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The Selector Switch

The selector switchref.20 used in the step-by-step system is of the basic type described on page 373. This switch is used for making intermediate connections between the line finder and connector switch in systems having more than 100 lines. A group of selectors is required for each of the digits of the call number except the last two (sometimes three). The vertical motion of the selector, controlled by the incoming impulses from the dial, raises the shaft and wipers to the desired level. Then, the selector switch automatically rotates its wipers over the contacts of that level to the first idle trunk in that group. The rotary motion of the selector is not controlled by the dial.

The principle functions of the selector may be summarized as follows: (1) to hold preceding switches operated until the control circuit is extended to the succeeding switch; (2) to connect dial tone to the calling line if it is a first selector; (3) to step to the selected level and hunt for an idle trunk in that group; (4) to clear the line of -all attachments after the succeeding switch is seized; (5) to return busy tone to the subscriber if all trunks are busy on the selected level; (6) to release without interference to other trunks when the calling party replaces the handset or receiver.



Last Update: 2011-05-28