Electrical Essentials for Powerline Workers

338 Pages·2004·137.355 MB·English

by  Wayne Van Soelen

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Contents
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re ace .... ......................................... . ......... .
111
Acknowledgmen ts ......................... , ..................... iv
CHAPTER 1 Electrical Power System Overview ... . . . . . . . . . . . . . . . . . . . . . 1
1.1 Introduction ................................................. 1
1.1.1 Three Systems within the Power System .................... , ... 1
1.2 Electrical Energy .............................................. 1
1.2.1 Energy .... .............................................. 1
1.2.2 Utilization of Electrical Energy ............................... 2
1.2.3 Uncontrolled Energy as a Hazard ............................. 2
1.3 Generation of Electrical Energy .................................. 3
1.3.1 Generation Basics ......................................... 3
1.3.2 Turning the Turbine ....................................... 4
1.3.3 Hydraulic Generation ................................. . .... 4
1.3.4 Generation from Steam .............................. . ...... 5
1.3.5 Nuclear Generation ........................................ 6
1.3.6 Gas Turbines ............................................. 6
1.3.7 Cogeneration ............................................. 6
1. 3.8 Alternative Electrical Energy Sources ........................... 6
1.4 Transmission of Electrical Energy ................................. 8
1.4, 1 Transmission of Electricity. ........................ . ......... 8
1.4.2 Typical Transmission Line Construction ........................ 8
1.4.3 Transmission Line Voltage ................................... 9
1.4.4 Transmission System Substations .............................. 9
1.4.5 Switchyards ............................................. 10
1.4.6 Communications between Stations ........................... 10
1.4.7 Electrical Power Pools ...... , .............................. 11
1.4.8 Blackouts and Brownouts .................................. 12
1.5 Electrical Distribution ........................................ 14
1.5.1 Distribution Basics ....................................... 14
1.5.2 Distribution System Designs ................................ 14
1. 5.3 Radial System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
1.5.4 Loop Primary ........................................... 16
1.5.5 Primary Network ........................................ 16
1.5.6 Overhead and Underground Systems .................... .. ... 16
1.5.7 Two Types of Underground Systems .......................... 18
1. 5.8 Managing a Distri butio n System. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
Review Questions ..... ......................................... . 19
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CHAPTER 2 Electrical Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
21
2.1 Introduction ................................................ 21
2.1.1 What is Electrici ty? ....................................... 21
2.1.2 Summary of Electrical Units ................................ 21
2.2 Electrical Potential ........................................... 22
2.2.1 Voltage Basics .... .. ........ .. . . ........ . ............ .... 22
2.2.2 Measuring Voltage ............... .. .. . .... . .. ...... . .... .. 22
2.2.3 Safety with Electrical Potential ....... . .. . .. .. ... . ........... 22
2.2.4 Maintaining Good Voltage ......... ..... ....... . ........... 23
2.2.5 Voltage Drop ..................... . . .... .. ... .. . .. . . .... . 23
2.2.6 Typical Utility Voltages ...... ... . .... .... .............. . . .. 23
2.3 Electrical C urrent .. . ... . .. ........ .... .. ............... . ..... 24
2.3.1 Current Basics ... . . . ...... . ....... .. .... ..... ... . .. .... .. 24
2.3.2 Measuring Current .... .. ..... . .... . ... .. ...... .. . . .. ..... 24
2.3.3 Electrical C urrent Needs a C ircuit ........... . ....... . ........ 25
2.3.4 Safety with Electrical C urrent ....... . . ... ... . .. . .... . ....... 25
2.3.5 Load Current ...... .. .... . .. . ... . ..... .. . .. ...... ...... . 26
2.3.6 Peak Load Curren t ....................................... 26
2.3.7 Cold Load Pickup .. . ........ ... ... .... . .. ........ . .... ... 26
