Document qar6QYqDN4Vjoeboe6xOBmB3M

ARTICLE 500--HAZARDOUS LOCATIONS (From National Electrical Code, NFPA No 70-1971) 500-1. Scope. The provisions of Articles 500-503 apply to locations m which the authority having jurisdiction judges the apparatus and wiring to be subject to the con ditions indicated by the following classifications It is intended that each room, sec tion or area (including motor and generator rooms, and rooms for the enclosure of control equipment) shall be considered individually m determining its classification Except as modified in Articles 500-503, all other applicable rules contained in this Code shall apply to electrical apparatus and wiring installed m hazardous locations For definitions of "approved" and "explosion-pioof" as used m these Articles, refer to Article 100, "dust-igmtion-prooF is defined m Section 502-1 Equipment and associated wiring approved as intrinsically safe may be installed in any hazardous location for which it is appioved, and the provisions of Articles 500-517 need not apply to such installation Intrinsically safe equipment and wiling are in capable of releasing sufficient electrical energv under normal oi abnormal conditions to cause ignition of a specific hazardous atmospheric mixtuie Abnormal conditions will include accidental damage to anv part of the equipment or wiring, insulation, or other failure of electrical components, application of overvoltage, adjustment and maintenance opeiations, and other similai conditions For further information see NFPA No 493--1969 Standard for Intrinsically Safe Process Control Equipment for use in Class I Hazardous Locations Through the exercise of ingenuity in the layout of electrical installations for hazardous loca tions, it is frequently possible to locate much of the equipment in less hazardous or m nonhazardous areas and thus to reduce the amount of special equipment required In some cases, hazards may be reduced or hazardous areas limited or eliminated by adequate positivepressure ventilation from a source of clean air in conjunction with effective safeguards against ventilation failure For further information see NFPA No 496--1967 Standard for Purged Enclosures for Electrical Equipment in Hazardous Locations It is recommended also that the authority having jurisdiction be familiar with such recorded industrial experience as well as with such standards of the National Fire Protection Association as may be of use in the classification of various areas with respect to hazard For further information, see NFPA No 30, Flammable and Combustible Liquids Code--1969, NFPA No 32, Dry Cleaning Plants-- 1970, NFPA No 35, Manufacture of Organic Coatings--1970, NFPA No 36, Solvent Extrac tion Plants--1967, NFPA No 58 (ANSI Z106 1) Storage and Handling of Liquefied Petroleum Gases--1969, and NFPA No 59, Storage and Handling of Liquefied Petroleum Cases at Utility Gas Plants--1968 For recommendations for protection against static electricity hazards, refer to the standards of the National Fire Protection Association on this subject Where rigid conduit is used in hazardous locations, it is necessary to have all threaded joints made up wrench tight to minimize sparking when fault current flows through the conduit system Where it is impractical to make a threaded joint tight, a bonding jumper should be utilized All conduit referred to herein shall be thieaded with a standaid conduit cutting die which provides S-mch tapei pei foot Such conduit shall be made up wrench tight to minimize spaikuig when fault cunent flows through the conduit system Wheie it is impiactical to make a threaded joint tight, a bonding jumpei shall be utilized Fic 41-6 --Article 500, National Electrical Code, describes locations where various types of explosionproof electncal equipment can be used Later editions of this code may change specific details Be sure to check Reproduced by permission from the National Electric Code, 1971 edition, copyright by the National Fire Protection Assn 1269