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National Electrical Code Top Ten Tips: Article 504, Intrinsically Safe Systems

  1. Article 504 covers the installation of intrinsically safe apparatus in Class I, Class II, and Class III locations (defined in Article 500.5) [504.1].
     
  2. An intrinsically safe circuit is one that won't ignite due to spark or thermal effect of (flammable or combustible) material in air under prescribed test conditions [504.2].
     
  3. If it's part of an intrinsically safe installation, you must install it per the control drawing(s) [504.10(A)].
     
  4. You can use a general enclosure with intrinsically safe apparatus [504.10(B)].
     
  5. You can use any of the wiring methods suitable for unclassified locations, when installing intrinsically safe apparatus [504.20].
     
  6. You must separate intrinsically safe conductors from nonintrinsically safe conductors [504.30(A)]. This requirement is the core of Article 504 and its details make up about half of Article 504.
     
  7. You must connect intrinsically safe apparatus, enclosures, and raceways (if metallic) to the equipment grounding conductor [504.50].
     
  8. Bond all metallic objects of an intrinsically safe system, per 250.100 [504.60]
     
  9. Enclosures that contain only intrinsically safe apparatus don't have to be sealed (except as required by 501.15(F)(3)) [504.70].
     
  10. Intrinsically safe circuits must be identified at terminal and junction locations, in a manner that prevents unintentional interference with the circuits during testing and servicing [504.80].
    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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