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

ARTICLE 250 - GROUNDING 70-113 250-26. Grounding Separately Derived Alternating-Current Systems. A separately derived ac system that is required to be grounded by Section 250-5 shall be grounded as specified in (a) through (d) below. (a) Bonding Jumper. A bonding jumper, sized in accordance with Section 250-79(d) for the derived phase conductors, shall be used to connect the equipment grounding conductors of the derived system to the grounded conductor. Except as permitted by Exception No. 4 or No. 5 of Section 250-23(a), this connection shall be made at any point on the separately derived system from the source to the first system disconnecting means or overcurrent device; or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices. Exception No. 1: The size of the bonding jumper for a system that supplies a Class 1, Class 2, or Class 3 circuit, and is derived from a transformer rated not more than 1000 volt-amperes, shall not be smaller than the derived phase conductors and shall not be smaller than No. 14 copper or No. 12 aluminum. Exception No. 2: As covered in Section 250-27 and Exception No. 5 for Section 250-5(b) for high-impedance grounded neutral systems grounding connection requirements. (b) Grounding Electrode Conductor. A grounding electrode conductor, sized in accordance with Section 250-94 for the derived phase conductors, shall be used to connect the grounded conductor of the derived system to the grounding electrode as specified in (c) below. Except as permitted by Exception No. 4 of Section 250-23(a), this connection shall be made at any point on the separately derived system from the source to the first system disconnecting means or overcurrent device; or it shall be made at the source of a separately derived system that has no disconnecting means or overcurrent devices. Exception No. 1: A grounding electrode conductor shall not be required for a system that supplies a Class 1, Class 2, or Class 3 circuit, and is derived from a transformer rated not more than 1000 volt-amperes, provided the system grounded conductor is bonded to the transformer frame or enclosure by a jumper sized in accordance with Section 250-26, Exception No. 1 for (a) above, and the transformer frame or enclosure is grounded by one of the means specified in Section 250-57. Exception No. 2: As covered in Section 250-27 and Exception No. 5 for Section 250-5(b) for high-impedance grounded neutral systems grounding connection requirements. (c) Grounding Electrode. The grounding electrode shall be as near as practicable to and preferably in the same area as the grounding conductor connection to the system. The grounding electrode shall be (1) the nearest available effectively grounded structural metal member of the structure; or (2) the nearest available effectively grounded metal water pipe; or (3) other electrodes as specified in Sections 250-81 and 250-83 where electrodes specified by (1) or (2) above are not available. (d) Grounding Methods. In all other respects, grounding methods shall comply with requirements prescribed in other parts of this Code. 70-114 NATIONAL ELECTRICAL CODE 250-27. High-Impedance Grounded Neutral System Connections. Highimpedance grounded neutral systems as permitted in Exception No. 5 of Section 250-5(b) shall comply with the provisions of (a) through (f) below. (a) Grounding Impedance Location. The grounding impedance shall be installed between the grounding electrode conductor and the system neutral. Where a neutral is not available, the grounding impedance shall be installed between the grounding electrode conductor and the neutral derived from a grounding transformer. (b) Neutral Conductor. The neutral conductor from the neutral point of the transformer or generator to its connection point to the grounding impedance shall be fully insulated. The neutral conductor shall have an ampacity of not less than the maximum current rating of the grounding impedance. In no case shall the neutral conductor be smaller than No. 8 copper or No. 6 aluminum, or copperclad aluminum. (c) System Neutral Connection. The system neutral conductor shall not be connected to ground except through the grounding impedance. (FPN): The impedance is normally selected to limit the ground-fault current to a value slightly greater than or equal to the capacitive charging current of the system. This value of impedance will also limit transient overvoltages to safe values. For guidance, refer to criteria for limiting transient overvoltages in Recommended Practice for Grounding of Industrial and Commercial Power Systems, ANSI/IEEE 142-1982. (d) Neutral Conductor Routing. The conductor connecting the neutral point of the transformer or generator to the grounding impedance shall be permitted to be installed in a separate raceway. It shall not be required to run this conductor with the phase conductors to the first system disconnecting means or overcurrent device. (e) Equipment Bonding Jumper. The equipment bonding jumper (the connection between the equipment grounding conductors and the grounding impedance) shall be an unspliced conductor run from the first system disconnecting means or overcurrent device to the grounded side of the grounding impedance. (f) Grounding Electrode Conductor Location. The grounding electrode conductor shall be attached at any point from the grounded side of the grounding impedance to the equipment grounding connection at the service equipment or first system disconnecting means. D. Enclosure Grounding 250-32. Service Raceways and Enclosures. Metal enclosures for service conductors and equipment shall be grounded. Exception: A metal elbow that is installed in an underground installation of rigid nonmetallic conduit and is isolated from possible contact by a minimum cover of 18 inches (457 mm) to any part of the elbow. 