Based on the 2008 NEC
National Electrical Code Articles and Information
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].
- 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].
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Learn more about:
How the NEC is arranged
- The first four Chapters of the NEC apply to all installations.
- Article 90 precedes Chapter One, and establishes the authority of the NEC.
- Article 80 follows the body of the NEC; it exists as Annex H. It provides the requirements for administration.
- Chapters 5, 6, and 7 are the "special" chapters, covering special: occupancies, equipment, and conditions (in that order).
- Chapter 8 provides the requirements for communications systems.
- Chapter 9 provides tables.
- The appendices provide mostly reference information.
- 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.