Safety Rules for Overhead Lines (2017) - NEC PDF

200 Part 2: Safety Rules for Overhead Lines 202 Part 2. Safety Rules for the Installation and Maintenance of Overhead Electric Supply and Communication Lines...

200 Part 2: Safety Rules for Overhead Lines 202 Part 2. Safety Rules for the Installation and Maintenance of Overhead Electric Supply and Communication Lines Section 20. Purpose, scope, and application of rules 200. Purpose The purpose of Part 2 of this Code is the practical safeguarding of persons during the installation, operation, or maintenance of overhead supply and communication lines and their associated equipment. 201. Scope Part 2 of this Code covers supply and communication conductors and equipment in overhead lines. It covers the associated structural arrangements of such systems and the extension of such systems into buildings. The rules include requirements for spacing, clearances, and strength of construction. They do not cover installations in electric supply stations except as required by Rule 162A. NOTE 1: Part 4 contains the approach distances and work rules required of supply and communication employers and their employees working on or near supply and communication lines and equipment. NOTE 2: The approach distances to energized parts, and other requirements applicable to the activities of utility or non-utility construction personnel, and others in close proximity to existing supply lines are governed by the Occupational Health and Safety Administration (OSHA), federal, state, or local statutes or regulations. 202. Application of rules The general requirements for application of these rules are contained in Rule 13. However, when a supporting structure is replaced, the arrangement of equipment shall confirm to the current edition of Rule 238C. 77 Copyright © 2016 IEEE. All rights reserved. 210 Part 2: Safety Rules for Overhead Lines 214A5a Section 21. General requirements 210. Referenced sections The Introduction (Section 1), Definitions (Section 2), References (Section 3), and Grounding methods (Section 9) shall apply to the requirements of Part 2. 211. Number 211 not used in this edition. 212. Induced voltages Rules covering supply-line influence and communication-line susceptiveness have not been detailed in this Code. Cooperative procedures are recommended in the control of voltages induced from proximate facilities. Therefore, reasonable advance notice should be given to owners or operators of other proximate facilities that may be adversely affected by new construction or changes in existing facilities. NOTE: Additional information about supply-line influence and communication-line susceptiveness may be obtained from IEEE Std 776™-1992 [B39] and IEEE Std 1137™-1991 [B51]. 213. Accessibility All parts that must be examined or adjusted during operation shall be arranged so as to be accessible to authorized persons by the provision of adequate climbing spaces, working spaces, working facili- ties, and clearances between conductors. 214. Inspection and tests of lines and equipment A. When in service 1. Initial compliance with rules Lines and equipment shall comply with these safety rules when placed in service. 2. Inspection Lines and equipment shall be inspected at such intervals as experience has shown to be necessary. NOTE: It is recognized that inspections may be performed in a separate operation or while performing other duties, as desired. 3. Tests When considered necessary, lines and equipment shall be subjected to practical tests to deter- mine required maintenance. 4. Inspection records Any conditions or defects affecting compliance with this Code revealed by inspection or tests, if not promptly corrected, shall be recorded; such records shall be maintained until the conditions or defects are corrected. 5. Corrections a. Lines and equipment with recorded conditions or defects that would reasonably be expected to endanger human life or property shall be promptly corrected, disconnected, or isolated. 78 Copyright © 2016 IEEE. All rights reserved. 214A5b Part 2: Safety Rules for Overhead Lines 215C1 b. Other conditions or defects shall be designated for correction. B. When out of service 1. Lines infrequently used Lines and equipment infrequently used shall be inspected or tested as necessary before being placed into service. 2. Lines temporarily out of service Lines and equipment temporarily out of service shall be maintained in a safe condition. 3. Lines permanently abandoned Lines and equipment permanently abandoned shall be removed or maintained in a safe condition. 215. Grounding of circuits, supporting structures, and equipment A. Methods Grounding required by these rules shall be in accordance with the applicable methods given in Section 9. B. Circuits 1. Common neutral A conductor used as a common neutral for primary and secondary circuits shall be effectively grounded. 2. Other neutrals Primary line, secondary line, and service neutral conductors shall be effectively grounded. EXCEPTION 1: Circuits designed for ground-fault detection and impedance-current-limiting devices. EXCEPTION 2: Primary circuits designed with a single point grounded neutral. This type of neutral con- ductor is not an effectively grounded neutral conductor. 3. Other conductors Line or service conductors, other than neutral conductors, that are intentionally grounded, shall be effectively grounded. 4. Surge arresters Where the operation of surge arresters is dependent upon grounding, they shall be effectively grounded. 5. Use of earth as part of circuit a. Supply circuits shall not be designed to use the earth normally as the sole conductor for any part of the circuit. b. Monopolar operation of a bipolar HVDC system is permissible for emergencies and lim- ited periods for maintenance. C. Non-current-carrying parts 1. General Metal or metal-reinforced supporting structures, including lamp posts; metal conduits and race- ways; cable sheaths; messengers; metal frames, cases, and hangers of equipment; and metal switch handles and operating rods shall be effectively grounded. For the purpose of this rule metallic stand-off brackets or straps, metal crossarm braces, metal through-bolts, etc., are not considered to be metal frames, cases, or hangers of equipment and therefore not required to be effectively grounded. For the purpose of this rule, a wood structure with metal-reinforcing trusses installed at its base for strength purposes is not considered to be a metal-reinforced structure and therefore not required to be effectively grounded. 79 Copyright © 2016 IEEE. All rights reserved. 215C1a Part 2: Safety Rules for Overhead Lines 215C3a(2) EXCEPTION 1: This rule does not apply where both (a) and (b) are met: (a) Frames, cases, and hangers of equipment; and switch handles and operating rods that are: 1. 2.45 m (8 ft) or more above readily accessible surfaces, or 2. Are otherwise isolated or guarded. (b) The practice of not grounding such items has been a uniform practice over a well-defined operating area. If the decision is made to ground new items located in the supply space, the rules do not require retrofitting existing ungrounded items. NOTE: Typical practice is to ground existing items whenever significant work is done on existing structures. EXCEPTION 2: This rule does not apply to isolated or guarded equipment cases in certain specialized applications, such as series capacitors where it is necessary that equipment cases be either ungrounded or connected to the circuit. Such equipment cases shall be considered as energized and shall be suitably iden- tified. EXCEPTION 3: This rule does not apply to equipment cases, frames, equipment hangers, conduits, mes- sengers, raceways, and cable sheaths enclosing or supporting only communication conductors, provided they are not exposed to contact with open supply conductors. 2. Guys a. Anchor guys Anchor guys shall be effectively grounded as specified in Rule 092C2. EXCEPTION: Anchor guys are not required to be effectively grounded where one or more guy insulators are inserted in the anchor guy and both of the following are met: (1) Guy insulators shall meet the requirements of Rule 279A and (2) Guy insulators shall be positioned so as to limit the likelihood of any portion of an anchor guy becoming energized within 2.45 m (8 ft) of the ground level in the event that the anchor guy becomes slack or breaks. b. Span guys Span guys shall be effectively grounded as specified in Rule 092C2. EXCEPTION: Span guys are not required to be effectively grounded where one or more guy insulators are inserted in the span guy and both of the following are met: (1) Guy insulators shall meet the requirements of Rule 279A and (2) Guy insulators shall be positioned so as to limit the likelihood of any portion of a span guy, becoming energized within 2.45 m (8 ft) of the ground level in the event that the span guy becomes slack. NOTE 1: For the purpose of Rule 215C2, if a span guy and its associated anchor guy are bonded together, they may be considered as one guy. NOTE 2: Nothing in Rule 215C2 limits a portion(s) of a guy from being insulated and another portion(s) being effectively grounded. 