250-33. Other Conductor Enclosures. Metal enclosures for other than service conductors shall be grounded. ARTICLE 250 - GROUNDING 70-115 Exception No. 1: Metal enclosures for conductors added to existing installations of open wire, knob-and-tube wiring, and nonmetallicsheathed cable, that do not provide an equipment ground, if in runs of less than 25 feet (7.62 m), if free from probable contact with ground, grounded metal, metal lath, or other conductive material, and if guarded against contact by persons, shall not be required to be grounded. Exception No. 2: Short sections of metal enclosures used to provide support or protection of cable assemblies from physical damage shall not be required to be grounded. Exception No. 3: Enclosures not required to be grounded by Section 250-43(i) shall not be required to be grounded. Exception No. 4: A metal elbow that is installed in an underground installation of rigid nonmetallic conduit and is isolated from possible contact by a minimum cover of 18 inches (457 mm) to any part of the elbow. E. Equipment Grounding 250-42. Equipment Fastened in Place or Connected by Permanent Wiring Methods (Fixed). Exposed noncurrent-carrying metal parts of fixed equipment likely to become energized shall be grounded under any of the conditions in (a) through (f) below. (a) Vertical and Horizontal Distances. Where within 8 feet (2.44 m) vertically or 5 feet (1.52 m) horizontally of ground or grounded metal objects and subject to contact by persons. (b) Wet or Damp Locations. Where located in a wet or damp location and not isolated. (c) Electrical Contact. Where in electrical contact with metal. (d) Hazardous (Classified) Locations. Where in a hazardous (classified) location as covered by Articles 500 through 517. (e) Wiring Methods. Where supplied by a metal-clad, metal-sheathed, metal-raceway, or other wiring method that provides an equipment ground, except as permitted by Section 250-33 for short sections of metal enclosures. (f) Over 150 Volts to Ground. Where equipment operates with any terminal at over 150 volts to ground. Exception No. 1: Enclosures for switches or circuit breakers used for other than service equipment and accessible to qualified persons only. Exception No. 2: Metal frames of electrically heated appliances, exempted by special permission, in which case the frames shall be permanently and effectively insulated from ground. Exception No. 3: Distribution apparatus, such as transformer and capacitor cases, mounted on wooden poles, at a height exceeding 8 feet (2.44 m) above ground or grade level. Exception No. 4: Listed equipment protected by a system of double insulation, or its equivalent, shall not be required to be grounded. Where such a system is employed, the equipment shall be distinctively marked. 70-116 NATIONAL ELECTRICAL CODE 250-43. Fastened in Place or Connected by Permanent Wiring Methods (Fixed) - Specific. Exposed, noncurrent-carrying metal parts of the kinds of equipment described in (a) through (j) below, and noncurrentcarrying metal parts of equipment and enclosures described in (k) and (1) below, shall be grounded regardless of voltage. (a) Switchboard Frames and Structures. Switchboard frames and structures supporting switching equipment. Exception: Frames of 2-wire dc switchboards where effectively insulated from ground. (b) Pipe Organs. Generator and motor frames in an electrically operated pipe organ. Exception: Where the generator is effectively insulated from ground and from the motor driving it. (c) Motor Frames. Motor frames, as provided by Section 430-142. (d) Enclosures for Motor Controllers. Enclosures for motor controllers. Exception No. 1: Enclosures attached to ungrounded portable equipment. Exception No. 2: Lined covers of snap switches. (e) Elevators and Cranes. Electric equipment for elevators and cranes. (f) Garages, Theaters, and Motion Picture Studios. Electric equipment in commercial garages, theaters, and motion picture studios. Exception: Pendant lampholders supplied by circuits not over 150 volts to ground. (g) Electric Signs. Electric signs and associated equipment. (h) Motion Picture Projection Equipment. Motion picture projection equipment. (i) Remote-Control, Signaling, and Fire Protective Signaling Circuits. Equipment supplied by Class 1, Class 2, and Class 3 remote-control and signaling circuits, and by fire protective signaling circuits, shall be grounded where system grounding is required by Part B of this article. (j) Lighting Fixtures. Lighting fixtures as provided in Part E of Article 410. (k) Motor-Operated Water Pumps. Motor-operated water pumps including the submersible type. (I) Metal Well Casings. Where a submersible pump is used in a metal well casing, the well casing shall be bonded to the pump circuit equipment grounding conductor. 