(a) The tubing must be located on the overhead or within 12 inches of the overhead on the bulkheads. Where liable to physical damage, the tubing must be suitably protected.

(b) In each enclosed space or separate room there must be exposed at least 5 percent of the total length of tubing in that circuit, but in no case may the amount be less than 25 feet.

(c) No spot on the overhead of a protected space may be more than 12 feet from the nearest point of tubing. Where beams or girders extend below the ceiling, or where the ceiling is installed at more than one level, the tubing must be located so as to be most effective.