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NFPA 780 Standard for the Installation of Lightning Protection Systems 2011 Edition MELVIN K. SANDERS SENIOR MEMBER, IEEE Things Electrical Co., Inc. (dba TECo., Inc.) 206 SE Eastlawn Drive Ankeny, IA 50021-3402, USA 515-240-6974 Cell [email protected]

Abstract—This paper will briefly summarize the nature of lightning, provide a brief history of the document, the lead taken by the National Fire Protection Association to incorporate experience proven protections, and highlight topics of interest in the 2011 edition. Index Terms—Bonding, Grounding, Lightning, Lightning Protection Systems, LPS, Lightning Risk Assessment, NFPA 780, Wind Turbine, Structures Housing Explosive Material, Helipad

I. INTRODUCTION Strike discharge current results from a breakdown of electrostatic potential. It is unidirectional (the majority of the discharges are negative relative to earth but they can also be positive relative to earth) and creates a broadband electromagnetic pulse ranging in frequency from a few hundred Hertz to several kilo-Hertz with the majority of the energy in its lower frequency components. They are of very short time duration, containing micro-second individual bursts that result in multiple flashes appearing as one continuous flash to the observer for some milliseconds of elapsed time. Depending upon the path taken, the magnitude of current flow can induce voltages in nearby metallic members or other metallic components, and insulations will break down due to the resultant voltage pressure. These voltages can exceed the dielectric strength of air, causing flash-over and arcing to occur, which can ignite combustible materials, and create explosive pressures due to the overheated air and any liquids involved that will flash into steam. In addition, the high temperature (approximately 50 000 degrees Kelvin) associated with the lightning channel and its resultant attachment point can create as much or even more damage. The National Fire Protection Association (NFPA) promulgates over 2000 national codes and standards that are

used world-wide for the application of facility and safety concerns. IEEE has representation on several, and among them is NFPA 780. It is among the earliest documents published by NFPA, and its topic linage leads directly back to the investigations undertaken by the noted Engineer Benjamin Franklin. It is intended to provide a solid foundation for providing protection from the totally random, uncontrollable, unpredictable natural phenomenon of environmental electrostatic discharges involving tremendous current paths linked between the atmosphere to earth and return to the atmosphere. These current paths develop seemingly instantaneous high voltage electrical fields. This leads to electrocutions and electrical shocks at many locations around the world, and causes a significant monetary loss. Reports on NFPA 780 Technical Committee activities are made to the Type 1 Standards Coordinating Council (SCC) 18 of IEEE.

II. DEVELOPMENT AND MAKEUP OF NFPA 780 National Fire Protection Association 780 Standard for the Installation of Lightning Protection Systems, 2011 Edition is among the earliest documents adopted (from 1904, NFPA). It was first published separate from, then combined with, a parallel American Standards Association (ASA) (from 1911, now ANSI) committee document in 1945 and was jointly sponsored by the National Bureau of Standards (NBS) (from 1904, now NIST) and AIEE (from 1884, now IEEE). Originally identified as NFPA 78 through 1992, it was then identified as NFPA 780, Standard for the Installation of Lightning Protection Systems in 1995. Following the requirements of NFPA Manual of Style (MOS), the text in this edition has again been changed to make it more user friendly and correlate with accepted document style. It

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continues to note the random natural phenomenon of the electrostatic discharge. The lightning frequency chart was changed to the present flash density chart in 1998, and the topic of open spaces protection was added in 2000. 2004 reflected additional requirements of the NFPA MOS, provided for administration, referenced publications and definitions in the first three chapters and then followed by five technical chapters. It reduced the use of exceptions, SI units were introduced throughout, and appendices were identified as annexes. The section on surge suppression was entirely rewritten, and “Faraday Cage” was changed to “metallic cage” because the deflection mechanism was more likely a lattice-like affair than that of solid strips as the technical definition of Faraday Cage would indicate. NFPA 780 now has a total of 10 chapters. They are: Chapter 1 covers the administration of the document; Chapter 2 its referenced publications; Chapter 3 contains definitions of terms as used in NFPA 780; Chapter 4 ordinary structure (typical building or constructions; Chapter 5 addresses those that are not included in Chapter 4; Chapter 6 discusses smoke stacks normally used where combustion by-products are dispersed at higher elevations; Chapter 7 will be of interest where structures containing flammable vapors, gases or liquids which emit flammable vapors are involved; a new Chapter 8 now provides information for those concerned about structure protection of explosives and other energetic materials, a second new Chapter 9 is for wind turbine generators. The new Chapter 9 resulted in the watercraft protection chapter being incremented by one. This allows a more logical placement of the new Chapters and is not intended to lessen the importance of protecting watercraft. It also has 15 Annexes (three of which are reserved for future use): ranging from an annex which provides specific additional information on certain sections within the main document, to a tutorial on lightning protection principles and related information to aid in minimizing side-flash issues, and to expected maintenance and inspection guidance, earthing measurement techniques. Additional information can be found in the annexes where historically significant natural or built protection is warranted or desired, cautions on open space protections for persons and livestock, aircraft parking areas, revised information on IEC methodology and lightning risk assessment, and concluding with references for additional reading. Immediately following these is an extensive Index for locating specific terms or conditions.

