Fig. 979.—Wooden pipe type of conduit. It consists of pieces of wood about 4½ inches square, and three to six feet long, with a wide hole about three inches in diameter, bored through them longitudinally.
Ques. How can this be prevented?
Ans. The decay of the wood can be prevented to a certain extent by the application of sterilizing processes, thereby preserving it in fairly good condition for about ten to fifteen years.
Ques. For what service is wooden conduit best adapted?
Ans. For temporary installations which will be discontinued before the wood decays.
Wooden Built-in Conduits.—Within recent years several forms of wooden built-in conduit have been designed and successfully used for permanent work. They possess several advantages over any of the duct systems, the chief of which are high insulating quality, the capability of using bare wire and rods for underground conductors, and reduced cost. An approved form of wooden built-in conduit is shown in [fig. 980].
Fig. 980.—Perspective view of wooden built-in conduit. It consists of an outer rectangular casing of wood which is lined inside with impregnated felt.