a) 3-foot minimum from combustible building surfaces to the edge of the pad. Non-combustible materials include brick, clay, concrete, steel, stone, and stucco. This bulletin presents information and the equations needed to determine the maximum span lengths that will meet NESC mid-span and supporting structure clearance requirements between conductors. 1 Purpose and Scope of Bulletin: The conductor clearance requirements of Rule 235 of. This standard provides the vertical clearance required for above ground conductors, communication wires, and span guys. Expanded note 10, including new Table 1, to add 12 kV and 25 kV conductor values. EXCEPTION:The minimum radial distances in this rule shall not apply to uncovered, grounded, non-dielectric fiber optic cables in transition on metallic structures, which must comply with Rule 38, Table 2, Case 16a.