Special Occupancies, Locations, and Equipment
Articles 500 through 590 classify locations by hazard and then impose wiring methods. The exam asks you to classify a space, then choose the permitted method, sealing, and equipment.
Classification systems
- Article 500 uses Class and Division; Article 505 uses Class and Zone for gases and vapors; Article 506 uses zones for dusts. Class I is flammable gas or vapor, Class II is combustible dust, Class III is ignitable fibers.
- 511.3: in a commercial garage where flammable liquids are handled, the space up to 450 mm (18 in) above the floor is Class I, Division 2; above that, ordinary Chapter 3 methods are permitted.
- Article 517 health care: the essential electrical system, hospital-grade receptacles, and the redundant grounding requirements of 517.13.
- Article 590 temporary wiring: GFCI protection for 125 V, 15 and 20 A receptacle outlets on construction sites, plus support rules that differ from permanent wiring.
- 406.9: receptacles in wet locations must be weather-resistant and in an enclosure that keeps the device dry whether or not a plug is inserted.
Worked example
A repair bay in a commercial garage. The owner wants a general-purpose 20 A receptacle 12 in above the floor for a drop light. Because 511.3 classifies the first 18 in above the floor as Class I, Division 2, a standard receptacle in a bubble cover is not acceptable there. The practical fix is to relocate the receptacle above 450 mm, where 511.7 permits ordinary Chapter 3 wiring, or to install equipment listed for the classified area. Answer: relocate it to 20 in.
Traps
- Treating "not normally hazardous" as unclassified - classification follows the location, not daily habit.
- Missing the seal-off requirement at a classified boundary.
- Using a standard receptacle in a wet location with only a flip cover.