2.3.8 Fault Current (Short-C ircuit Current) ......................... 27
2.4 Electrical Resistance .......................................... 27
2.4.1 Resistance Basics ...................... . ....... .. .. .... ... 27
2.4.2 Measuring Resistance with an Ohmmeter ...................... 27
2.4.3 Measuring Earth or Insulation Resistance . . . . .. : ... . ... .... .. .. 27
2.4.4 Ohm's Law ................................. . ... .... .... 28
2.4.5 Conductance ............................................ 29
2.4.6 Impedance .. .... ............... . .... .... ..... ....... ... . 29
2.4.7 Conductor Resistance ..................................... 29
2.4.8 High Resistance and Insulation .............................. 29
2.4.9 The Effect of Rain on Insulators ......... .. . . .. .. ........ . . . . 30
2.4.10 Safety and Electrical Resistance .. .... . .. .. ... . .. .. .......... 30
2.4.11 Second Point of Contact ................... . .............. 31
2.5 Electrical Power and Electrical Energy ............................ 31
2.5.1 Heat from Current Pass ing through a Resistance . ... .. ........... 31
2.5.2 Electrical Power and Energy Basics ....... ....... . .. .. ..... .. . 32
2.5.3 Power Formulas Derived from Ohm's Law ... . ......... ....... . 32
2.5.4 Large Units of Electrical Power .............................. 33
2.5.5 The Kilowatt-Hour .. . ............ . ... ...... ..... . ....... . 34
2.5.6 Kilowatt-Hours in Perspective .... ...... . . ................... 34
Review Questions ............................................... 35
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CHAPTER 3 Alternating Current (AC) . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3.1 Introduction ...................................... . .. . ... . . . 37
3.1.1 Why Alternating Current? ............ . .......... . ......... 37
3.2 Characteristics of AC ........................ . ................ 37
3.2.1 AC Basics ...................... . . . ............ . . . ...... 37
3.2.2 Frequency ........................... . ........... . ...... 38
3.2.3 Generation of AC Power ................. . .... . ..... . ..... . 38
3.2.4 Rise and Fall ofVolrage and Current. ............ . .......... . . 39
3.2.5 AC Represented by a Wave ............................ . .... 39
3.2.6 Sine Wave as a Graphical Representation ..... . ......... . . .... 40
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3.2.7 Values of AC and Voltage ............................ . .... . 41
3.2.8 Voltage and Current in Phase with Each Other. ................. 41
3.2.9 Circuits in Phase with Each Other .............. . ............ 42
3.3 Reactance in AC Circuits ..... . .. . . .. .................. . . .. .... 42
3.3.1 Loads Fed by AC Circuits ..................... . .....' .. . .... 42
3.3.2 Reactance in an AC Circuit ................ . ............... . 42
3.3.3 Impedance in an AC Circuit ................ . ........... . ... 43
3.3.4 Resistance in an AC Circuit ..................... . ........ . . 43
3.3.5 Induction in an AC Circuit. .......... . ........ . ............ 43
3.3.6 Inductive Reactance ...................... . .... . ....... . .. 44
3.3.7 Current Lagging Voltage ...................... . ............ 44
3.3.8 Applications of Inductive Reactance .................... . ..... 44
3.3.9 Capacitance .... . ......... . .................. .. .......... 45
3.3.10 Capacitors . . ........................................... 46
3.3.11 Capacitive Reactance ..... . ....................... . . .. .... 46
3.3.12 Current Leads the Voltage .................. . ............. . 47
3.3.13 Applications of Capacitive Reactance .......... . ......... .. .. 47
3.3.14 Effect of Frequency on Reactance ........................... 48
3.3.15 Summary of Resistance, Inductance, and Capacitance .... . ...... 48
3.4 AC Power . ............ . .. . ................................ . 49
3.4.1 Active Power . .. ......................................... 49
3.4.2 Apparent Power. ........................... . ............. 49
3.4.3 Reactive Power . ...................... . .. . . . ............. 49
3.4.4 The Power Triangle ....................................... 50
3.4.5 Power Factor ......................... . .................. 50
3.4.6 Power Factor Correction ................. . .. . . . ........ . ... 51
3.5 AC or DC Transmission ........... . .......... . ....... . ........ 51
3.5.1 AC or DC .............................................. 51
