Article 503 Class III Locations

I. General

Maximum surface temperatures for equipment permitted under operating conditions are 165°C (329°F) for normal operation or 120°C (248°F) if the equipment can be overloaded.

II. Wiring

(A) Class III, Division 1. Use only rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, electrical metallic tubing, dust-tight wireways or Type MI or MC cables with listed fittings. Fittings and boxes must be dust tight. Refer to this section for the requirements for flexible connections and nonincendive field wiring.

(B) Class III, Division 2. Same requirements as Division 1. An exception is made for storage areas with no machinery, where open wire on insulators can be used complying with Article 398, specifically Section 398.15(C).

There can be no uninsulated exposed parts such as conductors, buses, etc., that operate at more than 30 volts. This limit is reduced to 15 volts in wet locations. The protection must be in accordance with 500.7(E), 500.7(F), or 500.7(G). There is an exception as provided in 503.155.

As per Article 250. Also, the same requirements hold true for bonding and grounding as in Sections 501.16, and 502.16. There are exceptions. Rules for equipment grounding conductors are noted.

III. Equipment

Must be in accordance with Section 502.100(B).

These devices must have dust-tight metal enclosures.

Must be in dust-tight enclosures complying with temperature limitations in Section 503.5.

Must be totally enclosed pipe ventilated, totally enclosed non-ventilated, or totally enclosed fan cooled. There is an exception where the authority having jurisdiction will permit it.

Must be metal at least 533 mm (0.021 in.) thick or equal noncombustible material, have physical damage protection, go directly outside to clean air, and be screened. The pipes must be tight enough to prevent "appreciable quantities" of fibers or flyings from getting in and sparks getting out.

Protect against physical damage. Prevent entrance of fibers or flyings or escape of sparks. Pendant stems must be threaded rigid metal conduit, threaded intermediate metal conduit, or threaded metal tubing. Chains with approved fittings can be used for suspending fixtures. The same rules apply for bracing stems over 3.5 mm (12 in.) long as Class II. Portable lamps must have handles, guards, and the lampholders have no switches, exposed parts, or receptacles.

Heaters: identified for Class III locations. Motors: Section 503.125. Switches, circuit breakers, motor controllers, and fuses: 503.115.

They must be listed for extra-hard usage, have a grounding conductor, be connected in an approved manner, be supported so as to prevent tension on the connections, and have provisions to prevent fibers or flyings from entering the boxes or fittings.

They must be of the grounding type, and designed to prevent the escape of sparks or molten particles and minimize the entry of fibers or flyings. An exception is provided where permitted by the authority having jurisdiction.