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

(d) Oil-Filled Cutouts. (1) Continuous Current Rating. The continuous current rating of oilfilled cutouts shall not be less than the maximum continuous current through the cutout. (2) Interrupting Rating. The interrupting rating of oil-filled cutouts shall not be less than the maximum fault current the oil-filled cutout will be required to interrupt, including contributions from all connected sources of energy. (3) Voltage Rating. The maximum voltage rating of oil-filled cutouts shall not be less than the maximum circuit voltage. (4) Fault Closing Rating. Oil-filled cutouts shall have a fault closing rating not less than the maximum asymmetrical fault current that can occur at the cutout location, unless suitable interlocks or operating procedures preclude the possibility of closing into a fault. (5) Identification. Oil-filled cutouts shall have a permanent and legible nameplate showing the rated continuous current, rated maximum voltage, and rated interrupting current. (6) Fuse Links. Fuse links shall have a permanent and legible identification showing the rated continuous current. (7) Location. Cutouts shall be so located that they will be readily and safely accessible for re-fusing, with the top of the cutout not over 5 feet (1.52 m) above the floor or platform. (8) Enclosure. Suitable barriers or enclosures shall be provided to prevent contact with nonshielded cables or energized parts of oil-filled cutouts. (e) Load Interrupters. Load-interrupter switches shall be permitted if suitable fuses or circuit breakers are used in conjunction with these devices to interrupt fault currents. Where these devices are used in combination, they shall be so coordinated electrically that they will safely withstand the effects of closing, carrying, or interrupting all possible currents up to the assigned maximum short-circuit rating. ARTICLE 710 - OVER 600 VOLTS, NOMINAL GENERAL 70-745 Where more than one switch is installed with interconnected load terminals to provide for alternate connection to different supply conductors, each switch shall be provided with a conspicuous sign reading: "WARN- ING - SWITCH MAY BE ENERGIZED BY BACKFEED. (1) Continuous Current Rating. The continous current rating of interrupter switches shall equal or exceed the maximum continuous current at the point of installation. (2) Voltage Rating. The maximum voltage rating of interrupter switches shall equal or exceed the maximum circuit voltage. (3) Identification. Interrupter switches shall have a permanent and legible nameplate including the following information: manufacturer's type or designation, continuous current rating, interrupting current rating, fault closing rating, maximum voltage rating. (4) Switching of Conductors. The switching mechanism shall be arranged to be operated from a location where the operator is not exposed to energized parts and shall be arranged to open all ungrounded conductors of the circuit simultaneously with one operation. Switches shall be arranged to be locked in the open position. Metal-enclosed switches shall be operable from outside the enclosure. (5) Stored Energy for Opening. The stored energy operator shall be permitted to be left in the uncharged position after the switch has been closed if a single movement of the operating handle charges the operator and opens the switch. (6) Supply Terminals. Fused interrupter switches shall be so installed that all supply terminals shall be at the top of the switch enclosure. Exception: Supply terminals shall not be required to be at the top of the switch enclosure if barriers are installed to prevent persons from accidentally contacting energized parts or dropping tools or fuses into energized parts. 710-22. Isolating Means. Means shall be provided to completely isolate an item of equipment. The use of isolating switches shall not be required where there are other ways of deenergizing the equipment for inspection and repairs, such as drawout-type metal-enclosed switchgear units and removable truck panels. Isolating switches not interlocked with an approved circuit-interrupting device shall be provided with a sign warning against opening them under load. A fuseholder and fuse, designed for the purpose, shall be permitted as an isolating switch. 710-23. Voltage Regulators. Proper switching sequence for regulators shall be assured by use of one of the following: (1) mechanically sequenced regulator bypass switch(es); (2) mechanical interlocks; or (3) switching procedure prominently displayed at the switching location. 710-24. Metal-Enclosed Power Switchgear and Industrial Control Assemblies. (a) Scope. This section covers assemblies of metal-enclosed power switchgear and industrial control, including but not limited to switches, 70-746 NATIONAL ELECTRICAL CODE interrupting devices and their control, metering, protection and regulating equipment, where an integral part of the assembly, with associated interconnections and supporting structures. This section also includes metalenclosed power switchgear assemblies that form a part of unit substations, power centers, or similar equipment. (b) Arrangement of Devices in Assemblies. Arrangement of devices in assemblies shall be such that individual components can safely perform their intended function without adversely affecting the safe operation of other components in the assembly. (c) Guarding of High-Voltage Energized Parts Within a Compartment. Where access for other than visual inspection is required to a compartment follows: that contains energized