NESC C2 2017 Part 1 PDF

Contents Section Page Contents Letter symbols for units.......................................................................................................

Contents Section Page Contents Letter symbols for units................................................................................................................................ xlii Section 1. Introduction to the National Electrical Safety Code®..................................................................... 1 010. Purpose......................................................................................................................................... 1 011. Scope............................................................................................................................................ 1 A. Covered................................................................................................................................... 1 B. Not covered............................................................................................................................. 2 C. Types of requirements............................................................................................................ 3 012. General rules................................................................................................................................ 4 013. Application................................................................................................................................... 4 A. New installations and extensions............................................................................................ 4 B. Existing installations............................................................................................................... 4 C. Inspection and work rules....................................................................................................... 5 014. Waiver for emergency and temporary installations..................................................................... 5 A. Emergency installations.......................................................................................................... 5 B. Temporary overhead installations........................................................................................... 5 015. Intent............................................................................................................................................ 5 016. Effective date............................................................................................................................... 6 017. Units of measure.......................................................................................................................... 6 018. Method of calculation.................................................................................................................. 6 Section 2. Definitions of special terms............................................................................................................ 7 Section 3. References..................................................................................................................................... 21 Section 9. Grounding methods for electric supply and communications facilities....................................... 24 090. Purpose....................................................................................................................................... 24 091. Scope.......................................................................................................................................... 24 092. Point of connection of grounding conductor............................................................................. 24 A. Direct-current systems that are required to be grounded...................................................... 24 1. 750 V and below............................................................................................................. 24 2. Over 750 V...................................................................................................................... 24 B. Alternating current systems that are required to be grounded.............................................. 24 1. 750 V and below............................................................................................................. 24 2. Over 750 V...................................................................................................................... 24 3. Separate grounding conductor........................................................................................ 25 C. Messenger wires and guys.................................................................................................... 25 1. Messenger wires............................................................................................................. 25 2. Guys................................................................................................................................ 25 3. Common grounding of messengers and guys on the same supporting structure............ 25 D. Current in grounding conductor............................................................................................ 26 E. Fences.................................................................................................................................... 26 093. Grounding conductor and means of connection........................................................................ 27 A. Composition of grounding conductors.................................................................................. 27 B. Connection of grounding conductors.................................................................................... 27 C. Ampacity and strength.......................................................................................................... 27 1. System grounding conductors for single-grounded systems.......................................... 27 2. System grounding conductors for multi-grounded alternating current systems............. 28 3. Grounding conductors for instrument transformers........................................................ 28 4. Grounding conductors for primary surge arresters......................................................... 28 5. Grounding conductors for equipment, messenger wires, and guys................................ 28 xxi Copyright © 2016 IEEE. All rights reserved.  Contents Section Page 6. Fences............................................................................................................................. 28 7. Bonding of equipment frames and enclosures................................................................ 28 8. Ampacity limit................................................................................................................ 28 9. Strength........................................................................................................................... 29 D. Guarding and protection....................................................................................................... 29 E. Underground.......................................................................................................................... 29 F. Common grounding conductor for circuits, metal raceways, and equipment....................... 30 094. Grounding electrodes................................................................................................................. 30 A. Existing electrodes................................................................................................................ 30 1. Metallic water piping system.......................................................................................... 30 2. Local systems.................................................................................................................. 30 3. Steel reinforcing bars in concrete foundations and footings........................................... 30 B. Made electrodes.................................................................................................................... 30 1. General............................................................................................................................ 30 2. Driven rods, buried wire, strips, or plates....................................................................... 31 3. Pole-butt plates and wire wraps...................................................................................... 32 4. Concentric neutral cable................................................................................................. 32 5. Concrete-encased electrodes........................................................................................... 32 6. Directly embedded metal poles....................................................................................... 33 095. Method of connection to electrode............................................................................................ 33 A. Ground connections.............................................................................................................. 33 B. Point of connection to piping systems.................................................................................. 33 C. Contact surfaces.................................................................................................................... 34 096. Ground resistance requirements................................................................................................. 34 A. General.................................................................................................................................. 34 B. Supply stations...................................................................................................................... 34 C. Multi-grounded systems........................................................................................................ 34 D. Single-grounded (unigrounded or delta) systems................................................................. 35 097. Separation of grounding conductors.......................................................................................... 35 098. Number 098 not used in this edition.......................................................................................... 36 099. Additional requirements for grounding and bonding of communication apparatus.................. 36 A. Electrode............................................................................................................................... 36 B. Electrode connection............................................................................................................. 