250-44. Nonelectric Equipment. The metal parts of nonelectric equipment described in (a) through (e) below shall be grounded. (a) Cranes. Frames and tracks of electrically operated cranes. (b) Elevator Cars. Frames of nonelectrically driven elevator cars to which electric conductors are attached. ARTICLE 250 - GROUNDING 70-117 (c) Electric Elevators. Hand-operated metal shifting ropes or cables of electric elevators. (d) Metal Partitions. Metal partitions, grill work, and similar metal enclosures around equipment of 1 kV and over between conductors except substations or vaults under the sole control of the supply company. (e) Mobile Homes and Recreational Vehicles. Mobile homes and recreational vehicles as required in Articles 550 and 551. (FPN): Where extensive metal in or on buildings may become energized and is subject to personal contact, adequate bonding and grounding will provide additional safety. 250-45. Equipment Connected by Cord and Plug. Under any of the conditions described in (a) through (d) below, exposed noncurrent-carrying metal parts of cord- and plug-connected equipment likely to become energized shall be grounded. (a) In Hazardous (Classified) Locations. In hazardous (classified) locations (see Articles 500 through 517). (b) Over 150 Volts to Ground. Where operated at over 150 volts to ground. Exception No. 1: Motors, where guarded. Exception No. 2: Metal frames of electrically heated appliances, exempted by special permission, in which case the frames shall be permanently and effectively insulated from ground. Exception No. 3: Listed equipment protected by a system of double insulation, or its equivalent, shall not be required to be grounded. Where such a system is employed, the equipment shall be distinctively marked. (c) In Residential Occupancies. In residential occupancies: (1) refrigerators, freezers, and air conditioners; (2) clothes-washing, clothes-drying, dish-washing machines, kitchen waste disposers, sump pumps, electrical aquarium equipment; (3) hand-held motor-operated tools, stationary and fixed motor-operated tools, light industrial motor-operated tools; (4) motoroperated appliances of the following types: hedge clippers, lawn mowers, snow blowers, and wet scrubbers; (5) portable handlamps. Exception: Listed tools and listed appliances protected by a system of double insulation, or its equivalent, shall not be required to be grounded. Where such a system is employed, the equipment shall be distinctively marked. (d) In Other than Residential Occupancies. In other than residential occupancies: (1) refrigerators, freezers, and air conditioners; (2) clotheswashing, clothes-drying, dish-washing machines, electronic computer/data processing equipment, sump pumps, electrical aquarium equipment; (3) hand-held motor-operated tools, stationary and fixed motor-operated tools, light industrial motor-operated tools; (4) motor-operated appliances of the following types: hedge clippers, lawn mowers, snow blowers, and wet scrubbers; (5) cord- and plug-connected appliances used in damp or wet locations or by persons standing on the ground or on metal floors or working inside of metal tanks or boilers; (6) tools likely to be used in wet or conductive locations; and (7) portable handlamps. 70-118 NATIONAL ELECTRICAL CODE Exception No. 1: Tools and portable handlamps likely to be used in wet or conductive locations shall not be required to be grounded where supplied through an isolating transformer with an ungrounded secondary of not over 50 volts. Exception No. 2: Listed, hand-held, motor-operated tools, listed stationary and fixed motor-operated tools, listed, light industrial, motoroperated tools, and listed appliances protected by an approved system of double insulation or its equivalent shall not be required to be grounded. Where such a system is employed, the equipment shall be distinctively marked. (FPN): With reference to (c) and (d), portable tools or appliances are not intended to be used in damp, wet, or conductive locations unless they are grounded, double insulated, or supplied through an isolating transformer. 250-46. Spacing from Lightning Rods. Metal raceways, enclosures, frames, and other noncurrent-carrying metal parts of electric equipment shall be kept at least 6 feet (1.83 m) away from lightning rod conductors, or they shall be bonded to the lightning rod conductors. (FPN): See Sections 250-86 and 800-40(b)(3)(3). For further information, see Lightning Protection Code, NFPA 780-1992 (ANSI), which contains detailed information on grounding lightning protection systems. F. Methods of Grounding 250-50. Equipment Grounding Conductor Connections. Equipment grounding conductor connections at the source of separately derived systems shall be made in accordance with Section 250-26(a). Equipment grounding conductor connections at service equipment shall be made as indicated in (a) or (b) below. (a) For Grounded System. The connection shall be made by bonding the equipment grounding conductor to the grounded service conductor and the grounding electrode conductor. (b) For Ungrounded System. The connection shall be made by bonding the equipment grounding conductor to the grounding electrode conductor. Exception for (a) and (b) above: For replacement of nongrounding-type receptacles with grounding-type receptacles and for branch-circuit extensions only in existing installations that do not have an equipment grounding conductor in the branch circuit, the grounding conductor of a grounding-type receptacle outlet shall be permitted to be grounded to any accessible point on the grounding electrode system as described in Section 250-81. (FPN): See Section 210-7(d), Exception for the use of a ground-fault circuitinterrupter-type of receptacle. 