high-voltage parts, barriers shall be provided as (1) To prevent accidental contact with energized parts. Exception No. 1: Fuse and fuseholder designed to permit fuse replacement by qualified persons using equipment designed for the purpose without deenergizing the fuseholder. Exception No. 2: Exposed live parts shall be permitted within the compartment where accessible to qualified persons only. (2) To prevent tools or other equipment from being dropped on energized parts. (d) Guarding of Low-Voltage Energized Parts Within a Compartment. Energized bare parts mounted on doors shall be guarded where the door must be opened for maintenance of equipment or removal of drawout equipment. (e) Clearance for Cable Conductors Entering Enclosure. The unobstructed space opposite terminals or opposite raceways or cables entering a switchgear or control assembly shall be adequate for the type of conductor and method of termination. (f) Accessibility of Energized Parts. (1) Doors that would provide nonqualified persons access to highvoltage energized parts shall be locked. (2) Low-voltage control equipment, relays, motors, and the like shall not be installed in compartments with exposed high-voltage energized parts or high-voltage wiring unless the access door or cover is interlocked with I the high-voltage switch or disconnecting means to prevent the door or cover from being opened or removed unless the switch or disconnecting means is in its isolating position. voltage. Exception No. 1: Instrument or control transformers connected to high Exception No. 2: Space heaters. (g) Grounding. Frames of switchgear and control assemblies shall be grounded. ARTICLE 710 - OVER 600 VOLTS, NOMINAL GENERAL 70-747 (h) Grounding of Devices. Devices with metal cases and/or frames, such as instruments, relays, meters, and instrument and control transformers, located in or on switchgear or control, shall have the frame or case grounded. (i) Door Stops and Cover Plates. External hinged doors or covers shall be provided with stops to hold them in the open position. Cover plates intended to be removed for inspection of energized parts or wiring shall be equipped with lifting handles and shall not exceed 12 square feet (1.11 sq m) in area or 60 pounds (27.22 kg) in weight, unless they are hinged and bolted or locked. (j) Gas Discharge from Interrupting Devices. Gas discharged during operating of interrupting devices shall be so directed as not to endanger personnel. (k) Inspection Windows. Windows intended for inspection of disconnecting switches or other devices shall be of suitable transparent material. (I) Location of Devices. Control and instrument transfer switch handles or pushbuttons shall be in a readily accessible location at an elevation not over 78 inches (1.98 m). Exception No. 1: Operating handles requiring more than 50 pounds (22.68 kg) of force shall not be higher than 66 inches (1.68 m) in either the open or closed position. Exception No. 2: Operating handles for infrequently operated devices, such as drawout fuses, fused potential or control transformers and their primary disconnects, and bus transfer switches where they are otherwise safely operable and serviceable from a portable platform. (m) Interlocks - Interrupter Switches. Interrupter switches equipped with stored energy mechanisms shall have mechanical interlocks to prevent access to the switch compartment unless the stored energy mechanism is in the discharged or blocked position. (n) Stored Energy for Opening. The stored energy operator shall be permitted to be left in the uncharged position after the switch has been closed if a single movement of the operating handle charges the operator and opens the switch. (o) Fused Interrupter Switches. (1) Fused interrupter switches shall be so installed that all supply terminals shall be at the top of the switch enclosure. Exception: Supply terminals shall not be required to be at the top of the switch enclosure if barriers are installed to prevent persons from accidentally contacting energized parts or dropping tools or fuses into energized parts. (2) Where fuses can be energized by backfeed, a sign shall be placed on the enclosure door reading: "WARNING - FUSES MAY BE ENER- GIZED BY BACKFEED." (3) The switching mechanism shall be arranged to be operated from a location outside the enclosure where the operator. is not exposed to energized parts and shall be arranged to open all ungrounded conductors of the circuit simultaneously with one operation. Switches shall be capable of being locked in the open position. 70-748 NATIONAL ELECTRICAL CODE (p) Interlocks - Circuit Breakers. (1) Circuit breakers equipped with stored energy mechanisms shall be designed to prevent the release of the stored energy unless the mechanism has been fully charged. (2) Mechanical interlocks shall be provided in the housing to prevent the complete withdrawal of the circuit breaker from the housing when the stored energy mechanism is in the fully charged position. Exception: Where a suitable device is provided that prevents the complete blocked. withdrawal of the circuit breaker unless the closing function is D. Installations Accessible to Qualified Persons Only 710-31. Enclosure for Electrical Installations. See Section 110-31. 