go 95 rule 77.6

Detailed Construction Requirements for Trolley and Electric Railway
Contact and Feeder Conductors and Their Supporting Messengers,
Span Wires, Etc. (Class T Circuits)

77.6 Requirements for Sectionalizing Insulators

Span wires, backbones, messengers, etc., shall be sectionalized by means of insulators placed in them in accordance with the following rules.

Insulators used in the sectionalizing of span wires, backbones and messengers shall conform to the specifications for guy insulators as given in Rule 56.8 based on the voltage of the trolley contact conductor.

(1) Supporting One Contact Conductor: One insulator (preferably of the interlocking strain type) shall be placed in the span wire between 4 feet and 5 feet (measured along the span wire) from each hanger or point of support of the trolley contact conductor and its appurtenances which have electrical contact therewith. Where the angle between the span wire and contact conductor is so small that the insulator will interfere with the movement of the current collecting device, such insulator may be installed more than 5 feet (measured along the span wire) from the contact conductor, but shall be not more than 4 feet in a perpendicular direction from the contact conductor (see Appendix G, Figs. 68 and 69 ).

A second insulator (preferably of the interlocking strain type) shall be placed in the span wire not less than 6 feet and not more than 9 feet from the pole or structure.

The separation between the first and second insulators shall be at least 4 feet wherever practicable but where the distance between the pole or structure and the trolley contact conductor is less than 14 feet the second insulator shall be not less than 15 inches from the surface of the pole or structure and outside of the climbing and work spaces.

Where the span wire is attached to a building, the second insulator shall be not less than 3 feet from the building.

Where the support is a wood pole and all facilities supported thereon are of one ownership and are operated and maintained by the same crews of workmen, the second insulator may be omitted.

(2) Supporting Two or More Contact Conductors of Same Polarity: Span wires supporting two or more contact conductors of the same polarity shall be sectionalized in accordance with Rule 77.6–A1 , above. If the contact conductors are more than 18 feet apart, an insulator shall be placed in the section of the span wire between the contact conductors at a point between 4 feet and 5 feet from each contact conductor hanger or support. Where the distance between contact conductors is less than 18 feet this provision does not apply.

(3) Supporting Contact Conductors of Opposite Polarity: Span wires supporting contact conductors of opposite polarity shall be sectionalized in accordance with the provisions of Rule 77.6–A1 . For this purpose each pair of positive and negative contact conductors shall be treated as a single conductor, the measurement being made to the nearest contact conductor of the pair.

A span wire which supports trolley contact conductors of opposite polarity shall have an insulator placed in between the hangers of such opposite polarity conductors unless the hangers have a dry flashover insulating value of 6,000 volts or more.

Where contact conductors are more than 18 feet apart an insulator shall be placed in the section of the span wire between such contact conductors at a point between 4 feet and 5 feet from each contact conductor hanger or support.

(4) Feeder Cables Used as Span Wires: One insulator (preferably of the interlocking strain type) shall be placed in such a span wire at a distance of not less than 15 inches from the surface of the pole supporting the feeder (except where only Class T circuits of the same polarity are installed on the pole as specified in Rule 74.4–D ) and outside of the climbing and working spaces on such pole.

A second insulator (preferably of the interlocking strain type)shall be placed at the point where the feeder cable terminates, which point shall be not less than 1 foot nor more than 5 feet beyond the last trolley contact conductor to which it is electrically connected.

A third insulator (preferably of the interlocking strain type)shall be placed in the remaining section of the span wire at a distance of not less than 6 feet and not more than 9 feet (measured along the span wire) from the opposite pole or structure (see Appendix G, Figure 71 ).

In catenary construction, the point at which the second insulator is placed shall be not less than 1 foot plus the distance between the messenger and contact conductor, nor more than 5 feet, beyond the last trolley contact conductor to which the feeder cable is electrically connected.

