Detailed Construction Requirements for Trolley
and Electric Railway
Contact and Feeder Conductors and Their Supporting Messengers,
Span Wires, Etc. (Class T Circuits)
Except where specifically designated, Class T conductors take clearances specified for supply lines of like voltage.
A. Above Ground
The minimum vertical clearances above ground for Class T conductors shall be those specified in Rule 37, Table 1. References to rules modifying the tabulated values for supply conductors and Class T conductors and Class T conductors of equal voltage are given in Notes Table 1.
B. Above Railways
(1) Tracks: The vertical clearance of 19 feet above rails for trolley contact, feeder and span wires of Table 1, Case 2, Column C, applies only to those railways which do not transport or propose to transport freight cars. This value shall be increased to 22 feet where the railway involved does transport or proposes to transport freight cars.
(2) Crossings: Unless electric railroad systems are protected by interlocking plant at grade crossings with interurban or other heavy or high speed railway systems, the trolley contact conductors shall be at the same elevation above their own tracks throughout the crossing and next adjoining spans and, in addition thereto, catenary construction
C. Between Conductors
The minimum clearances specified in Case 2, Column D; Case 4, Column B; Case 5, Column E and Case 15, Column D of Table 2 are not required between Class T conductors of the same potential and system.
The minimum clearance of 24 inches specified in Table 2, Case 9, Column D, is not required between trolley feeders of the same system provided, however, that the clearance shall not be less than 12 inches.
The minimum clearance of 48 inches specified in Table 2, Case 2, Column D and Case 4, Column B, is not required in double trolley construction between feeder auxiliary span cables or equalizer cables and trolley contact conductors of opposite polarity provided, however, that the clearance shall be not less than 18 inches or, where the feeder cables are attached to span wires in accordance with Rule 74.4-G3, the clearance shall be not less than 3 inches at the point of crossing the trolley contact conductor.
Trolley contact conductors of the same system but of opposite polarity, (as in double trolley construction) or of different systems and of the same opposite, polarity, shall have a separation of not less than 11 ˝ inches. Excepted from this provision are conductors at switches, frogs, crossings, etc., in which locations a vertical separation of not less than 3 inches shall be maintained between conductors of opposite polarity.
D. From Poles
Class T conductors of not more than 750 volts and of the same polarity, potential and system when carried on poles supporting no other conductors are not required to obtain the clearance of 15 inches from center line of pole (Table 1, Case 8), but shall comply with the clearance of 3 inches from surface of pole (Table 1, Case 9). The attachment of clearance arms for either supply or communication service drop does not affect the pole clearance of Class T conductors which are carried on one side or top of a pole.
Where Class T conductors are carried on more than one side of jointly occupied poles the clearance of Table 1, Cases 8 and 9, shall apply and a climbing space conforming to Rule 54.7 shall be provided.
E. Under Bridges, ETC
A reduction of the clearances given in Table 1 to a minimum of 14 feet for trolley contact conductors is permitted for subways, tunnels or bridges, provided the railway does not operate freight cars where the vertical distance from the top of car or load to trolley contact conductor is less than 6 feet. This will require the grading of the trolley contact conductor from the prescribed construction down to the reduced elevation. (See App. G, Fig. 64)
No clearance is specified between the trolley contact conductor and structure. Where the structure is of material which will ground the trolley current in event the collector leaves the contact conductor, a properly insulated trolley trough or equivalent protection shall be installed to prevent contact between the collector and the structure. Where pantograph collectors are used, this protection is not required. See Rule 54.4-I for provisions applicable to conductors other than trolley contact conductors.
F. At Points of Failure
(1) Overhead Trolley Contact Conductors: All overhead trolley contact conductors shall be so supported and arranged that the breaking of a single “suspension” or fastening will not allow the trolley conductor, or live span wire, or current carrying connections to come within 10 feet from the ground of from any platform accessible to the general public. This does not apply to feeder taps to or from trolley conductors. (see App. G, Figs 65 and 66.)
(2) Trolley Contact Conductors of More Than 1500 Volts: Where in urban districts and not on fenced rights of way, trolley contact conductors of more than 1500 volts shall be so suspended that if the conductor is broken at a single point it can not fall within 10 feet from the ground or from any platform accessible to the general public. This practically requires catenary construction.
G. From span wires, guys and messengers
The minimum clearances of conductors from span wires, guys and messengers are specified in Table 2 and are modified for Class T conductors by the following rules and by Rule 78.
(1) Span Wires and Contact Conductors: The minimum clearance of 48 inches specified in Table 2, Case 1, Column B and Case 2, Column A, is not required between span wires and trolley contact conductors supported therefrom.
(2) Trolley Contact Conductors of 750-7500 Volts: The clearance specified in Table 2, Case 1, Column E, and Case 5, Column A, shall be increased to not less than 48 inches where trolley contact conductors of 750-7500 volts are involved. These clearances are not intended to apply to span wires and trolley contact conductors supported therefrom.
(3) Feeder and Equalizer Cables: Feeder auxiliary span cables or equalizer cables shall be installed at a distance not less than 18 inches above the span wire (see App. G, Fig. 67), or in lieu thereof, such cables, when protected by the equivalent of triple-braid weatherproof covering, may be supported not less than 2 ˝ inches above the span wire by insulating supports attached to the span wire at intervals of not more than 5 feet.