CODE FOR PROTECTION AGAINST LIGHTNING Miscellaneous Publication of the Bureau of Standards No. 92 DEPARTMENT OF COMMERCE BUREAU OF STANDARDS MISCELLANEOUS PUBLICATION, BUREAU OF STANDARDS, No. 92 CODE FOR PROTECTION AGAINST LIGHTNING April 8, 1929 Approved April 4, 1929, by the American Standards Association PRICE 25 CENTS UNITED STATES GOVERNMENT PRINTING OFFICE WASHINGTON : 1929 MEMBERS OF THE SECTIONAL COMMITTEE Sponsors: American Institute of Electrical Engineers. National Bureau of Standards. NAME AND BUSINESS AFFILIATION ORGANIZATION REPRESENTED *M. G. Lloyd (chairman), Bureau of Standards, National Bureau of Standards. Washington, D. C. *F. W. Peek, jr. (vice chairman), General Electric American Institute of Electrical Engi- Co., Pittsfield, Mass. neers. *0. S. Peters (secretary), Bureau of Standards, National Bureau of Standards. Washington, D. C. W. R. Arbuckle, superintendent of fire alarm, International Association of Municipal Bayonne, N. J. Electricians. A. L. Atherton, Westinghouse Electric & Manu- American Institute of Electrical Engi- facturing Co., East Pittsburgh, Pa. neers. *W. C. Beckjord, American Light & Traction Co., American Gas Association. New York, N. Y. J. C. Bogle, Cook Electric Co., Chicago, 111 United States Independent Telephone Association. Bureau of Construction and Repair, Navy De- United States Navy Department. partment, Washington, D. C. W. L. Cook, Reliable Electric Co., Chicago, ni._. United States Independent Telephone Association. R. N. Covert, United States Weather Bureau, United States Weather Bureau. Washington, D. C. *H. W. Drake, Western Union Telegraph Co., Western Union Telegraph Co. New York, N. Y. Frank E. Epps, Tidewater Oil Co., New York, National Safety Council. N. Y. (Alternate: William F. Rooney.) V. E. Goodwin, General Electric Co., Pittsfield, National Electrical Manufacturers' As- Mass, sociation. *F. L. Hunt, Turners Falls Power & Electric Co., American Institute of Electrical En- Greenfield, Mass. gineers. Holger Jensen, Maryland Casualty Co., Balti- National Bureau of Casualty and more, Md. Surety Underwriters. S. D. Kretzer, St. Louis Lightning Rod Co., St. National Lightning Rod Manufacturers Louis, Mo. Association. •Member of Executive Committee. Ill IV MEMBERS OP THE SECTIONAL COMMITTEE NAME AND BUSINESS AFFILIATION OBGANIZATION REPRESENTED F. McVittie, New York State Railways, Roch- American Electric Railway Association. ester, N. Y. (Alternate: P. V. C. See.) J. L. Niesse, C. C. C. & St. L. Railway, Indian- American Railway Association. apolis, Ind. P. Norton, Western Electric Co., New York, Western Electric Co. N. Y. J. P. O'Donohue, Postal Telegraph-Cable Co., Postal Telegraph-Cable Co. New York, N. Y. (Alternate: D. H. Gage.) Dana Pierce, Underwriters' Laboratories, Chi- Underwriters' Laboratories (Inc.). cago, 111. (Alternate: B. H. Glover.) D. W. Roper, Commonwealth Edison Co., Chi- National Electric Light Association. cago, 111. (Alternates: A. Maxwell and E. C. Stone.) E. R. Scales, Edison Lamp Works, Harrison, American Society of Safety Engineers- N. J. Engineering Section, National Safety Council. •A.M. Schoen, South-Eastern Underwriters Asso- National Fire Protection Association and ciation, Atlanta, Ga. American Institute of Architects. W. C. Shinn, W. C. Shinn Manufacturing Co., National Lightning Rod Manufacturers' Chicago, 111. Association. F B. Silsbee, Bureau of Standards, Washington, National Bureau of Standards. D. C. *C. E. Skinner, Westinghouse Electric & Manu- American Petroleum Institute. facturing Co., East Pittsburgh, Pa. Thomas Sproule, Public Service Electric & Gas National Electric Light Association. Co., Newark, N. J. (Alternate: R. N. Conwell.) E. R. Stbtts, Dodd & Struthers, Des Moines, National Lightning Rod Manufacturers' Iowa. Association. H. S. Warren, American Telephone & Telegraph American Telephone & Telegraph Co. Co., New York, N. Y. W. C. Wagner, Philadelphia Electric Co., Phila- Association of Edison Illuminating Com- delphia, Pa. panies. Member of Executive Committee. PREFACE The protection of persons and property against lightning is a subject of widespread interest and of considerable im- portance. Since the time of Benjamin Franklin the value of lightning rods in the protection of buildings has been recog- nized. Early in the art of utilization of electrical energy, the use of lightning arresters in connection with exposed overhead lines was introduced. In the fields of both build- ings and electrical equipment there has been a great variety of practice, and many installations have been made which did not adequately fulfill the purpose for which they were intended. In order to meet the definite need for standards of prac- tice in connection with lightning protection, the American Engineering Standards