Special Occupancies, Special Equipment, and Special Conditions
Chapters 5, 6 and 7 override the general rules
Special occupancies (Articles 500-517, 518-547, 550, 551, 555), special equipment (600-695, including 620 elevators, 625 EV charging, 680 pools, 690 solar photovoltaic and 695 fire pumps) and special conditions (700 emergency systems, 701 legally required standby, 702 optional standby, 705 interconnected sources, 706 energy storage, 725 Class 1, 2 and 3 circuits, 760 fire alarm, 800 communications) each add or change requirements. Read the article first, then fall back on Chapters 1 to 4.
Classified locations
Article 500 uses Class I (gas or vapor), Class II (dust) and Class III (fibers and flyings), each split into Division 1 (condition exists in normal operation) and Division 2 (condition exists only under abnormal circumstances). Articles 505 and 506 permit the zone system instead. Identify the condition, then choose the wiring method from the matching article.
Health care, pools, solar
Article 517 divides the essential electrical system into the life safety branch, the critical branch and the equipment system. Article 680 requires equipotential bonding of pool metal, GFCI protection for pool pump motors, and restricted receptacle locations near the water. Article 690.12 requires rapid shutdown: conductors within the array boundary limited to 80 V within 30 seconds, and outside the boundary reduced to 30 V.
Traps
Using ordinary Chapter 3 methods inside a classified location; confusing the array-boundary voltage limit with the limit outside the boundary; assuming an optional standby system must meet Article 700 emergency system rules; missing that a legally required standby system answers to 701, not 702.
Worked example
A room where flammable vapor is present during normal filling operations is Class I, Division 1. The same room with closed process equipment that releases vapor only on failure is Class I, Division 2. Determine the condition first, then apply the Article 501 wiring method.