California Code, Public Utilities Code - PUC § 8036

No person shall run, place, erect, or maintain any span wire attached to any wire or cable used to conduct electricity, without causing the span wire to be at all times effectively insulated between the outer point at which it is in any case fastened to the pole or other structure by which it is hung or supported, and at the point at which it is in any case thus attached. Such insulation shall not in any case be placed less than two (2) feet or more than four (4) feet from the point at which the span wire is so attached. When in any case such span wire is attached along its length to any two (2) such wires or cables, conducting electricity and extending parallel to each other, not more than eighteen (18) feet apart, such insulation shall not be required therein at any point between such parallel wires or cables. This section does not apply where feeder wires are used in place of span wires.