Detailed Construction Requirements for Trolley
and Electric Railway
Contact and Feeder Conductors and Their Supporting Messengers,
Span Wires, Etc. (Class T Circuits)
77.3 Material and Strength
Span wires, backbones, messengers, etc., shall be stranded and of galvanized steel or other corrosion-resisting material of equal durability.
The strength of span wires, backbones, messengers, etc., shall be such that the safety factors of Rule 44 are not met.