California Code, Public Utilities Code - PUC § 8034

No person shall run, place, erect, or maintain any suspension wire to which is attached any aerial cable of 75 pair No. 19 Brown and Sharpe gauge or over, or of 100 pair No. 22 Brown and Sharpe gauge or over suspended from a crossarm, or from any other structure or appliance from which the suspension wire is hung, by a single bolt and clamp without at the same time attaching the suspension wire to the crossarms, structure, or appliance by an additional safety bolt and clamp, or other safety appliance for thus attaching the suspension wire of tensile strength equal to the first bolt and clamp.