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General Order 64-A


Section VII


Detailed Construction Requirements For Trolley Lines

(Class T Circuits)


74.4    Clearances.

Except where specifically designated, Class T conductors take clearances specified for supply lines of like voltage.


A.    Above Ground


(1)    Normal:  The normal clearance of Class T circuits are given in Table 1.  References to rules modifying the tabulated values are given in notes following 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 shall be provided when crossing spans exceed 100 feet.  (See Appendix G, Figs. 66 and 67.)  This rule is not intended to apply where pantagraph collector or similar device is used.


C.    Between Conductors.

Trolley contact conductors and trolley feeders of the same potential system need not acquire the clearances given in Table 2, Case 2 Col. D, Case 4 Col. B and Case 15 Col. D.


D.    From Poles

Class T conductors of the same polarity and potential are not required to obtain a clearance of 15 inches from the center line of poles, a 3-inch minimum from the surface being required if no other conductors are supported thereon.  The attachment of clearance arms for either supply or communication conductors does not affect the pole clearance of such Class T conductors which are carried on a side or top of a pole.  Where Class T conductors are carried on more than one side of the pole a climbing space conforming to Rule 54.7-A shall be provided to the clearance arms installed above them.


E.    Under Bridges, ETC.

A reduction to a minimum of 14 feet of the clearance given in Table 1, 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 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 65.)

No clearance is specified between Class T conductors and the structure.
  Where the structure is of material which will ground the trolley current in the event the collector leaves the contact conductor, a properly insulated trolley through or equivalent protection shall be installed to prevent contact between the collector and the structure.  Where pantagraph is used, this protection is not required.


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 or from any platform accessible to the general public. This does not apply to feeder taps to or from trolley contact conductors (See App. G, Figs. 68 and 69 ).


(2)    Trolley Contact Conductors of More than 1,500 Volts: Where in urban districts and not on fenced rights–of–way, trolley contact conductors of more than 1,500 volts shall be so suspended that if the conductor is broken at a single point it cannot fall within 10 feet from the ground or from any platform accessible to the general public. This practically requires catenary construction.  (See App. G, Figs. 68 and 69 ).


G.    From Span Wires, Guys and Messengers.

The clearance given in Table 2, Case 1 Column E and Case 5 Column A, shall be increased to 48 inches where trolley contact conductors of 750-7500 volts are involved.