GB541415A - Improvements relating to telephone exchanges and electrical interconnecting means therefor - Google Patents

Abstract

541,415. Automatic exchange systems. STUART, A. J., and LOW, F. A. May 25, 1940, Nos. 9229/40 and 156/41. [Class 40 (iv)] In a system in which subscribers are connected to unattended switching stations provided with three-wire outgoing junctions to an exchange which may have no subscribers connected to it directly, some or all of these junctions are shared between two or more switching stations. Preferably a station has at least one first choice junction individual to it, later choices being shared with an increasing number of other stations. The commoning is effected in the stations or in separate junction boxes. Calls incoming to a switching station are completed over separate 2- or 3-wire junctions terminating in final selectors. The exchanges may be satellites of a non-director main exchange or may be director exchanges. In systems in which a calling subscriber is connected to an outgoing junction by a line-switch controlled by busy markings it is preferred, since these busy markings may be applied over a circuit of considerable resistance from another station, to use the switch shown in which a separate test relay N is initially energized over normal terminals and is subsequently held over the c-wires of busy lines. In systems depending on a batterymarking for idle lines, the cut-off relay has a low-resistance test winding and a high-resistance holding winding. Where finder/preliminary selector links are used a link is marked busv after use until the preliminary selector reaches normal to ensure that the junctions are tested in the right order.