710-32. Circuit Conductors. Circuit conductors shall be permitted to be installed in raceways, in cable trays, as metal-clad cable, as bare wire, cable, and busbars, or as Type MV cables, or conductors as provided in I Sections 710-4 through 710-6. Bare live conductors shall conform with Sections 710-33 and 710-34. Insulators, together with their mounting and conductor attachments, where used as supports for wires, single-conductor cables, or busbars, shall be capable of safely withstanding the maximum magnetic forces that would prevail when two or more conductors of a circuit were subjected to short-circuit current. Open runs of insulated wires and cables having a bare lead sheath or a braided outer covering shall be supported in a manner designed to prevent physical damage to the braid or sheath. Supports for lead-covered cables shall be designed to prevent electrolysis of the sheath. 710-33. Minimum Space Separation. In field-fabricated installations, the minimum air separation between bare live conductors and between such conductors and adjacent grounded surfaces shall not be less than the values given in Table 710-33. These values shall not apply to interior portions or exterior terminals of equipment designed, manufactured, and tested in accordance with accepted national standards. 710-34. Work Space and Guarding. See Section 110-34. E. Mobile and Portable Equipment 710-41. General. (a) Covered. The provisions of this part shall apply to installations and use of high-voltage power distribution and utilization equipment that is portable and/or mobile, such as substations and switch houses mounted on skids, trailers, or cars, mobile shovels, draglines, cranes, hoists, drills, dredges, compressors, pumps, conveyors, underground excavators, and the like. ARTICLE 710 - OVER 600 VOLTS, NOMINAL GENERAL 70-749 Table 710-33. Minimum Clearance of Live Parts* Minimum Clearance of Live Parts, Impulse Withstand, in Inches Nominal B.I.L. Voltage kV Phase-to-Phase Phase-to-Ground Rating, kV Indoors Outdoors Indoors Outdoors Indoors Outdoors 2.4-4.16 60 95 4.5 7 3.0 6 7.2 75 95 5.5 7 4.0 6 13.8 95 110 7.5 12 5.0 7 14.4 110 110 9.0 12 6.5 7 23 125 150 10.5 15 7.5 10 34.5 150 150 12.5 15 9.5 10 200 200 18.0 18 13.0 13 46 200 18 13 250 21 17 69 250 21 17 350 31 25 115 550 53 42 138 550 53 42 650 63 50 161 650 63 50 750 72 58 230 750 72 58 900 89 71 1050 105 83 For SI units: one inch = 25.4 millimeters. * The values given are the minimum clearance for rigid parts and bare conductors under favorable service conditions. They shall be increased for conductor movement or under unfavorable service conditions or wherever space limitations permit. The selection of the associated impulse withstand voltage for a particular system voltage is determined by the characteristics of the surge protective equipment. (b) Other Requirements. The requirements of this part shall be additional to, or amendatory of, those prescribed in Articles 100 through 725 of this Code. Special attention shall be paid to Article 250. (c) Protection. Adequate enclosures and/or guarding shall be provided to protect portable and mobile equipment from physical damage. (d) Disconnecting Means. Disconnecting means shall be installed for mobile and portable high-voltage equipment according to the requirements of Part H of Article 230 and shall disconnect all ungrounded conductors. 710-42. Overcurrent Protection. Motors driving single or multiple dc generators supplying a system operating on a cyclic load basis do not require running overcurrent protection, provided that the thermal rating of the ac drive motor cannot be exceeded under any operating condition. The branch-circuit protective device(s) shall provide short-circuit and lockedrotor protection, and shall be permitted to be external to the equipment. 70-750 NATIONAL ELECTRICAL CODE 710-43. Enclosures. All energized switching and control parts shall be enclosed in effectively grounded metal cabinets or enclosures. These cabinets or enclosures shall be marked "DANGER - HIGH VOLTAGE - KEEP OUT" and shall be locked so that only authorized and qualified persons can enter. Circuit breakers and protective equipment shall have the operating means projecting through the metal cabinet or enclosure so these units can be reset without opening locked doors. With doors closed, reasonable safe access for normal operation of these units shall be provided. 710-44. Collector Rings. The collector ring assemblies on revolving-type machines (shovels, draglines, etc.) shall be guarded to prevent accidental contact with energized parts by personnel on or off the machine. 710-45. Power Cable Connections to Mobile Machines. A metallic enclosure shall be provided on the mobile machine for enclosing the terminals of the power cable. The enclosure shall include provisions for a solid connection for the ground wire(s) terminal to effectively ground the machine frame. Ungrounded conductors shall be attached to insulators or terminated in approved high-voltage cable couplers (which include ground wire connectors) of proper voltage and ampere rating. The method of cable termination used shall prevent any strain or pull on the cable from stressing the electrical connections. The enclosure shall have provision for locking so only authorized and qualified persons may open it and shall be marked "DANGER - HIGH VOLTAGE - KEEP OUT." 710-46. High-Voltage Portable Cable for Main Power Supply. Flexible high-voltage cable supplying power to portable or mobile equipment shall comply with Article 250 and Article 400, Part C. 710-47. Grounding. Mobile equipment shall be grounded in accordance with Article 250. F. Tunnel Installations 710-51. General. (a) Covered. The provisions of this part shall apply to installation and use of high-voltage power distribution and utilization equipment that is portable and/or mobile, such as substations, trailers, or cars, mobile shovels, draglines, hoists, drills, dredges, compressors, pumps, conveyors, underground excavators, and the like. (b) Other Articles. The requirements of this part shall be additional to, or amendatory of, those prescribed in Articles 100 through 710 of this Code. Special attention shall be paid to Article 250. (c) Protection Against Physical Damage. Conductors and cables in tunnels shall be located above the tunnel floor and so placed or guarded to protect them from physical damage. 