The catenary of a transmission line or similar obstructions, should be lighted in accordance with the following specifications:

(1) Specification "C-1."

(a) The towers, poles, or similar structures supporting such a line should be lighted in accordance with the specifications hereinbefore prescribed for individual towers, poles, or similar obstructions of a corresponding over-all height above ground, or water if so situated.

(b) In each case where a transmission line within 15,000 feet of a landing area is required to be lighted in accordance with the provisions of RCW 14.04.340 - 14.04.350, one or more lights, each light consisting of a lamp of at least 100 watts enclosed in an aviation red obstruction light globe, should be displayed for each 150 feet or fraction thereof, of the over-all length of the overhead line. These lights should be equally spaced along the entire length of the overhead transmission line at points not more than 150 feet apart and each light should be placed not below the level of the highest wire at the point marked.

(c) When a transmission line more than 15,000 feet from a landing area is required to be lighted in accordance with the provisions of RCW 14.04.340 - 14.04.350, the distance between the obstruction lights displayed on such wires may be increased to not less than 600 feet.