3. Span wires a. Supporting luminaires or traffic signals Span wires supporting luminaires or traffic signals shall be effectively grounded. EXCEPTION: Span wires are not required to be effectively grounded where one or more guy insulators are inserted in the span wire and both of the following are met: (1) Span-wire insulators shall meet the requirements of Rule 279B and (2) Insulator(s) shall be positioned so as to limit the likelihood of any portion of a span wire becoming energized within 2.45 m (8 ft) of the ground level in the event that the span wire becomes slack. 80 Copyright © 2016 IEEE. All rights reserved. 215C3b Part 2: Safety Rules for Overhead Lines 216E b. Supporting energized trolley or electric railroad contact conductors (1) All span wires supporting energized trolley or electric railroad contact conductors, including bracket span wires, shall have a suitable insulator (in addition to an insulated hanger if used) inserted between each point of support of the span wire and the trolley or electric railroad contact conductor supported. EXCEPTION 1: Single insulators, as provided by an insulated hanger, may be permitted when the span wire or bracket is supported on wood poles supporting only trolley, railway feeder, or communication conductors used in the operation of the railway concerned. EXCEPTION 2: Insulators are not required if the span wire is effectively grounded. EXCEPTION 3: This rule does not apply to insulated feeder taps used as span wires. (2) In case insulated hangers are not used, the insulator shall be located so as to limit the likelihood of having the energized part of the span wire within 2.45 m (8 ft) of the ground level in the event of a broken wire. NOTE: Nothing in Rule 215C3 limits a portion(s) of a span wire from being insulated and another portion(s) being effectively grounded. 4. Insulators used to limit galvanic corrosion An insulator in the guy strand used exclusively for the limitation of galvanic corrosion of metal in ground rods, anchors, anchor rods, or pipe in an effectively grounded system shall meet the requirements of Rule 279A1c and shall be installed such that (a) the upper portion of a guy has been effectively grounded according to Rule 215C2a, and (b) the top of insulators used to limit galvanic corrosion shall be installed at an elevation below exposed energized conductors and parts. NOTE: See Rule 279A2a. 5. Multiple messengers on the same structure Communication cable messengers exposed to power contacts, power induction, or lightning, shall be bonded together at intervals specified in Rule 092C1. 216. Arrangement of switches A. Accessibility Switches or their control mechanisms shall be installed so as to be accessible to authorized persons. B. Indicating open or closed position Switch position shall be visible or clearly indicated. C. Locking Switch-operating mechanisms that are accessible to unauthorized persons shall have provisions for locking in each operational position and shall be locked or otherwise secured except during operation or testing. NOTE: See Rule 444C. D. Uniform position The handles or control mechanisms for all switches throughout any system should have consistent positions when opened and uniformly different positions when closed in order to minimize operat- ing errors. Where this practice is not followed, the switches should be marked to minimize mistakes in operation. E. Remotely controlled, automatic transmission, or distribution overhead line switching devices shall have local provisions to render remote or automatic controls inoperable. 81 Copyright © 2016 IEEE. All rights reserved. 217 Part 2: Safety Rules for Overhead Lines 217A2c(2) 217. General A. Supporting structures 1. Protection of structures a. Mechanical damage Appropriate physical protection shall be provided for supporting structures in parking lots, in alleys, or next to driveways subject to vehicular traffic abrasion that would materially affect their strength. This rule does not require protection or marking of structural components located outside of the traveled ways of roadways or established parking areas. NOTE: Experience has shown that it is not practical to protect structures from contact by out-of- control vehicles operating outside of established traveled ways. See Rule 231B for structure clearances to roadways. b. Fire Supporting structures shall be placed and maintained so as to be exposed as little as is practical to brush, grass, rubbish, or building fires. c. Attached to bridges Supporting structures attached to bridges for the purpose of carrying open supply conduc- tors exceeding 600 V shall be posted with appropriate safety signs. NOTE: ANSI Z535.1-2011, ANSI Z535.2-2011, and ANSI Z535.4-2011 contain information regarding safety signs. ANSI Z535.3-2011 contains information regarding safety symbols to be used in place of a safety word message. 2. Readily climbable supporting structures a. Readily climbable supporting structures, such as closely latticed poles, towers, or bridge attachments, carrying open supply conductors, which are adjacent to roads, regularly traveled pedestrian thoroughfares, or places where persons frequently gather (such as schools or public playgrounds), shall be equipped with barriers to inhibit climbing by unauthorized persons or posted with appropriate safety signs. EXCEPTION: This rule does not apply where access to the supporting structure is limited by a fence meeting the height requirements of Rule 110A1. NOTE: ANSI Z535.1-2011, ANSI Z535.2-2011, and ANSI Z535.4-2011 contain information regarding safety signs. ANSI Z535.3-2011 contains information regarding safety symbols to be used in place of a safety word message. b. Steps Steps permanently installed on supporting structures shall be not less than 2.45 m (8 ft) from the ground or other accessible surface. Where steps are temporarily installed less than 2.45 m (8 ft) from the ground or other accessible surface, structures shall be attended or barriers to inhibit climbing by unauthorized persons shall be installed. EXCEPTION 1: This rule does not apply where supporting structures are isolated. EXCEPTION 2: This rule does not apply where access to the supporting structure is limited by a fence meeting the height requirements of Rule 110A1. c. Standoff brackets Standoff brackets on supporting structures shall be arranged so that there is not less than 2.45 m (8 ft) between either: (1) The lowest bracket and ground or other accessible surface, or (2) The two lowest brackets. EXCEPTION: This rule does not apply where supporting structures are isolated. 82 Copyright © 2016 IEEE. All rights reserved. 217A3 Part 2: Safety Rules for Overhead Lines 218A2 3. Identification Supporting structures, including those on bridges, on which supply or communication conduc- tors are maintained shall be so constructed, located, marked, or numbered so as to facilitate identification by employees authorized to work thereon. 4. Attachments, decorations, and obstructions No attachment of any kind to a supporting structure of a utility line (including lighting and metering structures) shall be allowed without the concurrence of the structure owner. Non- utility attachments shall also have concurrence of the occupant(s) of the space in which the attachment is made. a. No attachment shall cause any portion of the resulting installation to be in noncompliance with the clearance, grounding, strength, or other requirements of the NESC. b. Attachments shall neither obstruct the climbing space nor present a climbing hazard to utility personnel. Through-bolts shall be properly trimmed. Vines, nails, tacks, or other items which may interfere with climbing should be removed before climbing. B. Unusual conductor supports Where line conductors are attached to structures other than those used solely or principally for their support, all rules shall be complied with as far as they apply. Such additional precautions as may be deemed necessary by the administrative authority shall be taken to avoid damage to the structures or injury to the persons using them. The supporting of conductors on trees and roofs should be avoided. C. Protection and marking of guys 1. The ground end of anchor guys exposed to pedestrian traffic shall be provided with a substan- tial and conspicuous marker. NOTE: There is no intent to require markers at all anchor guy locations. 2. Where an anchor is located in an established parking area, the guy shall either be protected from vehicle contact or marked. This rule does not require protection or marking of anchor guys located outside of the traveled ways of roadways or established parking areas. NOTE: Experience has shown that it is not practical to protect guys from contact by out of control vehi- cles operating outside of established traveled ways. See Rule 231B for clearances of structures adjacent to roadways. NOTE: Visibility of markers can be improved by the use of color or color patterns that provide contrast with the surroundings. 