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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.

    9.  
  9. 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.
     
  10. Per 503.16, wiring and equipment in Class III locations must be grounded and bonded as specified in Article 250, but with additional requirements.
    11.

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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.

 

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