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29、Protection Association are registered trademarks of the National Fire Protection Association, Quincy, Massachusetts 02169. Copyright 2016 National Fire Protection Association . All Rights Reserved. NFPA 496 Standard for Purged and Pressurized Enclosures for Electrical Equipment 2017 Edition This edi
30、tion of NFPA 496, Standard for Purged and Pressurized Enclosures for Electrical Equipment, was prepared by the Technical Committee on Electrical Equipment in Chemical Atmospheres. It was issued by the Standards Council on May 13, 2016, with an effective date of June 2, 2016, and supersedes all previ
31、ous editions. This edition of NFPA 496 was approved as an American National Standard on June 2, 2016. Origin and Development of NFPA 496 This standard was developed in two parts by the Technical Committee on Electrical Equipment in Chemical Atmospheres. The rst part, addressing purged enclosures for
32、 electrical equipment in Class I hazardous (classied) locations, was adopted as a tentative standard at the 1966 NFPA Annual Meeting and as an ofcial standard at the 1967 NFPA Annual Meeting. The second part, addressing pressurized enclosures for electrical equipment in Class II hazardous (classied)
33、 locations, was tentatively adopted at the 1970 NFPA Annual Meeting and ofcially adopted at the 1971 NFPA Annual Meeting. The Technical Committee on Electrical Equipment in Chemical Atmospheres presented a complete revision of the entire standard for the 1974 edition. In 1980, the committee began an
34、other complete revision, which culminated in the 1982 edition. In 1983, the Technical Committee recognized the need for specic requirements applicable to process control analyzers that have internal sources of a ammable or combustible material, such as a direct connection to the process stream. Two
35、chapters were added to address analyzer enclosures and analyzer rooms or buildings. Additional changes were also made to certain existing portions of the text specically to address problems in the interpretation of the existing text. The 1986 edition of NFPA 496 was the result of that effort. In 198
36、7, the Technical Committee recognized a need for editorial revisions to the gures in Chapter 2 as well as some minor editorial changes in Chapters 2 and 9 and Appendix A. The 1989 edition was the result of that effort. Beginning in 1990, an ad hoc committee consisting of members of the Technical Com
37、mittee on Electrical Equipment in Chemical Atmospheres started a major rewrite of the document to develop a more comprehensive standard and to reduce redundancy in the text. Denitions were added for further clarity, and references to Class III were deleted, since the standard did not cover that appl
38、ication and could create some confusion. The term purging was replaced with pressurizing, and protective gas was introduced as a new term. The requirements based on gross internal volume were deleted and replaced with general and specic requirements for all pressurized enclosures used in Class I and
39、 Class II locations. The result of the rewrite was the 1993 edition. In 1997, the Technical Committee entered NFPA 496 into the revision cycle to update the requirements. The standard was updated to include denitions and references to Article 505 in NFPA 70 , National Electrical Code , which deals w
40、ith Class I, Zone 1, and Zone 2 locations. It also was changed to provide an exception for control rooms, where doors and other openings used solely for equipment relocation are permitted to be excluded from the calculation for outward air velocity from the central room. In 2001, the Technical Commi
41、ttee on Electrical Equipment in Chemical Atmospheres entered NFPA 496 into the May 2003 revision cycle. The 2003 edition was signicantly revised and reorganized for conformance with the 2000 Manual of Style for NFPA Technical Committee Documents. The organizational and editorial changes enhanced the
42、 standards usability. Additionally, technicalPURGED AND PRESSURIZED ENCLOSURES FOR ELECTRICAL EQUIPMENT 496-2 2017 Edition changes included revision of the term alarm to clarify its function with protected enclosures, and a revision that permits the use of a means other than a timing device to ensur
43、e that electrical equipment within a protected enclosure is not energized until the specied amount of protective gas has passed through the enclosure. The 2008 edition was the culmination of a revision cycle that began with the document being entered into cycle in January 2006. NFPA 496 contains req
44、uirements on a protection technique for electrical and electronic equipment recognized by NFPA 70, National Electrical Code, for installations in hazardous (classied) locations. To ensure correlation with revisions occurring in the 2008 NEC, the Technical Committee on Electrical Equipment in Chemica
45、l Atmospheres requested and was granted permission by the NFPA Standards Council to enter into a three-year (Fall 2007) revision cycle. Signicant revisions to the 2008 edition included the following: (1) a new requirement to mark purged and pressurized enclosures with an asphyxiation hazard warning
46、where the protective gas is other than air and (2) deletion of 6.2.5, Table 6.2.5, and A.6.2.5 on Class II temperatures because the temperature class ratings for equipment in 4.5.3 correlate with the current temperature rating requirements for new equipment in Class I and Class II locations containe
47、d in 500.8(D)(1) and 500.8(D)(2) of the NEC. The 2013 edition was revised to ensure correlation with the 2011 edition of NFPA 70, National Electrical Code. The denition of energized and identied were extracted from NFPA 70. Equipment was required to be identied for use in a classied area, and the re
48、quirements for determining the suitability of identied equipment were claried. The denitions of Type X, Type Y, and Type Z pressurizing were claried to more clearly dene their usage. All NFPA references were updated. The 2017 edition has been revised to no longer include unenforceable language such
49、as near, close to, and signicant portion. Such terms cannot be quantied in the design or evaluation of an installation designed to the standard.COMMITTEE PERSONNEL 496-3 2017 Edition Technical Committee on Electrical Equipment in Chemical Atmospheres William T. Fiske, Chair Intertek Testing Services, NY RT Donald W. Ankele, UL LLC, IL RT Babanna Biradar, Bechtel India Pvt Ltd, India SE Ronald M. Brown, PPG Industries, Inc., PA U Jonathan L. Cadd, Electrical Systems and Instrumentation, Inc., TX M John H. Cawthon, State of Alas
