574,312. Automatic exchange systems. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., TAYLOR, R., and BAKER, G. T. Feb. 1, 1944, No. 1825. [Class 40 (iv)] In a subscriber's line switch of the homing type, on an outgoing call potential is applied to the guarding conductor leading to the final selector multiple through the cut-off relay, which is of low resistance, and a wiper of the switch in off-normal position, so that the relay may be released by the application of the same potential from a final selector extending a toll call. The operation of line relay L starts hunting in the usual manner, and cut-off relay K pulls up in series with the magnet DM when an idle outlet is found. After the relapse of relay L, the holding ground fed back from the seized selector is extended through relay K and over wiper D2 to the incoming test wire. If now direct ground is applied to this wire from a toll final selector, relay K is shortcircuited, the existing connection is opened and the switch restores to normal, whereupon circuits are made for both relays K, L, but K operates first and disconnects L. If the subscriber is the called party in an existing connection, the breakdown ground will maintain relay K and force down the switching relay in the final selector. Relay K may be shunted by a condenser to pass the toll tone that is usually provided on toll calls. The common battery (or ground) lead 10 to the line relays may include a key LDK which serves to disable non-priority subscribers as regards outgoing calls during overload conditions. On long lines the release lag of relay L may be reduced to provide greater winding space and therefore it is arranged that holding ground is fed back from the first selector immediately upon operation of the line relay. A selector is described that is otherwise similar to that disclosed in Specification 447,767.
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