adopted text of this new edition of NFPA 780. It is to provide an overview of the more critically important changes, so users can quickly turn to their topics of interest. All revisions, whether editorial or technical, are indicated by vertical lines in the margin (margin bars) associated with the changes. Text no longer applicable to a section or topic is indicated by “dots” in the margin as well. It is therefore important the previous edition be available for comparison when reviewing the 2011 version and these can be obtained by contacting NFPA, One Batterymarch Park, Quincy, MA 02169-7471 (USA) or from www.nfpa.org. This edition, like the others, depends upon the historical perspective of where we were, where we are now, and gain advance knowledge of future activities as they more and more relate to standards from other parts of the world. It is intended to apply to most structures exposed to this naturally occurring event, and is enforced at many military facilities as well as non-military locations. NFPA 780 is intended to be adopted by local, state and/or federal governmental entities and by insurance companies. In order to apply the information from this paper within the context of the complete document, a copy of NFPA 780 should be obtained from the National Fire Protection Association, 1 Batterymarch Park, Quincy, Massachusetts 02169-7471

IV. SCOPE AND CONTENT OF NFPA 780-2011

III. DISCLAIMER

The Scope in Chapter 1 states the traditional lightning protection system (LPS) installation applications and no longer prohibits covering structures housing explosive materials. It does not cover electric generating, transmission and distribution systems because these are subject to unique engineering review. However, these entities do have membership on NPPA 780 TC, and utilize applicable concepts. It goes on to further state it does not cover early streamer emission or charge dissipation systems, and it’s purpose is to provide for the safeguarding of persons and property from hazards arising from exposure to lightning. It is expected that components employed to meet this end are listed or labeled for this application and are used wherever possible. It is imperative that installations are made in a neat and workmanship manner, because that is the least expensive method to minimize unwanted direct or induced current flows and unnecessary exposure to dangerous surge voltages for both equipment and persons.

This report is not intended to provide a complete review, or complete listing, of the many discussions behind the

Chapter 2 specifically references NFPA 70, National Electrical Code® 2011 Edition. Other standards are

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ANSI/UL 1449 Standard for Safety for Surge Protection Devices, 3rd Edition September 29, 2009. Some text is extracted from NFPA 70 and from NFPA 115 Standard for Laser Fire Protection, 2008 Edition. Definitions unique for the application of NFPA 780 are contained within Chapter 3. Some are the primary definitions as found in NFPA 70 Article 100, but in many instances, the secondary meaning of common terms are utilized to ensure the correct understanding of NFPA 780 requirements. Among these latter are “grounding electrode” and “main conductor” because they terminate strike discharge current via a preferred conductive path to earth (ground) rather than leaving it to random chance and that the current loop involves returning to the atmosphere rather than back to a 60 HZ source. Definitions have been added to support the new Chapter 10 and to better align the surge protection device (SPD) definitions with ANSI/UL 1449. Chapter 4 Section and Figure 4.1.2 have been revised for clarity and employ common construction terminology. Section 4.8.1(A) and (B) were moved to become part of 4.1.2, Section 4.9.2 text for dead-end runs on dormers was clarified and Section 4.13.5.2 no longer restricts radials to a maximum of 90O degree divergent angle. Section 4.14.1.3 provides requirements for LPS connections to gas piping, and Sections 4.14.1.5 and A4.14.1.5 provides requirements and information where galvanic corrosion are a concern Section 4.16.1 specifies 4.8 mm (3/16 in) as the required minimum thickness of metal structural framework members. Section 4.18 for SPD has been extensively revised for clarity, to correlate with NFPA MOS for documents, and also with the new definition for voltage protection rating, and to correlate with ANSI/UL 1449 Standard. Section 4.18.6.4.1 requires SPD grounding to comply with NFPA 70 National Electrical Code, Chapter 8. A related note in A4.18.6.4.1 states that while good grounding is important, good bonding is imperative to minimize damage. Chapter 5 Section 5.2.2 states that electrically continuous metal structures are required to bond only to a grounding electrode or electrodes. Section 5.5 has been revised to allow strike termination devices to be directly mounted on airinflated structures as well as the continued use of mast type or catenary protection. Annex O material and Section 5.8 was replaced by new Chapter 9 Protection for Wind Turbines. New text for Section 5.8 addresses roof-top helipads and correlates with Federal Aviation Authority Regulations. Chapter 6 discusses heavy-duty (“tall”) stack protection, Chapter 7 subpart for overhead catenary protection has been moved into Chapter 4 for more general application, and has additional information for flammable vapor protections.

