General Order 64-A
35 Minimum Clearances of Wires Above Railroads, Thoroughfares, Buildings, Etc.
The clear space between the lowest overhead line conductor, guy, messenger or trolley span wire and top of rails, crown of streets, alleyways or other generally accessible spaces across, along or above which the former passes; also the clear space between the nearest conductor or other wire mentioned above, and buildings, pole structures and other obstructions, shall not be less than the values given in Table 1, at a temperature of 60° F. and no wind.
The clearance of Table 1 shall in no case be reduced more than 10% below the tabular values because of temperature, wind or mechanical loading.
Where supply conductors, at a crossing over railroads, a re supported by suspension insulators, the initial clearances shall be sufficient to prevent the minimum clearances over rails given in Table 1 from being reduced more than 10% through the breaking of a conductor in either of the adjoining spans.