3.5.2 Effect of AC Frequency on Transmission of Electricity ............ 52
3.5.3 Main Applications of DC Transmission .. . .................... 52
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3.5.4 Advantages of DC Transmission ............................. 52
3.5.5 Disadvantages of DC Transmission ........................... 53
3.5.6 Description of DC Transmission Lines ........................ 53
3.5.7 Resistance Current Flow on DC ........................... 53
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3.5.8 DC Underground or Submarine Cable ........................ 53
3.5.9 Working on DC Circuits .................................. 54
Review Questions ............. .................................. 54
CHAPTER 4 Three-Phase Circuits . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . 55
4.1 Introduction ................................................ 55
4.1.1 Three-Phase Basics ....................................... 55
4.2 Characteristics of Three-Phase Circuits ............................ 55
4.2.1 Why Three Phase? ....................................... 5 5
4.2.2 Generation of Three-Phase Power ............................ 56
4.2.3 Phases 120 Degrees Apart .................................. 57
4.2.4 Phase Designations ....................................... 58
4.2.5 Phase Rotation .......................................... 58
4.2.6 Three-Phase Connections .................................. 58
4.2.7 Wye and Delta Systems .................................... 58
4.3 Delta-Connected Systems ...................................... 59
4.3.1 Delta- or Series-Connected Three-Phase System ................. 59
4.3.2 Voltage in a Delta System .................................. 60
4.3.3 Current in a Delta System .................................. 60
4.3.4 Return Flow in a Delta Circuit .............................. 60
4.3.5 Ground Fault Protection in a Delta Circuit ..................... 61
4.4 Wye-Connected Systems ....................................... 61
4.4.1 Wye- or Parallel-Connected Three-Phase System ................. 61
4.4.2 Voltage and Current in a Wye System ......................... 61
4.4.3 The Neutral in a Wye System ............................... 62
4.4.4 Earth Return System Neutral ............................... 62
4.4.5 Converting from Delta to Wye .............................. 63
4.5 Three-Phase Power ........................................... 63
4.5.1 The Combined Power in Three Phases ........................ 63
4.5.2 Field Calculations ........................................ 64
4.5.3 Calculations Involving Power ............................... 64
4.5.4 Calculations with "Handy Numbers" ......................... 64
4.5.5 Examples Using "Handy Numbers" .......................... 64
Review Questions ............................................... 66
CHAPTER 5 Circuit Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5.1 Introduction ................................................ 67
5.1.1 Purpose of Circuit Protection ............................... 67
5.2 High-Voltage System Protection ......................... ....... 68
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5.2.1 Two Types of Switchgear ................................... 68
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5.2.2 Circuit Breakers in an Electrical System ....... . ..... . ......... 68
5.2.3 Types of Circuit Breakers .................................. 68
5.2.4 Fault Detection .......................................... 68
5.2.5 Protective Relaying ....................................... 69
5.2.6 Relays Controlling Circuit-Breaker Operation ..... . . . .......... 70
5.2.7 Circuit-Breaker Operation ..................... .. ... . ...... 71
5.2.8 Zone Protection ......................................... 71
5.2.9 The Blackout of 2003 ........... . ......................... 7 1
5.3 Distribution Protection ........................ . ..... . ........ 73
5.3.1 Distribution-Protection Requirements ........ . ... . ........... 73
5.3.2 Protection in a Distribution Substation ........................ 73
5.3.3 Protection Using Home Wiring as an Example .................. 73
5.3.4 The Need for Overcurrent Protection ......................... 75
5.3.5 Transient or Permanent Faults .. . ......... . .................. 76
5.3.6 Causes of Overcurrent ........................... . ......... 76
