ANSI/IEEE C2-2007

IEEE C2-2007 - National Electrical Safety Code (NESC), 2007 Edition
ISBN: 0738148938

August, 2006

Institute of Electrical and Electronics Engineers

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Published exclusively by the IEEE, the 2007 NESC is the single most important document for safeguarding persons against electrical hazards during the installation, operation and maintenance of electric supply and communication lines. More importantly, it contains extensive updates and critical revisions that directly impact the power utility industry. Adopted by law by the majority of states and Public Service Commissions across the US, the NESC is a performance code considered to be the authoritative source on good electrical engineering practice, for over 90 years.



This standard covers basic provisions for safeguarding of persons from hazards arising from the installation, operation, or maintenance of 1) conductors and equipment in electric supply stations, and 2) overhead and underground electric supply and communication lines. It also includes work rules for the construction, maintenance, and operation of electric supply and communication lines and equipment. The standard is applicable to the systems and equipment operated by utilities, or similar systems and equipment, of an industrial establishment or complex under the control of qualified persons. This standard consists of the introduction, definitions, grounding rules, list of referenced and bibliographic documents, and Parts 1, 2, 3, and 4 of the 2007 Edition of the National Electrical Safety Code.



The 2007 version of the code has been updated in many ways. Some of the topics that have been changed involve: Metal grounding poles Starting voltages and clearances Grounding and insulation for guys Clearances between transmission lines Multiplex cable attachment to neutral brackets Loading due to freezing rain and wind Fiber-reinforced polymer elements Worker loads Equipment bonding Arc exposure analysis Antenna radiation exposure limits

In addition, the 2007 version includes new appendices on loading and conductor movement, extreme wind loading, and maximum over-voltage at a work site.

2007 NESC VuSpec CD-ROM: You get the complete 2007 NESC in a new point-and-click HTML format as well as the official 2007 NESC in the Classic Adobe PDF format. With internet access, you get exclusive hyperlinks to essential resources including the IEEE Electrical Safety Resource Center, the NESC®Zone, and so much more.

New search, linking, and navigational features are available to assist you! No more thumbing through hundreds of pages for cross-referenced material. Just click! Rules are linked together enabling you to move forward and back as you like. Jump to any table in feet or meters with ease. Please Note: CD-ROM may not work with Windows Vista®

