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National Electrical Code Articles and Information

Based on the 2008 NEC

by Mark Lamendola

National Electrical Code Top Ten Tips: Article 503 -- Class III Hazardous Locations

  1. The definitions of Class I, Class II, and Class III locations are in Article 500.5. That's easy enough to remember.
  2. The general requirements (NEC Chapters 1 through 4) still apply to Hazardous locations--except as specifically modified in Chapter 5.
  3. Equipment installed in Class III locations must be able to function without getting hot enough to cause spontaneous ignition.
  4. The requirements for wiring methods are in 503.10. These differ from Class I and Class II methods.
  5. The definition of "dusttight" is in Article 100.
  6. Per 503.4, you must use dustight enclosures for circuit breakers, fuses, motor controllers, pushbuttons, relays, switches, and other devices intended to interrupt current during normal operation.
  7. Ditto for control transformers.
  8. The special requirements for motors and generators are in 503.6.

  10. Luminaires have special requirements, as outlined in 503.9. Other devices, such as flexible cords, plugs, and receptacles also have special requirements. Refer to the appropriate part of 503.
  11. Per 503.16, wiring and equipment in Class III locations must be grounded and bonded as specified in Article 250, but with additional requirements.

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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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