National Electrical Code Top Ten Tips:
Article 500, Hazardous Locations
- 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.
- How a location is classified depends on the properties of
materials in that location or that are likely to be in that location
[500.5].
- Class I locations are those in which flammable gases or
vapors are (or may be) present in sufficient quantities to
produce explosive or ignitible mixtures [500.5(B)].
- 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)].
- Class III locations are those in which combustible fibers or
flyings are (or may be) present in sufficient quantities to
produce a hazard of explosion or ignition 500.5(D)].
- Class locations are further broken down into Division 1 (normal
operations) and Division 2 (abnormal operations). Does this location
meet its Class I, II, or III designation during normal operations or
only during abnormal operations?
- 500.7 provides 12 of what it calls "protection techniques."
These are not actually "techniques," just as the Chapter Three to
"wiring methods" aren't actual "methods." But if you read this,
you'll understand what they mean.
- A given hazardous location can contain only equipment that is
approved for use in that location [500.8].
- You must address explosion properties and ignition temperature
separately [500.8].
- You must account for low temperatures, not just ignition
temperatures [500.8].
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