115    Special Strength Requirements At Crossings And Conflicts Where Grade “A” Construction Is Required.  (See Appendix D.)

 

(a)    Towers: Towers supporting crossing spans where Grade “A” construction is required by section V shall conform to Rule 77.

 

(b)    Poles:  Poles supporting crossing spans or in conflicts shall be designed:

 

1.    To withstand the designated factor of safety, the combined transverse stress due to their own weight, the specified wind pressure on the poles, and the specified conductor loadings of Section V throughout the conflicting section or in both the crossing span and the next adjoining span.

 

2.    To withstand at all times without failure, the unbalanced stress due to the combined pull toward the crossing or conflicting section of all conductors supported, the pull in each conductor being taken as tension due to the specified loading of Section V.  This unbalanced stress may be distributed over one or more poles adjoining the crossing span or conflicting section, provided all the construction from the crossing span or conflicting section to and including any such poles is Grade “A”.

 

3.    Where the requirements of 1 above can not be met except by the use of side guys or special structures and the conditions are such that it is physically impracticable to employ side guys to the crossing poles or on the poles within the conflict, the requirements of 1 above may be met as follows:

 

At Crossing:  By side guying the line as near as practicable to the crossing, but at a distance not exceeding 500 feet from the crossing pole, the line between such guyed poles and the crossing being substantially in a straight line with the crossing pole and the average length of span between the guyed pole and the crossing being not in excess of 150 feet.  The entire line between the guyed poles and the crossing shall be Grade “A” except as regards transverse strength of poles.  The poles between the guyed structure and the crossing shall be at least 8 inches in diameter of top and shall have not less circumference (6 feet from butt) than that given in the following table:

 

 

 

At Conflicts:  By Continuing the Grade “A” construction except as regards transverse strength to a point where it is practicable to place side guys.

 

(c)    Conductors:  The minimum size conductors in crossing is given in Rule 63.

 

(d)    Protection Against Conductor Breakage and Burning of Supports:

 

1.    Splices and Taps:  Splices and shall not be made in the crossing span and preferably not in the adjacent spans which are depended upon for withstanding the longitudinal stress of the crossing conductors.  If a splice or tap is made in any conductor in the span next to the crossing, it shall, where practicable, be placed at a point nearer to the crossing support than is the nearest conductor crossed over.

 

2.    Protection Against Burning:  In installing insulators and conductors precautions shall be taken to guard against the possibility of arcs or leakage current injuring conductors or burning any wooden parts of the supporting structure which would render the conductors liable to fall.  It is recommended that where steel pins are used in conjunction with wooden crossarms the pins be metallically bonded together but not grounded.  In cases where two or more circuits are carried on the same poles and wooden crossarms are used, the insulator pins of the different circuits should be bonded independently of each other.  The size of conductor used for bonding shall be not less than No. 10 A.W.G. copper wire or its equivalent.

 

3.    Ration Flash to Puncture Voltages:  Insulators should be so designed that their dry flash-over voltage is not more than 75 percent of their puncture voltage at a frequency of 60 cycles per second.

 

4.    Extra Strength Insulators for Grounded Pins:  Where grounded pins are used at crossings (nongrounded construction being used in other parts of the line) the insulators used on such metal or grounded supports shall be capable of withstanding a voltage of 25 percent greater than at other parts of the line, but in no case less than as specified in Rule 64 (b).  As an alternative the conductors at their points of attachment where suspension insulators are used may be protected by arcing shields.

 

(e)    Lighting Protection Wires:  Lightning protection wires or cables, if used shall conform as to material, size and strength to the requirements for conductors.

(f)    Screens and Cradles:  The use of screens or cables for crossing protection is not approved under these rules.

 

(g)    Short Span Crossings:  In cases where crossing span is constructed of such height that its length is less that the distance between either point of support of its lowest conductor and the highest conductor of the line crossed, the requirements for conductor sag and for size and type of conductors required are waived, provided that a permanently grounded guard arm is installed at each crossing support in such a manner as to prevent the conductors which may break in either adjacent span from swinging back into the conductors of the span crossed over.