Article 668

Electrolytic Cells

1. Scope. This article applies to the installation of the electrical components and accessory equipment of electrolytic cells, electrolytic cell lines, and process power supply for the production of aluminum, cadmium, chlorine, copper, fluorine, hydrogen peroxide, magnesium, sodium, sodium chlorate, and zinc.Not covered by this article are cells used as a source of elec‐ tric energy and for electroplating processes and cells used for the production of hydrogen.Informational Note No. 1: In general, any cell line or group of cell lines operated as a unit for the production of a particular metal, gas, or chemical compound may differ from any other cell lines producing the same product because of variations in the particular raw materials used, output capacity, use of propri‐ etary methods or process practices, or other modifying factors to the extent that detailed Code requirements become overly restrictive and do not accomplish the stated purpose of this Code.Informational Note No. 2: For further information, see IEEE 463-2013, Standard for Electrical Safety Practices in Electrolytic Cell Line Working Zones.
2. Definitions.Cell Line. An assembly of electrically interconnected electro‐ lytic cells supplied by a source of direct-current power.Cell Line Attachments and Auxiliary Equipment. As applied to this article, a term that includes, but is not limited to, auxiliary tanks; process piping; ductwork; structural supports; exposed cell line conductors; conduits and other raceways; pumps, posi‐ tioning equipment, and cell cutout or bypass electrical devices. Auxiliary equipment includes tools, welding machines, cruci‐ bles, and other portable equipment used for operation and maintenance within the electrolytic cell line working zone.In the cell line working zone, auxiliary equipment includes the exposed conductive surfaces of ungrounded cranes and crane-mounted cell-servicing equipment.Electrically Connected. A connection capable of carrying current as distinguished from connection through electromag‐ netic induction.Electrolytic Cell. A tank or vat in which electrochemical reac‐ tions are caused by applying electric energy for the purpose of refining or producing usable materials.Electrolytic Cell Line Working Zone. The space envelope wherein operation or maintenance is normally performed on or in the vicinity of exposed energized surfaces of electrolytic cell lines or their attachments.
3. Other Articles.

1. Lighting, Ventilating, Material Handling. Chapters 1 through 4 shall apply to services, feeders, branch circuits, and apparatus for supplying lighting, ventilating, material handling, and the like that are outside the electrolytic cell line working zone.668.3 ARTICLE 668 — ELECTROLYTIC CELLS
2. Systems Not Electrically Connected. Those elements of a cell line power-supply system that are not electrically connected to the cell supply system, such as the primary winding of a two- winding transformer, the motor of a motor-generator set, feed‐ ers, branch circuits, disconnecting means, motor controllers, and overload protective equipment, shall be required to comply with all applicable provisions of this Code.
3. Electrolytic Cell Lines. Electrolytic cell lines shall comply with the provisions of Chapters 1 through 4 except as amended in 668.3(C)(1) through (C)(4).
   1. Conductors. The electrolytic cell line conductors shall not be required to comply with the provisions of Articles 110, 210, 215, 220, and 225. See 668.11.
   2. Overcurrent Protection. Overcurrent protection of elec‐ trolytic cell dc process power circuits shall not be required to comply with the requirements of Article 240.
   3. Grounding. Equipment located or used within the electro‐ lytic cell line working zone or associated with the cell line direct-current power circuits shall not be required to comply with the provisions of Article 250.
   4. Working Zone. The electrolytic cells, cell line attachments, and the wiring of auxiliary equipment 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 668.30.

Informational Note: See 668.15 for equipment, apparatus, and structural component grounding.

