The main wires which supply the house with electricity—marked lead wires—are brought into the cabinet as shown in Fig. 231 and attached to the poles of the switch S. In passing through the switch the lead wires each contain a mica-covered fuse plug F, that will be described later. The current at any time may be entirely cut off from the house by pulling the handle H, which is connected by an insulating bar and the contacts N of the switch. When the handle H is pulled to separate the contact pieces, all electric connection is severed at that point.
Fig. 231.—Electric panel containing cutout blocks, fuses and switch.
The wattmeter for measuring the current is placed at the points marked meter, as a part of the main circuit. The main wires in the cabinet terminate in the porcelain cutouts, from which are taken off the various circuits of the house. In the figure, three such cutouts are shown making three circuits marked 1, 2, and 3. In circuit No. 1, the fuses are marked F. These wires are joined to the main wires at the points marked C and C´. The number of circuits the house will contain depends on the number of lights and the manner in which they are placed. The circuits are intended to be arranged so that in case of a short, no part of the house will be left entirely in darkness.
Fuses for general use are made in two different types—the plug type and the cartridge type—each of which conforms to the rules of the Underwriters Association. Those most commonly used for house wiring are the plug type shown in Fig. 232 and indicated in the figure just described. These plugs are made of porcelain and provided with a screw base which permits their being screwed into place like an incandescent lamp. The front of the plug is arranged with a mica window which allows inspection to be made in case of a short, the blown fuse indicating the circuit in which the trouble is located. Another style of the same type of plug, known as the re-fusable fuse plug, permits the fuse to be replaced after the wire has been destroyed by a short.
Fig. 232.—Mica covered fuse plug.
Fig. 233.—Cartridge fuse.
