Special Occupancies, Special Equipment, and Special Conditions
Special Occupancies
Hazardous (classified) locations
Articles 500–506 classify locations where fire or explosion hazards exist. Class I is flammable gas or vapor; Class II is combustible dust; Class III is ignitable fibers. Divisions describe whether the hazard is present under normal conditions (Division 1) or only abnormally (Division 2); the Zone system (505/506) is the international alternative. Groups subdivide by material - gasoline vapor is Class I, Group D. Protection techniques include explosionproof equipment, purged and pressurized enclosures, dust-ignitionproof, and intrinsically safe circuits. Seals, boundary distances, and wiring method restrictions are heavily tested details (501.15 for Class I seals).
Other occupancies
Article 511 covers commercial garages - the classification extends 18 in. above the floor throughout the garage. Article 514 covers motor fuel dispensing, with classified areas extending 20 ft from the dispenser and up to 18 in. above grade. Article 517 covers health care facilities and the essential electrical system; Article 518 covers assembly occupancies; 520 theaters; 525 carnivals and fairs; 547 agricultural buildings; 550/551 mobile homes and RVs; 555 marinas and boatyards.
Traps
Mixing Division 1 and Division 2 definitions, applying Group letters arbitrarily, forgetting that the garage boundary applies to the whole floor area rather than only near the vehicle, and assuming ordinary equipment is acceptable in a Division 2 location without a listed protection technique.
Worked example
A gasoline dispenser island: the area within 20 ft of the dispenser and up to 18 in. above grade is Class I, Division 1 or 2 depending on the specific zone under 514.3; all equipment there must be listed for the class, division, and group.
Special Equipment and Special Conditions
Chapter 6 highlights
Article 620 covers elevators and escalators; 625 electric vehicle supply equipment; 680 pools, spas, and fountains, where 680.26 requires equipotential bonding of pool shells and metal parts and 680.21 sets pump-motor wiring rules; 690 solar photovoltaic systems; 694 wind; 695 fire pumps, which may not be GFCI- or AFCI-protected and need short-circuit protection that will carry locked-rotor current indefinitely.
Chapter 7 highlights
Emergency systems (700) must be available within 10 seconds of a loss of normal power and supply life-safety loads. Legally required standby (701) and optional standby (702) are progressively less restrictive. Article 705 covers interconnected power sources, and 706 covers energy storage. Article 725 classifies remote-control and signal circuits as Class 1, 2, or 3 with distinct wiring rules, while 760 covers fire alarm systems and 770 optical fiber. Article 722 governs multiwire branch circuits and 712 covers direct-current systems.
Traps
Treating an optional standby system as an emergency system, applying Chapter 3 wiring methods to Class 2 circuits, installing GFCI protection ahead of a fire pump, and misapplying rapid shutdown requirements for PV.
Worked example
PV source-circuit conductors: 690.8 requires 125% of short-circuit current for the conductor ampacity calculation, and since PV output is continuous, another 125% applies - so size conductors at 156% of Isc before applying correction and adjustment factors.