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

by Mark Lamendola

Based on the 2011 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]. Keep all wiring in its own section, and don't mix wiring between sections.
  2. Bond all sections together, using a bonding jumper sized per Table 250.122 or Table 250.66 [408.3].
  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].
  4. On Delta systems, you must designate the phase with the highest voltage to ground as the B phase [408.3].
  5. Fill out the circuit directory, and do so legibly with sufficient detail [408.4].
  6. Close any unused openings [408.7].
  7. If locating in wet locations or near combustible materials, follow the rules in 408.16 and 408.17.
  8. Classify your panelboard as either a power panelboard or a lighting panelboard (per 408.30), and then follow the appropriate instructions in Article 408, Part II.
  9. Provide protection on the supply side to each lighting and appliance panelboard. You can use one or two overcurrent protection devices, but not more [408.36].
  10. Observe the minimum spacing requirements provided in Table 408.56.

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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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