Article 500 Hazardous (Classified) Locations, Classes I, II, and III, Divisions 1 and 2


ScopeArticles 500 through 504

Articles 500 through 504 describe the electrical and electronic equipment and wiring requirements in hazardous (classified) locations where a fire or explosion hazard can exist because of flammable gases or vapors, flammable liquids, combustible dust, or ignitible fibers or flyings. There are fine print notes.




Other Articles

All applicable sections of this Code apply unless they are modified by Articles 500 through 504.



(A) Documentation. All areas that are classified must have the proper documentation. This documentation must be available.

Note: Space does not permit a complete description of this chapter. This is true of the entire NEC® but is again stated here. Only the highlights are noted. The reader should refer to the NEC® for complete descriptions.

(B) Reference Standards


Classification of Locations

(A) Classifications of Locations. The classifications are made by the properties of the items in the room under the listings in this chapter.

(B) Class I Locations. Areas where flammable gases or vapors are in the air in quantities that can cause explosive or ignitible mixtures are classified as Class I. They are further broken down into two divisions:

(1) Class I, Division 1. This is where ignitible concentrations of gases or vapors can exist normally; where they may exist because of maintenance or leakage; or where they might exist because of breakdowns or faulty operations.

(2) Class I, Division 2. This is where volatile flammable liquids or flammable gases are used but are normally in closed containers or systems and can escape only as a result of a breakdown or rupture; where ignitible concentration of gases or vapors normally cannot occur because of mechanical ventilation; where an area is next to a Class I, Division 1, location and some leakage between areas occurs.

(C) Class II Locations. These are hazardous because of combustible dust. They are also broken down into two divisions.

(1) Class II, Division 1. This is where combustible dust is in the air and can ignite under normal conditions due to its concentration, or where a breakdown of equipment can cause these concentrations and an ignitible source, or Group E combustible dust may be present in hazardous quantities.

(2) Class II, Division 2. This is where combustible dust is in quantities in the air to have explosive or ignitible mixtures due to abnormal operations; or the combustible dust is not in high enough quantities to interfere with the normal operations of electrical equipment or other apparatus but it could be suspended in the air if there were infrequent malfunctions of the equipment; or where the accumulations of the combustible dust in the vicinity of electrical equipment could become ignitible or interfere with the safe dissipation of heat from the electrical equipment as a result of abnormal operation of this equipment.

(D) Class III Locations. Areas that have ignitible fibers or flyings in a concentration not likely to cause ignition are classified as Class III. They are also further broken down into two divisions.

(1) Class III, Division 1. Areas where the fibers or flyings are handled, manufactured, or used.

(2) Class III, Division 2. Areas where the fibers or flyings are stored or handled other than in the process of manufacture.


Material Groups

This section indicates the groupings of various air mixtures. Requirements are given for approval for class and properties, marking, and temperature.


Protection Techniques

This paragraph describes various protection techniques which are acceptable for electrical and electronic equipment in hazardous (classified) locations.



This paragraph describes the equipment construction and installation.

500.9 Specific Occupancies

These are covered in Articles 510 through 517 and include garages, aircraft hangars, gasoline dispensing and service stations, bulk storage plants, spray application, dipping and coating processes, and health care facilities.

Article 90 Introduction


Wiring and Protection

Wiring Methods and Materials

Equipment for General Use

Special Occupancies

Special Equipment

Special Conditions


Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size

Annex D. Examples

Annex E. Types of Construction

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 © 2008-2020.
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