WW-C-58la. Conduit fittings shall conform to the requirements of Federal Specification W-F-406,. All conduit shall be 1/2-inch trade size or larger. 1. Installation: Conduits shall be concealed within the walls, ceilings, and floors, where possible, unless conduit runs are shown exposed on the drawings. Exposed runs of conduit or tubing shell have supports spaced not more than 5 feet apart and shall be installed with runs parallel or perpendicular to walls, structural members, or intersections of vertical planes and ceilings, with rightangle turns consisting of cast-metal fittings or symmetrical bends. Bends and offsets shall be avoided where possti- ble, but where necessary shall be made with an approved hickey or conduit-bending machine. The use of pipe tee or vise for bending conduit or tubing will not be permitted. Conduit or tubing which has been crushed or deformed in any way shall not be installed. Expansion fittings or other approved devices shall be used to provide for expansion and contraction where conduit or tubing crosses expansion joints Wooden plugs inserted in masonry or concrete shall not be used as a base to secure conduit supports. Conduit and tubing shall be supported on approved types of galvanized wall brackets, ceiling trapeze, strap hangers, or pipe straps, secured by means of toggle bolts on hollow masonry units, ¢: pansion bolts in concrete or brick, machine screws on metéi surfaces, and wood screws on wood construction. Nails shail not be used as the means of fastening boxes or conduits. Conduit and tubing risers exposed in wire shafts shall be supported at each floor level by means. of approved U-clamp hangers. Conduit and tubing shall be installed in such man- ner as to insure against trouble from the collection of trapped condensation, and all runs of conduit shall be ar- ranged so as to be devoid of traps wherever possible. The Contractor shall exercise the necessary precautions tc pre- vent the lodgment of dirt, plaster, or ,trash in conduit, tubing, fittings, and boxes during the course of installa- tion. A run of conduit or tubing which has become clogged shall be entirely freed of these accumulations or shall be replaced. Conduit shall be securely fastened to all sheetmetal outlet, junction, and pull boxes with galvanized loc” nuts and one bushing installed in accordance with standarc. practice, care being observed to see that the full number of threads project through to permit bushing to be drawn tight against the end of conduit, after which the locknut shall be made up sufficiently tight to draw the bushing into firm electrical contact with the conduits unless other- wise specified. (a) Running threads shall not be used. 16-6