218. Vegetation management A. General 1. Vegetation management should be performed around supply and communication lines as expe- rience has shown to be necessary. Vegetation that may damage ungrounded supply conductors should be pruned or removed. NOTE 1: Factors to consider in determining the extent of vegetation management required include, but are not limited to: line voltage class, species’ growth rates and failure characteristics, right-of-way limitations, the vegetation’s location in relation to the conductors, the potential combined movement of vegetation and conductors during routine winds, and sagging of conductors due to elevated temperatures or icing. NOTE 2: It is not practical to prevent all tree-conductor contacts on overhead lines. 2. Where pruning or removal is not practical, the conductor should be separated from the tree with suitable materials or devices to avoid conductor damage by abrasion and grounding of the circuit through the tree. 83 Copyright © 2016 IEEE. All rights reserved. 218B Part 2: Safety Rules for Overhead Lines 218B B. At line crossings, railroad crossings, limited-access highway crossings, or navigable waterways requiring crossing permits The crossing span and the adjoining span on each side of the crossing should be kept free from over- hanging or decayed trees or limbs that otherwise might fall into the line. 84 Copyright © 2016 IEEE. All rights reserved. 220 Part 2: Safety Rules for Overhead Lines 220B2d Section 22. Relations between various classes of lines and equipment 220. Relative levels A. Standardization of levels The levels at which different classes of conductors are to be located should be standardized by agreement of the utilities concerned. B. Relative levels: supply and communication conductors and equipment 1. Preferred levels Supply conductors/cables or equipment should be carried at the higher level, where practical. EXCEPTION: This rule does not apply to any of the following: (a) Trolley feeders located for convenience approximately at the level of the trolley-contact conductor, (b) Antennas located in the supply space or a communication space, in accordance with clearances required by Rule 235 and Rule 238, (c) Effectively grounded switch handles and equipment cases (such as fire alarm boxes, control boxes, communication terminals, meters, or similar equipment cases, which may be mounted at a lower level in accordance with Footnote 7 of Table 232-2), or (d) Communication cables located within a supply space in accordance with clearances required by Rule 235. 2. Special construction for railroad supply circuits of 600 V or less and carrying power not in excess of 5 kW associated with railroad communication circuits. Where all circuits are owned or operated by one party or where cooperative consideration determines that the circumstances warrant and the necessary coordinating methods are employed, single-phase ac or two-wire dc circuits carrying a voltage of 600 V or less between conductors, with transmitted power not in excess of 5 kW, where located on structures with communication circuits, may be installed in accordance with Footnote 1 of Table 235-5, under the following conditions: a. That such supply circuits are of covered conductor not smaller than AWG No. 8 medium hard-drawn copper or its equivalent in strength, and the construction otherwise conforms with the requirements for supply circuits of the same class. b. That the supply circuits be placed on the end and adjacent pins of the lowest through signal support arm and that a 750 mm (30 in) climbing space be maintained from the ground up to a point at least 600 mm (24 in) above the supply circuits. The supply circuits shall be rendered conspicuous by the use of insulators of different form or color from others on the pole line or by stenciling the voltage on each side of the support arm between the pins carrying each supply circuit, or by indicating the voltage by means of metal characters. c. That there shall be a vertical clearance of not less than 600 mm (2 ft) between the support arm carrying these supply circuits and the next support arm above. The other pins on the support arm carrying the supply circuits may be occupied by communication circuits used in the operation or control of signal system or other supply system if owned, operated, and maintained by the same company operating the supply circuits. d. That such supply circuits shall be equipped with arresters and fuses installed in the supply end of the circuit and where the signal circuit is ac, the protection shall be installed on the secondary side of the supply transformer. The arresters shall be designed so as to break down at approximately twice the voltage between the wires of the circuit, but the 85 Copyright © 2016 IEEE. All rights reserved. 220B2e Part 2: Safety Rules for Overhead Lines 221 breakdown voltage of the arrester need not be less than 1 kV. The fuses shall have a rating not in excess of approximately twice the maximum operating current of the circuit, but their rating need not be less than 10 A. The fuses likewise in all cases shall have a rating of at least 600 V, and where the supply transformer is a step-down transformer, shall be capable of opening the circuit successfully in the event the transformer primary voltage is impressed upon them. e. Such supply circuits in cable meeting the requirements of Rule 230C1, 230C2, or 230C3 may be installed below communication attachments, with not less than 400 mm (16 in) vertical separation between the supply cable and the lowest communication attachment. Communication circuits other than those used in connection with the operation of the sup- ply circuits shall not be carried in the same cable with such supply circuits. f. Where such supply conductors are carried below communication conductors, transformers and other apparatus associated therewith shall be attached only to the sides of the support arm in the space between and at no higher level than such supply wires. g. Lateral runs of such supply circuits carried in a position below the communication space shall be protected through the climbing space by wood molding or equivalent covering, or shall be carried in insulated multiple-conductor cable, and such lateral runs shall be placed on the underside of the support arm. 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) 1. At crossings or conflicts Where supply conductors of different voltage classifications cross each other or structure con- flict exists, the higher-voltage lines should be carried at the higher level. 2. On structures used only by supply conductors Where supply conductors of different voltage classifications are on the same structures, relative levels should be as follows: a. Where all circuits are owned by one utility, the conductors of higher voltage should be placed above those of lower voltage. b. Where different circuits are owned by separate utilities, the circuits of each utility may be grouped together, and one group of circuits may be placed above the other group provided that the circuits in each group are located so that those of higher voltage are at the higher levels and that horizontal and vertical clearances of not less than those required by Rule 235 are maintained between the nearest line conductors of the respective utilities. D. Identification of overhead conductors and cables All conductors and cables of electric supply and communication lines should, as far as is practical, be arranged to occupy uniform positions throughout, or shall be constructed, located, marked, numbered, or attached to distinctive insulators or crossarms, so as to facilitate identification by employees authorized to work thereon. This does not prohibit systematic transposition of conductors. E. Identification of equipment on supporting structures All equipment of electric supply and communication lines should be arranged to occupy uniform positions throughout or shall be constructed, located, marked, or numbered so as to facilitate identi- fication by employees authorized to work thereon. 221. Avoidance of conflict Two separate lines, either of which carries supply conductors, should be so separated from each other that neither line conflicts with the other. 86 Copyright © 2016 IEEE. All rights reserved. 222 Part 2: Safety Rules for Overhead Lines 224A2b EXCEPTION: If elimination of conflict is not practical, the conflicting line or lines should be separated as far as practical and shall be built to the grade of construction required by Section 24 for a conflicting line, or the two lines shall be combined on the same structures. 