NEC Article 500 provides guidelines for electrical installations in hazardous (classified) locations where the risk of fire or explosion exists due to the presence of flammable gases, vapors, liquids, combustible dusts, or ignitible fibers and flyings. Here is a detailed overview of this article:

500.1 Scope

This section establishes the scope, covering general requirements for the classification of hazardous locations and the installation of electrical equipment in these areas.

500.2 Definitions

Defines essential terms such as “Class I,” “Class II,” and “Class III” locations to ensure clarity and consistency.

500.3 Other Articles

Indicates the relationship between Article 500 and other NEC articles addressing specific hazardous locations and related equipment.

500.4 Documentation

Requires documentation of all areas classified as hazardous (and unclassified), including area classification drawings. This documentation must be available to authorities and personnel involved in designing, installing, inspecting, maintaining, or operating electrical equipment in these areas.

500.5 Classifications of Locations

Outlines classifications into Classes I, II, and III, with Divisions 1 and 2 based on the type and likelihood of hazardous materials being present:

• Class I: Locations with flammable gases or vapors.
• Division 1: Ignitable concentrations present under normal conditions.
• Division 2: Ignitable concentrations present under abnormal conditions.
• Class II: Locations with combustible dust.
• Division 1: Dust present under normal conditions.
• Division 2: Dust present under abnormal conditions.
• Class III: Locations with ignitable fibers and flyings.
• Division 1: Fibers/flyings present during normal operations.
• Division 2: Fibers/flyings present under abnormal conditions.

500.6 Material Groups

Defines groups of hazardous materials to classify types of hazards and determine appropriate equipment and installation methods:

• Groups A, B, C, D: For gases.
• Groups E, F, G: For dusts.

500.7 Protection Techniques

Lists required protection techniques for ensuring the safety of electrical equipment in hazardous locations, including explosion-proof enclosures and intrinsically safe systems.

500.8 Equipment

Specifies the types of electrical equipment suitable for hazardous locations and requirements for their installation, ensuring they are listed or labeled for specific hazardous locations and meet necessary standards for construction and performance.

For more detailed information, consulting the NEC Handbook and additional NFPA resources is highly recommended.