Hazardous Locations and the National Electric Code

National Electric Code

The national electric code treats installation in hazardous locations in articles 500 through 516.  Hazardous locations are classified by NEC definitions.  The following are interpretations of these classifications and applications.

CLASS I LOCATIONS

Class I locations are those in which flammable gasses or vapors are or may be present in sufficient quantities to produce explosive or flammable mixtures. 

• Class I, Division 1:

Class I, Division 1 locations are where hazardous atmospheres may be present during normal operations.  It may be present continuously, intermittently, periodically or during normal repair or maintenance operations or those areas where a breakdown in processing equipment releases hazardous vapors with simultaneous failure of electrical equipment

• Class I, Division 2:

Class I, Division 2 locations are those in which volatile flammable liquids or gasses are handled, processed or used.  Normally they will be confined within closed containers or in closed systems from which they can only escape only in the case of rupture or deterioration of the containers or systems.

CLASS II LOCATIONS

Class I locations are those that are hazardous because of the presence of combustible dust. 

• Class II, Division 1:

Class II, Division 1 locations include areas where combustible dust may be in suspension in the air under normal conditions in sufficient quantities to produce explosive or ignitable mixtures (dust may be emitted into the air continuously , intermittently or periodically), or where failure or malfunction of equipment might cause a hazardous location to exist and provide an ignition source with the simultaneous failure of electrical equipment.  Included are also locations in which combustible dust of an electrically conductive nature may be present.

• Class II, Division 2:

Class II, Division 2 locations are those in which combustible will not normally be in suspension nor will normal operations put dust in suspension, but where accumulation of dust may interfere with heat dissipation from electrical equipment or where accumulations near electrical equipment may be ignited.