222. Joint use of structures Where the practice of joint use is mutually agreed upon by the affected utilities, facilities shall be subject to the appropriate grade of construction specified in Section 24. Joint use of structures should be considered for circuits along highways, roads, streets, and alleys. The choice between joint use of structures and separate lines shall be determined through cooperative consideration with other joint users of all the factors involved, including the character of circuits, worker safety, the total number and weight of conductors, tree conditions, number and location of branches and service drops, structure conflicts, availability of right-of-way, etc. 223. Communications protective requirements A. Where required Where communication apparatus is handled by other than qualified persons, it shall be protected by one or more of the means listed in Rule 223B if such apparatus is permanently connected to lines subject to any of the following: 1. Lightning 2. Contact with supply conductors whose voltage to ground exceeds 300 V 3. Transient rise in ground potential exceeding 300 V 4. Steady-state induced voltage of a hazardous level Where communication cables will be in the vicinity of supply stations where large ground currents may flow, the effect of these currents on communication circuits should be evaluated. NOTE: Additional information may be obtained from IEEE Std 487™-2007 [B34] and IEEE Std 1590™-2003 [B55]. B. Means of protection Where communication apparatus is required to be protected under Rule 223A, protective means ade- quate to withstand the voltage expected to be impressed shall be provided by insulation, protected where necessary by surge arresters used in conjunction with fusible elements. Severe conditions may require the use of additional devices such as auxiliary arresters, drainage coils, neutralizing transformers, or isolating devices. 224. Communication circuits located within the supply space and supply circuits located within the communication space A. Communication circuits located in the supply space 1. Communication circuits located in the supply space shall be installed and maintained only by personnel authorized and qualified to work in the supply space in accordance with the applicable rules of Sections 42 and 44. 2. Communication circuits located in the supply space shall meet the following clearance requirements, as applicable: a. Insulated communication cables supported by an effectively grounded messenger shall have the same clearances as neutrals meeting Rule 230E1 from communication circuits located in the communication space and from supply conductors located in the supply space. See Rules 235 and 238. b. Fiber-optic cables located in the supply space shall meet the requirements of Rule 230F. 87 Copyright © 2016 IEEE. All rights reserved. 224A2c Part 2: Safety Rules for Overhead Lines 224B2e c. Open-wire communication circuits permitted by other rules to be in the supply space shall have the same clearances from communication circuits located in the communication space and from other circuits located in the supply space as required by Rule 235 for ungrounded open supply conductors of 0 to 750 V. EXCEPTION: Service drops meeting Rules 224A3a and 224A3b may originate in the supply space on a line structure or in the span and terminate in the communication space on the building or struc- ture being served. 3. Communication circuits located in the supply space in one portion of the system may be located in the communication space in another portion of the system if the following requirements are met: a. Where the communication circuit is, at any point, located above an energized supply con- ductor or cable, the communication circuit shall be protected by fuseless surge arresters, drainage coils, or other suitable devices to limit the normal communication circuit voltage to 400 V or less to ground. NOTE: The grades of construction for communication conductors with inverted levels apply. b. Where the communication circuit is always located below the supply conductors, the com- munication protection shall meet the requirements of Rule 223. c. The transition(s) between the supply space and the communication space shall occur on a single structure; no transition shall occur between line structures. EXCEPTION: Service drops meeting Rules 224A3a and 224A3b may originate in the supply space on a line structure or in the span and terminate in the communication space on the building or struc- ture being served. d. The construction and protection shall be consistently followed throughout the extent of such section of the communications system. B. Supply circuits used exclusively in the operation of communication circuits Circuits used for supplying power solely to apparatus forming part of a communications system shall be installed as follows: 1. Open-wire circuits shall have the grades of construction, clearances, insulation, etc., prescribed elsewhere in these rules for supply or communication circuits of the voltage concerned. 2. Special circuits operating at voltages in excess of 90 V ac or 150 V dc and used for supplying power solely to communications equipment may be included in communication cables under the following conditions: a. Such cables shall have a conductive sheath or shield that is effectively grounded. b. All circuits in such cables shall be owned or operated by one party and shall be maintained only by qualified personnel. c. Supply circuits included in such cables shall be terminated at points accessible only to qualified personnel. d. Communication circuits brought out of such cables, if they do not terminate in a repeater station or terminal office, shall be protected or arranged so that in the event of failure within the cable, the voltage on the communication circuit will not exceed 400 V to ground. e. Terminal apparatus for the power supply shall be so arranged that the live parts are inaccessible when such supply circuits are energized. EXCEPTION: The requirements of Rule 224B2 do not apply to communication circuits where the transmitted power does not exceed 150 W. 88 Copyright © 2016 IEEE. All rights reserved. 225 Part 2: Safety Rules for Overhead Lines 225E 225. Electric railway construction A. Trolley-contact conductor fastenings All overhead trolley-contact conductors shall be supported and arranged so that the breaking of a single contact conductor fastening will not allow the trolley conductor live span wire, or current- carrying connection, to come within 3.0 m (10 ft) (measured vertically) from the ground, or from any platform accessible to the general public. Span-wire insulation for trolley-contact conductors shall comply with Rule 279B. B. High-voltage contact conductors Trolley-contact conductors energized at more than 750 V shall be suspended in such a way that, if broken at one point, the conductor will not come within 3.6 m (12 ft) (measured vertically) of the ground, or any platform accessible to the public. C. Third rails Third rails shall be protected by adequate guards composed of wood or other suitable insulating material. EXCEPTION: This rule does not apply where third rails are on fenced right-of-way. D. Prevention of loss of contact at railroad crossings at grade At crossings at grade with other railroads or other electrified railway systems, contact conductors shall be arranged as set forth in the following specifications 1, 2, 3, 4, and 5, following whichever apply: 1. Where the crossing span exceeds 30 m (100 ft), catenary construction shall be used for over- head trolley-contact conductors. 2. When pole trolleys, using either wheels or sliding shoes, are used: a. The trolley-contact conductor shall be provided with live trolley guards of suitable construction; or b. The trolley-contact conductor should be at a uniform height above its own track through- out the crossing span and the next adjoining spans. Where it is not practical to maintain a uniform height, the change in height shall be made in a gradual manner. EXCEPTION: Rule 225D2 does not apply where the crossing is protected by signals or interlocking. 3. When collectors of the pantograph type are used, the contact conductor and track through the crossing should be maintained in a condition where the rocking of pantograph-equipped cars or locomotives will not de-wire the pantograph. If this cannot be done, auxiliary contact conduc- tors shall be installed. Wire height shall conform with Rule 225D2. 4. Where two electrified tracks cross: a. When the trolley-contact conductors are energized from different supply circuits, or from different phases of the same circuit, the trolley-conductor crossover shall be designed to insulate both conductors from each other. The design shall not permit either trolley collec- tor to contact any conductor or part energized at a different voltage than at which it is designed to operate. b. Trolley-contact crossovers used to insulate trolley conductors of the same voltage but of different circuit sections shall be designed to limit the likelihood of both sections being simultaneously contacted by the trolley collector. 5. When third rail construction is used, and the length of the third rail gap at the crossings is such that a car or locomotive stopping on the crossing can lose propulsion power, the crossing shall be protected by signals or interlocking. E. Guards under bridges Trolley guards of suitable construction shall be provided where the trolley-contact conductor is so located that a trolley pole leaving the conductor can make simultaneous contact between it and the bridge structure. 89 Copyright © 2016 IEEE. All rights reserved. 230 Part 2: Safety Rules for Overhead Lines 230A3 Section 23. Clearances 230. General A. Application This section covers all clearances, including climbing spaces, involving overhead supply and communication lines. NOTE: The more than 70 years of historical development and specification of clearances in Rules 232, 233, and 234 were reviewed for consistency among themselves and with modern practice and were appropriately revised in both concept and content for the 1990 Edition. See Appendix A. 1. Permanent and temporary installations The clearances of Section 23 are required for permanent and temporary installations. 