Description and Application

DOE-HDBK-1092-98

5.7.1 DESCRIPTION AND APPLICATION

Type 7 enclosures shall be capable of withstanding the pressures resulting from an internal explosion

of specified gases and containing such an explosion sufficiently that an explosive gas-air mixture in

the atmosphere surrounding the enclosure will not be ignited. Enclosed heat-generating devices shall

not cause external surfaces to reach temperatures capable of igniting explosive gas-air mixtures in

the surrounding atmosphere. Enclosures shall meet explosion, hydrostatic, and temperature design

tests.

5.7.2 FEATURES AND TEST CRITERIA

When completely and properly installed, Type 7 enclosures:

1. Provide to a hazardous gas environment a degree of protection from an internal explosion or

from operation of internal equipment

2. Do not develop external surface temperatures that exceed prescribed limits for the specific gas

corresponding to the atmospheres for which the enclosure is intended when internal heat-

simulating equipment is operated at rated load

3. Withstand a series of internal explosion design tests:

a. That determine the maximum pressure effects of the gas mixture

b. That determine propagation effects of the gas mixtures.

4. Withstand, without rupture or permanent distortion, an internal hydrostatic design test based

on the maximum internal pressure obtained during explosion tests and on a specified safety

factor

5. Are marked with the appropriate class and groups for which they have been qualified.

5.8 TYPE 8 ENCLOSURES

Type 8 enclosures are designed for indoor or outdoor use in locations classified as Class I Groups

A, B, C, or D as defined in the NEC.

5.8.1 DESCRIPTION AND APPLICATION

Type 8 enclosures and enclosed devices are arranged such that all arcing contacts, connections, and

any parts that could cause arcing are immersed in oil. Arcing is confined under the oil such that it

will not ignite an explosive mixture of the specified gases in internal spaces above the oil or in the

atmosphere surrounding the enclosure. Enclosed heat-generating devices shall not cause external

surfaces to reach temperatures capable of igniting explosive gas-air mixtures in the surrounding

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