36 C. Bonding of electrodes........................................................................................................... 37 Part 1. Safety Rules for the Installation and Maintenance of Electric Supply Stations and Equipment Section 10. Purpose and scope of rules.......................................................................................................... 39 100. Purpose....................................................................................................................................... 39 101. Scope.......................................................................................................................................... 39 102. Application of rules................................................................................................................... 39 103. Referenced sections................................................................................................................... 39 Section 11. Protective arrangements in electric supply stations.................................................................... 40 110. General requirements................................................................................................................. 40 A. Enclosure of equipment........................................................................................................ 40 1. Types of enclosures........................................................................................................ 40 2. Safety clearance zone...................................................................................................... 40 B. Rooms and spaces................................................................................................................. 41 1. Construction.................................................................................................................... 41 2. Use.................................................................................................................................. 41 3. Ventilation...................................................................................................................... 41 4. Moisture and weather...................................................................................................... 41 xxii Copyright © 2016 IEEE. All rights reserved.  Contents Section Page C. Electric equipment................................................................................................................ 41 111. Illumination................................................................................................................................ 43 A. Under normal conditions....................................................................................................... 43 B. Emergency lighting............................................................................................................... 43 C. Fixtures.................................................................................................................................. 44 D. Attachment plugs and receptacles for general use................................................................ 44 E. Receptacles in damp or wet locations................................................................................... 44 112. Floors, floor openings, passageways, and stairs........................................................................ 45 A. Floors.................................................................................................................................... 45 B. Passageways.......................................................................................................................... 45 C. Railings................................................................................................................................. 45 D. Stair guards........................................................................................................................... 45 E. Top rails................................................................................................................................. 45 113. Exits........................................................................................................................................... 45 A. Clear exits............................................................................................................................. 45 B. Double exits.......................................................................................................................... 45 C. Exit doors.............................................................................................................................. 46 Section 12. Installation and maintenance of equipment................................................................................ 47 120. General requirements................................................................................................................. 47 121. Inspections................................................................................................................................. 47 A. In-service equipment............................................................................................................. 47 B. Idle equipment....................................................................................................................... 47 C. Emergency equipment........................................................................................................... 47 D. New equipment..................................................................................................................... 47 122. Guarding shaft ends, pulleys, belts, and suddenly moving parts............................................... 47 A. Mechanical transmission machinery..................................................................................... 47 B. Suddenly moving parts.......................................................................................................... 47 123. Protective grounding.................................................................................................................. 47 A. Protective grounding or physical isolation of non-current-carrying metal parts.................. 47 B. Grounding method................................................................................................................ 48 C. Provision for grounding equipment during maintenance...................................................... 48 D. Grounding methods for direct-current systems over 750 V.................................................. 48 124. Guarding live parts..................................................................................................................... 48 A. Where required...................................................................................................................... 48 B. Strength of guards................................................................................................................. 48 C. Types of guards..................................................................................................................... 49 1. Location or physical isolation......................................................................................... 49 2. Shields or enclosures...................................................................................................... 49 3. Supplemental barriers or guards within electric supply stations.................................... 49 4. Mats................................................................................................................................ 49 5. Live parts below supporting surfaces for persons.......................................................... 49 6. Insulating covering on conductors or parts..................................................................... 49 D. Taut-string distances............................................................................................................. 49 125. Working space about electric equipment................................................................................... 60 A. Working space (600 V or less).............................................................................................. 60 1. Clear spaces.................................................................................................................... 60 2. Access and entrance to working space........................................................................... 60 3. Working space................................................................................................................ 60 4. Headroom working space............................................................................................... 60 5. Front working space........................................................................................................ 60 B. Working space over 600 V.................................................................................................... 61 126. Equipment for work on energized parts..................................................................................... 61 127. Classified locations.................................................................................................................... 61 xxiii Copyright © 2016 IEEE. All rights reserved.  Contents Section Page A. Coal-handling areas.............................................................................................................. 61 B. Flammable and combustible liquids...................................................................................... 62 C. Flammable liquid storage area.............................................................................................. 62 D. Loading and unloading facilities for flammable and combustible liquids............................ 62 F. Boilers.................................................................................................................................... 62 G. Gaseous hydrogen systems for supply equipment................................................................ 62 H. Liquid hydrogen systems...................................................................................................... 63 I. Sulfur...................................................................................................................................... 63 J. Oxygen................................................................................................................................... 