2. Emergency installations The clearances required in Section 23 may be decreased for emergency installations if the following conditions are met. NOTE: See Rule 14. a. Open supply conductors of 0 to 750 V and supply cables meeting Rule 230C; and commu- nication conductors and cables, guys, messengers, and neutral conductors meeting Rule 230E1 shall be suspended not less than 4.8 m (15.5 ft) above areas where trucks are expected, or 2.70 m (9 ft) above areas limited to pedestrians or restricted traffic only where vehicles are not expected during the emergency, unless Section 23 permits lesser clearances. For the purpose of this rule, trucks are defined as any vehicle exceeding 2.5 m (8 ft) in height. Areas not subject to truck traffic are areas where truck traffic is neither normally encountered nor reasonably anticipated or is otherwise limited. Spaces and ways subject to pedestrians or restricted traffic only are those areas where riders on horseback or other large animals, vehicles, or other mobile units exceeding 2.5 m (8 ft) in height are prohibited by regulation or permanent terrain configurations or are otherwise neither normally encountered nor reasonably anticipated or are otherwise limited. b. Vertical clearances of open supply conductors above 750 V shall be increased above the applicable value of Rule 230A2a as appropriate for the voltage involved and the given local conditions. c. Reductions in horizontal clearances permitted by this rule shall be in accordance with accepted good practice for the given local conditions during the term of the emergency. d. Supply and communication cables may be laid directly on grade if they are guarded or otherwise located so that they do not unduly obstruct pedestrian or vehicular traffic and are appropriately marked. Supply cables operating above 600 V shall meet either Rule 230C or 350B. See Rules 311C and 014A2. e. No clearance is specified for areas where access is limited to qualified personnel only. 3. Measurement of clearance and spacing Unless otherwise stated, all clearances shall be measured from surface to surface and all spacings shall be measured center to center. For clearance measurements, energized metallic hardware used to secure or support supply line conductors and communication equipment used to secure or support communication line conductors shall be considered a part of the line conductors. Metallic bases of potheads, surge arresters, and similar devices shall be considered a part of the supporting structure. 90 Copyright © 2016 IEEE. All rights reserved. 230A4 Part 2: Safety Rules for Overhead Lines 230B1 4. Rounding of calculation results Unless otherwise specified in a table or rule within Section 23, clearance specifications that require a calculation to determine the required clearance shall have the resultant of the calculation rounded up to the same level of decimal places as the basic value shown in the rule or table, regardless of the numbers of significant digits of individual values required to be used in the calculation. If a calculated clearance is allowed a reduction by footnotes or EXCEPTIONS, the resultant calculation shall be rounded up before the reduction is applied, and the resultant calculation after the reduction is applied shall also be rounded up. EXCEPTION 1: Resultants of calculations expressed in millimeters shall be rounded up to the next multiple of 25 mm (1 in). EXCEPTION 2: When determining a clearance at specified conditions based on field measurements, the resultant calculation shall be rounded down. Example: Rounding of calculated ground clearance at maximum sag Actual clearance aboveground was measured to be 5.69 m (18.67 ft) when the conductor was measured to be at 28 °C (82 °F). The sag at that conductor temperature was measured to be 0.66 m (2.15 ft). The measured sag, conductor temperature, and span length were used in sag and tension software to calculate the change in sag from the measured condition to the maximum sag produced by either ice loading or maximum conductor temperature. The change in sag from the measurement condition to the maximum sag condition was calculated to be 0.77 m (2.52 ft). Thus, the ground clearance when at maximum sag is calculated to be 5.69 m – 0.77 m = 4.92 m (18.67 ft – 2.52 ft = 16.15 ft). Since the clearances of Table 232-1 are specified in 0.1 m (0.1 ft) increments, the calculated clearance 4.92 m (16.15 ft) must be rounded down to the next lower 0.1 m (0.1 ft) 4.9 m (16.1 ft) and compared to the required clearance to determine if the Code requirements are met. For example, if this conductor was an effectively grounded supply neutral conductor meeting Rule 230E1, crossing a field, it would meet the 4.7 m (15.5 ft) required for a neutral over a field when at final sag that is required by Table 232-1, row 4, other lands. However, if the conductor were a primary voltage supply conductor of 7200 V to ground, the clearance would not meet the 5.6 m (18.5 ft) required at maximum sag by the same table and row for that voltage. B. Ice and wind loading for clearances 1. Four general degrees of loading due to weather conditions are recognized and are designated as clearance zones 1, 2, 3, and 4. Figure 230-1 shows the zones where these loadings apply. NOTE: The localities are classified in the different zones according to the relative simultaneous prevalence of the wind velocity and thickness of ice that accumulates on wires. Zone 3 is for places where little, if any, ice accumulates on wires. Zone 4 applies to warm islands located from latitude 25 degrees 91 Copyright © 2016 IEEE. All rights reserved. 230B2 Part 2: Safety Rules for Overhead Lines 230B5 south through 25 degrees north where mild temperatures exist at sea level, but icing may occur at altitudes above 2743 m (9000 ft) above sea level. See Appendix B. 2. Table 230-1 shows the radial thickness of ice to be used in calculating sags for clearance purposes. See applicable clearance rules in Section 23. 3. Ice and wind loads are specified in Rule 230B1. a. Where a cable is attached to a messenger, the specified loads shall be applied to both cable and messenger. b. In determining wind loads on a conductor or cable without ice covering, the assumed projected area shall be that of a smooth cylinder whose outside diameter is the same as that of the conductor or cable. The force coefficient (shape factor) for cylindrical surfaces is assumed to be 1.0. NOTE: Experience has shown that as the size of multiconductor cable decreases, the actual projected area decreases, but the roughness factor increases and offsets the reduction in projected area. c. An appropriate mathematical model shall be used to determine the wind and weight loads on ice-coated conductors and cables. In the absence of a model developed in accordance with Rule 230B5, the following mathematical model shall be used: (1) On a conductor, lashed cable, or multiple-conductor cable, the coating of ice shall be considered to be a hollow cylinder touching the outer strands of the conductor or the outer circumference of the lashed cable or multiple-conductor cable. (2) On bundled conductors, the coating of ice shall be considered as individual hollow cylinders around each subconductor. d. It is recognized that the effects of conductor stranding or of non-circular cross section may result in wind and ice loadings more or less than those calculated according to assumptions stated in Rules 230B3b and 230B3c. No reduction in these loadings is permitted unless testing or a qualified engineering study justifies a reduction. 4. Table 230-2 shows the radial thickness of ice, wind pressures, temperatures, and additive con- stants to be used in calculating inelastic deformation. The load components shall be determined as follows: a. Vertical load component The vertical load on a wire, conductor, or messenger shall be its own weight plus the weight of conductors, spacers, or equipment that it supports, ice covered where required by Rule 230B1 and Table 230-2. b. Horizontal load component The horizontal load shall be the horizontal wind pressure determined under Rule 230B1 and Table 230-2, applied at right angles to the direction of the line using the projected area of the conductor or messenger and conductors, spacers, or equipment that it supports, ice covered where required by Rule 230B1 and Table 230-2. NOTE: The projected area of the conductor or messenger is equal to the diameter of the conductor or messenger, plus ice if appropriate, multiplied by the span length. See Rule 251A2 for force coefficient values of different surface shapes. c. Total load The total load on each wire, conductor, or messenger shall be the resultant of components in a) and b) above, calculated at the applicable temperature in Table 230-2, plus the corresponding additive constant in Table 230-2. 5. Final sag calculations shall include the effects of inelastic deformation due to both (a) initial and subsequent combined ice and wind loading, and (b) long-term material deformation (creep). See applicable sag definitions. Ice is assumed to weigh 913 kg/m3 (57 lb/ft3). 