Explosion-proof conduit fittings

Explosion-proof enclosures are characterized by strong metal enclosures with special close-fitting access covers and breathers that contain an ignition to the inside of the enclosure. Field wiring in the hazardous environment is enclosed in a metal conduit of the mineral-insulated-cable type. All conduit and cable connections or cable terminations are threaded and explosion-proof. Conduit seals are put into the conduit or cable system at locations defined by the National Electric Code (Article 501) to prevent gas and vapor leakage and to prevent flames from passing from one part of the conduit system to the other. 

A box or fitting must be installed at each conductor sphce connection point, receptacle, switch, junction point, or pull point for the connection of conduit system. In Division 1 areas only explosion-proof boxes or fittings are allowed. General purpose gasketed cover type fittings are allowed in Division 2 areas. 

Figure 17-24. Standard explosion-proof junction boxes ond conduit fittings. [Courtesy of Crouse-Hinds Electrical Construction Materials, a division of Cooper industries, Inc. ...

Design for Hazardous Areas. This type of area classification tends to simplify the electrical design by directive means, but poses alternate choice problems, dictated by economics. The cost of an explosion-proof installation is as much as twice that using standard equipment. As an example of more costly electrical equipment, rigid metal conduit with threaded explosion-proof boxes and fittings are required for all Class I, Division 1, hazardous locations either rigid metal conduit or electrical metal tubing is approved for both Class I and II, Division 2, locations. 

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