63 K. Liquefied petroleum gas (LPG)............................................................................................ 63 L. Natural gas (methane)........................................................................................................... 63 128. Identification.............................................................................................................................. 63 129. Mobile hydrogen equipment...................................................................................................... 63 Section 13. Rotating equipment..................................................................................................................... 64 130. Speed control and stopping devices........................................................................................... 64 A. Automatic overspeed trip device for prime movers.............................................................. 64 B. Manual stopping devices....................................................................................................... 64 C. Speed limit for motors........................................................................................................... 64 1. Separately excited dc motors.......................................................................................... 64 2. Series motors................................................................................................................... 64 D. Number 130D not used in this edition.................................................................................. 64 E. Adjustable-speed motors....................................................................................................... 64 F. Protection of control circuits................................................................................................. 64 131. Motor control............................................................................................................................. 64 132. Number 132 not used in this edition.......................................................................................... 65 133. Short-circuit protection.............................................................................................................. 65 Section 14. Storage batteries.......................................................................................................................... 66 140. General....................................................................................................................................... 66 141. Location..................................................................................................................................... 66 142. Ventilation................................................................................................................................. 66 143. Racks.......................................................................................................................................... 66 144. Floors in battery areas................................................................................................................ 66 145. Illumination for battery areas..................................................................................................... 66 146. Service facilities......................................................................................................................... 66 Section 15. Transformers and regulators....................................................................................................... 68 150. Current-transformer secondary circuits protection when exceeding 600 V.............................. 68 151. Grounding secondary circuits of instrument transformers....................................................... 68 152. Location and arrangement of power transformers and regulators............................................. 68 A. Outdoor installations............................................................................................................. 68 B. Indoor installations................................................................................................................ 68 153. Short-circuit protection of power transformers......................................................................... 69 Section 16. Conductors.................................................................................................................................. 70 160. Application................................................................................................................................. 70 161. Electrical protection................................................................................................................... 70 A. Overcurrent protection required............................................................................................ 70 B. Grounded conductors............................................................................................................ 70 C. Insulated power cables.......................................................................................................... 70 162. Mechanical protection and support............................................................................................ 70 163. Isolation..................................................................................................................................... 70 164. Conductor terminations.............................................................................................................. 70 xxiv Copyright © 2016 IEEE. All rights reserved.  Contents Section Page A. Insulation............................................................................................................................... 70 B. Metal-sheathed or shielded cable.......................................................................................... 70 Section 17. Circuit breakers, reclosers, switches, and fuses.......................................................................... 71 170. Arrangement.............................................................................................................................. 71 171. Application................................................................................................................................. 71 172. Circuit breakers, reclosers, and switches containing oil............................................................ 71 173. Switches and disconnecting devices.......................................................................................... 71 A. Capacity................................................................................................................................ 71 B. Provisions for disconnecting................................................................................................. 71 174. Disconnection of fuses............................................................................................................... 71 Section 18. Switchgear and metal-enclosed bus............................................................................................ 73 180. Switchgear assemblies............................................................................................................... 73 A. General requirements for all switchgear............................................................................... 73 B. Metal-enclosed power switchgear......................................................................................... 73 C. Dead-front power switchboards............................................................................................ 74 D. Motor control centers............................................................................................................ 74 E. Control switchboards............................................................................................................. 74 181. Metal-enclosed bus.................................................................................................................... 74 A. General requirements for all types of bus............................................................................. 74 B. Isolated-phase bus................................................................................................................. 75 Section 19. Surge arresters............................................................................................................................. 76 190. General requirements................................................................................................................. 76 191. Indoor locations......................................................................................................................... 76 192. Grounding conductors................................................................................................................ 76 193. Installation................................................................................................................................. 76 Part 2. Safety Rules for the Installation and Maintenance of Overhead Electric Supply and Communication Lines Section 20. Purpose, scope, and application of rules..................................................................................... 77 200. Purpose....................................................................................................................................... 77 201. Scope.......................................................................................................................................... 77 202. Application of rules................................................................................................................... 77 Section 21. General requirements.................................................................................................................. 78 210. Referenced sections................................................................................................................... 78 211. Number 211 not used in this edition.......................................................................................... 78 212. Induced voltages........................................................................................................................ 78 213. Accessibility............................................................................................................................... 78 214. Inspection and tests of lines and equipment.............................................................................. 78 A. When in service..................................................................................................................... 