92 Copyright © 2016 IEEE. All rights reserved. 230C Part 2: Safety Rules for Overhead Lines 230F1e C. Supply cables For clearance purposes, supply cables, including splices and taps, conforming to any of the following requirements are permitted lesser clearances than open conductors of the same voltage. Cables should be capable of withstanding tests applied in accordance with an applicable standard. 1. Cables that are supported on or cabled together with an effectively grounded bare messenger or neutral, or with multiple concentric neutral conductors, where any associated neutral conductor(s) meet(s) the requirements of Rule 230E1 and where the cables also meet one of the following: a. Cables of any voltage having an effectively grounded continuous metal sheath or shield b. Cables designed to operate on a multi-grounded system at 22 kV or less and having semiconducting insulation shielding in combination with suitable metallic drainage 2. Cables of any voltage, not included in Rule 230C1, covered with a continuous auxiliary semi- conducting shield in combination with suitable metallic drainage and supported on and cabled together with an effectively grounded bare messenger. 3. Insulated, nonshielded cable operated at not over 5 kV phase to phase, or 2.9 kV phase to ground, supported on and cabled together with an effectively grounded bare messenger or neutral. D. Covered conductors Covered conductors shall be considered bare conductors for all clearance requirements except that clearance between conductors of the same or different circuits, including grounded conductors, may be reduced below the requirements for open conductors when the conductors are owned, operated, or maintained by the same party and when the conductor covering provides sufficient dielectric strength to limit the likelihood of a short circuit in case of momentary contact between conductors or between conductors and the grounded conductor. Intermediate spacers may be used to maintain conductor clearance and to provide support. E. Neutral conductors 1. Neutral conductors that are effectively grounded throughout their length and associated with circuits of 0 to 22 kV to ground may have the same clearances as guys and messengers. 2. All other neutral conductors of supply circuits shall have the same clearances as the phase con- ductors of the circuit with which they are associated. F. Fiber-optic cable 1. Fiber-optic—supply cable a. Cable defined as “fiber-optic—supply” supported on a messenger that is effectively grounded throughout its length shall have the same clearance from communications facili- ties as required for a neutral conductor meeting Rule 230E1. b. Cable defined as “fiber-optic—supply” that is entirely dielectric, or supported on a messenger that is entirely dielectric, shall have the same clearance from communications facilities as required for a neutral conductor meeting Rule 230E1. NOTE: A fiber-optic cable that is entirely dielectric is one such as ADSS (All Dielectric Self- Supporting) cable. c. Fiber-optic—supply cables supported on or within messengers not meeting Rule 230F1a or 230F1b shall have the same clearances from communications facilities required for such messengers. d. Fiber-optic—supply cables supported on or within a conductor(s), or containing a conductor(s) or cable sheath(s) within the fiber-optic cable assembly shall have the same clearances from communications facilities required for such conductors. Such clearance shall be not less than that required under Rule 230F1a, 230F1b, or 230F1c, as applicable. e. Fiber-optic—supply cables meeting Rule 224A3 are considered to be communication cables when located in the communication space. 93 Copyright © 2016 IEEE. All rights reserved. 230F2 Part 2: Safety Rules for Overhead Lines F-230-1 2. Fiber-optic—communication cable Cable defined as “fiber-optic—communication” shall have the same clearance from supply facilities as required for a communication messenger. G. Alternating- and direct-current circuits The rules of this section are applicable to both ac and dc circuits. For dc circuits, the clearance requirements shall be the same as those for ac circuits having the same crest voltage to ground. NOTE: Although the corresponding crest voltage for a common sinusoidal ac circuit may be calculated by multiplying its rms value by 1.414 (square root of 2), this may not be appropriate for other type ac circuits. An example of the latter is represented by non-sinusoidal power supplies such as used in some coaxial cable type communication systems. H. Constant-current circuits The clearances for constant-current circuits (such as series lighting circuits) shall be determined on the basis of their normal full-load voltage. I. Maintenance of clearances and spacings The clearances and spacing required shall be maintained at the values and under the conditions specified in Section 23 of the applicable edition. The clearances of Section 23 are not intended to be maintained during the course of or as a result of abnormal events such as, but not limited to, actions of others or weather events in excess of those described under Section 23. Utilities are responsible for correcting known non-compliant conditions in accordance with Rule 214A4 or Rule 214A5 as applicable. NOTE: See Rule 13 to determine the applicable edition. Figure 230-1—Clearance zone map of the United States Clearance Zone 4 includes American Samoa, Guam, Hawaii, Puerto Rico, Virgin Islands, and other warm islands located from 0 to 25 degrees latitude, north or south. 94 Copyright © 2016 IEEE. All rights reserved. T-230-1 Part 2: Safety Rules for Overhead Lines T-230-2 Table 230-1—Ice thickness for purposes of calculating clearances Clearance zone (for use with Rules 232, 233, 234, and 235) Zone 4: Warm islands  Zone 1 Zone 2 Zone 3 see see see Altitudes Altitudes Figure 230-1 Figure 230-1 Figure 230-1 sea level to above 2743 m 2743 m (9000 ft) (9000 ft) Radial thickness of ice (mm) 12.5 6.5 0 0 6.5 (in) 0.50 0.25 0 0 0.25  Warm islands are those located from latitude 25 degrees south through 25 degrees north and include American Samoa (14°S), Guam (13°N), Hawaii (22°N), Puerto Rico (18°N), and Virgin Islands (18°N). Table 230-2—Ice, wind pressures, temperatures, and additive constants for purposes of calculating final inelastic deformation Clearance zone (for use with Rules 232, 233, 234, and 235) Zone 4: Warm islands  Zone 1 Zone 2 Zone 3 Heavy ice: Moderate ice: Little or no Altitudes Altitudes see see ice: see sea level to above Figure 230-1 Figure 230-1 Figure 230-1 2743 m 2743 m (9000 ft) (9000 ft) Radial thickness of ice (mm) 12.5 6.5 0 0 6.5 (in) 0.50 0.25 0 0 0.25 Horizontal wind pressure (Pa) 190 190 430 430 190 (lb/ft2) 4 4 9 9 4 Temperature (C) –20 –10 –1 +10 –10 (F) 0 +15 +30 +50 +15 Constant to be added to the resultant  (N/m) 4.40 2.90 0.73 0.73 2.90 (lb/ft) 0.30 0.20 0.05 0.05 0.20  Warm islands are those located from latitude 25 degrees south through 25 degrees north and include American Samoa (14°S), Guam (13°N), Hawaii (22°N), Puerto Rico (18°N), and Virgin Islands (18°N).  For cable arrangements supported by a messenger using spacers or rings and where each conductor or cable is sep- arately loaded with ice and wind as described in Rule 230B3c(2) [as opposed to being analyzed with the ice and wind applied to a hollow cylinder touching the outer strands of the conductors as described in Rule 230B3c(1)], the constant specified here shall be added to the resultant load of each component conductor and the messenger. 95 Copyright © 2016 IEEE. All rights reserved. 231 Part 2: Safety Rules for Overhead Lines 232A1 231. Clearances of supporting structures from other objects Supporting structures, support arms, anchor guys, and equipment attached thereto, and braces shall have the following clearances from other objects. The clearance shall be measured between the nearest parts of the objects concerned. A. From fire hydrants Not less than 1.2 m (4 ft). EXCEPTION 1: Where conditions do not permit, a clearance of not less than 900 mm (3 ft) is allowed. EXCEPTION 2: Clearances in Rule 231A may be reduced by agreement with the local fire authority and the pole owner. B. From streets, roads, and highways 1. Where there are curbs: supporting structures, support arms, anchor guys, or equipment attached thereto, up to 4.6 m (15 ft) above the road surface shall be located a sufficient distance behind the curb to avoid contact by ordinary vehicles using and located on the traveled way. 2. Where there are no curbs, supporting structures should be located a sufficient distance from the roadway to avoid contact by ordinary vehicles using and located on the traveled way. 3. Location of overhead utility installations on roads, streets, or highways with narrow rights-of- way or closely abutting improvements are special cases that must be resolved in a manner consistent with the prevailing limitations and conditions. 