Figs. 860 to 866.—Various porcelain knobs and cleats. In open work various forms of these devices are used.
Fig. 867.—Porcelain tube for entrance of wire into a building. There must be a drip loop outside to drain off water, and the hole through which the conductor passes must be bushed with a non-combustible, non-absorptive insulating tube slanting downward toward the outside. The object of the inclination is to allow any water that might enter the tube to gravitate to the drip loop.
Fig. 868.—Interior bushing. Wires must be separated from contact with walls, floors, timbers or partitions through which they may pass by non-combustible, non-absorptive, insulating tubes, such as glass or porcelain, except at outlets where approved flexible tubing is required. Bushings must be long enough to bush the entire length of the hole in one continuous piece, or else the hole must first be bushed by a continuous water proof tube. This tube may be a conductor, such as iron pipe, but in that case an insulating bushing must be pushed into each end of it, extending far enough to keep the wire out of contact with the pipe.
Wires Run in Mouldings.—Wooden mouldings are extensively used in connection with the wiring of stores, factories and buildings. The advantages of this type of construction are: simplicity, cheapness, and accessibility, and when the moulding is run straight and accurately mitred it makes a neat job. Any class of wooden moulding wiring, however, is not sufficiently impervious to moisture to render it suitable for use in damp places, and it is liable to be crushed or punctured. Furthermore, it is naturally very combustible. These difficulties are overcome to a certain extent by impregnating the moulding with some kind of moisture repellant, or by coating it both inside and out with water proof paint. Hardwood moulding should be used wherever possible, but soft wood moulding usually conforms much better to the wall line.
