National Electrical Code Top Ten Tips: Article 504 -- Intrinsically Safe Systems
- 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].
- 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].
- If it's part of an intrinsically safe installation, you must
install it per the control drawing(s) [504.10(A)].
- You can use a general enclosure with intrinsically safe
- You can use any of the wiring methods suitable for unclassified
locations, when installing intrinsically safe apparatus [504.20].
- 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
- You must connect intrinsically safe apparatus, enclosures, and
raceways (if metallic) to the equipment grounding conductor
- Bond all metallic objects of an intrinsically safe system, per
- Enclosures that contain only intrinsically safe apparatus don't
have to be sealed (except as required by 501.15(F)(3)) [504.70 exception].
- 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].