NFPA 780-2017 Standard for the Installation of Lightning Protection Systems (Effective date 06 02 2016).pdf

1、 NFPA 780 Standard for the Installation of Lightning Protection Systems 2017IMPORTANT NOTICES AND DISCLAIMERS CONCERNING NFPA STANDARDS NOTICE AND DISCLAIMER OF LIABILITY CONCERNING THE USE OF NFPA STANDARDS NFPA codes, standards, recommended practices, and guides (“NFPA Standards”), of which the do

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10、 Errata, visit the “Codes email: stds_adminnfpa.org. For more information about NFPA, visit the NFPA website at www.nfpa.org. All NFPA codes and standards can be viewed at no cost at www.nfpa.org/docinfo.780-1 NFPA, and National Fire Protection Association are registered trademarks of the National F

11、ire Protection Association, Quincy, Massachusetts, 02169 Copyright 2016 National Fire Protection Association . All Rights Reserved. NFPA 780 Standard for the Installation of Lightning Protection Systems 2017 Edition This edition of NFPA 780, Standard for the Installation of Lightning Protection Syst

12、ems, was prepared by the Technical Committee on Lightning Protection. It was issued by the Standards Council on May 13, 2016, with an effective date of June 2, 2016, and supersedes all previous editions. This edition of NFPA 780 was approved as an American National Standard on June 2, 2016. Origin a

13、nd Development of NFPA 780 NFPA rst adopted Specications for Protection of Buildings Against Lightning in 1904. Revised standards were adopted in 1905, 1906, 1925, 1932, and 1937. In 1945, the NFPA Committee and the parallel American Standards Association (ASA) Committee on Protection Against Lightn

14、ing were reorganized and combined under the sponsorship of NFPA, the National Bureau of Standards, and the American Institute of Electrical Engineers (now the IEEE). In 1946, NFPA acted to adopt Part III and in 1947 published a revised edition incorporating this part. Further revisions recommended b

15、y the Committee were adopted by NFPA in 1949, 1950, 1951, 1952, 1957, 1959, 1963, 1965, 1968, 1975, 1977, 1980, 1983, 1986, 1989, and 1992. Commencing with the 1992 edition of the Lightning Protection Code, the NFPA numerical designation of the document was changed from NFPA 78 to NFPA 780. With the

16、 issuance of the 1995 edition, the name of the document was changed from Lightning Protection Code to Standard for the Installation of Lightning Protection Systems. This change was directed by the Standards Council in order to make the title more accurately reect the documents content. In addition,

17、the Council directed certain changes to the scope of the document to clarify that the document did not cover lightning protection installation requirements for early streamer emission systems or lightning dissipater array systems. The 1997 edition of NFPA 780 incorporated editorial changes to make t

18、he document more user friendly. In issuing this document, the Standards Council noted that lightning is a stochastic, if not capricious, natural process. Its behavior is not yet completely understood. This standard is intended to provide requirements, within the limits of the current state of knowle

19、dge, for the installation of those lightning protection systems covered by the standard. The 2000 edition of NFPA 780 was amended to provide requirements for open structures such as those found on golf courses. A 1998 lightning ash density chart replaced the 1972 lightning frequency isokeraunic char

20、t. The 2004 edition of NFPA 780 reected an extensive editorial revision of the standard to comply with the concurrent edition of the Manual of Style for NFPA Technical Committee Documents. Those revisions included the addition of three administrative chapters at the beginning of the standard: Admini

21、stration, Referenced Publications, and Denitions. Five technical chapters followed the administrative chapters in the same sequence as in the 2000 edition. Other editorial revisions included the breakout of paragraphs with multiple requirements into an individually numbered paragraph for each requir

22、ement, the minimization of the use of exceptions, the use of consistent headings for sections and section subdivisions, and reorganization to limit paragraph numbering to six digits. The International System of Units, commonly known as SI or metric, was used throughout the document. The appendixes w

23、ere renamed annexes and reordered in a more logical sequence. The 2004 edition also contained a number of technical revisions throughout the standard. Those revisions included the following: a main conductor, solid strip, was added for Class II material requirements for ordinary structures exceeding

