Functions of Cabinet. The purpose of the cabinet is not only to form a support for the various pieces of apparatus but also to protect them from dust and mechanical injury, and to hold those parts that must be manipulated by the operator in such relation that they may be most convenient for use, and thus best adapted for carrying out their various functions.  Other points to be provided for in the design of the cabinet and the arrangement of the various parts within are:  that all the apparatus that is in any way liable to get out of order may be readily accessible for inspection and repairs; and that provision shall be made whereby the wiring of these various pieces of apparatus may be done in a systematic and simple way so as to minimize the danger of crossed, grounded, or open circuits, and so as to provide for ready repair in case any of these injuries do occur.

Wall-Type Switchboards. The simplest form of switchboard is that for serving small communities in rural districts.  Ordinarily the telephone industry in such a community begins by a group of farmers along a certain road building a line connecting the houses of several of them and installing their own instruments.  This line is liable to be extended to some store at the village or settlement, thus affording communication between these farmers and the center of their community.  Later on those residing on other roads do the same thing and connect their lines to the same store or central point.  Then it is that some form of switchboard is established, and perhaps the storekeeper’s daughter or wife is paid a small fee for attendance.

[Illustration:  Fig. 292.  Wall Switchboard with Telephone]

A switchboard well-adapted for this class of service where the number of lines is small, is shown in Fig. 292.  In this the operator’s talking apparatus and her calling apparatus are embodied in an ordinary magneto wall telephone.  The switchboard proper is mounted alongside of this, and the two line binding posts of the telephone are connected by a pair of wires to terminals of the operator’s plug, which plug is shown hanging from the left-hand portion of the switchboard.  The various lines centering at this point terminate in the combined drops and jacks on the switchboard, of which there are 20 shown in this illustration.  Beside the operator’s plug there are a number of pairs of plugs shown hanging from the switchboard cabinet.  These are connected straight through in pairs, there being no clearing-out drops or keys associated with them in the arrangement.  Each line shown is provided with an extra jack, the purpose of which will be presently understood.