Keywords :NESC


Contents
xii Copyright © 2006 IEEE. All rights reserved.
Section Page
Contents
Section Page
Letter symbols for units ............................................................................................................................xxxiii
Sec. 1. Introduction to the National Electrical Safety Code
010. Purpose......................................................................................................................................... 1
011. Scope............................................................................................................................................ 1
012. General rules ................................................................................................................................ 1
013. Application................................................................................................................................... 1
A. New installations and extensions ............................................................................................1
B. Existing installations .............................................................................................................. 2
014. Waiver.......................................................................................................................................... 2
A. Emergency installations.......................................................................................................... 2
B. Temporary overhead installations .......................................................................................... 2
015. Intent ............................................................................................................................................ 2
016. Effective date ............................................................................................................................... 3
017. Units of measure .......................................................................................................................... 3
018. Method of calculation .................................................................................................................. 4
Sec. 2. Definitions of special terms ................................................................................................................. 5
Sec. 3. References............................................................................................................................................ 5
Sec. 9. Grounding methods for electric supply and communications facilities
090. Purpose....................................................................................................................................... 17
091. Scope.......................................................................................................................................... 17
092. Point of connection of grounding conductor ............................................................................. 17
A. Direct-current systems that are to be grounded .................................................................... 17
1. 750 V and below.............................................................................................................. 17
2. Over 750 V....................................................................................................................... 17
B. Alternating current systems that are to be grounded............................................................ 17
1. 750 V and below .............................................................................................................. 17
2. Over 750 V ...................................................................................................................... 17
3. Separate grounding conductor......................................................................................... 18
C. Messenger wires and guys ....................................................................................................18
1. Messenger wires .............................................................................................................. 18
2. Guys................................................................................................................................. 18
3. Common grounding of messengers and guys on the same supporting structure ............. 18
D. Current in grounding conductor ........................................................................................... 19
E. Fences ................................................................................................................................... 19
093. Grounding conductor and means of connection ........................................................................ 20
A. Composition of grounding conductors ................................................................................. 20
B. Connection of grounding conductors ................................................................................... 20
C. Ampacity and strength .......................................................................................................... 20
1. System grounding conductors for single-grounded systems ........................................... 20
2. System grounding conductors for multi-grounded alternating current systems .............. 20
3. Grounding conductors for instrument transformers ........................................................ 20
4. Grounding conductors for primary surge arresters .......................................................... 21
5. Grounding conductors for equipment, messenger wires, and guys................................. 21
6. Fences .............................................................................................................................. 21
7. Bonding of equipment frames and enclosures ................................................................. 21
8. Ampacity limit................................................................................................................. 21
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9. Strength............................................................................................................................ 21
D. Guarding and protection ....................................................................................................... 21
E. Underground ......................................................................................................................... 22
F. Common grounding conductor for circuits, metal raceways, and equipment ...................... 22
094. Grounding electrodes................................................................................................................. 22
A. Existing electrodes ............................................................................................................... 22
1. Metallic water piping system ........................................................................................... 23
2. Local systems ................................................................................................................... 23
3. Steel reinforcing bars in concrete foundations and footings ........................................... 23
B. Made electrodes .................................................................................................................... 23
1. General ............................................................................................................................. 23
2. Driven rods ...................................................................................................................... 23
3. Buried wire, strips, or plates ............................................................................................ 24
4. Pole-butt plates and wire wraps ....................................................................................... 24
5. Concentric neutral cable .................................................................................................. 24
6. Concrete-encased electrodes ............................................................................................ 25
7. Directly embedded metal poles ....................................................................................... 25
095. Method of connection to electrode ............................................................................................ 25
A. Ground connections .............................................................................................................. 25
B. Point of connection to piping systems .................................................................................. 26
C. Contact surfaces .................................................................................................................... 26
096. Ground resistance requirements................................................................................................. 26
A. General ................................................................................................................................. 26
B. Supply stations ...................................................................................................................... 26
C. Multi-grounded systems ....................................................................................................... 27
D. Single-grounded (unigrounded or delta) systems ................................................................. 27
097. Separation of grounding conductors ..........................................................................................27
098. Number 098 not used in this edition.......................................................................................... 28
099. Additional requirements for grounding and bonding of communication apparatus.................. 28
A. Electrode ............................................................................................................................... 28
B. Electrode connection ............................................................................................................ 29
C. Bonding of electrodes ........................................................................................................... 29
Part 1. Rules for the Installation and Maintenance of Electric Supply Stations and Equipment
Sec. 10. Purpose and scope of rules............................................................................................................... 31
100. Purpose ..................................................................................................................................... 31
101. Scope ........................................................................................................................................ 31
102. Application of rules .................................................................................................................. 31
103. Referenced sections .................................................................................................................. 31
Sec. 11. Protective arrangements in electric supply stations ......................................................................... 32
110.General requirements ................................................................................................................ 32
A. Enclosure of equipment ........................................................................................................ 32
1. Types of enclosures .......................................................................................................... 32
2. Safety clearance zone .......................................................................................................32
B. Rooms and spaces ................................................................................................................. 32
1. Construction ..................................................................................................................... 32
2. Use ................................................................................................................................... 32
3. Ventilation ....................................................................................................................... 33
4. Moisture and weather ...................................................................................................... 33
C. Electric equipment ................................................................................................................ 33
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Section Page
111. Illumination................................................................................................................................ 34
A. Under normal conditions ...................................................................................................... 34
B. Emergency lighting .............................................................................................................. 34
C. Fixtures ................................................................................................................................. 34
D. Attachment plugs and receptacles for general use ............................................................... 35
E. Receptacles in damp or wet locations ................................................................................... 35
112. Floors, floor openings, passageways, and stairs ........................................................................ 37
A. Floors .................................................................................................................................... 37
B. Passageways ......................................................................................................................... 37
C. Railings ................................................................................................................................. 37
D. Stair guards ........................................................................................................................... 37
E. Top rails ................................................................................................................................ 37
113. Exits ........................................................................................................................................... 37
A. Clear exits............................................................................................................................. 37
B. Double exits.......................................................................................................................... 37
C. Exit doors .............................................................................................................................. 38
114. Fire-extinguishing equipment .................................................................................................... 38
Sec. 12. Installation and maintenance of equipment...................................................................................... 39
120. General requirements................................................................................................................. 39
121. Inspections ................................................................................................................................. 39
A. In-service equipment ............................................................................................................ 39
B. Idle equipment ...................................................................................................................... 39
C. Emergency equipment .......................................................................................................... 39
D. New equipment .................................................................................................................... 39
122. Guarding shaft ends, pulleys, belts, and suddenly moving parts............................................... 39
A.Mechanical transmission machinery ..................................................................................... 39
B. Suddenly moving parts ......................................................................................................... 39
123. Protective grounding.................................................................................................................. 39
A. Protective grounding or physical isolation of non-current-carrying metal parts .................. 39
B. Grounding method ................................................................................................................ 40
C. Provision for grounding equipment during maintenance ..................................................... 40
D. Grounding methods for direct-current systems over 750 V ................................................. 40
124. Guarding live parts..................................................................................................................... 40
A. Where required ..................................................................................................................... 40
B. Strength of guards ................................................................................................................. 40
C. Types of guards .................................................................................................................... 40
1. Location or physical isolation .......................................................................................... 40
2. Shields or enclosures .......................................................................................................41
3. Supplemental barriers or guards within electric supply stations ..................................... 41
4. Mats ................................................................................................................................. 41
5. Live parts below supporting surfaces for persons ........................................................... 41
6. Insulating covering on conductors or parts ...................................................................... 41
125. Working space about electric equipment................................................................................... 51
A. Working space (600 V or less) ............................................................................................. 51
1. Clear spaces ..................................................................................................................... 51
2. Access and entrance to working space ............................................................................ 51
3. Working space ................................................................................................................. 52
4. Headroom working space ................................................................................................ 52
5. Front working space ........................................................................................................ 52
B. Working space over 600 V ................................................................................................... 52
126. Equipment for work on energized parts..................................................................................... 52
127. Classified locations .................................................................................................................... 52
A. Coal-handling areas .............................................................................................................. 53
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B. Flammable and combustible liquids ..................................................................................... 53
C. Flammable liquid storage area.............................................................................................. 54
D. Loading and unloading facilities for flammable and combustible liquids........................... 54
E. Gasoline-dispensing stations ................................................................................................ 54
F. Boilers ................................................................................................................................... 54
G. Gaseous hydrogen systems for supply equipment ............................................................... 54
H. Liquid hydrogen systems .....................................................................................................54
I. Sulfur .................................................................................................................................... 55
J. Oxygen .................................................................................................................................. 55
K. Liquefied petroleum gas (LPG) ............................................................................................ 55
L. Natural gas (methane) ........................................................................................................... 55
128. Identification.............................................................................................................................. 55
129. Mobile hydrogen equipment...................................................................................................... 55
Sec. 13. Rotating equipment .......................................................................................................................... 56
130. Speed control and stopping devices........................................................................................... 56
A. Automatic overspeed trip device for prime movers............................................................. 56
B. Manual stopping devices ...................................................................................................... 56
C. Speed limit for motors .......................................................................................................... 56
D. Number 130D not used in this edition ................................................................................. 56
E. Adjustable-speed motors ...................................................................................................... 56
F. Protection of control circuits ................................................................................................. 56
131. Motor control ............................................................................................................................. 56
132. Number 132 not used in this edition.......................................................................................... 57
133. Short-circuit protection .............................................................................................................. 57
Sec. 14. Storage batteries............................................................................................................................... 58
140. General....................................................................................................................................... 58
141. Location ..................................................................................................................................... 58
142. Ventilation.................................................................................................................................. 58
143. Racks.......................................................................................................................................... 58
144. Floors in battery areas................................................................................................................ 58
145. Illumination for battery areas..................................................................................................... 58
146. Service facilities......................................................................................................................... 58
Sec. 15. Transformers and regulators ............................................................................................................ 60
150. Current-transformer secondary circuits protection when exceeding 600 V .............................. 60
151. Grounding secondary circuits of instrument transformers........................................................ 60
152. Location and arrangement of power transformers and regulators ............................................. 60
A. Outdoor installations ............................................................................................................ 60
B. Indoor installations ............................................................................................................... 60
153. Short-circuit protection of power transformers.......................................................................... 61
Sec. 16. Conductors ....................................................................................................................................... 62
160. Application................................................................................................................................. 62
161. Electrical protection................................................................................................................... 62
A. Overcurrent protection required ........................................................................................... 62
B. Grounded conductors ............................................................................................................ 62