78 1. Initial compliance with rules........................................................................................... 78 2. Inspection........................................................................................................................ 78 3. Tests................................................................................................................................ 78 4. Inspection records........................................................................................................... 78 5. Corrections...................................................................................................................... 78 B. When out of service.............................................................................................................. 79 1. Lines infrequently used................................................................................................... 79 2. Lines temporarily out of service..................................................................................... 79 3. Lines permanently abandoned........................................................................................ 79 xxv Copyright © 2016 IEEE. All rights reserved.  Contents Section Page 215. Grounding of circuits, supporting structures, and equipment.................................................... 79 A. Methods................................................................................................................................. 79 B. Circuits.................................................................................................................................. 79 1. Common neutral............................................................................................................. 79 2. Other neutrals.................................................................................................................. 79 3. Other conductors............................................................................................................. 79 4. Surge arresters................................................................................................................. 79 5. Use of earth as part of circuit.......................................................................................... 79 C. Non-current-carrying parts.................................................................................................... 79 1. General............................................................................................................................ 79 2. Guys................................................................................................................................ 80 3. Span wires....................................................................................................................... 80 4. Insulators used to limit galvanic corrosion..................................................................... 81 5. Multiple messengers on the same structure.................................................................... 81 216. Arrangement of switches........................................................................................................... 81 A. Accessibility.......................................................................................................................... 81 B. Indicating open or closed position........................................................................................ 81 C. Locking................................................................................................................................. 81 D. Uniform position................................................................................................................... 81 E. Remotely controlled, automatic transmission, or distribution overhead line switching devices.......................................................................................... 81 217. General....................................................................................................................................... 82 A. Supporting structures............................................................................................................ 82 1. Protection of structures................................................................................................... 82 2. Readily climbable supporting structures......................................................................... 82 3. Identification................................................................................................................... 83 4. Attachments, decorations, and obstructions.................................................................. 83 B. Unusual conductor supports.................................................................................................. 83 C. Protection and marking of guys............................................................................................ 83 218. Vegetation management............................................................................................................ 83 A. General.................................................................................................................................. 83 B. At line crossings, railroad crossings, limited-access highway crossings, or navigable waterways requiring crossing permits............................................................. 84 Section 22. Relations between various classes of lines and equipment......................................................... 85 220. Relative levels............................................................................................................................ 85 A. Standardization of levels....................................................................................................... 85 B. Relative levels: supply and communication conductors and equipment.............................. 85 1. Preferred levels............................................................................................................... 85 2. Special construction for railroad supply circuits of 600 V or less and carrying power not in excess of 5 kW............................................................................. 85 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, over 22 kV to 50 kV, and over 50 kV).................................................................................................................... 86 1. At crossings or conflicts................................................................................................. 86 2. On structures used only by supply conductors............................................................... 86 D. Identification of overhead conductors and cables................................................................. 86 E. Identification of equipment on supporting structures............................................................ 86 221. Avoidance of conflict................................................................................................................. 86 222. Joint use of structures................................................................................................................ 87 223. Communications protective requirements................................................................................. 87 A. Where required...................................................................................................................... 87 B. Means of protection............................................................................................................... 87 xxvi Copyright © 2016 IEEE. All rights reserved.  Contents Section Page 224. Communication circuits located within the supply space and supply circuits located within the communication space................................................................................... 87 A. Communication circuits located in the supply space............................................................ 87 B. Supply circuits used exclusively in the operation of communication circuits...................... 88 225. Electric railway construction..................................................................................................... 89 A. Trolley-contact conductor fastenings.................................................................................... 89 B. High-voltage contact conductors........................................................................................... 89 C. Third rails.............................................................................................................................. 89 D. Prevention of loss of contact at railroad crossings at grade.................................................. 89 E. Guards under bridges............................................................................................................. 89 Section 23. Clearances................................................................................................................................... 90 230. General....................................................................................................................................... 90 A. Application............................................................................................................................ 90 1. Permanent and temporary installations........................................................................... 90 2. Emergency installations.................................................................................................. 90 3. Measurement of clearance and spacing.......................................................................... 90 4. Rounding of calculation results...................................................................................... 91 B. Ice and wind loading for clearances...................................................................................... 91 C. Supply cables........................................................................................................................ 93 D. Covered conductors.............................................................................................................. 93 E. Neutral conductors................................................................................................................ 93 F. Fiber-optic cable.................................................................................................................... 93 1. Fiber-optic—supply cable............................................................................................... 