Miller, Kempster Blanchard, 1870-1933 · New York : McGraw publishing company · leaf 433
attend-ant at the private branch exchange may call central by plugginginto the jack and throwing her listening key, this act allowing theflow of current over the trunk line and operating the line relay be-longing to the trunk line. The call will then be answered by themain office operator in… … FIG. 310.-PEIVATE-ERANCH EXCHANGE TRUNK CIRCUIT OF CHICAGOTELEPHONE COMPANY. or more of the trunk lines when idle. This is accomplished in thetrunk line circuit shown in Fig. 310, it being obvious that when thetrunk line is not in use a flow of current will exist from the live sideof the battery.…
Telephone
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