Code books
 

Construction Codebooks and Estimating Guides

+National Electrical Code Explanations

National Electrical Code Top Ten Tips: Article 506, Zone 20, 21, and 22 Locations

  1. Article 506 covers the requirements for the zone classification system as an alternative to the division classification system covered in Articles 500, 502, and 503 for Zone 20, 21, and 22.
     
  2. Dust-ignitionproof refers to keeping equipment enclosed in a manner that keeps sparks and flames contained within the enclosure and keeps dust out [506.2].
     
  3. If you use the zone system, you must generate and maintain specific documentation [506.4]. The documentation requirements are far from casual.
     
  4. Exactly how you may classify a location depends on the properties of the ignitible fibers or flyings that may be present and on their concentration [506.5].
     
  5. Summary of Zone 20 definition: Ignitible fibers or flyings are consistently present and are present for long periods [506.5(B)(1)].
     
  6. Summary of Zone 21 definition: Ignitible fibers or flyings are likely to exist under normal operations, during repair, or during breakdown [506.5(B)(2)].
     
  7. Summary of Zone 22 definition: Ignitible fibers or flyings are not likely to exist under normal operations [506.5(B)(3)].
     
  8. Note that we have oversimplified the definitions of Zone 20, 21, and 22 so that you can easily see how they differ. Read the references thoroughly to understand the implications for a given location.
     
  9. Dual classification and reclassification are permitted [506.6].
     
  10. Article 506 lists 11 protection techniques. Five of those are new with the 2008 Revision. Two of the new techniques are encapsulation techniques (maD and mbD). The other three are protection by enclosure, pressurization, and intrinsic safety. Only a qualified person can determine the area classification and only a qualified person can determine which mix of protection techniques to apply to a given installation.
    11.

We work closely with Mike Holt. If you want to boost your Code competence dramatically, check out the Holt courses and guides we offer. These are well-researched and noted for their accuracy and clarity. Go with the best, so you can be one of the best.

Other Codes

More NFPA 70 Resources
Learn more about: Mike Holt Ultimate Electrician Training Library

Contractor Cafe Code Site | Joe Tedesco's National Electrical Code

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.

 

 

Pass the Electrical Exam | Get Codebooks | Get Estimating Guides
Codebookcity is a subsidiary of Mindconnection, LLC. If you have any questions, comments, or concerns, please write to sales @ mindconnection.com. We do want your business.
 

We support engineering and the construction trades. Based in Kansas City, we also participate locally. Here are the meetings of the IEEE Kansas City Section and Society Chapters: