California Code, Public Utilities Code - PUC § 8033

No person shall run, place, erect, or maintain any wire or cable carrying more than 15,000 volts of electricity across any wire or cable carrying less than that voltage or across any public highway, except on a pole of such height and so placed at each crossing that under no circumstances can the wire or cable of a voltage higher than 15,000 volts in case of breakage thereof or otherwise, come in contact with any wire or cable of less than that voltage, or fall within a distance of ten (10) feet from the surface of any public highway;  or in lieu thereof double strength construction may be installed, in which case the wires carrying a voltage higher than 15,000 volts shall, between the points of crossing, be of a cross-section area equal to at least twice that used in the line outside of such crossing, except where the conductor used is equal to number four (4) stranded Brown and Sharpe gauge or greater, in which case the wires or cables will be considered as complying with the law.