possible for the operator at each position of the switchboard to reach one of the line jacks of any calling or called station
connected to the switchboard, greatly increasing the traffic which the switchboard can handle. The discussion which
follows will concern itself with the description and operation of a nonmultiple common-battery switchboard.
c. Description of front of switchboard. In general, the equipment arrangement is similar in all cord-type
switchboards, but it is not exactly the same. The switchboard in figure 39 can be used at a small central office.
(1) The illustration shows the vertical portion of the plugshelf, sometimes called the cordshelf, divided into two
panels by the vertical separator through its center. The left panel carries 50 line (station) jacks with their associated line
lamps, a supervisory pilot lamp, fuse-alarm lamp, and a line pilot lamp. The right panel has, in addition to 50 line jacks
and line signals, a single row of jacks and signals to which exchange lines are connected.
(2) The plugshelf holds 15 pairs of cords and 1 single cord. The paired cords are used to complete
interconnections. The single cord, when present, is used by the operator to advise a calling station when all the paired
cords are in use. This single cord is not standard equipment on all switchboards.
(3) The switchshelf carries the control levers of the listening and ringing switches, the associated supervisory
lamp signals, and the switchboard dial. Each pair of cords is associated with a pair of supervisory lamp signals and a pair
of switches. The dial is used in completing connections between one of the switchboard stations and a station associated
with a dial central office.
(4) The extreme left-hand cord (fig. 39) is the A (answering) cord of the first pair of cords. The cord immediately
in front of that cord, toward the operator, is the C (calling) cord of the first pair of cords. The term answering cord means
that on a station line signal this cord is used in answering the signal, leaving the C cord available for making connections
to an exchange if this is required. This association of cords to lines is necessary to proper supervision. Calls to another
switchboard station can be completed with the C cord. Answering and calling cords sometimes are referred to as back and
front cords, respectively.