Article 502 Class II Locations

I. General

502.1

Scope

502.5

General

This article refers to areas classified as Class II. Explosion-proof equipment cannot be required and used unless identified for Class II locations.

II. Wiring

502.10

Wiring Methods

(A) Class II, Division 1. Only threaded rigid metal conduit, threaded steel intermediate metal conduit, Type MI cable can be used. Boxes and fittings can have no openings and have threaded bosses so that no dust can come in. If used where the dust is combustible electrically conductive, they must be approved for Class II locations. If a flexible connection must be used, it has to be either a dust-tight flexible connector, liquidtight flexible metal conduit, liquidtight non-metallic conduit, certain types of interlocked armor type MC cable with certain requirements, or a flexible cord for extra-hard usage and bushed fittings. The flexible cord must comply with section 502.140. There is an exception for certain industrial establishments.

(B) Class II, Division 2. Methods permitted are rigid metal conduit, intermediate metal conduit, electrical metal tubing, dust-tight wireways, or Type MI or MC cable that have listed termination fittings or Type PLTC, MC, ITC, or TC cable, all under certain conditions. There is an exception. Also, wireways, fittings, and boxes must be dust tight. The requirements for flexible connections are noted in 502.10(A)(2). There are additional requirements.

502.15

Sealing, Class II, Divisions 1 and 2

If a raceway connects two enclosures, one being dust-ignition-proof, the other not, provision must be made to prevent dust from getting into the dust-ignition-proof enclosures. This can be done with seals, a minimum of 3.05 m (10 ft.) of horizontal raceway, or a minimum of 1.5 m (5 ft.) of vertical raceway or a raceway extending only horizontally and downward from the dust-ignition proof enclosure and complying with the above requirements for horizontal or vertical raceways. If the dust-ignition-proof enclosure is connected to one in an unclassified area, a seal is not required.

502.25

Uninsulated Exposed Parts, Class II, Divisions 1 and 2

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).

502.30

Grounding and Bonding, Class II, Divisions 1 and 2

Ground, in accordance with Article 250 and the requirements of 502.30(A) and (B), all wiring and equipment.

(A) Bonding jumpers with proper fittings or other approved means must be used. Locknut bushings and double lock-nut contacts alone are not to be depended on. The means of bonding applies to all raceways, fittings, boxes, enclosures, etc., between Class II locations and the grounding point for service equipment or separately derived systems. There is an exception.

(B) If flexible conduit is used, it must have internal or external bonding jumpers in parallel with each conduit. It must also comply with the requirements of Section 250.102. There is an exception.

502.35

Surge Protection, Class II, Divisions 1 and 2

502.40

Multiwire Branch Circuits

 

III. Equipment

502.100

Transformers and Capacitors

(A) Class II, Division 1

  1. Containing liquid that will burn. They must be installed in vaults complying with Section 450.41 through 450.48 outside the Division I location with self-closing fire doors, and have proper ventilation and pressure relief.
  2. Not containing liquid that will burn. They must be installed in a vault as per Sections 450.41 through 450.48 or have the entire assembly identified for a Class II location.
  3. If the area has a metal dust such as magnesium, aluminum, etc., you cannot install a transformer or capacitor.

(B) Class II, Division 2

  1. Containing liquid that will burn. Must be installed in vaults as per Sections 450.41 through 450.48.
  2. Containing Askarel. If it is larger than 25 kVA, it must have a pressure relief vent, have a way of absorbing gases from inside, and have an air space of at least 150 mm (6 in.) between the case and any combustible material.
  3. Dry-type transformers. Must be in vaults or not operate over 600 V, with the windings and terminals enclosed without ventilating or other openings.

502.115

Switches, Circuit Breakers, Motor Controllers, and Fuses

(A) Class II, Division 1. Their enclosures must be dust-ignition-proof. If the dust is a hazardous metal (magnesium, etc.), the enclosure must be identified for this specific type of location. If disconnecting and isolating switches are not installed where there is electrically conductive dust, are not to interrupt current, and have no fuses, the enclosure only has to be tight so as to keep the entrance of dust to a minimum and have no openings, as well as have close-fitting or telescoping covers.