C. Insulated power cables ......................................................................................................... 62
162. Mechanical protection and support............................................................................................ 62
163. Isolation...................................................................................................................................... 62
164. Conductor terminations.............................................................................................................. 62
A. Insulation .............................................................................................................................. 62
B. Metal-sheathed or shielded cable ......................................................................................... 62
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Section Page
Sec. 17. Circuit breakers, reclosers, switches, and fuses ............................................................................... 63
170. Arrangement .............................................................................................................................. 63
171. Application................................................................................................................................. 63
172. Circuit breakers, reclosers, and switches containing oil............................................................ 63
173. Switches and disconnecting devices ..........................................................................................63
A. Capacity ................................................................................................................................ 63
B. Provisions for disconnecting ................................................................................................63
174. Disconnection of fuses............................................................................................................... 63
Sec. 18. Switchgear and metal-enclosed bus ................................................................................................. 65
180. Switchgear assemblies ............................................................................................................... 65
A. General requirements for all switchgear .............................................................................. 65
B. Metal-enclosed power switchgear ........................................................................................ 65
C. Dead-front power switchboards ........................................................................................... 66
D. Motor control centers ........................................................................................................... 66
E. Control switchboards............................................................................................................ 66
181. Metal-enclosed bus .................................................................................................................... 66
A. General requirements for all types of bus ............................................................................ 66
B. Isolated-phase bus ................................................................................................................ 67
Sec. 19. Surge arresters.................................................................................................................................. 68
190. General requirements................................................................................................................. 68
191. Indoor locations ......................................................................................................................... 68
192. Grounding conductors................................................................................................................ 68
193. Installation.................................................................................................................................. 68
Part 2. Safety Rules for the Installation and Maintenance of Overhead Electric Supply and
Communication Lines
Sec. 20. Purpose, scope, and application of rules .......................................................................................... 69
200. Purpose....................................................................................................................................... 69
201. Scope.......................................................................................................................................... 69
202. Application of rules.................................................................................................................... 69
Sec. 21. General requirements ....................................................................................................................... 70
210. Referenced sections ................................................................................................................... 70
211. Number 211 not used in this edition.......................................................................................... 70
212. Induced voltages ........................................................................................................................ 70
213. Accessibility............................................................................................................................... 70
214. Inspection and tests of lines and equipment .............................................................................. 70
A. When in service .................................................................................................................... 70
1. Initial compliance with rules ........................................................................................... 70
2. Inspection ........................................................................................................................ 70
3. Tests ................................................................................................................................. 70
4. Record of defects ............................................................................................................. 70
5. Remedying defects .......................................................................................................... 70
B. When out of service.............................................................................................................. 71
1. Lines infrequently used ................................................................................................... 71
2. Lines temporarily out of service ...................................................................................... 71
3. Lines permanently abandoned ......................................................................................... 71
215. Grounding of circuits, supporting structures, and equipment.................................................... 71
A. Methods ................................................................................................................................ 71
B. Circuits ................................................................................................................................. 71
1. Common neutral ............................................................................................................... 71
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2. Other neutrals .................................................................................................................. 71
3. Other conductors.............................................................................................................. 71
4. Surge arresters ................................................................................................................. 71
5. Use of earth as part of circuit ........................................................................................... 71
C. Non-current-carrying parts ................................................................................................... 71
1. General ............................................................................................................................. 71
2. Anchor guys and span guys ............................................................................................. 72
3. Span wires carrying luminaires or traffic signals ............................................................ 72
4. Span wires carrying trolley or electric railway contact conductors ................................. 72
5. Use of insulators in anchor guys, span guys, and span wires
supporting luminaires or traffic signals ........................................................................... 72
6. Use of insulators in span wires supporting trolley or
electric railroad contact conductors ................................................................................ 72
7. Insulators used to limit galvanic corrosion ...................................................................... 72
8. Multiple messengers on the same structure ..................................................................... 73
216. Arrangement of switches ........................................................................................................... 73
A. Accessibility ......................................................................................................................... 73
B. Indicating open or closed position ........................................................................................ 73
C. Locking ................................................................................................................................. 73
D. Uniform position .................................................................................................................. 73
E. Remotely controlled, automatic transmission, or
distribution overhead line switching devices........................................................................ 73
217. General....................................................................................................................................... 73
A. Supporting structures ............................................................................................................ 73
1. Protection of structures.................................................................................................... 73
2. Readily climbable supporting structures ......................................................................... 73
3. Identification .................................................................................................................... 74
4. Obstructions ..................................................................................................................... 74
5. Decorative lighting .......................................................................................................... 74
B. Unusual conductor supports ................................................................................................. 74
C. Protection and marking of guys ............................................................................................ 74
218. Vegetation management............................................................................................................. 75
A. General ................................................................................................................................. 75
B. At line crossings, railroad crossings and limited-access highway crossings........................ 75
Sec. 22. Relations between various classes of lines and equipment.............................................................. 76
220. Relative levels............................................................................................................................ 76
A. Standardization of levels ...................................................................................................... 76
B. Relative levels: supply and communication conductors ...................................................... 76
1. Preferred levels ................................................................................................................ 76
2. Special construction for supply circuits, the voltage of which is 600 V or less
and carrying power not in excess of 5 kW ...................................................................... 76
C. Relative levels: Supply lines of different voltage classifications
(0 to 750 V, over 750 V to 8.7 kV, over 8.7 kV to 22 kV, and over 22 kV to 50 kV) ......... 77
1. At crossings or conflicts .................................................................................................. 77
2. On structures used only by supply conductors ................................................................ 77
D. Identification of overhead conductors .................................................................................. 77
E. Identification of equipment on supporting structures........................................................... 77
221. Avoidance of conflict................................................................................................................. 77
222. Joint use of structures................................................................................................................. 77
223. Communications protective requirements ................................................................................. 78
A. Where required ..................................................................................................................... 78
B. Means of protection .............................................................................................................. 78
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224. Communication circuits located within the supply space and supply circuits
located within the communication space................................................................................... 78
A. Communication circuits located in the supply space ........................................................... 78
B. Supply circuits used exclusively in the operation of communication circuits ..................... 79
225. Electric railway construction ..................................................................................................... 79
A. Trolley-contact conductor fastenings ................................................................................... 79
B. High-voltage contact conductors .......................................................................................... 80
C. Third rails ............................................................................................................................. 80
D. Prevention of loss of contact at railroad crossings at grade ................................................. 80
E. Guards under bridges ............................................................................................................ 80
Sec. 23. Clearances ........................................................................................................................................ 81
230. General....................................................................................................................................... 81
A. Application ........................................................................................................................... 81
1. Permanent and temporary installations ........................................................................... 81
2. Emergency installations .................................................................................................. 81
3. Measurement of clearance and spacing ........................................................................... 81
4. Rounding of calculation results ....................................................................................... 82
B. Ice and wind loading for clearances ..................................................................................... 82
C. Supply cables........................................................................................................................ 83
D. Covered conductors .............................................................................................................. 83
E. Neutral conductors ................................................................................................................ 83
F. Fiber-optic cable ................................................................................................................... 83
1. Fiber-optic—supply cable ............................................................................................... 83
2. Fiber-optic—communication cable ................................................................................. 84
G. Alternating- and direct-current circuits................................................................................ 84
H. Constant-current circuits ...................................................................................................... 84
I. Maintenance of clearances and spacings ............................................................................... 84
231. Clearances of supporting structures from other objects............................................................. 85
A. From fire hydrants ................................................................................................................ 85
B. From streets, roads, and highways ....................................................................................... 86
C. From railroad tracks ............................................................................................................. 86
232. Vertical clearances of wires, conductors, cables, and equipment
above ground, roadway, rail, or water surfaces......................................................................... 86
A. Application ........................................................................................................................... 86
B. Clearance of wires, conductors, cables, equipment, and support arms
mounted on supporting structures ........................................................................................ 87
1. Clearance to wires, conductors, and cables ..................................................................... 87
2. Clearance to unguarded rigid live parts of equipment ..................................................... 87
3. Clearance to support arms, switch handles, and equipment cases................................... 87
4. Street and area lighting ....................................................................................................87
C. Additional clearances for wires, conductors, cables, and unguarded rigid live parts
of equipment ........................................................................................................................ 87
1. Voltages exceeding 22 kV ............................................................................................... 87
D. Alternate clearances for voltages exceeding 98 kV ac to ground or
139 kV dc to ground ............................................................................................................88
1. Sag conditions of line conductors .................................................................................... 88
2. Reference heights ............................................................................................................. 88
3. Electrical component of clearance................................................................................... 88
4. Limit ................................................................................................................................. 88
233. Clearances between wires, conductors, and cables carried on
different supporting structures ................................................................................................... 98
A. General ................................................................................................................................. 98
1. Conductor movement envelope ....................................................................................... 99
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2. Clearance envelope ..........................................................................................................99
B. Horizontal clearance............................................................................................................. 99
1. Clearance requirements .................................................................................................... 99
2. Alternate clearances for voltages exceeding 98 kV ac to ground or
139 kV dc to ground ........................................................................................................ 99
C. Vertical clearance ................................................................................................................. 99
1. Clearance requirements .................................................................................................... 99
2. Voltages exceeding 22 kV ............................................................................................. 100
3. Alternate clearances for voltage exceeding 98 kV ac to ground or
139 kV dc to ground....................................................................................................... 100
234. Clearance of wires, conductors, cables, and equipment from buildings, bridges,
rail cars, swimming pools, and other installations................................................................... 109
A. Application ......................................................................................................................... 109
1. Vertical and horizontal clearances (no wind displacement).......................................... 109
2. Horizontal clearances (with wind displacement) ........................................................... 110
3. Transition between horizontal and vertical clearances .................................................. 110
B. Clearances of wires, conductors, and cables from other supporting structures .................. 110
1. Horizontal clearances .................................................................................................... 110
2. Vertical clearances ........................................................................................................ 111
C. Clearances of wires, conductors, cables, and rigid live parts from buildings,
signs, billboards, chimneys, radio and television antennas, tanks, and
other installations except bridges ...................................................................................... 111
1. Vertical and horizontal clearances ................................................................................. 111
2. Guarding of supply conductors and rigid live parts....................................................... 112
3. Supply conductors attached to buildings or other installations ..................................... 112
4. Communication conductors attached to buildings or other installations ....................... 113
5. Ladder space .................................................................................................................. 113
D. Clearance of wires, conductors, cables, and unguarded rigid live parts from bridges ....... 113
1. Vertical and horizontal clearances ................................................................................ 113
2. Guarding trolley-contact conductors located under bridges.......................................... 114
E. Clearance of wires, conductors, cables, or unguarded rigid live parts installed
over or near swimming areas with no wind displacement.................................................. 114
1. Swimming pools ............................................................................................................ 114
2. Beaches and waterways restricted to swimming ........................................................... 114
3. Waterways subject to water skiing ................................................................................ 114
F. Clearances of wires, conductors, cables, and rigid live parts from grain bins.................... 114
1. Grain bins loaded by permanently installed augers, conveyers,
or elevator systems......................................................................................................... 114
2. Grain bins loaded by portable augers, conveyers, or elevators
(with no wind displacement) .......................................................................................... 114
G. Additional clearances for voltages exceeding 22 kV for wires, conductors,
cables, and unguarded rigid live parts of equipment ......................................................... 115
H. Alternate clearances for voltages exceeding 98 kV ac to ground or
139 kV dc to ground ........................................................................................................... 115
1. Sag conditions of line conductors .................................................................................. 115
2. Reference distances ....................................................................................................... 115
3. Electrical component of clearance ................................................................................. 115