93 2. Fiber-optic—communication cable................................................................................ 94 G. Alternating- and direct-current circuits................................................................................. 94 H. Constant-current circuits....................................................................................................... 94 I. Maintenance of clearances and spacings................................................................................ 94 231. Clearances of supporting structures from other objects............................................................. 96 A. From fire hydrants................................................................................................................. 96 B. From streets, roads, and highways........................................................................................ 96 C. From railroad tracks.............................................................................................................. 96 232. Vertical clearances of wires, conductors, cables, and equipment aboveground, roadway, rail, or water surfaces................................................................................................. 96 A. Application............................................................................................................................ 96 B. Clearance of wires, conductors, cables, equipment, and support arms mounted on supporting structures....................................................................................................... 97 1. Clearance to wires, conductors, and cables.................................................................... 97 2. Clearance to unguarded rigid live parts of equipment.................................................... 97 3. Clearance to support arms, switch handles, and equipment cases.................................. 97 4. Street and area lighting................................................................................................... 97 C. Additional clearances for wires, conductors, cables, and unguarded rigid live parts of equipment......................................................................................................... 97 1.Voltages exceeding 22 kV............................................................................................... 97 D. Alternate clearances for voltages exceeding 98 kV ac to ground or 139 kV dc to ground............................................................................................................. 98 1. Sag conditions of line conductors................................................................................... 98 2. Reference heights............................................................................................................ 98 3. Electrical component of clearance.................................................................................. 98 4. Limit................................................................................................................................ 99 233. Clearances between wires, conductors, and cables carried on different supporting structures................................................................................................. 114 A. General................................................................................................................................ 114 1. Conductor movement envelope.................................................................................... 115 xxvii Copyright © 2016 IEEE. All rights reserved.  Contents Section Page 2. Clearance envelope....................................................................................................... 115 B. Horizontal clearance............................................................................................................ 115 1. Clearance requirements................................................................................................. 115 2. For voltages exceeding 50 kV....................................................................................... 115 3. Alternate clearances between conductors of different circuits...................................... 115 C. Vertical clearance................................................................................................................ 115 1. Clearance requirements................................................................................................. 115 2. Voltages between the wires, conductors, or cables exceeding 22 kV.......................... 116 3. Alternate clearances for voltage exceeding 98 kV ac to ground or 139 kV dc to ground................................................................................................... 116 234. Clearance of wires, conductors, cables, and equipment from buildings, bridges, rail cars, swimming pools, and other installations................................................................... 126 A. Application.......................................................................................................................... 126 1. Vertical and horizontal clearances (no wind displacement)......................................... 126 2. Horizontal clearances (with wind displacement).......................................................... 126 3. Transition between horizontal and vertical clearances................................................. 126 B. Clearances of wires, conductors, and cables from other supporting structures.................. 127 1. Horizontal clearances.................................................................................................... 127 2. Vertical clearances........................................................................................................ 127 C. Clearances of wires, conductors, cables, and rigid live parts from buildings, signs, billboards, chimneys, radio and television antennas, tanks, flagpoles and flags, banners, and other installations except bridges.................................................. 128 1. Vertical and horizontal clearances................................................................................ 128 2. Guarding of supply conductors and rigid live parts...................................................... 128 3. Supply conductors attached to buildings or other installations.................................... 128 4. Communication conductors attached to buildings or other installations...................... 129 D. Clearance of wires, conductors, cables, and unguarded rigid live parts from bridges........ 130 1. Vertical and horizontal clearances................................................................................ 130 2. Guarding trolley-contact conductors located under bridges......................................... 130 E. Clearance of wires, conductors, cables, or unguarded rigid live parts installed over or near swimming areas with no wind displacement.................................................. 130 1. Swimming pools........................................................................................................... 130 2. Beaches and waterways restricted to swimming.......................................................... 131 3. Waterways subject to water skiing............................................................................... 131 F. Clearances of wires, conductors, cables, and rigid live parts from grain bins.................... 131 1. Grain bins loaded by permanently installed augers, conveyers, or elevator systems.... 131 2. Grain bins loaded by portable augers, conveyers, or elevators.................................... 131 G. Additional clearances for voltages exceeding 22 kV for wires, conductors, cables, and unguarded rigid live parts of equipment...................................................................... 132 H. Alternate clearances for voltages exceeding 98 kV ac to ground or 139 kV dc to ground........................................................................................................... 132 1. Sag conditions of line conductors................................................................................. 132 2. Reference distances....................................................................................................... 132 3. Electrical component of clearance................................................................................ 132 4. Limit.............................................................................................................................. 133 I. Clearance of wires, conductors, and cables to rail cars........................................................ 133 J. Clearance of equipment mounted on supporting structures................................................. 133 1. Clearance to unguarded rigid live parts of equipment.................................................. 133 2. Clearance to equipment cases....................................................................................... 133 235. Clearance for wires, conductors, or cables carried on the same supporting structure............. 157 A. Application of rule.............................................................................................................. 157 1. Multiconductor wires or cables..................................................................................... 157 2. Conductors supported by messengers or span wires.................................................... 157 3. Line conductors of different circuits............................................................................. 157 xxviii Copyright © 2016 IEEE. All rights reserved.  Contents Section Page B. Horizontal clearance between line conductors.................................................................... 158 1. Fixed supports............................................................................................................... 158 2. Suspension insulators.................................................................................................... 159 3. Alternate clearances for different circuits where one or both circuits exceed 98 kV ac to ground or 139 kV dc to ground................................................................. 159 C. Vertical clearance at the support for line conductors and service drops............................. 160 1. Basic clearance for line wires, conductors, and cables, and service drops of same or different circuits........................................................................................... 160 2. Additional clearances.................................................................................................... 