Sections 7.3.2.6.3 and 7.3.2.6.4 revision requires mast or overhead ground wires to be grounded and interconnected with the structure grounding systems in compliance with Chapter 4. Section 7.4.1.1 clarifies that fixed roof tanks and any fixed roof internal floating roofs are not required to have shunt or by-pass conductors. Section 7.4.1.2 provides information on external floating-roof tanks for placement of by-pass conductors and Section 7.4.1.5 new text requires gauge or guide poles that penetrate the floating roof are to be electrically insulated from that roof to 1 kV or greater. New Chapter 8 includes information from 2008 Edition Annex K and from the United States Department of Defense for protection requirements for structures housing explosive materials. Section 5.8 was deleted and 2008 Edition Annex O material for protection of wind turbines was placed into new Chapter 9. This chapter does not cover the turbine blades and related electrical generating equipment, essentially treating this as another type of “tall” structure. Chapter 10 (formerly Chapter 8) addresses LPS and galvanic protection for watercraft. Section 10.5.3.4 allows a main bonding grounding electrode to be single or multiple solid conductor at least 0.09 mm2 (1 ft2) immersed during normal operations, interconnected by at least one main conductor. Annex A contains additional information to provide more detailed criteria on various requirements. Annex K was deleted because of new Chapter 8, Annex L extensively revised to incorporate addition information when performing lightning risk assessment, Annex M Guide for Personnel Safety from Lightning revised for clarity, Annex N was deleted because of new Chapter 9, and Annex O now provides for informational references. Annex O was revised to include more military publications due to new Chapter 8 Protection of Structures Housing Explosive Materials.

V. FUTURE ISSUES A proposal to add information for protection of airfield lighting was held for additional study and to report back for the next cycle. Text relocation for topic alignment and NFPA Manual of Style issues will be continuing. IEEE will need to review these to ensure they relate to the IEEE Standard 142 Recommended Practice for Grounding of Industrial and Commercial Power Systems (Green Book),

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and are not in conflict with country specific codes or standards, whether NFPA or IEC, or elsewhere.

BIOGRAPHY Melvin K. Sanders (A ’88, M ’02, SM ’03) Mel was Principal member for IEEE on NFPA 780 Standard for Lightning Protection Installation and he received his Associate in Liberal Arts from Des Moines (IA) Area Community College 1980. A former instructor in electrical apprenticeship training, he now develops

and presents Codes and Standards industrial electrical application and safety programs, Mel remains a Principal on NFPA 79 and was IEEE Principal on both NFPA 70-NEC CMP 03 and NFPA 70B. He retired as Industrial Maintenance Electrician John Deere Des Moines (IA), serves as SAE HS 1738 Vice-Chair, and is a member of UL STP 508A and UL STP 810. Mel is a member of IAEI and its Iowa Chapter and Western Section Past President, a member of NFPA and SAE. He earlier received the Iowa State Governor’s Award for Safety Education, the I & CPS Departmental Award in 2005, awarded Iowa Chapter IAEI Honorary Chapter Membership in April 2010 and the NFPA Committee Service Award June 2010 for his efforts serving NFPA Technical Committees. Mel is IEEE-SA SB Official Board/Committee Standards Chair of Coordinating Committee 18 IEEE-External Representatives to NFPA 70, NFPA 70B, NFPA 70E, NFPA 73 and NFPA 780 Technical Committees.

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