4. Limit .............................................................................................................................. 116
I. Clearance of wires, conductors, and cables to rail cars ....................................................... 116
J. Clearance of equipment mounted on supporting structures ................................................ 116
1. Clearance to unguarded rigid live parts of equipment .................................................. 116
2. Clearance to equipment cases ........................................................................................ 116
235. Clearance for wires, conductors, or cables carried on the same supporting structure............. 134
A. Application of rule .............................................................................................................. 134
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1. Multiconductor wires or cables ..................................................................................... 134
2. Conductors supported by messengers or span wires ..................................................... 134
3. Line conductors of different circuits.............................................................................. 134
B. Horizontal clearance between line conductors ................................................................... 135
1. Fixed supports ................................................................................................................ 135
2. Suspension insulators .................................................................................................... 136
3. Alternate clearances for different circuits where one or both circuits exceed
98 kV ac to ground or 139 kV dc to ground .................................................................. 136
C. Vertical clearance between line conductors ....................................................................... 137
1. Basic clearance for conductors of same or different circuits ........................................ 137
2. Additional clearances .................................................................................................... 137
3. Alternate clearances for different circuits where one or both exceed 98 kV ac,
or 139 kV dc to ground .................................................................................................. 139
4. Communication worker safety zone .............................................................................. 139
D. Diagonal clearance between line wires, conductors, and cables located at
different levels on the same supporting structure .............................................................. 140
E. Clearances in any direction from line conductors to supports, and to vertical or
lateral conductors, span, or guy wires attached to the same support ................................. 140
1. Fixed supports ................................................................................................................ 140
2. Suspension insulators .................................................................................................... 140
3. Alternate clearances for voltages exceeding 98 kV ac to ground or
139 kV dc to ground ...................................................................................................... 140
F. Clearances between circuits of different voltage classifications located in the
supply space on the same support arm ............................................................................... 141
G. Conductor spacing: vertical racks or separate brackets ..................................................... 141
H. Clearance and spacing between communication conductors, cables, and equipment ....... 142
I. Clearances in any direction from supply line conductors to communication antennas
in the supply space attached to the same supporting structure .......................................... 142
1. General .......................................................................................................................... 142
2. Communication antenna................................................................................................ 142
3. Equipment case that supports a communication antenna .............................................. 142
4. Vertical or lateral communication conductors and cables attached to a
communication antenna................................................................................................ 142
236. Climbing space......................................................................................................................... 158
A. Location and dimensions.................................................................................................... 158
B. Portions of supporting structures in climbing space........................................................... 158
C. Support arm location relative to climbing space ................................................................ 158
D. Location of equipment relative to climbing space ............................................................. 158
E. Climbing space between conductors .................................................................................. 159
F. Climbing space on buckarm construction ........................................................................... 159
G. Climbing space past longitudinal runs not on support arms .............................................. 159
H. Climbing space past vertical conductors ............................................................................ 160
I. Climbing space near ridge-pin conductors ......................................................................... 160
237. Working space ......................................................................................................................... 162
A. Location of working spaces................................................................................................ 162
B. Dimensions of working spaces ........................................................................................... 162
1. Along the support arm ................................................................................................... 162
2. At right angles to the support arm .................................................................................. 162
3. Vertically ........................................................................................................................ 162
C. Location of vertical and lateral conductors relative to working spaces ............................. 162
D. Location of buckarms relative to working spaces .............................................................. 162
1. Standard height of working space ................................................................................. 162
2. Reduced height of working space................................................................................... 162
E. Guarding of energized equipment ...................................................................................... 162
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F. Working clearances from energized equipment ................................................................. 163
238. Vertical clearance between certain communications and supply facilities located
on the same structure ............................................................................................................... 163
A. Equipment .......................................................................................................................... 163
B. Clearances in general.......................................................................................................... 163
C. Clearances for span wires or brackets ................................................................................ 163
D. Clearance of drip loops of luminaire or traffic signal brackets .......................................... 163
E. Communication worker safety zone ................................................................................... 163
239. Clearance of vertical and lateral facilities from other facilities and surfaces
on the same supporting structure ............................................................................................. 165
A. General ............................................................................................................................... 165
B. Location of vertical or lateral conductors relative to climbing spaces, working spaces,
and pole steps..................................................................................................................... 165
C. Conductors not in conduit .................................................................................................. 165
D. Guarding and protection near ground ................................................................................. 166
E. Requirements for vertical and lateral supply conductors on supply line structures
or within supply space on jointly used structures ............................................................... 166
1. General clearances ......................................................................................................... 166
2. Special cases .................................................................................................................. 166
F. Requirements for vertical and lateral communication conductors on communication
line structures or within the communication space on jointly used structures ................... 166
1. Clearances from communication conductors ................................................................ 166
2. Clearances from supply conductors............................................................................... 166
G. Requirements for vertical supply conductors and cables passing through
communication space on jointly used line structures ........................................................ 167
1. Guarding—General ....................................................................................................... 167
2. Cables and conductors in conduit or covering............................................................... 167
3. Protection near trolley, ungrounded traffic signal, or ungrounded
luminaire attachments.................................................................................................... 167
4. Aerial services ............................................................................................................... 167
5. Clearance from through bolts and other metal objects .................................................. 167
H. Requirements for vertical communication conductors passing through
supply space on jointly used structures .............................................................................. 168
1. Metal-sheathed communication cables .......................................................................... 168
2. Communication conductors ............................................................................................ 168
3. Communication grounding conductors .......................................................................... 168
4. Clearance from through bolts and other metal objects .................................................. 168
I. Operating rods..................................................................................................................... 168
J. Additional rules for standoff brackets ................................................................................. 168
Sec. 24. Grades of construction ................................................................................................................... 171
240. General..................................................................................................................................... 171
241. Application of grades of construction to different situations................................................... 171
A. Supply cables ...................................................................................................................... 171
B. Order of grades ................................................................................................................... 171
C. At crossings ........................................................................................................................ 171
1. Grade of upper line ........................................................................................................ 171
2. Grade of lower line ........................................................................................................ 171
3. Multiple crossings.......................................................................................................... 171
D. Conflicts ............................................................................................................................. 171
242. Grades of construction for conductors..................................................................................... 172
A. Constant-current circuit conductors ................................................................................... 172
B. Railway feeder and trolley-contact circuit conductors....................................................... 172
C. Communication circuit conductors located in the supply space ........................................ 172
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xxii Copyright © 2006 IEEE. All rights reserved.
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D. Fire-alarm circuit conductors ............................................................................................. 172
E. Neutral conductors of supply circuits ................................................................................. 172
F. Surge-protection wires........................................................................................................ 172
243. Grades of construction for line supports.................................................................................. 176
A. Structures ............................................................................................................................ 176
B. Crossarms and support arms ............................................................................................... 176
C. Pins, armless construction brackets, insulators, and conductor fastenings ........................ 176
Sec. 25. Loadings for Grades B and C......................................................................................................... 177
250. General loading requirements and maps.................................................................................. 177
A. General ............................................................................................................................... 177
B. Combined ice and wind district loading............................................................................. 177
C. Extreme wind loading ......................................................................................................... 177
1. Velocity pressure exposure coefficient, k
z
.................................................................... 178
2. Gust response factor, G
RF
............................................................................................. 178
D. Extreme ice with concurrent wind loading ........................................................................ 179
251. Conductor loading.................................................................................................................... 193
A. General ............................................................................................................................... 193
B. Load components ................................................................................................................ 193
1. Vertical load component ................................................................................................ 193
2. Horizontal load component ............................................................................................ 193
3. Total load ....................................................................................................................... 194
252. Loads on line supports ............................................................................................................. 194
A. Assumed vertical loads ....................................................................................................... 194
B. Assumed transverse loads ................................................................................................... 194
1. Transverse loads from conductors and messengers....................................................... 194
2. Wind loads on structures ................................................................................................ 194
3. At angles ......................................................................................................................... 195
4. Span lengths ................................................................................................................... 195
C. Assumed longitudinal loading............................................................................................ 195
1. Change in grade of construction .................................................................................... 195
2. Jointly used poles at crossings over railroads, communication lines,
or limited access highways ............................................................................................ 195
3. Deadends........................................................................................................................ 195
4. Unequal spans and unequal vertical loads ..................................................................... 196
5. Stringing loads ............................................................................................................... 196
6. Longitudinal capability .................................................................................................. 196
7. Communication conductors on unguyed supports at railroad and
limited access highway crossings .................................................................................. 196
D. Simultaneous application of loads ...................................................................................... 196
253.Load factors for structures, crossarms, support hardware, guys, foundations,
and anchors ............................................................................................................................... 196
Sec. 26. Strength requirements .................................................................................................................... 199
260. General..................................................................................................................................... 199
A. Preliminary assumptions .................................................................................................... 199
B. Application of strength factors ........................................................................................... 199
261. Grades B and C construction ................................................................................................... 199
A. Supporting structures .......................................................................................................... 199
1. Metal, prestressed-, and reinforced-concrete structures................................................. 200
2. Wood structures ............................................................................................................. 200
3. Fiber-reinforced polymer structures............................................................................... 201
4. Transverse strength requirements for structures where side guying is required,
but can be installed only at a distance ............................................................................ 201
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5. Longitudinal strength requirements for sections of higher grade in lines of a
lower grade construction................................................................................................ 201
B. Strength of foundations, settings, and guy anchors............................................................ 202
C. Strength of guys and guy insulators ................................................................................... 202
1. Metal and prestressed-concrete structures ..................................................................... 202
2. Wood and reinforced-concrete structures...................................................................... 202
3. Fiber-reinforced polymer structures .............................................................................. 202
D. Crossarms and braces......................................................................................................... 202
1. Concrete and metal crossarms and braces ..................................................................... 202
2. Wood crossarms and braces........................................................................................... 202
3. Fiber-reinforced polymer crossarms and braces ............................................................ 203
4. Crossarms and braces of other materials ....................................................................... 203
5. Additional requirements................................................................................................. 203
E. Insulators ............................................................................................................................. 203
F. Strength of pin-type or similar construction and conductor fastenings .............................. 204
1. Longitudinal strength ..................................................................................................... 204
2. Double pins and conductor fastenings ........................................................................... 204
3. Single supports used in lieu of double wood pins ......................................................... 204
G. Armless construction .......................................................................................................... 204
1. General ........................................................................................................................... 204
2. Insulating material ......................................................................................................... 204
3. Other components .......................................................................................................... 204
H. Open supply conductors and overhead shield wires .......................................................... 204
1. Tensions ......................................................................................................................... 204
2. Splices, taps, dead-end fittings, and associated attachment hardware ........................... 205
3. Trolley-contact conductors ............................................................................................ 205
I. Supply cable messengers .................................................................................................... 205
J. Open-wire communication conductors............................................................................... 205
K. Communication cables ....................................................................................................... 205
1. Communication cables .................................................................................................. 205
2. Messenger...................................................................................................................... 205
L. Paired communication conductors...................................................................................... 206
1. Paired conductors supported on messenger ................................................................... 206
2. Paired conductors not supported on messenger ............................................................. 206
M. Support and attachment hardware ..................................................................................... 206
N. Climbing and working steps and their attachments to the structure .................................. 206
262. Number 262 not used in this edition........................................................................................ 209
263. Grade N construction ............................................................................................................... 209
A. Poles ................................................................................................................................... 209
B. Guys.................................................................................................................................... 209
C. Crossarm strength............................................................................................................... 209
D. Supply-line conductors ....................................................................................................... 209
1. Size ................................................................................................................................. 209
E. Service drops ...................................................................................................................... 209