4. Where a governmental authority exercising jurisdiction over structure location has issued a per- mit for, or otherwise approved, specific locations for supporting structures, that permit or approval shall govern. C. From railroad tracks Where railroad tracks are parallel to or crossed by overhead lines, all portions of the supporting structures, support arms, anchor guys, and equipment attached thereto less than 6.7 m (22 ft) above the nearest track rail shall have horizontal clearances not less than the values required by Rule 231C1 or 231C2 for the situation concerned. NOTE: See Rule 234I. 1. Not less than 3.6 m (12 ft) from the nearest track rail. EXCEPTION 1: A clearance of not less than 2.13 m (7 ft) may be allowed where the supporting structure is not the controlling obstruction, provided sufficient space for a driveway is left where cars are loaded or unloaded. EXCEPTION 2: Supports for overhead trolley-contact conductors may be located as near their own track rail as conditions require. If very close, however, permanent screens on cars will be necessary to protect passengers. EXCEPTION 3: Where necessary to provide safe operating conditions that require an uninterrupted view of signals, signs, etc., along tracks, the parties concerned shall cooperate in locating structures to provide the necessary clearance. EXCEPTION 4: At industrial sidings, a clearance of not less than 2.13 m (7 ft) shall be permitted, provided sufficient space is left where cars can be loaded or unloaded. 2. The clearances of Rule 231C1 may be reduced by agreement with the railroad(s). 232. Vertical clearances of wires, conductors, cables, and equipment aboveground, roadway, rail, or water surfaces A. Application The vertical clearances specified in Rule 232B1 apply under the following conductor temperature and loading conditions, whichever produces the largest final sag: 1. 50 °C (120 °F), no wind displacement 96 Copyright © 2016 IEEE. All rights reserved. 232A2 Part 2: Safety Rules for Overhead Lines 232C1b 2. The maximum conductor temperature for which the line is designed to operate, if greater than 50 °C (120 °F), with no wind displacement 3. 0 °C (32 °F), no wind displacement, with radial thickness of ice, if any, specified in Table 230-1 for the zone concerned EXCEPTION: The conductor temperature and loading condition for trolley and electrified railroad contact conductors shall be 15 °C (60 °F), no wind displacement, final sag, or initial sag in cases where these facilities are maintained approximately at initial sags. NOTE: The phase and neutral conductors of a supply line are normally considered separately when determining the sag of each due to temperature rise. B. Clearance of wires, conductors, cables, equipment, and support arms mounted on supporting structures NOTE: Neither horizontal nor diagonal clearances are specified in this rule. As a result, Rule 012C requires good practice for the given local conditions. 1. Clearance to wires, conductors, and cables The vertical clearance of wires, conductors, and cables aboveground in generally accessible places, roadway, rail, or water surfaces, shall be not less than that shown in Table 230-1. 2. Clearance to unguarded rigid live parts of equipment The vertical clearance above ground, roadway, or water surfaces for unguarded rigid live parts such as potheads, transformer bushings, surge arresters, and short lengths of supply conductors connected thereto, which are not subject to variation in sag, shall be not less than that shown in Table 232-2. For clearances of drip loops of service drops, see Table 230-1. 3. Clearance to support arms, switch handles, and equipment cases The vertical clearance of switch handles, equipment cases, support arms, platforms, and braces that extend beyond the surface of the structure shall be not less than that shown in Table 232-2. These clearances do not apply to internal structural braces for latticed towers, X-braces between poles, and pole-type push braces. 4. Street and area lighting a. The vertical clearance of street and area lighting luminaires shall be not less than that shown in Table 232-2. For this purpose, grounded luminaire cases and brackets shall be considered as effectively grounded equipment cases; ungrounded luminaire cases and brackets shall be considered as a rigid live part of the voltage contained. EXCEPTION: This rule does not apply to post-top mounted luminaires with effectively grounded or entirely dielectric cases. b. Insulators, as specified in Rule 279A, should be inserted at least 2.45 m (8 ft) from the ground in metallic suspension ropes or chains supporting lighting units of series circuits. C. Additional clearances for wires, conductors, cables, and unguarded rigid live parts of equipment Greater clearances than specified by Rule 232B shall be provided where required by Rule 232C1. 1. Voltages exceeding 22 kV a. For voltages between 22 and 470 kV, the clearance specified in Rule 232B1 (Table 232-1) or Rule 232B2 (Table 232-2) shall be increased at the rate of 10 mm (0.4 in) per kilovolt in excess of 22 kV. For voltages exceeding 470 kV, the clearance shall be determined by the method given in Rule 232D. All clearances for lines over 50 kV shall be based on the maximum operating voltage. EXCEPTION: For voltages exceeding 98 kV ac to ground or 139 kV dc to ground, clearances less than those required above are permitted for systems with known maximum switching-surge factors (see Rule 232D). b. For voltages exceeding 50 kV, the additional clearance specified in Rule 232C1a shall be increased 3% for each 300 m (1000 ft) in excess of 1000 m (3300 ft) above mean sea level. 97 Copyright © 2016 IEEE. All rights reserved. 232C1c Part 2: Safety Rules for Overhead Lines 232D3c c. For voltages exceeding 98 kV ac to ground, either the clearances shall be increased or the electric field, or the effects thereof, shall be reduced by other means as required to limit the steady-state current due to electrostatic effects to 5 mA rms if the largest anticipated truck, vehicle, or equipment under the line were short-circuited to ground. The size of the anticipated truck, vehicle, or equipment used to determine these clearances may be less than but need not be greater than that limited by federal, state, or local regulations governing the area under the line. For this determination, the conductors shall be at a final sag at 50 °C (120 °F). D. Alternate clearances for voltages exceeding 98 kV ac to ground or 139 kV dc to ground The clearances specified in Rules 232B and 232C may be reduced for circuits with known switching-surge factors, but shall be not less than the alternate clearance, which is computed by adding the reference height from Rule 232D2 to the electrical component of clearance from Rule 232D3. 1. Sag conditions of line conductors The vertical clearance shall be maintained under the conductor temperature and loading condition given in Rule 232A. 2. Reference heights The reference height shall be selected from Table 232-3. 3. Electrical component of clearance a. The electrical component (D) shall be computed using the following equations. Selected values of D are listed in Table 232-4. V   PU   a 1.667 D = 1.00 ---------------------------- bc (m) 500K V   PU   a 1.667 D = 3.28 ---------------------------- bc (ft) 500K where V = maximum ac crest operating voltage to ground or maximum dc operating voltage to ground in kilovolts PU = maximum switching-surge factor expressed in per-unit peak voltage to ground and defined as a switching-surge level for circuit breakers corresponding to 98% probability that the maximum switching surge generated per breaker operation does not exceed this surge level, or the maximum anticipated switching-surge level generated by other means, whichever is greater a = 1.15, the allowance for three standard deviations b = 1.03, the allowance for nonstandard atmospheric conditions c = 1.2, the margin of safety K = 1.15, the configuration factor for conductor-to-plane gap b. The value of D shall be increased 3% for each 300 m (1000 ft) in excess of 450 m (1500 ft) above mean sea level. c. For voltages exceeding 98 kV ac to ground, either the clearances shall be increased or the electric field, or the effects thereof, shall be reduced by other means as required to limit the steady state current due to electrostatic effects to 5 mA, rms, if the largest anticipated truck, vehicle, or equipment under the line were short-circuited to ground. The size of the anticipated truck, vehicle, or equipment used to determine these clearances may be less than but need not be greater than that limited by federal, state, or local regulations 98 Copyright © 2016 IEEE. All rights reserved. 232D4 Part 2: Safety Rules for Overhead Lines T-232-1(m) governing the area under the line. For this determination, the conductors shall be at a final sag at 50 °C (120 °F). 