California Code, Public Utilities Code - PUC § 8027

No person shall run, place, erect, or maintain in the vicinity of any pole (and unattached thereto) within the distance of 13 inches from the center line of the pole, any wire or cable used to conduct electricity, or place, erect or maintain any pole (to which is attached any wire or cable used to conduct electricity) within the distance of 13 inches (measured from the center of such pole) from any wire or cable used to conduct or carry electricity. As between any wire or cable and any pole, only the wire, cable, or pole last in point of time run, placed, or erected, shall be held to be run, placed, erected, or maintained in violation of the provisions of this section.

This section does not apply to signal wires, or cables on poles to which are attached no other wires, as between such wires and poles to which are attached no other wires or cables than signal wires if such wires, cables, and poles are not within the corporate limits of a city.

Telephone toll lines may be exempt from this section if proper evidence introduced before the commission proves to the satisfaction of the commission, that compliance would seriously interfere with long distance telephone transmission.