1. Size of open-wire service drops..................................................................................... 209
2. Tension of open-wire service drops ............................................................................... 209
3. Cabled service drops ...................................................................................................... 209
F. Trolley-contact conductors ................................................................................................. 210
G. Communication conductors ................................................................................................ 210
H. Street and area lighting equipment ..................................................................................... 210
I. Insulators............................................................................................................................. 210
264. Guying and bracing.................................................................................................................. 211
A. Where used ......................................................................................................................... 211
B. Strength ............................................................................................................................... 211
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xxiv Copyright © 2006 IEEE. All rights reserved.
Section Page
C. Point of attachment............................................................................................................. 211
D. Guy fastenings .................................................................................................................... 212
E. Electrolysis ......................................................................................................................... 212
F. Anchor rods......................................................................................................................... 212
Sec. 27. Line insulation................................................................................................................................ 213
270. Application of rule ................................................................................................................... 213
271. Material and marking............................................................................................................... 213
272. Ratio of flashover to puncture voltage..................................................................................... 213
273. Insulation level......................................................................................................................... 213
274. Factory tests ............................................................................................................................. 214
275. Special insulator applications .................................................................................................. 214
A. Insulators for constant-current circuits............................................................................... 214
B. Insulators for single-phase circuits directly connected to three-phase circuits .................. 214
276. Number 276 not used in this edition........................................................................................ 214
277. Mechanical strength of insulators ............................................................................................ 214
278. Aerial cable systems ................................................................................................................ 215
A. Electrical requirements....................................................................................................... 215
B. Mechanical requirements .................................................................................................... 215
279. Guy and span insulators........................................................................................................... 215
A. Insulators ............................................................................................................................ 215
1. Properties of guy insulators ........................................................................................... 215
2. Galvanic corrosion and BIL insulation.......................................................................... 216
B. Properties of span-wire insulators ...................................................................................... 216
1. Material.......................................................................................................................... 216
2. Insulation level .............................................................................................................. 216
3. Mechanical strength....................................................................................................... 216
Sec. 28. Section number 28 not used in this edition. ................................................................................... 217
Sec. 29. Section number 29 not used in this edition. ................................................................................... 217
Part 3. Safety Rules for the Installation and Maintenance of Underground Electric Supply and
Communication Lines
Sec. 30. Purpose, scope, and application of rules ........................................................................................ 219
300. Purpose..................................................................................................................................... 219
301. Scope........................................................................................................................................ 219
302. Application of rules.................................................................................................................. 219
Sec. 31. General requirements applying to underground lines .................................................................... 220
310. Referenced sections ................................................................................................................. 220
311. Installation and maintenance.................................................................................................... 220
312. Accessibility............................................................................................................................. 220
313. Inspection and tests of lines and equipment ............................................................................ 220
A. When in service .................................................................................................................. 220
1. Initial compliance with safety rules............................................................................... 220
2. Inspection ....................................................................................................................... 220
3. Tests ............................................................................................................................... 220
4. Record of defects ........................................................................................................... 220
5. Remedying defects ........................................................................................................ 220
B. When out of service ............................................................................................................ 220
1. Lines infrequently used ................................................................................................. 220
2. Lines temporarily out of service.................................................................................... 220
3. Lines permanently abandoned ....................................................................................... 221
314. Grounding of circuits and equipment ...................................................................................... 221
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Copyright © 2006 IEEE. All rights reserved. xxv
Section Page
A. Methods .............................................................................................................................. 221
B. Conductive parts to be grounded........................................................................................ 221
C. Circuits ............................................................................................................................... 221
1. Neutrals.......................................................................................................................... 221
2. Other conductors ............................................................................................................ 221
3. Surge arresters ............................................................................................................... 221
4. Use of earth as part of circuit.......................................................................................... 221
315. Communications protective requirements ............................................................................... 221
A. Where required ................................................................................................................... 221
B. Means of protection ............................................................................................................ 221
316. Induced voltage........................................................................................................................ 222
Sec. 32. Underground conduit systems........................................................................................................ 223
320. Location ................................................................................................................................... 223
A. Routing ............................................................................................................................... 223
1. General .......................................................................................................................... 223
2. Natural hazards.............................................................................................................. 223
3. Highways and streets..................................................................................................... 223
4. Bridges and tunnels ....................................................................................................... 223
5. Crossing railroad tracks ................................................................................................. 223
6. Submarine crossing ....................................................................................................... 223
B. Separation from other underground installations ............................................................... 224
1. General .......................................................................................................................... 224
2. Separations between supply and communication conduit systems ............................... 224
3. Sewers, sanitary and storm............................................................................................ 224
4. Water lines ..................................................................................................................... 224
5. Gas and other lines that transport flammable material .................................................. 224
6. Steam lines .................................................................................................................... 224
321. Excavation and backfill............................................................................................................ 224
A. Trench ................................................................................................................................. 224
B. Quality of backfill ............................................................................................................... 224
322. Ducts and joints........................................................................................................................ 225
A. General ............................................................................................................................... 225
B. Installation .......................................................................................................................... 225
1. Restraint ......................................................................................................................... 225
2. Joints .............................................................................................................................. 225
3. Externally coated pipe ................................................................................................... 225
4. Building walls ................................................................................................................ 225
5. Bridges........................................................................................................................... 225
323. Manholes, handholes, and vaults ............................................................................................. 225
A. Strength............................................................................................................................... 225
B. Dimensions......................................................................................................................... 226
C. Manhole access ................................................................................................................... 226
D. Covers ................................................................................................................................. 227
E. Vault and utility tunnel access............................................................................................ 227
F. Ladder requirements ........................................................................................................... 227
G. Drainage ............................................................................................................................. 227
H. Ventilation .......................................................................................................................... 227
I. Mechanical protection......................................................................................................... 227
J. Identification....................................................................................................................... 227
Sec. 33. Supply cable................................................................................................................................... 229
330. General..................................................................................................................................... 229
331. Sheaths and jackets .................................................................................................................. 229
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xxvi Copyright © 2006 IEEE. All rights reserved.
Section Page
332. Shielding .................................................................................................................................. 229
A. General ............................................................................................................................... 229
B. Material ............................................................................................................................... 229
333. Cable accessories and joints..................................................................................................... 229
Sec. 34. Cable in underground structures .................................................................................................... 231
340. General..................................................................................................................................... 231
341. Installation................................................................................................................................ 231
A. General............................................................................................................................... 231
B. Cable in manholes and vaults ............................................................................................. 231
1. Supports......................................................................................................................... 231
2. Clearance ....................................................................................................................... 231
3. Identification ................................................................................................................. 232
342. Grounding and bonding ........................................................................................................... 232
343. Fireproofing ............................................................................................................................. 232
344. Communication cables containing special supply circuits ...................................................... 233
Sec. 35. Direct-buried cable......................................................................................................................... 234
350. General..................................................................................................................................... 234
351. Location and routing................................................................................................................ 235
A. General ............................................................................................................................... 235
B. Natural hazards ................................................................................................................... 235
C. Other conditions.................................................................................................................. 235
1. Swimming pools (in-ground) ........................................................................................ 235
2. Buildings and other structures....................................................................................... 235
3. Railroad tracks ............................................................................................................... 235
4. Highways and streets ..................................................................................................... 235
5. Submarine crossings...................................................................................................... 235
352. Installation................................................................................................................................ 236
A. Trenching ........................................................................................................................... 236
B. Plowing............................................................................................................................... 236
C. Boring.................................................................................................................................. 236
D. Depth of burial ................................................................................................................... 236
353. Deliberate separations—Equal to or greater than 300 mm (12 in) from
underground structures or other cables.................................................................................... 237
A. General ............................................................................................................................... 237
B. Crossings ............................................................................................................................ 237
C. Parallel facilities ................................................................................................................. 237
D. Thermal protection ............................................................................................................. 237
354. Random separation—Separation less than 300 mm (12 in) from
underground structures or other cables.................................................................................... 237
A. General ............................................................................................................................... 237
B. Supply cables or conductors............................................................................................... 237
C. Communication cables or conductors ................................................................................ 238
D. Supply and communication cables or conductors .............................................................. 238
1. General........................................................................................................................... 238
2. Grounded bare or semiconducting jacketed neutral supply cables ................................ 238
3. Insulating jacketed grounded neutral supply cables ...................................................... 239
4. Insulating jacketed grounded neutral supply cables in nonmetallic duct ...................... 239
E. Supply and communication cables or conductors and non-metallic water
and sewer lines ................................................................................................................... 239
Sec. 36. Risers.............................................................................................................................................. 240
360. General..................................................................................................................................... 240
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Section Page
361. Installation................................................................................................................................ 240
362. Pole risers—Additional requirements...................................................................................... 240
363. Pad-mounted installations........................................................................................................ 240
Sec. 37. Supply cable terminations.............................................................................................................. 241
370. General..................................................................................................................................... 241
371. Support at terminations............................................................................................................ 241
372. Identification............................................................................................................................ 241
373. Clearances in enclosures or vaults ........................................................................................... 241
374. Grounding ................................................................................................................................ 241
Sec. 38. Equipment ...................................................................................................................................... 242
380. General..................................................................................................................................... 242
381. Design ...................................................................................................................................... 242
382. Location in underground structures ......................................................................................... 243
383. Installation................................................................................................................................ 243
384. Grounding and bonding ........................................................................................................... 243
385. Identification............................................................................................................................ 243
Sec. 39. Installation in tunnels ..................................................................................................................... 244
390. General..................................................................................................................................... 244
391. Environment............................................................................................................................. 244
Part 4. Rules for the Operation of Electric Supply and Communications Lines and Equipment
Sec. 40. Purpose and scope.......................................................................................................................... 245
400. Purpose..................................................................................................................................... 245
401. Scope........................................................................................................................................ 245
402. Referenced Sections................................................................................................................. 245
Sec. 41. Supply and communications systems—Rules for employers ........................................................ 246
