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

Exception No. 3: Equipment located or used within the electrolytic cell line working zone or associated with the cell line dc power circuits shall not be required to comply with the provisions of Article 250. Exception No. 4: The electrolytic cells, cell line attachments, and the wiring of auxiliary equipments and devices within the cell line working zone shall not be required to comply with the provisions of Articles 110, 210, 215, 220, and 225. See Section 668-30. (FPN): See Section 668-15 on equipment, apparatus, and structural component grounding. 668-10. Cell Line Working Zone. (a) Area Covered. The space envelope of the cell line working zone shall encompass any space: (1) Within 96 inches (2.44 m) above energized surfaces of electrolytic cell lines or their energized attachments. (2) Below energized surfaces of electrolytic cell lines or their energized attachments, provided the head room in the space beneath is less than 96 inches (2.44 m). (3) Within 42 inches (1.07 m) horizontally from energized surfaces of electrolytic cell lines or their energized attachments or from the space envelope described in Section 668-10(a)(1) or (a)(2). (b) Area Not Covered. The cell line working zone shall not be required to extend through or beyond walls, floors, roofs, partitions, barriers, or the like. ARTICLE 668 - ELECTROLYTIC CELLS 70-685 668-11. DC Cell Line Process Power Supply. (a) Not Grounded. The dc cell line process power supply conductors shall not be required to be grounded. (b) Metal Enclosures Grounded. All metal enclosures of dc cell line process power supply apparatus operating at a power supply potential between terminals of over 50 volts shall be grounded: (1) Through protective relaying equipment, or (2) By No. 2/0 minimum copper grounding conductor or a conductor I of equal ampacity. (c) Grounding Requirements. The grounding connections required by Section 668-11(b) shall be installed in accordance with Sections 250-112, 250-113, 250-115, 250-117, and 250-118. 668-12. Cell Line Conductors. (a) Insulation and Material. Cell line conductors shall be either bare, covered, or insulated and of copper, aluminum, copper-clad aluminum, steel, or other suitable material. (b) Size. Cell line conductors shall be of such cross-sectional area that the temperature rise under maximum load conditions and at maximum ambient shall not exceed the safe operating temperature of the conductor insulation or the material of the conductor supports. (c) Connections. Cell line conductors shall be joined by bolted, welded, clamped, or compression connectors. 668-13. Disconnecting Means. (a) More than One Process Power Supply. Where more than one dc cell line process power supply serves the same cell line, a disconnecting means shall be provided on the cell line circuit side of each power supply to disconnect it from the cell line circuit. (b) Removable Links or Conductors. Removable links or removable conductors shall be permitted to be used as the disconnecting means. 668-14. Shunting Means. (a) Partial or Total Shunting. Partial or total shunting of cell line circuit current around one or more cells shall be permitted. (b) Shunting One or More Cells. The conductors, switches, or combination of conductors and switches used for shunting one or more cells shall comply with the applicable requirements of Section 668-12. 668-15. Grounding. For equipment, apparatus, and structural components that are required to be grounded by provisions of Article 668, the provisions of Article 250 shall apply. Exception No. 1: A water pipe electrode shall not be required to be used. Exception No. 2: Any electrode or combination of electrodes described in Sections 250-81 and 250-83 shall be permitted. 70-686 NATIONAL ELECTRICAL CODE 668-20. Portable Electrical Equipment. (a) Portable Electrical Equipment Not to Be Grounded. The frames and enclosures of portable electrical equipment used within the cell line working zone shall not be grounded. Exception No. 1: Where the cell line circuit voltage does not exceed 200 volts dc, these frames and enclosures shall be permitted to be grounded. Exception No. 2: These frames and enclosures shall be permitted to be grounded where guarded. (b) Isolating Transformers. Electrically powered, hand-held, cordconnected portable equipment with ungrounded frames or enclosures used within the cell line working zone shall be connected to receptacle circuits having only ungrounded conductors such as a branch circuit supplied by an isolating transformer with an ungrounded secondary. (c) Marking. Ungrounded portable electrical equipment shall be distinctively marked and shall employ plugs and receptacles of a configuration that prevents connection of this equipment to grounding receptacles and that prevents inadvertent interchange of ungrounded and grounded portable electrical equipments. 