General Order 64

General Clearance Requirements – All Classes Of Lines

42    Minimum Clearance Of Wires Above Railroads, Streets And From Buildings, Etc.

The clear space between the lowest overhead line conductor, guy, messenger or trolley span wire and the heads of rails, crowns of streets, alleyways, or other generally accessible spaces across or along or above which the former passes, also the clear space between the nearest conductor, or other wires mentioned above, and buildings, pole structures and other obstructions shall not be less than the values given in Table 1 under the most severe conditions of temperature and loading that apply, as well as side swing due to wind.
 
Where conductors are supported by suspension or disc type insulators and not dead ended at the pole or structure or otherwise prevented from swinging the side swing mentioned above shall be figured on the assumption that the maximum deflection of the supporting insulators is forty-five degrees from the vertical.

Where the lowest supply conductor at a crossing over railroads is 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 per cent through the breaking of a conductor in either adjoining span.  An arrangement of insulators preventing displacement toward the crossing will avoid the necessity of any increase over the clearance given.