410. General requirements............................................................................................................... 246
A. General ............................................................................................................................... 246
B. Emergency procedures and first aid rules .......................................................................... 247
C. Responsibility..................................................................................................................... 247
411. Protective methods and devices............................................................................................... 250
A. Methods.............................................................................................................................. 250
B. Devices and equipment ....................................................................................................... 250
C. Inspection and testing of protective devices ....................................................................... 250
D. Signs and tags for employee safety .................................................................................... 250
E. Identification and location .................................................................................................. 250
F. Fall protection ..................................................................................................................... 251
Sec. 42. General rules for employees........................................................................................................... 252
420. Personal general precautions.................................................................................................... 252
A. Rules and emergency methods ........................................................................................... 252
B. Qualifications of employees ............................................................................................... 252
C. Safeguarding oneself and others......................................................................................... 252
D. Energized or unknown conditions ...................................................................................... 252
E. Ungrounded metal parts...................................................................................................... 253
F. Arcing conditions ................................................................................................................ 253
G. Liquid-cell batteries ............................................................................................................ 253
H. Tools and protective equipment ......................................................................................... 253
I. Clothing ................................................................................................................................ 253
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J. Ladders and supports .......................................................................................................... 253
K. Fall protection..................................................................................................................... 253
L. Fire extinguishers................................................................................................................ 254
M. Machines or moving parts .................................................................................................. 254
N. Fuses ................................................................................................................................... 254
O. Cable reels .......................................................................................................................... 255
P. Street and area lighting ........................................................................................................ 255
Q. Communication antennas ................................................................................................... 255
421. General operating routines....................................................................................................... 255
A. Duties of a first-level supervisor or person in charge......................................................... 255
B. Area protection ................................................................................................................... 255
1. Areas accessible to vehicular and pedestrian traffic ..................................................... 255
2. Areas accessible to employees only .............................................................................. 255
3. Locations with crossed or fallen wires .......................................................................... 256
C. Escort .................................................................................................................................. 256
422. Overhead line operating procedures ........................................................................................ 256
A. Setting, moving, or removing poles in or near energized electric supply lines ................. 256
B.Checking structures before climbing................................................................................... 256
C. Installing and removing wires or cables............................................................................. 256
423. Underground line operating procedures................................................................................... 257
A. Guarding manhole and street openings .............................................................................. 257
B. Testing for gas in manholes and unventilated vaults .......................................................... 257
C. Flames ................................................................................................................................. 257
D. Excavation .......................................................................................................................... 257
E. Identification....................................................................................................................... 257
F. Operation of power-driven equipment................................................................................ 258
Sec. 43. Additional rules for communications employees........................................................................... 259
430. General..................................................................................................................................... 259
431. Approach to energized conductors or parts ............................................................................. 259
432. Joint-use structures................................................................................................................... 260
433. Attendant on surface at joint-use manhole............................................................................... 260
434. Sheath continuity ..................................................................................................................... 261
Sec. 44. Additional rules for supply employees .......................................................................................... 262
440. General..................................................................................................................................... 262
441. Energized conductors or parts.................................................................................................. 262
A. Minimum approach distance to live parts .......................................................................... 262
1. General........................................................................................................................... 262
2. Precautions for approach—Voltages from 51 V to 300 V ............................................ 262
3. Precautions for approach—Voltages from 301 V to 72.5 kV ....................................... 262
4. Precautions for approach above 72.5 kV....................................................................... 263
5. Temporary (transient) overvoltage control device (TTOCD) ....................................... 264
6. Altitude correction ......................................................................................................... 264
7. Determining the minimum approach distances (distances to employee) ...................... 264
B. Additional approach requirements ..................................................................................... 264
C. Live-line tool clear insulation length.................................................................................. 265
1. Clear live-line tool length .............................................................................................. 265
2. Live-line conductor support tool length ........................................................................ 265
442. Switching control procedures .................................................................................................. 273
A. Designated person .............................................................................................................. 273
B. Specific work...................................................................................................................... 273
C. Operations at stations ......................................................................................................... 273
D. Re-energizing after work .................................................................................................... 273
E. Tagging electric supply circuits associated with work activities ........................................ 273
F. Restoration of service after automatic trip .......................................................................... 274
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G. Repeating oral messages .................................................................................................... 274
443. Work on energized lines and equipment.................................................................................. 274
A. General requirements ......................................................................................................... 274
B. Requirement for assisting employee .................................................................................. 275
C. Opening and closing switches ............................................................................................ 275
D. Working position................................................................................................................ 275
E. Protecting employees by switches and disconnectors ........................................................ 275
F. Making connections............................................................................................................. 275
G. Switchgear .......................................................................................................................... 275
H. Current transformer secondaries ........................................................................................ 275
I. Capacitors ........................................................................................................................... 275
J. Gas-insulated equipment ..................................................................................................... 276
K. Attendant on surface ........................................................................................................... 276
L. Unintentional grounds on delta circuits.............................................................................. 276
444. De-energizing equipment or lines to protect employees.......................................................... 276
A. Application of rule .............................................................................................................. 276
B. Employee’s request ............................................................................................................. 276
C. Operating switches, disconnectors, and tagging................................................................. 276
D. Employee’s protective grounds .......................................................................................... 276
E. Proceeding with work ......................................................................................................... 277
F. Reporting clear—Transferring responsibility ..................................................................... 277
G. Removal of tags.................................................................................................................. 277
H. Sequence of re-energizing .................................................................................................. 277
445. Protective grounds ................................................................................................................... 277
A. Installing grounds ............................................................................................................... 277
1. Current-carrying capacity of grounds............................................................................ 278
2. Initial connections.......................................................................................................... 278
3. Test for voltage............................................................................................................... 278
4. Completing grounds ...................................................................................................... 278
B. Removing grounds 278
446. Live work................................................................................................................................. 278
447. Protection against arcing and other damage while installating and maintaining
insulators and conductors......................................................................................................... 279
Appendix A—Uniform system of clearances (Adopted in the 1990 Edition)............................................. 281
Appendix B—Uniform clearance calculations for conductors under ice and wind conditions
(Adopted in the 2007 Edition) .............................................................................................................. 287
Appendix C—Example applications for Rule 250C Tables 250-2 and 250-3............................................. 290
Appendix D—Determining maximum anticipated per-unit overvoltage factor (T)
at the worksite....................................................................................................................................... 301
Appendix E—Bibliography ......................................................................................................................... 302
Index ............................................................................................................................................................ 307
Procedure for revising the National Electrical Safety Code ........................................................................ 329
Time schedule for the next revision of the National Electrical Safety Code............................................... 331
Working Group assignments and activities for the 2012 Edition................................................................ 332
Contents
xxx Copyright © 2006 IEEE. All rights reserved.
Figure D-1 Sag and apparent sag........................................................................Sec. 2 11
Figure 110-1 Safety clearance to electric supply station fences ............................110A2 33
Figure 124-1 Clearance from live parts .................................................................124A1 42
Figure 124-2 Railings or fences used as guards.....................................................124 42
Figure 230-1 Clearance zone map of the United States.........................................230B 84
Figure 233-1 Use of clearance envelope and conductor movement envelopes
to determine applicable clearance ....................................................233A 101
Figure 233-2 Conductor movement envelope (m).................................................233A1a 102
Figure 233-2 Conductor movement envelope (ft) .................................................233B 103
Figure 233-3 Clearance envelope...........................................................................233B 104
Figure 234-1(a) Clearance diagram for building........................................................234A3 117
Figure 234-1(b) Clearance diagram for other structures ............................................234A3 118
Figure 234-1(c) Transitional clearance when H is greater than V .............................234 118
Figure 234-2 Clearances of service drop terminating on support mast .................234C3d(1)(b) 119
Figure 234-3 Swimming pool clearances ..............................................................234E3 119
Figure 234-4(a) Clearance envelope for grain bins filled by permanently
installed augers, conveyors, or elevators .........................................234F2c 120
Figure 234-4(b) Clearance envelope for grain bins filled by portable augers,
conveyors, or elevators....................................................................234F2a 120
Figure 234-5 Rail car clearances............................................................................234I 121
Figure 235-1 Clearance diagram for energized conductor ....................................235D 142
Figure 236-1 Rule 236G, Exception 3 ...................................................................236G 160
Figure 237-1 Obstruction of working space by buckarm ......................................237D1 163
Figure 250-1 General loading map of United States with respect to
loading of overhead lines .................................................................250B 179
Figure 250-2(a) Basic wind speeds ............................................................................250C 180
Figure 250-2(b) Basic wind speeds ............................................................................250C 181
Figure 250-2(c) Western Gulf of Mexico hurricane coastline ...................................250C 182
Figure 250-2(d) Eastern Gulf of Mexico and southeastern US hurricane coastline...250C 182
Figure 250-2(e) Mid and northern Atlantic hurricane coastline.................................250C 183
Figure 250-3(a) Uniform ice thickness with concurrent wind ...................................250D 184
Figure 250-3(b) Uniform ice thickness with concurrent wind ...................................250D 185
Figure 250-3(c) Uniform ice thickness with concurrent wind ...................................250D 186
Figure 250-3(d) Uniform ice thickness with concurrent wind ...................................250D 186
Figure 250-3(e) Uniform ice thickness with concurrent wind ...................................250D 187
Figure 250-3(f) Uniform ice thickness with concurrent wind ...................................250D 188
Figure 279-1 Insulator used for BIL insulation .....................................................279A2 217
Figure 323-1 Roadway vehicle load ......................................................................323A1 228
Figure 323-2 Wheel load area................................................................................323A1 228
Figure 350-1 Symbols for identification of buried cables .....................................350G 234
Appendix figure
Figure A-1—Clearance at maximum sag ....................................................................................................286
Figure Rule Page
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Copyright © 2006 IEEE. All rights reserved. xxxi
Table 110-1 Values for use with Figure 110-1.....................................................11B2 34
Table 111-1 Illumination levels ...........................................................................111A 35
Table 124-1 Clearances from live parts................................................................124A1 43
Table 125-1 Working space..................................................................................125A3 52
Table 230-1 Ice thickness for purposes of calculating clearances........................230B 85
Table 230-2 Ice, wind pressures, temperatures, and additive constants for
purposes of calculating final inelastic deformation .........................230B 85
Table 232-1 Vertical clearance of wires, conductors, and cables above
ground, roadway, rail, or water surfaces..........................................232B1 89
Table 232-2 Vertical clearance of equipment cases, support arms, platforms,
braces and unguarded rigid live parts above ground, roadway,
or water surfaces .............................................................................232B2 95
Table 232-3 Reference heights ............................................................................232D2 97
Table 232-4 Electrical component of clearance in Rule 232D3a ........................232D3a 98
Table 233-1 Vertical clearance between wires, conductors, and cables
carried on different supporting structures ........................................233C1 104
Table 233-2 Clearance between supply wires, conductors, and
cables in Rule 233C3b(1).................................................................233C3b(1) 107
Table 233-3 Reference heights.............................................................................233C3a 109
Table 234-1 Clearance of wires, conductors, cables, and unguarded rigid
live parts adjacent but not attached to buildings and
other installations except bridges.....................................................234C1a 122
Table 234-2 Clearance of wires, conductors, cables, and unguarded rigid
live parts from bridges ....................................................................234D1a 128
Table 234-3 Clearance of wires, conductors, cables, or unguarded rigid live
parts over or near swimming pools ..................................................234E1 131
Table 234-4 Electrical component of clearance of buildings, bridges, and
other installations ............................................................................234H3a 133
Table 234-5 Reference distances .........................................................................234H2 134
Table 235-1 Horizontal clearance between wires, conductors, or
cables at supports ............................................................................235B1a 143
Table 235-2 Horizontal clearances between line conductors smaller than
AWG No. 2 at supports, based on sags ...........................................235B1b(1) 144
Table 235-3 Horizontal clearances between line conductors AWG No. 2
or larger at supports, based on sags .................................................235B1b(2) 146
Table 235-4 Electrical clearances in Rule 235B3a(1) .........................................235B3a(1) 148
Table 235-5 Vertical clearance between conductors at supports ........................235C1 149
Table 235-6 Clearance in any direction from line conductors to supports
and to vertical or lateral conductors, span, or guy wires
attached to the same support ...........................................................235E1 153
Table 235-7 Clearance in any direction from line conductors to supports .........235E3b 157
Table 235-8 Vertical spacing between conductors supported on vertical
racks or separate brackets.................................................................235 158
Table 236-1 Horizontal clearance between conductors bounding
the climbing space............................................................................236E 161
Table 238-1 Vertical clearance between supply conductors and
communications equipment, between communication
conductors and supply equipment, and between supply
and communications equipment .....................................................238B 164
Table 238-2 Vertical clearance of span wires and brackets from
communication lines .......................................................................238C 164
Table 239-1 Clearance of open vertical and lateral conductors ...........................239E1 169
Table 239-2 Clearance between open vertical conductors and pole surface........239E2a(1) 170
Table Rule Page
Contents
xxxii Copyright © 2006 IEEE. All rights reserved.
Table 242-1 Grades of construction for supply conductors alone, at
crossing, or on the same structures with other conductors ..............242 173
Table 242-2 Grades of construction for communication conductors alone
or in upper position of crossing or on joint poles.............................242 175
Table 250-1 Ice, wind, and temperature...............................................................250C 189
Table 250-2 Velocity pressure exposure coefficient kz, structure, structure
location, component, and wire .........................................................250C 190
Table 250-3 Structure and wire gust response factors, G
RF
.................................250C 191
Table 250-4 Wind speed conversions to pressure ...............................................250D 193
Table 251-1 Temperatures and constants .............................................................251B3 194
Table 253-1 Load factors for structures, crossarms, support hardware,
guys, foundations, and anchors to be used with the
strength factors of Table 261-1A .....................................................253 197
Table 253-2 Alternate load factors for wood and reinforced
(not prestressed) concrete structures

