The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
Practical Electricity And House Wiring
Testing.—Proceed exactly as when using armored cable.
Thin-wall Conduit.—A new type of conduit known as thin-wall conduit or "Electrical Metallic Tubing" is fast replacing the regular or "rigid" conduit. It serves the same purpose and is used the same way, but its walls are never threaded, and connections instead of being by means of threaded fittings, are by means of connectors and couplings and other fittings that clamp on. This saves a great deal of time; as a matter of fact, a hacksaw and a reamer are the only tools needed. Being lighter it bends easier, costs less, and weighing less, costs less to ship. A short piece of this conduit and the connectors and couplings used are shown in Fig. 166. It is commonly known as "EMT."
Wiring New Houses: Knob-And-Tube System
In this chapter we will cover the wiring of the same house wired in previous chapters, except that the knob and-tube system will be used. This was the first system used in electrical wiring, and while today practically unknown in some areas, it is still widely used in other areas. It is particularly common in the Cleveland area, in the Southwest from Kansas to Texas, and also on the Pacific Coast, and to lesser degrees elsewhere.
In this system rubber-covered wires are used, mounted on porcelain insulators; splices are permitted as required. Outlet boxes must still be used, except in permanently exposed installations. The Code requires that all wires must be kept at least 3 in. apart, and at least 1 in. from any other object or surface. Where this can't be done, porcelain insulators are used to separate the wires by these distances, from their surroundings. Porcelain insulators are of three common kinds: knobs, tubes and cleats.
Porcelain Knobs.—The usual porcelain knob is the 2piece split-knob of Fig. 82, provided with a nail for mounting, and a leather washer under the head to prevent damaging the knob when the nail is driven home. The knob has two grooves, but only one wire may be mounted on a single knob. The only exception is in the case of the tapped wire as shown in Fig. 167—here one wire is connected to the other and the two therefore must be considered as a single wire.