(5) Feeder Cables Used as Auxiliary Span Wires: Where the feeder cable is used as an auxiliary span wire, it shall be installed and maintained at a distance of not less than 18 inches above the span wire, or it may be attached to the span wire as provided in Rule 74.4–G3 . Auxiliary feeder cable spans shall be sectionalized in accordance with the provisions of Rule 77.6–A4 above (see Appendix G, Figure 67 ). In this type of construction the attachment of the feeder to the trolley contact conductor shall preferably be made on the side of the contact conductor opposite approaching traffic (see Appendix G, Figure 70) .

(6) Feeder Cables Crossing Poles: Where a feeder cable crosses the pole laterally, it shall not impair the climbing or working spaces and it is recommended that the cable be installed under a crossarm in fiber conduit or other suitable protective covering (see Rule 54.6–C ).

(1) Backbones Supported on Crossarms: A backbone which is supported by insulators on crossarms, pole brackets or trolley brackets shall be treated as a Class T line conductor except in that section between the last such support and its dead–end attachment where it shall be sectionalized by means of an insulator placed not less than 6 feet and not more than 9 feet from each support (see Appendix G, Figure 72 ).

(2) Backbone Attached to Poles: A backbone run between and attached directly to poles shall have insulators placed in it not less than 6 feet and not more than 9 feet (measured along the line of the backbone) from the points of attachment to the poles (see Appendix G, Figure 73 ).

(3) Pull–offs: Each pull–off from the contact conductor to that section of the backbone between the insulators specified in Rule 77.6–B2, above, shall have an insulator placed in it at a distance between 4 and 5 feet from the nearest contact conductor; or if this is not practicable, the insulator shall be installed as far as possible from the contact conductor. Any pull–off from the contact conductor to a point between the supporting pole and the backbone insulator shall have two insulators installed in it and the insulator nearest the pole or the backbone shall be not less than 15 inches from the center line of pole and shall be outside the climbing and working spaces (see Appendix G, Figure 73).

C. Brackets or Bracket Arms

In bracket construction span wires which support, or are attached to other span wires which support, trolley contact conductors or appurtenances in electrical contact therewith shall be sectionalized as follows:

(1) General: An insulator shall be inserted in the span wire between the suspension of the trolley contact conductor and each point of support of the span wire, such insulators to be not less than 12 inches from the nearest trolley contact conductor (see Appendix G, Figs. 74 and 75 ).

Where the span wire supports contact conductors of opposite polarity an additional insulator shall be inserted between the hangers of such opposite polarity conductors unless the hangers have a dry flashover insulating value of 6,000 volts or more.

(2) EXCEPTIONS: Where the brackets are supported on wood poles which support only conductors of one ownership, the insulators between the hangers and points of span wire support may be omitted (see Appendix G, Figs. 76 and 77 ).

Where brackets and their lift spans are suitably insulated along their length (perpendicular to the poles) and from the span wire, that part of Rule 77.6–C1 which prescribes an insulator between the contact conductor suspension and the point of bracket support need not apply (see Appendix G, Figure 78 )

Insulators placed in metal brackets and lift spans shall be not less than 12 inches radially from the trolley contact conductor (see Appendix G, Figure 79 ).

(3) Feeder Conductors: Feeder wires used as bracket span wires shall be sectionalized as follows:

One insulator (preferably of the interlocking strain type) shall be placed in the span wire at a distance of not less than 15 inches from the surface of poles (except where only Class T circuits of the same polarity are installed on the pole as specified in Rule 74.4–D ) and outside the climbing and working spaces. A second insulator shall be placed at the point where the feeder terminates (see Appendix G, Figure 80 ).

On high speed lines it is recommended that in lieu of this type of construction the bracket span be installed as specified in Rule 77.6–C1 and the feeder span be installed as a bracket guy or lift span. In this case, one insulator shall be placed in the lift span so that the horizontal distance between the insulator and the surface of the supporting pole or structure shall be not less than 15 inches, and a second insulator shall be placed along the line of this lift span adjacent to the point of attachment to the bracket.

D. Messengers

When an extended messenger is treated as a guy, the requirements specified for guys shall be met.