to be used with
the strength factors of Table 261-1B................................................253 198
Table 261-1A Strength factors for structures, crossarms, braces, support
hardware, guys, foundations, and anchors for use with
load factors of Table 253-1..............................................................261M 207
Table 261-1B Strength factors for structures,

crossarms, and braces for use
with load factors of Table 253-2 ......................................................261D2 208
Table 261-2 Dimensions of crossarm cross section of select Southern Pine
and Douglas Fir................................................................................261D2 208
Table 263-1 Sizes for Grade N supply line conductors........................................263D1 210
Table 263-2 Sizes of service drops of 750 V or less ............................................263E1a(1) 211
Table 273-1 Insulation level requirements ...........................................................273 214
Table 277-1 Allowed percentages of strength ratings..........................................277 215
Table 341-1 Clearance between supply and communications facilities in
joint-use manholes and vaults ..........................................................341B2b(5) 232
Table 352-1 Supply cable or conductor burial depth ...........................................352D2 236
Table 410-1 Clothing and clothing systems—voltage, fault current, and
maximum clearing time for voltages 1 to 46 kV..............................410A3 247
Table 410-2 Live-line tool work clothing and clothing systems—voltage,
fault current, and maximum clearing time for voltages
46.1 to 800 kV..................................................................................410A3 248
Table 431-1 Communication work minimum approach distances ......................431 259
Table 441-1 AC live work minimum approach distance .....................................441A4 266
Table 441-2 AC live work minimum approach distances for altitudes
less than 900 m above sea level, where T has been determined
according to Rule 441A5 .................................................................441A4 267
Table 441-3 AC live work minimum approach distances for altitudes
less than 3000 ft above sea level, where the T has been
determined according to Rule 441A5 ..............................................441A4 269
Table 441-4 DC live work minimum approach distance for altitudes
less than 900 m above sea level .......................................................441A1 271
Table 441-5 Altitude correction factor ................................................................441A4 272
Table 441-6 Maximum use voltage for rubber insulating equipment ..................441A4 272
Appendix tables
Table A-1 ..................................................................................................................................................... 282
Table A-2a—Reference components of Rule 232....................................................................................... 283
Table A-2b—Reference components of Rule 234....................................................................................... 285
Table Rule Page

