor involved, fixtures shall comply with (a)(1) above or shall be of a type that has been tested in order to determine the marked operating temperature or temperature range. (3) Pendant Fixtures. Pendant fixtures shall be suspended by threaded rigid metal conduit stems, threaded steel intermediate metal conduit stems, or by other approved means. For rigid stems longer than 12 inches (305 mm), permanent and effective bracing against lateral displacement shall be provided at a level not more than 12 inches (305 mm) above the lower end of the stem, or flexibility in the form of an approved fitting or flexible connector shall be provided not more than 12 inches (305 mm) from the point of attachment to the supporting box or fitting. (4) Switches. Switches that are a part of an assembled fixture or of an individual lampholder shall comply with Section 501-6(b)(1). (5) Starting Equipment. Starting and control equipment for electricdischarge lamps shall comply with Section 501-7(b). Exception: A thermal protector potted into a thermally protected fluorescent lamp ballast if the lighting fixture is approved for locations of this Class and Division. ARTICLE 501 - CLASS I LOCATIONS 70-483 501-10. Utilization Equipment. (a) Class I, Division 1. In Class I, Division 1 locations, all utilization equipment shall be approved for Class I, Division 1 locations. (b) Class I, Division 2. In Class I, Division 2 locations, all utilization equipment shall comply with the following: (1) Heaters. Electrically heated utilization equipment shall conform with either item a or b below. a. The heater shall not exceed 80 percent of the ignition temperature in degrees Celsius of the gas or vapor involved on any surface that is exposed to the gas or vapor when continuously energized at the maximum rated ambient temperature. If a temperature controller is not provided, these conditions shall apply when the heater is operated at 120 percent of rated voltage. Exception No. 1: For motor-mounted anticondensation space heaters, see Section 501-8(b). Exception No. 2: A current-limiting device is applied to the circuit serving the heater that will limit the current in the heater to a value less than that required to raise the heater surface temperature to 80 percent of the ignition temperature. b. The heater shall be approved for Class I, Division 1 locations. Exception: Electrical resistance heat tracing approved for Class 1, Division 2 locations. (2) Motors. Motors of motor-driven utilization equipment shall comply with Section 501-8(b). (3) Switches, Circuit Breakers, and Fuses. Switches, circuit breakers, and fuses shall comply with Section 501-6(b). 501-11. Flexible Cords, Class I, Divisions 1 and 2. A flexible cord shall be permitted only for connection between portable lighting equipment or other portable utilization equipment and the fixed portion of its supply circuit; and, where used, shall (1) be of a type approved for extra-hard usage; (2) contain, in addition to the conductors of the circuit, a grounding conductor complying with Section 400-23; (3) be connected to terminals or to supply conductors in an approved manner; (4) be supported by clamps or by other suitable means in such a manner that there will be no tension on the terminal connections; and (5) be provided with suitable seals where the flexible cord enters boxes, fittings, or enclosures of the explosionproof type. Exception: As provided in Sections 501-3(b)(6) and 501-4(b). Electric submersible pumps with means for removal without entering the wet-pit shall be considered portable utilization equipment. The extension of the flexible cord within a suitable raceway between the wet-pit and the power source shall be permitted. Electric mixers intended for travel into and out of open-type mixing tanks or vats shall be considered portable utilization equipment. (FPN): See Section 501-13 for flexible cords exposed to liquids having a deleterious effect on the conductor insulation. 70-484 NATIONAL ELECTRICAL CODE 501-12. Receptacles and Attachment Plugs, Class I, Divisions 1 and 2. Receptacles and attachment plugs shall be of the type providing for connection to the grounding conductor of a flexible cord and shall be approved for the location. Exception: As provided in Section 501-3(b)(6). 501-13. Conductor Insulation, Class I, Divisions 1 and 2. Where condensed vapors or liquids may collect on, or come in contact with, the insulation on conductors, such insulation shall be of a type approved for use under such conditions; or the insulation shall be protected by a sheath of lead or by other approved means. 