General Order 64-A
Detailed Construction Requirements For Supply Lines
(Class H, L and T Circuits)
Cables which are grounded may be attached directly to surface of poles and installed at a distance less than 6 feet below different circuits of open wire supply conductors. Where so installed, they shall be protected by a guard arm at least 4 feet in length, placed as close to them and as nearly parallel with them as practicable. In lieu of the guard arm, a suitable insulating covering of the length specified may be placed around the cable and supporting messenger. (See Rule 58.1 for cable terminals; also App. G, Fig 87.)
Messengers which are grounded, where dead-ended or wrapped around a pole, shall be at least 6 feet vertically below supply conductors of other circuits. Should it be impracticable to maintain such vertical clearance, a reduction to 4 feet below supply conductors of 0-750 volts will be permitted, provided the messenger is suitably guarded with the equivalent of double guard arms placed directly above it and substantially parallel with it.