Product Referenced By

API RP 500 (R2002) - Recommended Practice for Classification of Locations for Electrical Installations at Petroleum Facilities Classified as Class I, Division I and Division 2 (Edition: 2nd)

Product Replaces

IEEE C2-2002 - National Electrical Safety Code (NESC)

Product References

NEMA C29.4-1989 (R2002) - American National Standard for Wet-Process Porcelain Insulators - Strain Type
NEMA C29.1-1988 (R2002) - American National Standard for Electrical Power Insulators - Test Methods
NEMA C29.3-1986 (R2002) - American National Standard for Wet-Process Porcelain Insulators - Spool Type
NEMA C29.5-1984 (R2002) - American National Standard for Wet-Process Porcelain Insulators - Low- and Medium-Voltage Types
NEMA C29.6-1994 (R2002) - American National Standard for Wet-Process Porcelain Insulators - High-Voltage Pin Type
The Authoritative Dictionary of IEEE Standard Terms Seventh Edition
NFPA (Fire) 8503 - Pulverized Fuel Systems
IEEE Standard Techniques for High-Voltage Testing
NEMA C29.7-1996 (R2002) - American National Standard for Wet-Process Porcelain Insulators - High-Voltage Line - Post Type
Vehicle-Mounted Elevating and Rotating Aerial Devices
ANSI C84.1-1995 (R2005) - Electric Power Systems and Equipment - Voltage Ratings (60 Hz)
Minimum Design Loads for Buildings and Other Structures
IEEE Guide for the Application of Insulation Coordination (Edition: 1st)
AMT B15.1-2000 (R2008) - Safety Standard for Mechanical Power Transmission Apparatus
NFPA (Fire) 30 - Flammable and Combustible Liquids Code, 2000 edition
NFPA (Fire) 58 - Liquified Petroleum Gas Code, 2001 Edition
Accident Prevention Tags (for temporary hazards)
NEMA Z535.4-2002 - Product Safety Signs and Labels
Safety Color Code
Criteria for Safety Symbols
Environmental and Facility Safety Signs
NFPA (Fire) 496 - Standard for Purged and Pressurized Enclosures for Electrical Equipment, 2003 Edition
NFPA (Fire) 70-99 - 1999 National Electrical Code
NFPA (Fire) 59 - Utility LP-Gas Plant Code, 2004 Edition
Standard Specification for Rubber Insulating Matting
Minimum Design Loads for Buildings and Other Structures
NFPA (Fire) 59A - Production, Storage and Handling of Liquefied Natural Gas (LNG)
ASTM D178-01(2005) - Standard Specification for Rubber Insulating Matting

Product is Related To

IEEE C2-2007-HB - National Electrical Safety Code Handbook (NESC), Sixth Edition