Side Switch. Another important element of the selecting switches is the so-called side switch which might better be called a pilot switch—but we are not responsible for its name. This side switch has for its function the changing of the control of the subscriber's line to successive portions of the selector mechanism, rendering inoperative those portions that have already performed their functions and that, therefore, are no longer needed. This switch may be seen best in Fig. 392 just above the upper bank of contacts. It is shown in Fig. 390 greatly distorted mechanically so as to better illustrate its electrical functions.

Fig. 390. Circuits of First Selector
[View full size illustration.]

The contact levers 1, 2, 3, and 4 of the side switch are carried upon the arm 5 which is pivoted at 6. All of these contact levers, therefore, move about 6 as an axis. The side switch has three positions and it is shown, in Fig. 390, in the first one of these. When the private magnet armature is attracted and released once, the escapement carried by it permits the spring 7 to move the arm 5 so as to bring the wipers of the side switch into its second position; the second pulling up and release of the private magnet armature will cause the movement of the side switch wipers into the third position. It is to be noted that the escapement which releases the side switch arm may be moved either by the private or by the rotary magnet, since the armature of the latter has a finger which engages the private magnet armature.

Fig. 391. Rear View of First Selector
[View full size illustration.]

Functions of Side Switch. The functions of the side switch may be briefly outlined in connection with the first selector, as an example. In the first position it extends the control of the subscriber's signal transmitter through the first selector trunk and line relays to the vertical and private magnets so that these magnets will be responsive to the selecting impulses corresponding to the first digit. In its second position it brings about such a condition of affairs that the rotary magnet will be brought into play and automatically move the wipers over the bank contacts in search of an idle trunk. In its third position, both the vertical and rotary relays are cut off and the line is cut straight through to the second selector trunk, and only those parts of the first selector apparatus are left in an operative state which have to do with the private or guarding circuits and with the release. Similar functions are performed by the side switch in connection with the other selecting switches.

Fig. 392. Side View of Second Selector
[View full size illustration.]