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.

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