Page:Incandescent electric lighting- A practical description of the Edison system.djvu/79

 When this cut-out is in place, the three wires entering the building are secured to it by means of the screws on one side of the sockets, while the three wires leading to and through the metre are secured to the screws on the opposite side of the sockets, the circuit remaining open however until a plug is screwed into each of the sockets. This

. 22.

plug, shown in Fig. 22, is formed of glass, and is hollow. On its bottom end is fixed a metal button, which is connected to a screw shell arranged on the outside by a strip of the fusible alloy before mentioned, located in the hollow space, in the interior of the plug; the top being provided with a metal screw cap perforated to allow the gases to escape, if for