(B) Class II, Division 2. The enclosures only have to be dust-tight.

502.120

Control Transformers and Resistors

(A) Class II, Division 1. The enclosures must be dust-ignition-proof identified for a Class II location. If they are installed in a location with hazardous metal dust (magnesium, etc.), the enclosure must be identified for this specific type of location.

(B) Class II, Division 2. In these locations, the switching mechanisms must have a dust-tight enclosure. If they are in the same location as the switching mechanism, they must have tight metal enclosures with no openings. Resistors must have identified Class II enclosures unless their temperature is not higher than 248°F and they are either nonadjustable or part of an automatic timing system. In that case the enclosures have only to be tight with no openings. There are other requirements.

502.125

Motors and Generators

(A) Class II, Division 1. They must be either totally enclosed pipe-ventilated and meet the temperature restrictions of Section 502.5 or be identified for locations classified as Class II, Division 1.

(B) Class II, Division 2. They must be either totally enclosed pipe-ventilated, totally enclosed fan-cooled, totally enclosed waterair-cooled, totally enclosed nonventilated or dust-ignition-proof with full load external temperature in accordance with Section 500.8(C)(2). There are exceptions for these types of motors if the authority having jurisdiction feels that the machines are easily cleaned and maintained and there will not be a large accumulation of dust.

502.128

Ventilating Piping

The piping must (1) be metal at least 0.53 mm (0.021 in.) thick or of noncombustible material of equal substance, (2) be screened at the outside ends, (3) lead to the outside of the building and have clean air available, and (4) be protected against corrosion and physical damage. In addition, it must comply with:

(A) Class II, Division 1. The pipes must be entirely dust-tight. They must also be either riveted and soldered, bolted and soldered, welded, or be dust-tight by another effective means.

(B) Class II, Division 2. The pipes must be tight enough to prevent the entrance of dust in appreciable quantities.

502.130

Luminaires (Lighting Fixtures)

(A) Class II, Division 1. The luminaires (fixtures) must be identified for Class II locations and additionally for hazardous metal dust if so located. They must be protected against physical damage. Pendant fixtures must be suspended using threaded rigid metal conduit, threaded steel intermediate metal conduit, or approved chains or other means. If the stem is longer than 300 mm (12 in.), it must be braced within 300 mm (12 in.) from the lower end or have a flexible fitting not more than 300 mm (12 in.) from the upper end. If conduit is not used for the wiring, the cord must be listed for hard usage and proper seals must be used. All boxes, fittings, etc., must be identified for Class II locations.

(B) Class II, Division 2. Portable lighting equipment must be identified for Class II locations. A fixed luminaire (lighting fixture) must only minimize the collection of dust and prevent the escape of sparks. It must also have maximum wattage permitted for temperatures in accordance with Section 500.8(C)(2). Luminaires (fixtures) in these locations must also be protected against physical damage. Requirements for pendant fixtures in Division 2 are basically the same as for Division 1. One difference is that seals are not required. The requirements of Section 502.120(B) apply here for starters and control equipment for electric-discharge lamps.

502.135

Utilization Equipment

(A) Class II, Division 1. Must be identified for Class II locations. If hazardous dust is present, it must also be identified for that location.

(B) Class II, Division 2. Heaters must be identified for Class II locations. There is one exception. Motors must be in accordance with Section 502.125(B). Dust-tight enclosures are required for circuit breakers, switches, and fuses. Section 502.120(B) is applied to transformers, impedance coils, and resistors.

502.140

Flexible Cords, Class II, Divisions 1 and 2

502.145

Receptacles and Attachment Plugs

(A) Class II, Division 1. Must be identified for Class II locations and have a grounding conductor connection.

(B) Class II, Division 2. Must also have a grounding conductor connection. They cannot permit the supply circuit to open with exposed live parts.

502.150

Signaling, Alarm, Remote-Control, and Communication Systems; Meters, Instruments, and Relays






Pocket Guide to the National Electrical Code 2005
Pocket Guide to the National Electrical Code(R), 2005 Edition (8th Edition)
ISBN: 0131480014
EAN: 2147483647
Year: 2004
Pages: 120
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