Based on the 2017 NEC

by Mark Lamendola

National Electrical Code Top Ten Tips: Article 505 -- Class I, Zone 0, 1, and 2 Locations

  1. Article 505 covers the requirements for the zone classification system as an alternative to the division classification system covered in Article 500 for Class I, Zone 0, 1, and 2.
     
  2. Flameproof refers to keeping flames contained within the enclosure, not whether something is flammable [505.2].
     
  3. If you use the zone system, you must generate and maintain specific documentation [505.4]. The documentation requirements are far from casual.
     
  4. Exactly how you may classify a location depends on the properties of the flammable substances that may be present and on their concentration [505.5].
     
  5. Class 1, Zone 0 basically means ignitible concentrations of vapors or gases are consistently present [505.5(B)(1)].
     
  6. Class 1, Zone 1 basically means ignitible concentrations of vapors or gases are likely to exist under normal operations [505.5(B)(2)].
     
  7. Class 1, Zone 2 basically means ignitible concentrations of vapors or gases are not likely to exist under normal operations [505.5(B)(3)].
     
  8. Note that we have oversimplified the definitions of 0, 1, and 2 so that you can easily see how they differ. Read the references thoroughly to understand the implications for a given location.
     
  9. Material Groups provide another twist. Which Material Group you have depends on which specific gases you are dealing with [505.6].
     
  10. Once you know the exact classification and Material Group, you must apply the applicable protection techniques from 505.8.