NEC 500: Hazardous (Classified) Locations
What This Article Covers
NEC Article 500 introduces the classification system for hazardous locations — Class I (gases/vapors), Class II (dusts), and Class III (fibers/flyings) — and Divisions 1 and 2 within each class. Articles 501, 502, and 503 contain the actual installation requirements.
Key Requirements
- Class I = flammable gases or vapors; Class II = combustible dust; Class III = ignitable fibers
- Division 1 = hazard present in normal operation; Division 2 = present only under fault conditions
- Equipment must be listed for the specific class, division, and gas/dust group
- Wiring methods are restricted in each location type
- Seal fittings required where conduit passes from a Division 1 location to another area
Common Field Applications
- Gas station forecourt (Class I Div 2 around dispensers)
- Spray paint booth (Class I Div 1 inside, Div 2 around)
- Grain elevator (Class II Div 1 inside processing)
Common Mistakes & Inspection Failures
- Using ordinary wiring in a classified location
- Missing or improperly poured seal fittings
- Substituting non-listed luminaires
Related NEC Articles
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Frequently Asked Questions
What does NEC 500 cover?
NEC Article 500 introduces the classification system for hazardous locations — Class I (gases/vapors), Class II (dusts), and Class III (fibers/flyings) — and Divisions 1 and 2 within each class. Articles 501, 502, and 503 contain the actual installation requirements.
What are the key requirements of NEC 500?
Key requirements include: Class I = flammable gases or vapors; Class II = combustible dust; Class III = ignitable fibers; Division 1 = hazard present in normal operation; Division 2 = present only under fault conditions; Equipment must be listed for the specific class, division, and gas/dust group. See the full requirements list on this page.
What are common mistakes with NEC 500?
Using ordinary wiring in a classified location Missing or improperly poured seal fittings Substituting non-listed luminaires
Related Resources
Michael Briglio
IBEW Local 134 Journeyman · Licensed Contractor · IL Educator
Michael started in the IBEW at 18 and made foreman as a 3rd-year apprentice. Thirteen years in, he’s a Local 134 journeyman, a licensed electrical contractor, a licensed Illinois teacher, and OSHA 30 and EPA 608 certified. He teaches a federally recognized pre-apprenticeship on the south side of Chicago — where he’s helped 100+ students get into the IBEW. He built Sparky AI around exactly what the NJATC exam tests and what trips people up. Prep with this and you walk in ready.
Facts on this page trace to primary sources or first-hand IBEW Local 134 experience — see sources & methodology.