5.3.7 Magnitude of Fault Current ..... . .......................... 76
5.3.8 Impedance to Fault Current . . .............................. 77
5.3.9 Distribution-Protection Scheme ............................. 77
5.3.10 SCADA Systems . . . ......... ; ... . ....................... 78
5.4 Distribution Switchgear and Their Operation .......... . ........... 78
5.4.1 Two Types of Switching in Distribution ................... . .. . 78
5.4.2 Reasons to Operate a Switch ................................ 79
5.4.3 Arc Length ................................ . ...... . ..... 80
5.4.4 Arc-Len gth Fo rm ula ........... . .......................... 81
5.4.5 Designs to Extinguish Arcs ................................. 81
5.4.6 Zero-Awaiting and Zero-Forcing Interrupters ............... . ... 81
5.4.7 Disconnect Switches .......... . ........................... 81
5.4.8 Load-Interrupter Switches ................... . .............. 82
5.4.9 Operating a Disconnect Switch ............ . ................. 84
5.4.10 Operating a Live-Line Clamp .................. . ........... 84
5.4.11 Operating a Distribution Fused Cutout ............ . ......... 85
5.4.12 Use of a Load Break Tool ..... . ........................... 85
5.4.13 Fuses. ........................................... . .. . 86
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5.4.14 Expulsion Cutout Fuse Links .............................. 86
5.4.15 Solid-Material Fuses ...... . .................... . ......... 86
5.4.16 Current-Limiting Fuses .......................... . ........ 87
5.4.17 Types of Current-Limiting Fuses ....... . ......... . .......... 87
5.4.18 Reclosers . . ................................... . ........ 88
5.4.19 Hydraulic Reclosers ................ . ................. . ... 89
5.4.20 Electronic Reclosers ....................................... 89
5.4.21 Operating an Electr-onic Recloser ........................... 89
5.4.22 Non-Reclose Feature on Reclosers .......... . ................ 91
5.4.23 Typical Recloser Ratings .................................. 91
5.4.24 Sectionalizers ...... . ....... . ............................ 92
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5.4.25 Operating Three-Pole Switches ............................. 92
5.4.26 Bypassing Defective Switchgear. ........ .................... 92
5.5 Underground Distribution Switchgear . ......... ....... . ........ .. 93
5.5.1 Switchgear in Underground Distribution Systems ................ 93
5.5.2 Cable Separable Connectors (Elbows) ... .... .......... ........ 94
5.5.3 Metal-Clad Switchgear .................................... 95
5.5.4 NX-Type Switches ... .... .............. .................. . 96
5.6 SpecifYing Protection for a Distribution Feeder ...... ; .............. 96
5.6.1 Planning a Protection Scheme ............................... 96
5.6.2 Gather Feeder Data ....................................... 96
5.6.3 Calculating Feeder Information .............................. 97
5.6.4 Protection-Scheme Philosophy .............................. 98
5.6.5 Interpreting the Results of a Feeder Study ...... .... .....' ....... 99
5.6.6 SpecifYing a Hydraulic- Recloser Frame Size ................... 100
5.6.7 SpecifYing a Trip-Coil Size ................................ 100
5.6.8 A Recloser Protection Zone .......... . ....... . .... .. . .... .. 100
5.6.9 SpecifYing Recloser Speed and Operating Sequence .. .. ..... .... 101
5.6.10 Typical TCC Curve for a Recloser. ......................... 10 1
5.6.11 SpecifYing a Downstream Recloser ......... . ... ............ 101
5.6.12 SpecifYing Fuse Size and Speed ... ............ ..... ... .... . 101
5.6.13 SpecifYing Downstream Fuses ...................... .. ..... 104
5.6.14 SpecifYing Sectionalizers .... ................. . .. ..... .... 105
5.6.15 Overcurrent Trouble Calls ................................ 105
5.6.16 High-Voltage Distribution Conversion .. ; . . .. . .............. 106
5.7 Overvoltage Protection ....................................... 106
5.7.1 Causes of Overv oltage . ......................... .......... 106
5.7.2 Convection and Frontal Thunderstorms ...................... 107
5.7.3 Description of Lightning .................................. 107
5.7.4 Estimating Distance from Lightning .... ........ . ...... ...... 108
5.7.5 Effects of a Direct Stroke of Lightning ....................... 108
