[Illustration:  Fig. 303.  Sectional Switchboard—­Wall Type]

This line of switchboards is illustrated in Figs. 303 to 306.  The beginning may be made with either a wall type or an upright type of switchboard, the former being mounted on brackets secured to the wall, and the latter on a table.  A good idea of the wall type is shown in Fig. 303.  Three different kinds of sectional units are involved in this:  first, the unit which includes the cords, plugs, clearing-out drops, listening jacks, operator’s telephone set and generator; second, the unit containing the line equipment, including a strip of ten magneto line signals and their corresponding jacks; third, the finishing top, which includes no equipment except the support for the operator’s talking apparatus.

[Illustration:  Fig. 301.  Sectional Switchboard—­Wall Type]

The first of the units in Fig. 303 forms the foundation on which the others are built.  Two of the line-equipment units are shown; these provide for a total of twenty lines.  The top rests on the upper line-equipment unit, and when it becomes necessary to add one or more line-equipment units as the switchboard grows, this top is merely taken off, the other line-equipment units put in place on top of those already existing, and the top replaced.  The wall type of sectional switchboard is so arranged that the entire structure may be swung out from the wall, as indicated in Fig. 304, exposing all of the apparatus and wiring for inspection.  Each of the sectional units is provided with a separate door, as indicated, so that the rear door equipment is added to automatically as the sections are added.  In the embodiment of the sectional switchboard idea shown in these two figures just referred to, no ringing and listening keys are provided, but the operator’s telephone and generator terminate in a special plug—­the left-hand one shown in Fig. 303—­and when the operator desires to converse with the connected subscribers, she does so by inserting the operator’s plug into one of the jacks immediately below the clearing-out drop corresponding to the pair of plugs used in making the connection.  The arrangement in this case is exactly the same in principle as that described in Fig. 292.  The operator’s generator is so arranged in connection with this left-hand operator’s plug that the turning of the generator crank automatically switches the operator’s telephone set off and switches the generator on, just the same as a switch hook may do in a subscriber’s series telephone.

[Illustration:  Fig. 305.  Sectional Switchboard—­Table Type]

[Illustration:  Fig. 306.  Sectional Switchboard—­Table Type]

The upright type of sectional switchboard is shown in Figs. 305 and 306, which need no explanation in view of the foregoing, except to say that, in the particular instrument illustrated, ringing and listening keys are provided instead of the jack-and-plug arrangement of the wall type.  In this case also, the top section carries an arm for supporting a swinging transmitter instead of the hook support for the combined transmitter and receiver.