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National Electrical Code Articles and Information

Based on the 2011 NEC

by Mark Lamendola

National Electrical Code Top Ten Tips: Article 668 -- Electrolytic Cells

An electrolytic cell, by general definition, is any container that holds an electrolytic solution. Electrolysis occurs when you pass electricity through a chemical solution (or melted substance) to break it down into its components. The solution may be a chemical compound, such as water (break it down into hydrogen and oxygen) or a material dissolved in a liquid (sodium dissolved in water, for example).

Batteries have electrolytes, so are they electrolytic cells? No, not really. The reason is instead of adding electricity to break down what's in the battery, you break down what's in the battery to generate electricity. Thus, Article 668 does not cover batteries. It doesn't cover electroplating processes or cells used for generating hydrogen. Those are covered in Articles 669 and 692, respectively.

  1. Article 668 pertains to the installation of the electrical components and accessory equipment used n producing a list of elements and compounds [668.1]. Equipment used to make materials not in the list probably should be installed per Article 668, but there's no code requirement to do so.
     
  2. Equipment related to the electrolytic cells but not within the electrolytic zone need not comply with Article 668. Apply Chapters 1 through 4, though [668.3(A)].
     
  3. Actually, Chapters 1 through 4 apply to all equipment except as amended in specifically applicable Articles in Chapters 5 through 7. For electrolytic cells, the amendments are in Article 668 [668.3(C)].
     
  4. One big amendment is items specifically listed in [668.3(C)(1)] don't need to comply with Articles 110, 210, 215, 220, and 225, if those items are in the cell line working zone.
     
  5. The vertical boundaries of a cell line working zone are 2.5 m (96 in) above or below energized surfaces of electrolytic cells or their energized attachments [668.10(A)].
     
  6. The horizontal boundaries of a cell line working zone are 1m (42 in) from such surfaces or attachments.
     
  7.  This zone does not extend through walls, floors, ceilings, or similar barriers.
     
  8. Don't ground portable electrical equipment [668.20]. Such grounding is permitted by two exceptions listed in 668.20.
     
  9. The portion of an overhead crane or hoist that contacts energized surfaces of electrolytic cells or their energized attachments must be insulated from ground [668.32)A).
     
  10. You can use general-purpose electrical enclosures only if a natural draft ventilation system prevents the accumulation of gases [668.40]. Note that air movement alone does not qualify. Gases may rise into upper cavities or sink into lower compartments. It's better to do a gas survey rather than simply assume. Adding a fan doesn't solve the problem; the ventilation must exist without power being applied.

 

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How the NEC is arranged

  1. The first four Chapters of the NEC apply to all installations.
  2. Article 90 precedes Chapter One, and establishes the authority of the NEC.
  3. Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
  4. Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
  5. Chapter 8 provides the requirements for communications systems.
  6. Chapter 9 provides tables.
  7. The appendices provide mostly reference information.
  8. Appendix D contains examples that every NEC user should study.

Try your NEC moxy:

  • Do you know the difference between bonding and grounding? Hint: Look in the NEC, Article 100.
  • Does the NEC refer to grounding incorrectly in any of its articles? Yes! So be careful to apply the Article 100 definitions. Don't ground where you should bond.
  • When doing motor load calculations, which Article covers hermetic motors? Answer: While Article 440 covers the application of hermetic motors, it does so only by amending Article 430 because hermetic motors are a special case of motors. For motor load calculations, refer to Article 430.
  • Does the NEC provide a voltage drop requirement? Yes! It does so in a special case, which is Article 648 Sensitive Electronic Equipment. But for general applications, it does not provide a requirement; it merely provides a recommendation in a couple of FPNs.
  • Take our Code Quizzes.

Remember other applicable codes, rules, standards, and references:

  • OSHA's electrical worker safety rules.
  • IEEE standards.
  • NETA standards.
  • NFPA standards.
  • International Codes (if applicable to the installation).
  • State Codes (if the state has them).
  • Local ordinances and permit requirements.
  • Local fire codes.
  • Manufacturer requirements or guidelines.
  • Customer security requirements.
  • Industry standards.
  • Your company's own internal standards, practices, and procedures.
  • Engineering drawing notes.

 

 

 

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