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NOTE: This is an unformatted excerpt from our online fire protection training library.

Classification Basics

Electrical Equipment

Surface Temperatures

Luminaire for use in some Class I areas. (Courtesy of Appleton Electric Company) Some electrical equipment such as motors, transformers, heaters, and lights produce heat and normally operate at relatively high temperatures. Enclosures for such equipment must be designed to limit surface temperatures limit surface temperatures
Surface temperatures may be designated by "T-codes" which correspond to specific maximum temperatures and are selected so as not to exceed the ignition temperature of the specific gas, vapor, or dust encountered. (See the Class I and Class II Temperatures button for more information.) For some types of utilization equipment, such as electric heaters, the surface temperature is limited to 80 percent of the ignition temperature (in degrees Celsius) of a specific gas or vapor. Surface temperatures in Class III areas are limited to the same specific values for all fibers and flyings. Generally temperature markings are not required for enclosures for non-heat-producing equipment, such as junction boxes, conduit, and fittings. and marked with an operating temperature or a temperature code to indicate the maximum surface temperature. This requirement is intended to ensure that flammable or combustible materials are not ignited by contact with the enclosures. Although control of surface temperatures is critical in all classified areas, fibers, flyings, and dusts often make the problem worse because they can build up on the enclosures, entrap heat, and increase the surface temperatures. In addition, dusts, fibers, and flyings that are allowed to blanket the surfaces of electrical equipment may be made more dangerous and more easily ignitable by the heat produced by the electrical equipment.  Mouse over the picture for additional information.

General Requirements

Class I and Class II  Temperatures

Class III Temperatures
NOTE: This is an unformatted excerpt from our online fire protection training library.

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