160 3. Alternate clearances for different circuits where one or both exceed 98 kV ac, or 139 kV dc to ground.................................................................................................. 163 4. Communication worker safety zone............................................................................. 163 D. Diagonal clearance between line wires, conductors, and cables located at different levels on the same supporting structure............................................................... 163 E. Clearances in any direction at or near a support from line conductors to supports, and to vertical or lateral conductors, service drops, and span or guy wires, attached to the same support............................................................................................... 163 1. Fixed supports............................................................................................................... 163 2. Suspension insulators.................................................................................................... 163 3. Alternate clearances for voltages exceeding 98 kV ac to ground or 139 kV dc to ground...................................................................................................... 163 F. Clearances between circuits located in the supply space on the same support arm............ 164 G. Conductor spacing: vertical racks or separate brackets...................................................... 165 H. Clearance and spacing between communication conductors, cables, and equipment........ 165 I. Communication antenna clearances in any direction from supply and communication lines attached to the same supporting structure......................................... 165 1. General.......................................................................................................................... 165 2. Communication antenna clearances.............................................................................. 165 3. Equipment case that supports or is adjacent to a communication antenna................... 166 4. Vertical or lateral communication conductors and cables attached to a communication antenna................................................................................................ 166 236. Climbing space........................................................................................................................ 184 A. Location and dimensions.................................................................................................... 184 B. Portions of supporting structures in climbing space........................................................... 184 C. Support arm location relative to climbing space................................................................. 184 D. Location of equipment relative to climbing space.............................................................. 184 E. Climbing space between conductors................................................................................... 184 F. Climbing space on buckarm construction........................................................................... 184 G. Climbing space past longitudinal runs not on support arms............................................... 185 H. Climbing space past vertical conductors............................................................................. 185 I. Climbing space near ridge-pin conductors........................................................................... 185 237. Working space......................................................................................................................... 188 A. Location of working spaces................................................................................................ 188 B. Dimensions of working spaces............................................................................................ 188 1. Along the support arm.................................................................................................. 188 2. At right angles to the support arm................................................................................ 188 3. Vertically...................................................................................................................... 188 C. Location of vertical and lateral conductors relative to working spaces.............................. 188 D. Location of buckarms relative to working spaces............................................................... 188 1. Standard height of working space................................................................................. 188 2. Reduced height of working space................................................................................. 188 E. Guarding of energized equipment....................................................................................... 188 F. Working clearances from energized equipment.................................................................. 189 xxix Copyright © 2016 IEEE. All rights reserved.  Contents Section Page 238. Vertical clearance between specified communications and supply facilities located on the same structure................................................................................................... 189 A. Equipment........................................................................................................................... 189 B. Clearances in general.......................................................................................................... 189 C. Clearances for span wires or brackets................................................................................. 189 D. Clearance of drip loops associated with luminaires and traffic signals.............................. 189 E. Communication worker safety zone.................................................................................... 190 239. Clearance of vertical and lateral facilities from other facilities and surfaces on the same supporting structure............................................................................................. 191 A. General................................................................................................................................ 191 B. Location of vertical or lateral conductors relative to climbing spaces, working spaces, and pole steps...................................................................................................................... 191 C. Conductors not in conduit................................................................................................... 191 D. Guarding and protection near ground................................................................................. 191 E. Requirements for vertical and lateral supply conductors on supply line structures or within supply space on jointly used structures............................................................... 192 1. General clearances........................................................................................................ 192 2. Special cases................................................................................................................. 192 F. Requirements for vertical and lateral communication conductors on communication line structures or within the communication space on jointly used structures.................... 192 1. Clearances from communication conductors................................................................ 192 2. Clearances from supply conductors.............................................................................. 192 G. Requirements for vertical supply conductors and cables passing through communication space on jointly used line structures......................................................... 193 1. Guarding—General....................................................................................................... 193 2. Cables and conductors in conduit or covering.............................................................. 193 3. Protection near trolley, ungrounded traffic signal, or ungrounded luminaire attachments................................................................................................... 193 4. Service drops................................................................................................................. 193 5. Clearance from through bolts and other metal objects................................................. 193 H. Requirements for vertical communication conductors passing through supply space on jointly used structures.............................................................................. 194 1. Metal-sheathed communication cables......................................................................... 194 2. Communication conductors.......................................................................................... 194 3. Communication grounding conductors......................................................................... 194 4. Clearance from through bolts and other metal objects................................................. 194 I. Operating rods...................................................................................................................... 194 J. Additional rules for standoff brackets.................................................................................. 195 Section 24. Grades of construction.............................................................................................................. 198 240. General..................................................................................................................................... 198 241. Application of grades of construction to different situations.................................................. 198 A. Supply cables...................................................................................................................... 198 B. Order of grades.................................................................................................................... 198 C. At crossings......................................................................................................................... 198 1. Wires, conductors, or other cables of one line............................................................... 198 2. Grade of upper line....................................................................................................... 198 3. Grade of lower line....................................................................................................... 198 4. Multiple crossings......................................................................................................... 