710-52. Overcurrent Protection. Motor-operated equipment shall be protected from overcurrent in accordance with Article 430. Transformers shall be protected from overcurrent in accordance with Article 450. ARTICLE 710 - OVER 600 VOLTS, NOMINAL GENERAL 70-751 710-53. Conductors. High-voltage conductors in tunnels shall be installed in (1) metal conduit or other metal raceway; (2) Type MC cable; or (3) other approved multiconductor cable. Multiconductor portable cable shall be permitted to supply mobile equipment. 710-54. Bonding and Equipment Grounding Conductor. (a) Grounded and Bonded. All noncurrent-carrying metal parts of electric equipment and all metal raceways and cable sheaths shall be effectively grounded and bonded to all metal pipes and rails at the portal and at intervals not exceeding 1000 feet (305 m) throughout the tunnel. (b) Equipment Grounding Conductor. An equipment grounding conductor shall be run with circuit conductors inside the metal raceway or inside the multiconductor cable jacket. The equipment grounding conductor shall be permitted to be insulated or bare. 710-55. Transformers, Switches, and Electric Equipment. All transformers, switches, motor controllers, motors, rectifiers, and other equipment installed below ground shall be protected from physical damage by location or guarding. 710-56. Energized Parts. Bare terminals of transformers, switches, motor controllers, and other equipment shall be enclosed to prevent accidental contact with energized parts. 710-57. Ventilation System Controls. Electrical controls for the ventilation system shall be so arranged that the airflow can be reversed. 710-58. Disconnecting Means. A switching device meeting the requirements of Article 430 or 450 shall be installed at each transformer or motor location for disconnecting the transformer or motor. The switching device shall open all ungrounded conductors of a circuit simultaneously. 710-59. Enclosures. Enclosures for use in tunnels shall be dripproof, weatherproof, or submersible as required by the environmental conditions. Switch or contactor enclosures shall not be used as junction boxes or raceways for conductors feeding through or tapping off to other switches, unless special designs are used to provide adequate space for this purpose. 710-60. Grounding. Tunnel equipment shall be grounded in accordance with Article 250. G. Electrode-type Boilers 710-70. General. The provisions of this part shall apply to boilers operating over 600 volts, nominal, in which heat is generated by the passage of current between electrodes through the liquid being heated. 710-71. Electric Supply System. Electrode-type boilers shall be supplied only from a 3-phase, 4-wire solidly grounded wye system, or from isolating transformers arranged to provide such a system. Control circuit voltages shall not exceed 150 volts, shall be supplied from a grounded system, and shall have the controls in the ungrounded conductor. 70-752 NATIONAL ELECTRICAL CODE 710-72. Branch Circuit Requirements. (a) Rating. Each boiler shall be supplied from an individual branch circuit rated not less than 100 percent of the total load. (b) Common-Trip Fault Interrupting Device. The circuit shall be protected by a 3-phase common-trip fault interrupting device, which shall be permitted to automatically reclose the circuit upon removal of an overload condition but shall not reclose after a fault condition. (c) Phase Fault Protection. Phase fault protection shall be provided in each phase, consisting of a separate phase overcurrent relay connected to a separate current transformer in the phase. (d) Ground Current Detection. Means shall be provided for detection of the sum of the neutral and ground currents and shall trip the circuit interrupting device if the sum of those currents exceeds the greater of 5 amperes or 7½ percent of the boiler full-load current for 10 seconds or exceeds an instantaneous value of 25 percent of the boiler full-load current. (e) Grounded Neutral Conductor. The grounded neutral conductor shall: (1) Be connected to the pressure vessel containing the electrodes. (2) Be insulated for not less than 600 volts. (3) Have not less than the ampacity of the largest ungrounded branchcircuit conductor. (4) Be installed in the same raceway or cable tray with the ungrounded conductors. (5) Not be used for any other circuit. 710-73. Pressure and Temperature Limit Control. Each boiler shall be equipped with a means to limit the maximum temperature and/or pressure by directly or indirectly interrupting all current flow through the electrodes. Such means shall be in addition to the temperature and/or pressure regulating systems and pressure relief or safety valves. 710-74. Grounding. All exposed noncurrent-carrying metal parts of the boiler and associated exposed grounded structures or equipment shall be bonded to the pressure vessel or to the neutral conductor to which the vessel is connected, in accordance with Section 250-79, except the ampacconductor. ity of the bonding jumper shall be not less than the ampacity of the neutral