501-14. Signaling, Alarm, Remote-Control, and Communication Systems. (a) Class I, Division 1. In Class I, Division 1 locations, all apparatus and equipment of signaling, alarm, remote-control, and communication systems, regardless of voltage, shall be approved for Class I, Division 1 locations, and all wiring shall comply with Sections 501-4(a) and 501-5(a) and (c). (b) Class I, Division 2. In Class I, Division 2 locations, signaling, alarm, remote-control, and communication systems shall comply with the following: (1) Contacts. Switches, circuit breakers, and make-and-break contacts of pushbuttons, relays, alarm bells, and horns shall have enclosures approved for Class I, Division 1 locations in accordance with Section 501-3(a). Exception: General-purpose enclosures shall be permitted if currentinterrupting contacts are: a. Immersed in oil; or b. Enclosed within a chamber hermetically sealed against the entrance of gases or vapors; or C. In nonincendive circuits that under normal conditions do not release sufficient energy to ignite a specific ignitible atmospheric mixture. (2) Resistors and Similar Equipment. Resistors, resistance devices, thermionic tubes, rectifiers, and similar equipment shall comply with Section 501-3(b)(2). (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. (4) Wiring and Sealing. All wiring shall comply with Sections 501-4(b) and 501-5(b) and (c). 501-15. Live Parts, Class I, Divisions 1 and 2. There shall be no exposed live parts. 501-16. Grounding, Class I, Divisions 1 and 2. Wiring and equipment in Class I, Division 1 and 2 locations shall be grounded as specified in Article 250 and with the following additional requirements: ARTICLE 501 - CLASS I LOCATIONS 70-485 (a) Bonding. The locknut-bushing and double-locknut types of contacts shall not be depended upon for bonding purposes, but bonding jumpers with proper fittings or other approved means of bonding shall be used. Such means of bonding shall apply to all intervening raceways, fittings, boxes, enclosures, etc., between Class I locations and the point of grounding for service equipment or point of grounding of a separately derived system. Exception: The specific bonding means shall only be required to the point of grounding of a building disconnecting means as specified in Sections 250-24(a), (b), and (c), provided that branch-circuit overcurrent protection is located on the load side of the disconnecting means. (FPN): See Section 250-78 for additional bonding requirements in hazardous (classified) locations. (b) Types of Equipment Grounding Conductors. Where flexible metal conduit or liquidtight flexible metal conduit is used as permitted in Section 501-4(b) and is to be relied upon to complete a sole equipment grounding path, it shall be installed with internal or external bonding jumpers in parallel with each conduit and complying with Section 250-79. Exception: In Class I, Division 2 areas, the bonding jumper shall be permitted to be deleted where all the following conditions are met: a. Approved liquidtight flexible metal conduit 6 feet (1.83 m) or less in length, with approved fittings, is used; b. Overcurrent protection in the circuit is limited to 10 amperes or less; c. The load is not a power utilization load. 501-17. Surge Protection. (a) Class I, Division 1. Surge arresters, including their installation and connection, shall comply with Article 280. The surge arresters and capacitors shall be installed in enclosures approved for Class I, Division 1 locations. Surge-protective capacitors shall be of a type designed for specific duty. (b) Class I, Division 2. Surge arresters shall be nonarcing, such as metal-oxide varistor (MOV), sealed type, and surge-protective capacitors shall be of a type designed for specific duty. Installation and connection shall comply with Article 280. Enclosures shall be permitted to be of the general-purpose type. Surge protection of types other than described above shall be installed in enclosures approved for Class I, Division 1 locations. 501-18. Multiwire Branch Circuits. In a Class I, Division 1 location, a separate grounded conductor shall be installed in each single-phase branch circuit that is part of a multiwire branch circuit. Exception: Where the disconnect device(s) for the circuit opens all ungrounded conductors of the multiwire circuit simultaneously. 70-486 NATIONAL ELECTRICAL CODE