24、 75 ft in height; handrails could be used as aINSTALLATION OF LIGHTNING PROTECTION SYSTEMS 780-2 2017 Edition substitute for down conductors; additional separation between ground rods was required where multiple ground rods are used; additional guidance was provided for those instances where it is n

25、ecessary to install the grounding conductor directly on bedrock; the section entitled Surge Suppression was entirely rewritten; titanium strike termination devices were permitted to be used; and in Annex K, the term Faraday cage was replaced with metallic cage. The 2008 edition provided requirements

26、 for surge protective devices to be installed at all power service entrances, at the entrance of conductive communications systems and antenna systems, and where an electrical or electronic system conductor leaves the structure. The new denition for lightning protection system included the term cond

27、uctive structural members. Clarication was provided relative to the use of ancillary metal parts that cannot be substituted for the main conductor. Strike termination devices included air terminals, metal masts, certain permanent metal parts of structures, and elevated conductors. Revisions claried

28、that metal masts and overhead ground wires were included in the requirements of Chapter 4. Signicant changes were made to the requirements for the use of bimetallic clamps and aluminum in proximity to earth. The standard has long required that grounding electrodes be located near the outside perimet

29、er of the structure, and in the 2008 edition additional guidance was provided to assist the system designer. Changes were also made to better address the requirements for grounding electrodes in shallow topsoil applications. The requirements for the use of multiple ground rods were revised. Revision

30、s were also made in numerous areas of the standard for clarity and to enhance its usability. Revisions to the graphs and formulas for the rolling sphere method were made to facilitate their use in metric units. Requirements were added to address proper installation of lightning protection equipment

31、on large roof top mechanical units. The installation of air terminals and main-size conductors in these applications were quantied and detailed. Revisions were made to enhance and clarify the requirements for the bonding together of all grounded media and underground metallic piping. The intent was

32、to provide for potential equalization and not to use the metallic piping as a lightning protection system grounding electrode. All grounding media and buried metallic conductors that might assist in providing a path for lightning currents in or on a structure must be interconnected to provide a comm

33、on ground potential. Guidance was provided on the use of isolating spark gaps. Signicant changes were made to the requirements pertaining to the conductors and other lightning protection system hardware used near the top of a heavy-duty stack. Other signicant changes included a complete rewrite of C

34、hapter 8, Protection for Watercraft, providing a number of technical revisions; more user information added in Annex B, Principles of Lightning Protection; and a revision of Annex F, Protection for Trees. In addition to signicant technical changes, the 2011 edition included new and revised text. Wit

35、h the addition of two new chapters, the 2011 edition of the standard presented a major change in the scope of the document. The rst new chapter addressed the protection of structures housing ammunition and explosive materials. The second new chapter included requirements for providing lightning prot

36、ection for wind turbines, specically wind turbine structures that comprise externally rotating blades, a nacelle, and a supporting tower. The 2011 edition was substantially reorganized to accommodate these new chapters in a logical order. The sections pertaining to strike termination devices, zones

37、of protection, and the rolling sphere method were totally reorganized for better usability. The text clearly provided that strike termination devices include air terminals, metal masts, permanent metal parts of structures, and overhead ground wires. The text qualied where a metal mast would be permi

38、tted to serve as the down conductor. The requirements for overhead ground wires and masts and overhead ground wires were relocated. The 2011 edition claried the requirements for strike termination devices at the eaves for a pitched roof, and a gure was added to graphically illustrate that condition.

39、 A new section on roof top helipads provided requirements to ensure that an adequate level of protection is provided to those areas within the height and safety criteria set forth by the Federal Aviation Administration (FAA) or other AHJs. Chapter 7 provided requirements for the protection of struct

40、ures containing ammable vapors, ammable gases, or liquids that can give off ammable vapors. The section on oating roof tanks was revised in its entirety as a result of recent testing and research conducted for aboveground storage tanks. The lightning risk assessment methodology provided in Annex L w

41、as completely rewritten. The lightning risk assessment was provided to assist the building owner, safety professional, or architect/engineer in determining the risk of damage or injury due to lightning. This annex provided both a simplied, quick-look assessment and a more detailed assessment for those requiring a more detailed analysis. Once the level of risk has been determined, the development of appropriate lightning protection measures can begin.