Committee included in the first list of safety codes on its program a code of practice on this subject. The American Institute of Electrical Engineers and the National Bureau of Standards were designated as sponsors for this project, whose scope included the protec- tion of buildings, oil tanks and other structures, trees, live- stock, and persons; overhead electrical lines, and apparatus which is connected to them. A sectional committee was organized by the sponsors in 1921 and has been working for a number of years upon the formulation of definite standards which should be a guide in securing protection from this hazard. The needs of both Y VI PREFACE industry and the public have been kept in mind, and the standards now set up have been taken largely from Amer- ican practice and experience, although foreign practice has also been given consideration. The subject matter contemplated for this code comprises five parts, three of which are presented here. The other two parts, dealing with electrical apparatus and lines, are with- held for further consideration. In each part an introduc- tory statement to the particular subject in hand is given, and the code Is followed by an appendix in which is given a general discussion of lightning, its origin and characteris- tics, and the effects which it produces. An attempt is made in the appendix to indicate how much is definitely known about lightning and its properties and also theories of its origin and speculations regarding the magnitude of the electrical quantities involved in lightning phenomena. There is also appended a bibliography in which the more impor- tant contributions to the present state of the art are listed. The part of the code dealing with specifications for light- ning rods used to protect buildings goes into the questions of practical construction and sets forth in detail the require- ments of good design for such installations. These are of general application, and particular types of buildings may need more specific consideration. For the protection of per- sons and of oil tanks the standards are not so detailed but are aimed rather to state the general principles which should be applied. In spite of the value of lightning rods in the protection of buildings their use has at times and in places come into disrepute owing to a general lack of information as to the best methods of protection, and it is hoped that the publica- PREFACE VII tion of definite standards on this subject will enable the public to demand installations which will give them adequate protection. Lightning is considered responsible for a majority of tank fires of the petroleum industries. A realization of the im- portance of this source of loss to the industry and to the re- sources of the Nation has awakened a general interest in proper standards of protection. In this field, as in the pro- tection of ordinary buildings, many inadequate installations have been made in the past. By the application of the proper principles and standards of construction it is believed that this loss can be greatly reduced. Further experience and the accumulating knowledge of the properties of lightning may lead later to changes in these specifications, and future revisions are contemplated from time to time as experience and progress in the art may warrant. Comments regarding these specifications and recommended changes are invited by the committee from all who may have experience in applying them. CONTENTS Page Members of the sectional committee in Preface v Part I.—Protection of persons 1 Introduction 1 100. Purpose 2 101. Personal conduct 2 Part II.—Protection of buildings and miscellaneous property 3 Introduction 3 Relative losses from lightning 4 Factors to be considered 5 Fundamental principles of protection 10 Sec. 20. Scope, definitions, etc 14 200. Scope and purpose 14 201. Interpretations and exceptions 14 202. Mandatory and advisory requirements 15 203. Terms and definitions 15 Sec. 21. Lightning rods for ordinary buildings 16 210. Conductors 16 (a) Materials , 16 (b) Form and size 18 (c) Joints 19 (d) Fasteners 20 211. Points and elevation rods 21 (a) Attachment of points 21 (&) Elevation rods 21 (c) Braces for elevation rods 22 212. Prevention of deterioration 23 (0) General 23 (&) Corrosion 23 (c) Mechanical injury 23 (d) Use of ornaments 23 IX — X CONTEXTS Part IL—Protection of buildings and miscellaneous property Continued. Page 213. Location of air terminals 24 (a) General 24 (6) Projections 24 (c) Ridges, parapets, and edges of flat roofs— 24 (d) Metal projections and parts of buildings. 24 (e) Coursing of conductors 24 (f) Roof conductors 25 (g) Down conductors 25 (70 Obstructions 25 (i) Bends 25 214. Metal-roofed and metal-clad buildings 25 (a) Metal in overlapping sections 25 (&)