N.Y.C. Admin. Code § 27-642: § 27-642 Protection of suspenders.

(a) Protected locations. All wires in bridge strands, bridge ropes, or other wire rope or strand suspenders placed on the interior of structures or concealed from exposure by interior finish shall have at least a class A coating of zinc. Rods, bars, plates, or shapes used for suspenders shall be given a protective coating as specified for the protection of like material in the applicable reference standard.

(b) Exposed locations. The outside wires of bridge strand or bridge rope suspenders placed in locations exposed to the weather shall have at least a class B coating of zinc and the inside wires shall have at least a class A coating. Rods, bars, plates, or shapes used for suspenders shall be given a protective coating as specified for the protection of like material in the applicable reference standard.