5.7.6 Ground-Gradient Effect ... : .......................... ..... 109
5.7.7 Safety Tips for Working Near Lightning ...................... 110
5.7.8 Tracking Lightning Storms ................................ 110
5.7.9 Effect of Lightning on a Circuit ............................ 110 '
5.7.10 Switching Surges ....................................... III
5.7. 11 Effects f a Voltage Surge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . III
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5.7.12 Circuit Protection from Overvoltage ........................ III
5.7.13 Surge Arresters ..................... ... ............ .. .. 112
5.7.14 Types of Surge Arresters ................................. 112
5.7.15 Classes of Surge Arresters ....... .. ...................... . 115
5.7.16 Insulation Coordination ................................. 115
5.7.17 Equipment Voltage-Time Curves .......................... 116
5.7.18 Shorting Insulators for Live-Line Work ..................... . 116
5.7.19 Surge Protection at Problem Locations ...................... 117
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5.8 System Grounding for Protection ............................... 118
5.8.1 Importance of System Grounding ........................... 118
5.8.2 Purposes of System Grounding ............... . ....... . ..... 118
5.8.3 System Grounding for People Protection ................... . . 118
5.8.4 Ground versus Neutral Connections ..... . ........ . . .. ....... 119
5.8.5 The Neutral as Part of the Grounded System ........... . ...... 119
5.8. 6 Neutral Potential. ....................... . .. . ............ 119
5.8.7 Grounding for Overcurrent Protection .................... . .. 120
5.8.8 Inserting an Impedance in the Ground Return .. . . . . . ... . ...... 121
5.8.9 Surge Protection ............................. . .......... 121
5.8.10 Good Ground ........................................ . 121
5.8.11 Measuring Ground-Rod Resistance ....... . ............ . ... . 121
Review Questions ..................................... . ........ 123
CHAPTER 6 Working in an Electrical Environment . . . . . . . . . . . . . . . . 125
6.1 Introduction ............................................... 125
6.1.1 Working on or Near Electrical Circuits ....................... 125
6.1.2 Making Contact with an Electrical Circuit .................... 125
6.2 Connecting a Load in Series with a Circuit ................. . ..... 126
6.2.1 What Is a Series Circuit? ... . .............................. 126
6.2.2 Characteristics of a Series Circuit ........................... 126
6.2.3 Loads Placed in Series ................................... . 127
6.2.4 Making Series Connections ............................ .. .. 127
6.2.5 The Human Body in a Series Circuit ....... . ............ . ... 127
6.2.6 Accident Examples Involving Series Contact ................... 127
6.2. 7 Protection from Series Contact ............................. 128
6.3 Connecting a Load in Parallel with a Circuit ................... . .. 128
6.3.1 Making Parallel Contact ........................... . .... . . 128
6.3.2 What Is a Parallel Circuit? .. . .................... ... . . . . .. 128
6.3.3 Characteristics of a Parallel Circuit .......................... 128
6.3.4 Calculating the Total Resistance of a Parallel Circuit. ............ 130
6.3.5 Loads Connected in Parallel ............................... 130
6.3.6 Leakage Current ........................................ 131
6.3.7 Leakage Current Working Barehand .............. . .......... 131
6.3.8 The Human Body in a Parallel Circuit ............... .. ... . . . 131
6.3.9 Accident Examples Involving Parallel Contact ........ . . . ... . ... 131
6.3.10 Protection from Parallel Contact ............ . .............. 132
6.4 Electrical and Magnetic Induction .............................. 132
6.4.1 Three Electrical Effects without Any Contact .................. 132
6.4.2 Static Electricity ....... . .............. . ... . ............. 133
6.4.3 Electric-Field (Capacitive) Induction ......................... 133
6.4.4 Electric-Field Effect on an Isolated Conductor .. . ..... . ........ 134
6.4.5 Electric-Field Effect Working in a High-Voltage Environment .. . .. 134
6.4.6 Magnetic-Field Induction ............... . ................. 134
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6.4.7 Working in an Environment with High Induction .............. 135
