Improvements in or relating to cross bar switches for automatic telephone systems

833,722. Automatic exchange switches. TELEFONKTIEBOLAGET L. M. ERICSSON. May 1, 1957, No. 13944/57. Class 40 (4). In a cross-bar switch of the type in which each selecting bar has associated therewith a plurality of contact spring sets, one per operating bar, and in which each set consists of two or more groups of contact springs located one above another, a driver being individually associated with each set and being so positioned by the operation of the relevant selecting magnet that on subsequent operation of the relevant operating magnet the movement of the operating bar concerned causes the driver to bring all the contact springs of the groups of that set into contact with the wires of two or more corresponding groups of transverse intermediate conductors, that group of contact springs of the set which is to be effectively included in a connection through the switch is determined by providing an auxiliary selecting bar associated with a plurality of auxiliary contact spring sets, one per operating bar, each such set being arranged in groups as are those of the main sets, an auxiliary driver for each group in each auxiliary set, and change-over means in association with each operating bar for controlling the auxiliary drivers of the auxiliary contact spring set concerned, which means is operated by the auxiliary selecting bar so that one only of the auxiliary drivers becomes capable of being engaged by the operating bar so as to effect contact between the relevant group of the auxiliary set and the corresponding group of intermediate conductors. Twenty-five or twenty-six line selector.-Figs. 1 and 2 show separately one embodiment of an auxiliary contact spring set and of a main contact spring set, respectively. Operation of the relevant selecting magnet moves selecting bar 31 (Fig. 2) downwards whereupon the driver 41, attached thereto by the spring 41a, turns anti-clockwise so that its lower end is above the operating bar 6. The auxiliary spring set has two drivers 4 and 5 (Fig. 1) associated with the spring set groups 2a, and 2b, respectively, the drivers being normally in the positions shown with the lower end 5b of driver 5 engageable with the left-hand edge of the hole 6a in the operating bar 6. Operation of the auxiliary select magnet S pulls the auxiliary selecting bar 3 downwards, whereupon the drivers turn anti-clockwise so that the lower end of driver 5 is located above the hole 6a and that of driver 4 becomes engageable with the edge of the