Abstract: A switching arrangement by which a telecommunication subscriber station selection unit is connected into the central office line is described. The selection unit involved is of the key-operated type wherein key actuation produces a specific surge current corresponding to the specific key depressed. Semiconductor elements form impulse contacts which are operated by a key-controlled pulse generator. A bistable relay is provided for disabling the station's speech circuit during the dialing phase, and at the same time maintains a transmission and feeder circuit, of which the selection unit forms a part and which is completed by actuation of a key. The operation of the bistable relay is influenced via a parallel circuit which offers a high impedance to the transmission and feeder circuit, so that the bistable relay can be rendered inoperative if it is erroneously in an operative state. Depression of a key is required to close the transmitter and feeder circuit, and when this occurs, i.e.

Abstract: A switching arrangement for telephone subsets having key-controlled selection units is described. The selection unit has three connection points and is replaceable. It includes a pulsing relay responsive to a pulse generator actuated by the selection keys. A bistable relay disables a speech circuit, and maintains a connection of a transmitting and feeding circuit extending through the selection unit.