figure 41, the line circuits are shown as consisting only of line jacks, one for each telephone line connected to the
switchboard, into which the plugs of the cord circuits may be inserted by the operator. Actually, several kinds of line
circuits are associated with common-battery switchboards, all of them including some means for signaling the operator
automatically when a station wishes to make a call. Since the present discussion is concerned only with the basic
elements of the common-battery system, however, consideration of the line circuits actually used in common-battery
switchboards, including such necessary requirements as signaling and supervisory circuits, must be deferred. Note that
the line jacks illustrated have three contacts, also called tip, ring, and sleeve, to correspond to the contacts of the plugs and
the conductors of the cords.
FIGURE 41. Simplified Common-Battery
Cord and Line Circuit
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