668-21. Power Supply Circuits and Receptacles for Portable Electrical Equipment. (a) Isolated Circuits. Circuits supplying power to ungrounded receptacles for hand-held, cord-connected equipments shall be electrically isolated from any distribution system supplying areas other than the cell line working zone and shall be ungrounded. Power for these circuits shall be supplied through isolating transformers. Primaries of such transformers shall operate at not more than 600 volts between conductors and shall be provided with proper overcurrent protection. The secondary voltage of such transformers shall not exceed 300 volts between conductors, and all circuits supplied from such secondaries shall be ungrounded and shall have an approved overcurrent device of proper rating in each conductor. (b) Noninterchangeability. Receptacles and their mating plugs for ungrounded equipment shall not have provision for a grounding conductor and shall be of a configuration that prevents their use for equipment required to be grounded. (c) Marking. Receptacles on circuits supplied by an isolating transformer with an ungrounded secondary shall be a distinctive configuration, distinctively marked, and shall not be used in any other location in the plant. 668-30. Fixed and Portable Electrical Equipment. (a) Electrical Equipment Not Required to Be Grounded. AC systems supplying fixed and portable electrical equipments within the cell line working zone shall not be required to be grounded. (b) Exposed Conductive Surfaces Not Required to Be Grounded. Exposed conductive surfaces, such as electrical equipment housings, ARTICLE 668 - ELECTROLYTIC CELLS 70-687 cabinets, boxes, motors, raceways, and the like that are within the cell line working zone shall not be required to be grounded. (c) Wiring Methods. Auxiliary electrical devices such as motors, transducers, sensors, control devices, and alarms, mounted on an electrolytic cell or other energized surface, shall be connected to premises wiring systems by any of the following means: (1) Multiconductor hard usage cord; (2) Wire or cable in suitable raceways or metal or nonmetallic cable trays. If metal conduit, cable tray, armored cable, or similar metallic systems are used, they shall be installed with insulating breaks such that they will not cause a potentially hazardous electrical condition. (d) Circuit Protection. Circuit protection shall not be required for control and instrumentation that are totally within the cell line working zone. (e) Bonding. Bonding of fixed electrical equipment to the energized conductive surfaces of the cell line, its attachments, or auxiliaries shall be permitted. Where fixed electrical equipment is mounted on an energized conductive surface, it shall be bonded to that surface. 668-31. Auxiliary Nonelectric Connections. Auxiliary nonelectric connections, such as air hoses, water hoses, and the like, to an electrolytic cell, its attachments, or auxiliary equipments shall not have continuous conductive reinforcing wire, armor, braids, and the like. Hoses shall be of a nonconductive material. 668-32. Cranes and Hoists. (a) Conductive Surfaces to Be Insulated from Ground. The conductive surfaces of cranes and hoists that enter the cell line working zone shall not be required to be grounded. The portion of an overhead crane or hoist that contacts an energized electrolytic cell or energized attachments shall be insulated from ground. (b) Hazardous Electrical Conditions. Remote crane or hoist controls that may introduce hazardous electrical conditions into the cell line working zone shall employ one or more of the following systems: (1) Insulated and ungrounded control circuit in accordance with Section 668-21(a); (2) Nonconductive rope operator; (3) Pendant pushbutton with nonconductive supporting means and having nonconductive surfaces or ungrounded exposed conductive surfaces; (4) Radio. 668-40. Enclosures. General-purpose electrical equipment enclosures shall be permitted where a natural draft ventilation system prevents the accumulation of gases. 70-688 NATIONAL ELECTRICAL CODE