6.4.8 Transpositions .......................................... 135
6.5 Voltage Gradients ........................................... 136
6.5.1 Ground Faults .......................................... 136
6.5.2 Voltage Gradients ....................................... 137
6.5.3 A Voltage-Gradient Example ................. ; ............. 138
6.5.4 Setting a Pole in a Live Distribution Line ..................... 138 .
6.5.5 Step Potential and Touch Potential'. ......................... 139
6.5.6 Magnitude of Step and Touch Potentials ...................... 139
6.5.7 The Size of the Step-Potential Gradient ....................... 140
6.5.8 Voltage Gradients on a Pole ................................ 140
6.6 Working with Neutrals ....................................... 140
6.6.1 Voltage and Current on a Neutral ... . ....................... 140
6.6.2 Sources of Neutral Current ................................ 140
6.6.3 Sources of Neutral Voltage ................................ 141
6.6.4 An Open Neutral ....................................... 141
6.6.5 Precautions for Working with a Neutral ...................... 142
6. 7 Vehicle Grounding and Bonding ............................... 142
6.7.1 The Vehicle as an Electrical Hazard .......................... 142
6.7.2 How Vehicles Can Become Alive .................. . ......... 142
6.7.3 Ground-Gradient Hazards near the Vehicle .................... 143
6.7.4 Protection from Shock ................................... 144
6.7.5 Grounding the Vehicle ................................... 145
6.7.6 Choice of Ground Electrodes .......... ..................... 145
6.7.7 Typical Values during a Boom Contact ....................... 145
6.7.8 Examples of Using a Ground Rod to Ground a Vehicle .......... 146
6.7.9 Boom in Contact with an Isolated and Grounded Conductor ..... 147
6.7.10 Examples of Hazards Using a Boom around Isolated Conductors .. 147
6.8 Electromagnetic Fields (EMF) ................................. 148
6.8.1 Why the Interest in EMFs? ................................ 148
6.8.2 What are EMFs? ........................................ 148
6.8.3 Electromagnetic Spectrum ................................. 148
6.8.4 Sources of Power-Frequency EMF ........................... 149
6.8.5 Methods of Reducing the Strength of EMF ................... 149
6.8.6 Measurement of EMF ............................. , ...... 151
6.8.7 Dose .... " ... ......................................... . 152
6.8.8 Natural Levels of Electric and Magnetic Fields ................. 153
6.8.9 Health Risk ............................................ 153
6.8.10 Limits of Exposure ..................................... 153
6.9 Minimum Approach Distance ........ . ........................ 153
6.9.1 Minimum Approach Distance as a Barrier .................... 153
6.9.2 Factors Considered for a Minimum Approach Distance .......... 154
6.9.3 The Electrical Factor (F X B) in a Minimum Approach Distance ... 155
6.9.4 The Human Factor (A) in a Minimum Approach Distance ........ 155
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6.10 Fire in an Electrical Environment .............................. 156
6.10.1 Line-Crew Involvement with Fires ......................... 156
6.10.2 An Electrical Fire ...................... ; ................ 156
6.10.3 Water and Electricity .................................... 157
6.11 Electrical Influence on Corrosion .............................. 157
6.11.1 Corrosion Hazards ..................................... 157
6.11.2 Dissimilar Metals in a Circuit ............................. 157
6.11.3 Galvanic Series of Metals Used in Line Hardware .............. 158
6.11.4 Galvanic Corrosion ..................................... 158
6.11.5 Copper-to-Aluminum Connections ........................ 159
6.11.6 Cathodic Protection .................................... 159
6.11. 7 Stray-Current Corrosion ................................. 159
6.11.8 Pipeline Cathodic-Protection Hazard ....................... 159
Review Questions .............................................. 160
CHAPTER 7 . Installing and Removing Protective Grounds . . . . . . . . . . . . 161
7.1 Introduction ............................................... 161
7.1.1 Grounding Procedure .................................... 161
7.1.2 Reasons for Grounding ................................... 161
7.1.3 Control of Current and Voltage When Grounding .............. 162
7.2 The Grounding Principle ..................................... 162
7.2.1 The Grounding Principle Defined ........................... 162
7.2.2 Grounding for Fault Current .............................. 162
7.2.3 Grounding to Provide a Parallel Shunt ....................... 163
7.2.4 Does All the Current Take the Easiest Path to Ground? .......... 163
7.2.5 Resistance of a Human Body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
7.3 The Bonding Principle ....................................... 165
7.3.1 The Bonding Principle Defined ............................ 165
7.3.2 Voltage Rise Due to Induction or Reenergization ............... 165
7.3.3 Equipotential Bonding ................................... 165
7.3.4 Physical Makeup of Bonds ...... : ......................... 166
7.4 Grounding to Provide Protection from Induction .................. 166
7.4.1 Grounding to Control Induction ........................... 166
7.4.2 Grounding for Electric-Field Induction ....................... 166
7.4.3 Grounding for Magnetic-Field Induction ..................... 167
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7.5 Specific Grounding Hazards and Procedural Controls ............... 168
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7.5.1 Cutting or Joining a Grounded Conductor. ................... 168
7.5.2 Working on a Circuit One Span from a Single Set of Grounds ..... 168
7.5.3 Electrical Hazards Workers on the Ground ......... ; ........ 169
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7.5.4 Wood Pole Work in Poor Soil or in High-Induction Areas ........ 170
7.5.5 Grounding Only One Phase ............................... 171
7.5.6 Grounds Whipping during a Fault .......................... 171
7.5.7 Grounding for Backfeed from a Portable Generator ............. 171