1. Cell Line Working Zone.
   1. Area Covered. The space envelope of the cell line work‐ ing zone shall encompass spaces that meet any of the following conditions:
      1. Is within 2.5 m (96 in.) above energized surfaces of elec‐ trolytic cell lines or their energized attachments
      2. Is below energized surfaces of electrolytic cell lines or their energized attachments, provided the headroom in the space beneath is less than 2.5 m (96 in.)
      3. Is within 1.0 m (42 in.) horizontally from energized surfa‐ ces of electrolytic cell lines or their energized attach‐ ments or from the space envelope described in 668.10(A) (1) or (A)(2)
   2. 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.
2. Direct-Current Cell Line Process Power Supply.
   1. Not Grounded. The direct-current cell line process power-supply conductors shall not be required to be grounded.
   2. Metal Enclosures Grounded. All metal enclosures of power-supply apparatus for the direct-current cell line process operating with a power supply over 50 volts shall be grounded by either of the following means:
      1. Through protective relaying equipment
      2. By a minimum 2/0 AWG copper grounding conductor or a conductor of equal or greater conductance
   3. Grounding Requirements. The grounding connections required by 668.11(B) shall be installed in accordance with 250.8, 250.10, 250.12, 250.68, and 250.70.
3. Cell Line Conductors.
   1. 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.
   2. 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.
   3. Connections. Cell line conductors shall be joined by bolted, welded, clamped, or compression connectors.
4. Disconnecting Means.
   1. More Than One Process Power Supply. Where more than one direct-current 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.
   2. Removable Links or Conductors. Removable links or removable conductors shall be permitted to be used as the disconnecting means.
5. Shunting Means.
   1. Partial or Total Shunting. Partial or total shunting of cell line circuit current around one or more cells shall be permit‐ ted.
   2. 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 668.12.
6. 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, except a water pipe electrode shall not be required to be used. Any elec‐ trode or combination of electrodes described in 250.52 shall be permitted.

1. Portable Electrical Equipment.
   1. 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 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.
   2. Isolating Transformers. Electrically powered, hand-held, cord-connected portable equipment with ungrounded frames or enclosures used within the cell line working zone shall be connected to receptacle circuits that have only ungrounded conductors such as a branch circuit supplied by an isolating transformer with an ungrounded secondary.
   3. Marking. Ungrounded portable electrical equipment shall be distinctively marked and shall employ plugs and recep‐ tacles of a configuration that prevents connection of this equip‐ ment to grounding receptacles and that prevents inadvertent interchange of ungrounded and grounded portable electrical equipments.
   ARTICLE 669 — ELECTROPLATING 669.6
2. Power-Supply Circuits and Receptacles for Portable Electrical Equipment.

1. Isolated Circuits. Circuits supplying power to ungroun‐ ded receptacles for hand-held, cord-connected equipment 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 1000 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 conduc‐ tor.
2. 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.
3. Marking. Receptacles on circuits supplied by an isolating transformer with an ungrounded secondary shall be a distinc‐ tive configuration, shall be distinctively marked, and shall not be used in any other location in the plant.

1. Fixed and Portable Electrical Equipment.
   1. Electrical Equipment Not Required to Be Grounded. Alternating-current systems supplying fixed and portable elec‐ trical equipment within the cell line working zone shall not be required to be grounded.
   2. Exposed Conductive Surfaces Not Required to Be Groun‐ ded. Exposed conductive surfaces, such as electrical equip‐ ment housings, cabinets, boxes, motors, raceways, and the like, that are within the cell line working zone shall not be required to be grounded.
   3. Wiring Methods. Auxiliary electrical equipment 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 do not cause a potentially hazardous electrical condition.
   4. Circuit Protection. Circuit protection shall not be required for control and instrumentation that are totally within the cell line working zone.
   5. 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 equip‐ ment is mounted on an energized conductive surface, it shall be bonded to that surface.
2. Auxiliary Nonelectrical Connections. Auxiliary nonelectrical connections, such as air hoses, water hoses, and the like, to an electrolytic cell, its attachments, or auxiliary equipment shall not have continuous conductive reinforcing wire, armor, braids, and the like. Hoses shall be of a noncon‐ ductive material.
3. Cranes and Hoists.

1. 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 ener‐ gized electrolytic cell or energized attachments shall be insula‐ ted from ground.
2. Hazardous Electrical Conditions. Remote crane or hoist controls that could introduce hazardous electrical conditions into the cell line working zone shall employ one or more of the following systems:

1. Isolated and ungrounded control circuit in accordance with 668.21(A)
2. Nonconductive rope operator
3. Pendant pushbutton with nonconductive supporting means and having nonconductive surfaces or ungroun‐ ded 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.