Special Occupancies, Special Equipment, and Low-Voltage/Communications Systems
Special Occupancies
Classified and special locations
Articles 500 through 517 and later articles address hazardous classified locations, health care facilities, assembly occupancies, mobile homes, marinas, agricultural buildings, and temporary installations. Classified locations depend on the flammable material present and the likelihood of ignition. Division 1 generally means the hazard is present under normal conditions; Division 2 means it is present only under abnormal conditions. Equipment must be listed for the class, division or zone, and group. Seals, boundaries, grounding, and wiring methods are tightly controlled.
Health care and assembly traps
Health care facilities use essential electrical systems and patient-care area rules, including redundant grounding and special receptacle requirements. Assembly occupancies have emergency lighting and exit requirements. Marinas and agricultural buildings have wet-location and equipotential bonding rules. A frequent trap is assuming ordinary equipment is acceptable because it is in a raceway. In classified locations, the enclosure and fittings must be identified for the location, not just installed in conduit.
Worked example
A conduit enters a Class I, Division 1 enclosure. A seal must be placed within 18 in. of the enclosure to prevent gases from passing through the conduit system. The seal fitting must be listed for the purpose. Rule of thumb: classified location questions turn on the class, division or zone, material group, and required listing of every component.
Special Equipment and Low-Voltage/Communications Systems
Special equipment and limited-energy circuits
Special equipment articles cover elevators, pools, signs, solar photovoltaic systems, electric vehicle supply equipment, generators, fire pumps, cranes, and similar equipment. Low-voltage and communications systems are in Articles 725, 760, 800, 820, 830, and 840. Article 725 separates Class 1, Class 2, and Class 3 circuits. Class 2 and Class 3 circuits are limited in power and have strict separation rules from power conductors. Fire alarm systems are covered by Article 760. Communications circuits, CATV, network-powered broadband, and optical fiber have their own cable and grounding requirements.
Separation and plenum traps
A common question asks whether low-voltage cable can share a raceway or box with power conductors. Class 2 circuits generally cannot be mixed with power conductors unless the equipment is listed for the combination or a barrier separates them. Communications cables generally require separation from power conductors. Cable installed in a plenum must be listed for plenum use. Abandoned communications cable must be removed where the code requires it. Do not assume all low-voltage cable is interchangeable.
Worked example
A 24 V Class 2 thermostat cable is routed toward a furnace. It may not be run in the same raceway as the 120 V furnace power conductors unless the installation provides a listed barrier or the equipment is listed for the combination. The low-voltage cable must also be suitable for the location, such as plenum-rated cable above a suspended ceiling. Rule of thumb: identify the article first, then check power limitation, separation, and cable listing.