Overhead Distribution Lines – Design and Applications

About the Author xi Preface xiii Acknowledgments xv 1 Introduction 1 1.1 Scope 1 1.2 Background 2 2 Pole Structures 7 2.1 General 7 2.2 Wood Pole Strength 8 2.3 Loads 13 2.4 Embedment Depth 15 2.5 Guying 17 2.6 Column Buckling 19 2.7 Grounding and Bonding 22 3 Pole Installation and Maintenance 23 3.1 Pole Placement 23 3.2 Guys and Anchors 24 3.3 Pole Maintenance 26 4 Wires, Conductors, and Cables 31 4.1 Categories 31 4.2 Messenger Wire/Strand 31 4.3 Electric Supply (Power) Cables 33 4.4 Communications Cables 35 4.5 Wireless Attachments 38 5 Cable Installation 39 5.1 Conductor and Cable Placement 39 5.2 Lashing Operation 40 5.3 Overlashing 41 6 NESC(r) Requirements (Strength and Loading) 45 6.1 National Electrical Safety Code (NESC) 45 6.2 Loading Requirements 46 6.3 Strength Requirements 49 6.4 Wire Tensions 52 6.5 Guyed Poles 53 6.6 Extreme Wind Loads (“60 ft Limit”) 54 6.7 Allowable Deterioration 56 6.8 Overlashed Cables 57 6.9 Software Tools and Pole Loading Analysis 60 7 NESC(r) Requirements (Clearances) 63 7.1 Clearances 63 7.2 Clearance Zones 63 7.3 Clearances Above Surfaces and Buildings 66 7.4 Clearances Between Wires 67 7.5 Overlashed Cables 67 8 Principles of Wire Sag 71 8.1 Catenary 71 8.2 Initial and Final Sag 72 8.3 Sag-Tension Relationship 72 8.4 Determining Change in Sag (and Tension) 73 8.5 Ruling Span 76 8.6 Point Load 77 9 General Order 95 (California) 81 9.1 General Order 95 (GO 95) 81 9.2 Loading Requirements 81 9.3 Strength Requirements 83 9.4 Clearances 84 10 Examples 85 10.1 Purpose 85 10.2 Tangent Line 85 10.3 Line Angle 88 10.4 Line Angle – Buckling Consideration 90 10.5 Additional Attachment 94 10.6 Summary 96 Appendix A Properties of Messenger Strands 99 Appendix B Wireless Attachments 101 Appendix C Extreme Wind and Extreme Ice Loadings 103 Appendix D Solution of Cubic Equation 107 Appendix E Point Load 109 E.1 Parabolic Model 109 E.2 Intersecting Straight Lines Model 111 Glossary 115 References 121 Index 123