198 D. Structure conflicts............................................................................................................... 199 242. Grades of construction for conductors..................................................................................... 199 A. Constant-current circuit conductors.................................................................................... 199 B. Railway feeder and trolley-contact circuit conductors........................................................ 199 C. Communication circuit conductors and cables................................................................... 199 xxx Copyright © 2016 IEEE. All rights reserved.  Contents Section Page D. Fire-alarm circuit conductors.............................................................................................. 199 E. Neutral conductors of supply circuits.................................................................................. 199 F. Surge-protection wires......................................................................................................... 199 243. Grades of construction for line supports.................................................................................. 202 A. Structures............................................................................................................................ 202 B. Crossarms and support arms............................................................................................... 202 C. Pins, armless construction brackets, insulators, and conductor fastenings......................... 202 Section 25. Loadings for Grades B and C................................................................................................... 203 250. General loading requirements and maps.................................................................................. 203 A. General................................................................................................................................ 203 B. Combined ice and wind district loading.............................................................................. 203 C. Extreme wind loading......................................................................................................... 203 1. Velocity pressure exposure coefficient, kz................................................................... 204 2. Gust response factor, GRF............................................................................................. 204 D. Extreme ice with concurrent wind loading......................................................................... 205 251. Conductor loading.................................................................................................................... 221 A. General................................................................................................................................ 221 B. Load components................................................................................................................ 221 1. Vertical load component............................................................................................... 221 2. Horizontal load component........................................................................................... 222 3. Total load...................................................................................................................... 222 252. Loads on line supports............................................................................................................. 222 A. Assumed vertical loads....................................................................................................... 222 B. Assumed transverse loads................................................................................................... 223 1. Transverse loads from conductors and messengers...................................................... 223 2. Wind loads on structures............................................................................................... 223 3. At angles....................................................................................................................... 223 4. Wind span..................................................................................................................... 223 C. Assumed longitudinal loading............................................................................................. 223 1. Change in grade of construction................................................................................... 223 2. Jointly used poles at crossings over railroads, communication lines, or limited access highways............................................................................................... 224 3. Deadends....................................................................................................................... 224 4. Unequal spans and unequal vertical loads.................................................................... 224 5. Stringing loads.............................................................................................................. 224 6. Communication conductors on unguyed supports at railroad and limited access highway crossings................................................................................. 224 D. Simultaneous application of loads...................................................................................... 224 253. Load factors for structures, crossarms, support hardware, guys, foundations, and anchors.... 224 Section 26. Strength requirements............................................................................................................... 226 260. General (see also Section 20)................................................................................................... 226 A. Preliminary assumptions..................................................................................................... 226 B. Application of strength factors............................................................................................ 226 261. Grades B and C construction................................................................................................... 227 A. Supporting structures.......................................................................................................... 227 1. Metal, prestressed-, and reinforced-concrete structures............................................... 227 2. Wood structures............................................................................................................ 227 3. Fiber-reinforced polymer structures............................................................................. 228 4. Transverse strength requirements for structures where side guying is required, but can be installed only at a distance.......................................................................... 228 5. Longitudinal strength requirements for sections of higher grade in lines of a lower grade construction.............................................................................................. 228 xxxi Copyright © 2016 IEEE. All rights reserved.  Contents Section Page B. Strength of foundations, settings, and guy anchors............................................................. 229 C. Strength of guys and guy insulators.................................................................................... 229 1. Metal and prestressed-concrete structures.................................................................... 229 2. Wood and reinforced-concrete structures..................................................................... 229 3. Fiber-reinforced polymer structures............................................................................. 229 D. Crossarms and braces.......................................................................................................... 229 1. Concrete and metal crossarms and braces.................................................................... 229 2. Wood crossarms and braces.......................................................................................... 230 3. Fiber-reinforced polymer crossarms and braces........................................................... 230 4. Crossarms and braces of other materials...................................................................... 230 5. Additional requirements............................................................................................... 230 E. Insulators............................................................................................................................. 231 F. Strength of pin-type or similar construction and conductor fastenings............................... 231 1. Longitudinal strength.................................................................................................... 231 2. Double pins and conductor fastenings.......................................................................... 231 3. Single supports used in lieu of double wood pins........................................................ 231 G. Armless construction.......................................................................................................... 231 1. General.......................................................................................................................... 231 2. Insulating material........................................................................................................ 232 3. Other components......................................................................................................... 232 H. Open supply conductors and overhead shield wires........................................................... 232 1. Tensions........................................................................................................................ 232 2. Splices, taps, dead-end fittings, and associated attachment hardware.......................... 232 3. Trolley-contact conductors........................................................................................... 233 I. Supply cable messengers...................................................................................................... 233 J. Open-wire communication conductors................................................................................ 233 K. Communication cables and messengers.............................................................................. 233 1. Communication cables.................................................................................................. 