250-51. Effective Grounding Path. The path to ground from circuits, equipment, and metal enclosures for conductors shall (1) be permanent and continuous; (2) have capacity to conduct safely any fault current likely to be imposed on it; and (3) have sufficiently low impedance to limit the voltage to ground and to facilitate the operation of the circuit protective devices. ARTICLE 250 - GROUNDING 70-119 The earth shall not be used as the sole equipment grounding conductor. 250-53. Grounding Path to Grounding Electrode at Services. (a) Grounding Electrode Conductor. A grounding electrode conductor shall be used to connect the equipment grounding conductors, the serviceequipment enclosures, and, where the system is grounded, the grounded service conductor to the grounding electrode. Exception: As covered in Section 250-27 for high-impedance grounded neutral system connections. (FPN): See Section 250-23(a) for alternating-current system grounding connections. (b) Main Bonding Jumper. For a grounded system, an unspliced main bonding jumper shall be used to connect the equipment grounding conductor and the service-disconnect enclosure to the grounded conductor of the system at each service disconnect. Exception No. 1: Where more than one service disconnecting means are located in an assembly listed for use as service equipment, one grounded conductor shall be required to be run to the assembly, and it shall be bonded to the assembly enclosure. Exception No. 2: As covered in Section 250-27 for high-impedance grounded neutral system connections. 250-54. Common Grounding Electrode. Where an ac system is connected to a grounding electrode in or at a building as specified in Sections 250-23 and 250-24, the same electrode shall be used to ground conductor enclosures and equipment in or on that building. Where separate services supply a building and are required to be connected to a grounding electrode, the same grounding electrode shall be used. Two or more grounding electrodes that are effectively bonded together shall be considered as a single grounding electrode system in this sense. 250-55. Underground Service Cable. Where served from a continuous underground metal-sheathed cable system, the sheath or armor of underground service cable metallically connected to the underground system, or underground service conduit containing a metal-sheathed cable bonded to the underground system, shall not be required to be grounded at the building and shall be permitted to be insulated from the interior conduit or piping. 250-56. Short Sections of Raceway. Isolated sections of metal raceway or cable armor, where required to be grounded, shall be grounded in accordance with Section 250-57. 250-57. Equipment Fastened in Place or Connected by Permanent Wiring Methods (Fixed)-Grounding. Noncurrent-carrying metal parts of equipment, raceways, and other enclosures, where required to be grounded, shall be grounded by one of the methods indicated in (a) or (b) below. Exception: Where equipment, raceways, and enclosures are grounded by connection to the grounded circuit conductor as permitted by Sections 250-24, 250-60, and 250-61. 70-120 NATIONAL ELECTRICAL CODE (a) Equipment Grounding Conductor Types. By any of the equipment grounding conductors permitted by Section 250-91(b). (b) With Circuit Conductors. By an equipment grounding conductor contained within the same raceway, cable, or cord or otherwise run with the circuit conductors. Bare, covered, or insulated equipment grounding conductors shall be permitted. Individually covered or insulated equipment grounding conductors shall have a continuous outer finish that is either green or green with one or more yellow stripes. Exception No. 1: An insulated or covered conductor larger than No. 6 copper or aluminum shall, at the time of installation, be permitted to be permanently identified as an equipment grounding conductor at each end and at every point where the conductor is accessible. Identification shall be accomplished by one of the following: a. Stripping the insulation or covering from the entire exposed length, b. Coloring the exposed insulation or covering green, or c. Marking the exposed insulation or covering with green colored tape or green colored adhesive labels. Exception No. 2: For direct-current circuits only, the equipment grounding conductor shall be permitted to be run separately from the circuit conductors. Exception No. 3: As provided in the exception to Sections 250-50(a) and (b), the equipment grounding conductor shall be permitted to be run separately from the circuit conductors. Exception No. 4: Where the conditions of maintenance and supervision assure that only qualified persons will service the installation, one or more insulated conductors in a multiconductor cable shall, at the time of installation, be permitted to be permanently identified as equipment grounding conductors at each end and at every point where the conductors are accessible by one of the following means: a. Stripping the insulation from the entire exposed length, b. Coloring the exposed insulation green, or c. Marking the exposed insulation with green tape or green colored adhesive labels. (FPN No. 1): See Section 250-79 for equipment bonding jumper requirements. (FPN No. 2): See Section 400-7 for use of cords for fixed equipment. 250-58. Equipment Considered Effectively Grounded. Under the conditions specified in (a) and (b) below, the noncurrent-carrying metal parts of the equipment shall be considered effectively grounded. (a) Equipment Secured to Grounded Metal Supports. Electric equipment secured to and in electrical contact with a metal rack or structure provided for its support and grounded by one of the means indicated in