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National Electrical Code Articles and Information

Based on the 2020 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. It's important to understand that it's not up to an electrician or engineer to decide to use this system. You can't say, "I see this requirement for Class I, Div 1 but it would be easier to use the Zone system in this instance." he facility and its insurer are using either the Division classification system or the Zone classification system for the area and equipment under question.
  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. So what doe this mean to the electrician or engineer? You are using the Zone system because that is what the facility has decided you will use. And as a consequence, you must generate specific documentation; the owner (usually via the maintenance organization ) will keep the records updated and on file. If you are a contractor bidding on a job, make sure you take into consideration the extra labor needed to produce the required documentation.
  4. Exactly how the facility's owners/managers may classify a location depends on the properties of the flammable substances that may be present and on their concentration [505.5]. This can vary within a facility.
  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. For example, Class I, Zone 1 also applies when the vapors are frequently present.
  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. Whether you are a contractor or inhous maintenance,, this will need to be deterimined as part of defining the scope of work. That determination has big ramifactions for job preparation, duration, and cost.