Based on the 2017 NEC

by Mark Lamendola

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 exception].
  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].