678,319. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Feb. 3, 1950 [Feb. 9, 1949], No. 2829/50. Class 40 (iv). To enable the lines of a PBX group to be scattered over a plurality of final selectors, the PBX lines are multipled to consecutive outlets in an auxiliary final selector over which calls entailing PBX hunting are set up, normal calls and calls to individual PBX lines being set up over the normal selectors. Any outlet of a PBX group in the normal final selector may be chosen as the common PBX number but the corresponding outlet in the auxiliary final selector must be the first of the PBX group. First arrangement, Fig. 1. The register O.REG sets up a connection over a train of translator switches ITS ... FTS, similar to the normal selector train IGS ... FS. If the call is not to a common PBX number, battery received over the test wiper of the final translator switch signals the register to release the translator train and to set up the call over the normal selectors IGS ... FS. If the call is to a common PBX number, earth received over the test wiper of FTS signals the register that the call is to be set up over the auxiliary or PBX train of selectors PBX-4GS and PBS-FS. At the same time the register receives over other wipers of FTS electrical markings which are translated by the register into the code number required to set the auxiliary switches to the first line of the desired PBX group. In an alternative arrangement, the selectors IGS ... FS and ITS ... FTS are set simultaneously, the former being released and the call routed over the auxiliary selectors if the call is to a common PBX number. Second arrangement, Figs. 2-4. In a 10,000-line PAX facilities are provided for 400 PBX's averaging 5 lines each. The translator switches are dispensed with and the normal switching train IGS.FS carries out its functions. When the register is taken into use, relay Cg pulls up. The connection is set up under the control of a sequence switch OM which steps to contacts A when the final selector FS is set to the called line. Wires a, b of a line associated with a common PBX number are each marked by an A.C. having one of a range of 10 phases and a voltage of 3 or 4.5. If the call is to a common PBX number, a static switch is operated by direct battery connected over wire d and causes Px to lock up followed by Ya. Px, Ya connect one of the transformers STI of a discriminating device similar to that described in Specification 631,156 to wiper trsme of a translator switch TRS, the other transformer ST2 being connected to wire a. Relay Hp operates and TRS rotates until the wiper trsme is connected to a current identical to the marking on wire a, whereupon tube SV2 strikes and relay Wp stops the switch TRS. Relay Pc operates and Hp, Wp, SV2 returns to normal. A circuit is completed for relay G to connect up Hp, and the discriminating device makes a check test. If this is a failure, sluggish relay Pc releases followed by G and the translator switch hunts afresh. Otherwise SV2 strikes to bring up Wp, and Ok earths wipers trsma ... trsmd of the translator switch to operate a combination of relays Aa ... Ad (1, 2, 4, 6) together with Af (3-volt marking) or Ae (4.5 volt marking). Relay Pc releases and temporarily operates Te to release relays Hp, Wp, Ok, G. Relay Ag substitutes relays Ba ... Bf for Aa ... Af, and the marking current on the wire b is recorded on relays Ba ... Bf similarly to that on the wire a. When the record is completed, relay Bg releases Px and Fs, and Ya and PA follow. PA releases the switch train IGS ... FS. Supposing that a 4.5 volt current was applied to the wire a, the required PBX is then in a first main group consisting of 20 PBX groups reached over an auxiliary switch train seized by the digits 97. In this case relay Bg connects up relays Za, Zb, Zd to apply a current having a phase representing the digit 9 to transformer STI. Relay Hp operates and the first group selector IGS selects an idle outlet in the ninth level, and when successful relays Wp, Ok operate, the sequence switch OM is rotated to position B and relay O pulls up for a short time to disconnect Za ... Zd. The release of O is followed by the operation of relays Za, Zd and the second group selector 2GS selects an idle outlet in its seventh level to a selector PBX-4GS. In position C the sequence switch connects relays Za ... Zd in parallel to relays Aa ... Ad and so a PBX final selector is selected according to the phase of the wire a marking current. Similarly in position D, relays Za ... Zd are operated in correspondence to relays Ba ... Bg and apply a current having the phase corresponding to the wanted PBX group to the transformer STI. A maximum of 20 PBX groups may be connected to a PBX final selector which is of a type, such as a singlemotion selector, capable of hunting over all outlets. If the marking on the wire b was 4.5 volts, the operated relay Be completes a circuit over wiper omme for Ya to connect the inner part of the winding of transformer STI so that the discriminating device responds only to a 4.5 volt marking. If the marking was 3 volts, the whole of the winding of STI is connected. Supposing the marking on wire a was 3 volts, the required PBX is then in the second main group and the operated relay Af causes the group selector IGS to be set to its tenth level and completes a circuit for the sequence switch OM to step over position B to position C, the further operations being as described above. The number of PBX groups in the exchange may be increased by using the operated thousands digit register to select from extra levels of selectors 1GS or 2GS leading to PBX selectors. Specification 663,037 also is referred to.