4. Limit The alternate clearance shall be not less than the clearance given in Table 232-1 or Table 232-2 computed for 98 kV ac to ground in accordance with Rule 232C. m Table 232-1— Vertical clearance of wires, conductors, and cables above ground, roadway, rail, or water surfaces (Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent breaker operations. See the definitions section for voltages of other systems. See Rules 232A, 232B1, 232C1a, and 232D4.) Insulated Supply Trolley and communication cables over electrified railroad conductors and 750 V contact conductors cable; and associated span messengers; meeting Open Rule 230C2 or messenger overhead shield/ supply surge-protection or 230C3; conductors, wires  Noninsulated wires; open supply over 750 V effectively communica- to 22 kV; conductors, grounded guys; tion unground- 0 to ungrounded conductors; ed portions Nature of surface 750 V ; portions of guys supply cables of guys underneath wires, ungrounded meeting Rules of 0 to 750 V meeting conductors, or cables 215C2 and portions of Rules meeting Rule 0 to Over 279A1 exposed 230C2 or guys 215C2 and 750 V to 750 V to 0 to 230C3 meeting 279A1 22 kV 300 V   ; exposed to to (m) Rules 215C2 to neutral 750 V to ground ground and 279A1 conductors exposed to 22 kV (m) (m) meeting Rule over 300 V (m) 230E1; supply cables meeting to Rule 230C1 750 V  (m) (m) Where wires, conductors, or cables cross over or overhang 1. Track rails of railroads 7.2 7.3 7.5 8.1 6.7  6.7  (except electrified railroads using overhead trolley conductors)   2. Roads, streets, and other 4.7 4.9 5.0 5.6 5.5  6.1  areas subject to truck traffic  3. Driveways, parking lots, 4.7   4.9   5.0  5.6 5.5  6.1  and alleys  4. Other areas traversed by 4.7 4.9 5.0 5.6 — — vehicles, such as cultivated, grazing, forest, and orchard lands, industrial sites, commercial sites, etc.  5. Spaces and ways subject 2.9 3.6  3.8  4.4 4.9 5.5 to pedestrians or restricted traffic only  99 Copyright © 2016 IEEE. All rights reserved. T-232-1(m) Part 2: Safety Rules for Overhead Lines T-232-1(m) m Table 232-1— (continued) Vertical clearance of wires, conductors, and cables above ground, roadway, rail, or water surfaces (Voltages are phase to ground for effectively grounded circuits and those other circuits where all ground faults are cleared by promptly de-energizing the faulted section, both initially and following subsequent breaker operations. See the definitions section for voltages of other systems. See Rules 232A, 232B1, 232C1a, and 232D4.) Insulated Supply Trolley and communication cables over electrified railroad conductors and 750 V contact conductors cable; and associated span messengers; meeting Open Rule 230C2 or messenger overhead shield/ supply surge-protection or 230C3; conductors, wires  Noninsulated open supply wires; over 750 V effectively communica- conductors, to 22 kV; grounded guys; tion 0 to unground- ungrounded conductors; ed portions Nature of surface 750 V ; portions of guys supply cables of guys underneath wires, meeting Rules ungrounded meeting of 0 to 750 V conductors, or cables 215C2 and portions of Rules Over meeting Rule 0 to 279A1 exposed 230C2 or guys 215C2 and 750 V to to 0 to 279A1 750 V 230C3 meeting 22 kV 300 V   ; exposed to to to (m) Rules 215C2 ground neutral and 279A1 750 V to ground conductors exposed to 22 kV (m) (m) meeting Rule over 300 V (m) 230E1; supply cables meeting to Rule 230C1 750 V  (m) (m) 6. Water areas not suitable 4.0 4.4 4.6 5.2 — — for sailboating or where sailboating is prohibited  7. Water areas suitable for sailboating including lakes, ponds, reservoirs, tidal waters, rivers, streams, and canals with an unobstructed surface area of      a. Less than 0.08 km2 5.3 5.5 5.6 6.2 — — b. Over 0.08 to 0.8 km2 7.8 7.9 8.1 8.7 — — c. Over 0.8 to 8 km2 9.6 9.8 9.9 10.5 — — 2 d. Over 8 km 11.4 11.6 11.7 12.3 — — 8. Established boat ramps and associated rigging Clearance aboveground shall be 1.5 m greater than in 7 above, areas; areas posted with for the type of water areas served by the launching sites sign(s) for rigging or launching sail boats Where wires, conductors, or cables run along and within the limits of highways or other road rights-of-way but do not overhang the roadway 9. Roads, streets, or alleys 4.7  4.9 5.0 5.6 5.5  6.1  10. Roads where it is unlikely 4.1   4.3  4.4  5.0 5.5  6.1  that vehicles will be crossing under the line NOTE: The clearance values shown in this table are computed by adding the applicable Mechanical and Electrical (M & E) value of Table A-1 to the applicable Reference Component of Table A-2a of Appendix A. 100 Copyright © 2016 IEEE. All rights reserved. T-232-1(m) Part 2: Safety Rules for Overhead Lines T-232-1(m) Where subways, tunnels, or bridges require it, less clearance above ground or rails than required by Table 232-1 may be used locally. The trolley and electrified railroad contact conductor should be graded gradually from the regular construction down to the reduced elevation. For wires, conductors, or cables crossing over mine, logging, and similar railways that handle only cars lower than standard freight cars, the clearance may be reduced by an amount equal to the difference in height between the highest loaded car handled and 6.1 m, but the clearance shall not be reduced below that required for street crossings. Does not include neutral conductors meeting Rule 230E1. In communities where 6.4 m has been established, this clearance may be continued if carefully maintained. The elevation of the contact conductor should be the same in the crossing and next adjacent spans. (See Rule 225D2 for conditions that must be met where uniform height above rail is impractical.) In communities where 4.9 m has been established for trolley and electrified railroad contact conductors 0 to 750 V to ground, or 5.5 m for trolley and electrified railroad contact conductors exceeding 750 V, or where local conditions make it impractical to obtain in the clearance given in the table, these reduced clearances may be used if carefully maintained. These clearance values also apply to guy insulators. Where vehicles exceeding 2.45 m in height are not normally encountered nor reasonably anticipated, service drop(s) clearances over residential driveways only may be reduced to the following: (m) (a) Insulated supply service drops limited to 300 V to ground 3.8 (b) Insulated drip loops of supply service drops limited to 300 V to ground 3.2 (c) Supply service drops limited to 150 V to ground and meeting Rule 230C1 or 230C3 3.6 (d) Drip loops only of service drops limited to 150 V to ground and meeting Rule 230C1 or 230C3 3.0 (e) Insulated communication service drops 3.5 These clearance values for service drops to residential buildings only may be reduced to the following: (m) (a) Insulated supply service drops limited to 300 V to ground 3.2 (b) Insulated drip loops of supply service drops limited to 300 V to ground 3.2 (c) Supply service drops limited to 150 V to ground and meeting Rule 230C1 or 230C3 3.0 (d) Drip loops only of supply service drops limited to 150 V to ground and meeting Rule 230C1 or 230C3 3.0 Spaces and ways subject to pedestrians or restricted traffic only are those areas where riders on horses or other large animals, vehicles, or other mobile units exceeding a total height of 2.45 m, are prohibited by regulation or permanent terrain configurations, or are otherwise not normally encountered nor reasonably anticipated. Where a supply or communication line along a road is located relative to fences, ditches, embankments, or other terrain features so that the ground under the line would not be expected to be traveled except by pedestrians, the clearances may be reduced to the following values: (m) (a) Insulated communication conductor and communication cables 2.9 (b) Conductors of other communication circuits 2.9 (c) Supply cables of any voltage meeting Rule 230C1 and neutral conductors meeting Rule 230E1 2.9 (d) Insulated supply conductors limited to 300 V to ground 3.8 (e) Insulated supply cables limited to 150 V to ground meeting Rule 230C2 or 230C3 3.1 (f) Effectively grounded guys, insulated guys meeting Rules 279A1 and 215C2 exposed to 0 to 300 V 2.9 No clearance from ground is required for anchor guys not crossing tracks, rails, streets, driveways, roads, or pathways. This clearance may be reduced to 4.0 m for communication conductors and guys. Where this construction crosses over or runs along (a) alleys, non-residential driveways, or parking lots not subject to truck traffic, or (b) residential driveways, this clearance may be reduced to 4.6 m. The portion(s) of span guys between guy insulators and the portion(s) of anchor guys above guy insulators that are not effectively grounded shall have clearances based on the highest voltage to which they may be exposed due to a slack conductor or guy. The portion of anchor guys below the lowest insulator meeting Rules 279A1 and 215C2a may have the same clear- ance as effectively grounded guys. Adjacent to tunnels and overhead bridges that restrict the height of loaded rail cars to less than 6.1 m, these clearances may be reduced by the difference between the highest loaded rail car handled and 6.1 m, if mutually agreed to by the parties at interest. For controlled impoundments, the surface area and corresponding clearances shall be based upon the design high- water level. For uncontrolled water flow areas, the surface area shall be that enclosed by its annual high-water mark. Clearances shall be based on the normal flood level; if available, the 10-year flood level may be assumed as the normal flood level. 101 Copyright © 2016 IEEE. All rights reserved. T-232-1(m) Part 2: Safety Rules for Overhead Lines T-232-1(m) The clearance over rivers, streams, and canals shall be based upon the largest surface area of any 1.6 km long