Identifier: americantelepho00mill (find matches)
Title: American telephone practice
Year: 1905 (1900s)
Authors: Miller, Kempster B. (from old catalog)
Subjects:
Publisher:
Contributing Library: The Library of Congress
Digitizing Sponsor: The Library of Congress

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the cut-offrelay on account of its higher resistance and more delicate adjust-ment. The circuit of the line lamp is controlled by the armatureof both the line and the cut-off relays, the cut-off relay having itscontact normally closed, that of the line relay being normally open.When, therefore, the line relay only is operated, the line lamp willbe illuminated. The cord circuit contains three relays, two ofwhich, A and B> are connected between the negative side of thebattery and the tip strands of the answering and calling plugs,respectively, the points of connection between these two relays andtheir respective tip strands being separated by a two-microfarad con-denser. The relay, C, is connected between the negative side ofthe battery and the sleeve strand of both the calling and answer-ing plugs, this latter strand being continuous from the sleeve ofthe answering plug to the sleeve of the calling plug. This latterrelay serves to control the connection between the negative side of
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FIG. 279.-INTERNATIONAL MULTIPLE SWITCH-BOARD CIRCUIT. 341 THE COMMON BATTERY MULTIPLE SWITCH-BOARD. 345 the battery and both supervisory lamps, this contact being nor-mally open, but closed upon the operation of the relay. When the answering plug is inserted into the jack of a callingsubscriber the cut-off relay of the line, and the relay, C, of the cordcircuit are at once operated, the circuit being traced from the nega-tive side of the battery through the coil of the relay, C, thence overthe sleeve strand of the answering cord to the sleeve contact of thejack, thence to the positive pole of the battery through the coil of thecut-off relay. The energization of the cut-off relay opens the cir-cuit of the line lamp, thus extinguishing it, and at the same timerelay, C, completes the circuit between the negative side of the bat-tery and both of the supervisory lamps. The calling supervisorylamp will thus be lighted upon the insertion of the answering plug,because the relay, B, which con

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