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National Electrical Code Articles and Information

National Electrical Code Top Ten Tips: Article 408 -- Switchboards and Panelboards

by Mark Lamendola

Based on the 2017 NEC

Please note, we do quote from copyrighted material. While the NFPA does allow such quotes, it does so only for the purposes of education regarding the National Electrical Code. This article is not a substitute for the NEC.

These are the 10 NEC Article 408 items we deem most important, based on the pervasiveness of confusion and the potential costs of same.

  1. Respect the "modular integrity" philosophy of switchboard and panelboard installation. Donít use any vertical section as a wireway between other vertical sections [408.3(A)]. Keep all wiring in its own section, and don't mix wiring between sections.
  2. If used as service equipment, bond all sections together using a bonding jumper sized per Table 250.122 or Table 250.66 [408.3(C)]. If not used as service equipment, also bond all sections together even though this isn't explicitly required here. That will eliminate dangerous differences of potential.
  3. You must arrange the phases in a particular order. That order is A, B, C--from front to back and from top to bottom (or left to right), when viewing the cabinet from the front [408.3(E)].
  4. On Delta systems, you must designate the phase with the highest voltage to ground as the B phase [408.3(F)].
  5. Fill out the circuit directory, and do so legibly with sufficient detail [408.4(A)]. Rather than handwriting, use a professional-level labeler. The cleanest way to fill out the directory is to print the information on an overlay that you paste over the factory directory. Consult the manufacturer for more information on best practices for directories.
  6. Close any unused openings [408.7].
  7. If locating switchboards in wet locations or near combustible materials, follow the rules in 408.16 and 408.17.
  8. All panelboards must have a rating of at least the minimum feeder capacity required for the load calculated per Article 220, Parts III, IV, and V as applicable [408.30].
  9. Provide overcurrent protection on the supply side to each panelboard. The rating of the OCPD cannot exceed the rating of the panelboard [408.36].
  10. Observe the minimum spacing requirements provided in Table 408.56. Please note that these are minimums. Actual conditions and common sense, not to mention sound engineering practices and maintenance needs, may require exceeding these minimums.

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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