construction code books

Home | Search | About us                  Bookmark and Share

nec training

National Electrical Code Articles and Information

Based on the 2017 NEC

by Mark Lamendola

National Electrical Code Top Ten Tips: Article 500 -- Hazardous Locations

  1. Article 500 provides the basis for interpreting and correctly applying Articles 501 - 516. For one thing, you will find the definitions for those Articles in Article 500.
  2. How a location is classified depends on the properties of materials in that location or that are likely to be in that location [500.5].
  3. Class I locations are those in which flammable gases or vapors are (or may be) present in sufficient quantities to produce explosive or ignitible mixtures [500.5(B)].
  4. Class II locations are those in which combustible dust is (or may be) present in sufficient quantities to produce a hazard of explosion or ignition 500.5(C)].
  5. Class III locations are those in which combustible fibers or flyings are (or may be) present in sufficient quantities to produce a hazard of explosion or ignition 500.5(D)].
  6. Class locations are further broken down into Division 1 (normal operations) and Division 2 (abnormal operations). Does this location meet its Class I, II, or III designation during normal operations or only during abnormal operations?
  7. 500.7 provides 12 of what it calls "protection techniques." These are not actually "techniques," just as the Chapter Three to "wiring methods" aren't actual "methods." But if you read this, you'll understand what they mean.
  8. A given hazardous location can contain only equipment that is approved for use in that location [500.8(B)].
  9. You must address explosion properties and ignition temperature separately [500.8, Informational Note No. ].
  10. You must account for temperatures other than just ignition temperatures [500.8(C) and (D)].


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.

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.


Codebookcity is a subsidiary of Mindconnection, LLC. If you have any questions, comments, or concerns, please write to sales @ We do want your business.