Rubber insulation should always be used where the wire is in a damp place, such as a cellar, and either weather proof or rubber insulation may be used to protect it against corrosive vapors.
Figs. 842 to 844.—Open or exposed wiring. Fig. 842, wires passing through beams. The holes are bored at an angle and wire run through in zig-zag course. Porcelain tubes are used where the wire passes through beams; [fig. 843], cleat work across beams, the cleats are carried by boards attached to the beams; [fig. 844], method of carrying wires on cleats around beams.
Ques. How are the wires installed?
Ans. They are laid on some cornice, wainscoting, beam, or other architectural feature suitable for the purpose, by means of porcelain knobs and cleats, as shown in figs. 842 to 844.
Porcelain knobs should preferably be of the two piece type ([fig. 863]) in which the wire is carried between the upper and lower portions rather than being tied to a one piece knob with a tie wire as in [fig. 860]. Various porcelain knobs and cleats are shown in figs. 860 to 866.
Ques. What are the disadvantages of open wiring?