Special Occupancies, Special Conditions, and Special Equipment
Special-location questions reward classification skills: name the hazard, name the location class or zone, then apply the wiring and equipment rules for that classification.
Hazardous locations
Flammable gases and vapours fall into classes and divisions (or zones), combustible dusts into their own class, and fibres and flyings into another. Equipment must be approved for the class and division, and its temperature code must not exceed the ignition temperature of the material present. Seals prevent flames and gases from travelling through conduit; boundary seals are required where a raceway leaves the classified area, and conduit must be explosion-proof or otherwise approved for the location. Intrinsically safe circuits are energy-limited so they cannot ignite the atmosphere.
Other special occupancies and equipment
- Health care facilities: redundant grounding, isolated receptacles, patient-care area rules.
- Places of assembly, commercial cooking, and agricultural buildings have their own requirements.
- Pools, spas, and fountains: equipotential bonding, GFCI protection, separation distances.
- Solar photovoltaic systems: dc ratings, rapid shutdown, labelling, conductor sizing at 125 percent of short-circuit current.
- Electric vehicle charging, welders, cranes, signs, fire alarm circuits, emergency systems, and temporary installations each carry specific rules.
Traps
Mixing zone and division concepts, choosing a temperature code that is too high, omitting a boundary seal, treating emergency circuits like normal branch circuits, and forgetting that photovoltaic dc conductors are energized in daylight even when the system is off.
Rule of thumb
First determine the classification boundary, then choose equipment and wiring that are listed for that classification and the material group, and only then size conductors.