Based on the 2020 NEC

by Mark Lamendola

National Electrical Code Top Ten Tips: Article 502 -- Class II Locations

  1. Read Article 500 before reading Article 502. Why? Because 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. So, do not work with Article 502 until you have read and understood Article 500.
     
  2. 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)].
     
  3. Class locations are further broken down into Division 1 (normal operations) and Division 2 (abnormal operations). That is, point #2 above applies in normal or abnormal conditions.
     
  4. You must use Division 1 wiring methods when combustibles are present under normal operations [502.10(A)]. This subsection underwent significant changes in the 2020 revision.
     
  5. You must use Division 2 wiring methods when combustibles are present under  abnormal operations [502.10(B)]. This subsection underwent significant changes in the 2020 revision
     
  6. Seal requirements for Class II locations [502.15] are very simple, compared to the highly detailed and far more extensive seal requirements of Class I locations [501.15]. Do not confuse the two. Also, Class I locations have different seal requirements for Division 1 than for Division 2 while Class II seal location requirements are the same regardless of Division.
     
  7. Any electrical parts that operate at more than 30V can't be exposed, but this drops to 15V under wet conditions. Further, you must apply the appropriate protection technique from 500.7(E), (F), or (G) to these parts [502.25]. It seems odd that you might have dust under wet conditions, but it can happen. For example, it just finished raining and an abnormal event happens where huge quantities of dust are released. Or think of a coal yard (outdoors, by definition), where combustible dust is always present.
     
  8. The grounding and bonding requirements for Class II locations are in 502.30. If you ground where you should, instead, bond, you will leave a difference of potential that violates 502.30 and poses a threat to people and property. To avoid catastrophic consequences, read the definitions of grounding and bonding in Article 100, and take some time to study Article 250, Part V. Grounding means a connection to the earth. Earth resistance (grounding) is enormous compared the resistance of a copper conductor (bonding), so grounding cannot possibly create equipotential.
     
  9. Class I, Division 2 dry-type transformers must be in vaults or have their windings and terminal connections enclosed in tight metal housings without ventilation or other openings. And they can't operate at over 600V nominal [502.100(B)(3)]
  10. usly [502.40].
     
  11. Any luminaire used in a Class II location must be identified for use in Class II locations [502.130(A)(1)] and [502.130(B)(1)].