233 2. Messenger..................................................................................................................... 233 L. Paired metallic communication conductors........................................................................ 233 1. Paired conductors supported on messenger.................................................................. 233 2. Paired conductors not supported on messenger............................................................ 234 M. Support and attachment hardware...................................................................................... 234 262. Number 262 not used in this edition........................................................................................ 236 263. Grade N construction............................................................................................................... 236 A. Poles.................................................................................................................................... 236 B. Guys.................................................................................................................................... 236 C. Crossarm strength................................................................................................................ 236 D. Supply line conductors........................................................................................................ 236 1. Size................................................................................................................................ 236 E. Service drops....................................................................................................................... 236 1. Size of open-wire service drops.................................................................................... 236 2. Tension of open-wire service drops.............................................................................. 237 3. Cabled service drops..................................................................................................... 237 F. Trolley-contact conductors.................................................................................................. 237 G. Communication conductors................................................................................................ 237 H. Street and area lighting equipment..................................................................................... 237 I. Insulators.............................................................................................................................. 237 264. Guying and bracing.................................................................................................................. 238 A. Where used.......................................................................................................................... 238 B. Strength............................................................................................................................... 238 C. Point of attachment............................................................................................................. 238 D. Guy fastenings.................................................................................................................... 239 xxxii Copyright © 2016 IEEE. All rights reserved.  Contents Section Page E. Electrolysis.......................................................................................................................... 239 F. Anchor rods......................................................................................................................... 239 Section 27. Line insulation.......................................................................................................................... 240 270. Application of rule................................................................................................................... 240 271. Material and marking............................................................................................................... 240 272. Ratio of flashover to puncture voltage..................................................................................... 240 273. Insulation level......................................................................................................................... 240 274. Factory tests............................................................................................................................. 241 275. Special insulator applications.................................................................................................. 241 A. Insulators for constant-current circuits............................................................................... 241 B. Insulators for single-phase circuits directly connected to three-phase circuits................... 241 276. Number 276 not used in this edition........................................................................................ 242 277. Mechanical strength of insulators............................................................................................ 242 278. Aerial cable systems................................................................................................................ 243 A. Electrical requirements....................................................................................................... 243 B. Mechanical requirements.................................................................................................... 243 279. Guy and span insulators........................................................................................................... 244 A. Insulators............................................................................................................................. 244 1. Properties of guy insulators.......................................................................................... 244 2. Galvanic corrosion and BIL insulation......................................................................... 244 B. Properties of span-wire insulators....................................................................................... 244 1. Material......................................................................................................................... 244 2. Insulation level.............................................................................................................. 245 3. Mechanical strength...................................................................................................... 245 Section 28. Section number 28 not used in this edition............................................................................... 245 Section 29. Section number 29 not used in this edition............................................................................... 245 Part 3. Safety Rules for the Installation and Maintenance of Underground Electric Supply and Communication Lines Section 30. Purpose, scope, and application of rules................................................................................... 247 300. Purpose..................................................................................................................................... 247 301. Scope........................................................................................................................................ 247 302. Application of rules................................................................................................................. 247 Section 31. General requirements applying to underground lines............................................................... 248 310. Referenced sections................................................................................................................. 248 311. Installation and maintenance................................................................................................... 248 312. Accessibility............................................................................................................................. 248 313. Inspection and tests of lines and equipment............................................................................ 248 A. When in service................................................................................................................... 248 1. Initial compliance with safety rules.............................................................................. 248 2. Inspection...................................................................................................................... 248 3. Tests.............................................................................................................................. 248 4. Inspection records......................................................................................................... 248 5. Corrections.................................................................................................................... 248 B. When out of service............................................................................................................ 249 1. Lines infrequently used................................................................................................. 249 2. Lines temporarily out of service................................................................................... 249 3. Lines permanently abandoned...................................................................................... 249 314. Grounding of circuits and equipment...................................................................................... 249 A. Methods............................................................................................................................... 249 B. Conductive parts to be grounded......................................................................................... 249 xxxiii Copyright © 2016 IEEE. All rights reserved.  Contents Section Page C. Circuits................................................................................................................................ 249 1. Neutrals......................................................................................................................... 249 2. Other conductors........................................................................................................... 249 3. Surge arresters............................................................................................................... 249 4. Use of earth as part of circuit........................................................................................ 249 315. Communications protective