322,241. Standard Telephones & Cables, Ltd., and Wright, E. P. G. Sept. 5, 1928. Automatic exchange systems.-The conversational switches employed in a connection are of the no-normal single-motion type, and at each switching stage a temporarily-used marking switch operates to select an idle trunk or the wanted line, and, in the former case, extends the impulse circuit to the next switching stage until the conversational switch has been set on the selected trunk. The marking switches are connected in multiple to the switches they control, and are of the singlemotion type with two sets of wipers. Dialled impulses are received in each marking switch by a set of relays P, Q, R which control the numerical setting by applying marking potential to particular terminals of the switch. The marking switch associated with the connector tests the wanted line, and may be arranged to select an idle line in a private branch exchange group. Group selector, Fig. 1. upon seizure, relays K, P energize over the incoming test wire, the former completing the circuits to the marking switch, and the latter disconnecting its lowresistance winding to busy the marking switch and the associated selectors. Line relay 1 energizes and connects up release relay 4, which applies a fresh busy marking. Impulses are now repeated at contact 1 (1) to the set of relays P, Q, R in parallel with relay 3, which holds up throughout the train. At the first impulse, relay Q energizes, locks and transfers the locking circuit of relay P over back contact 3 (1), so that this relay falls back when the loop is reclosed. At the second impuse, relay R energizes, locks and changes the locking circuit of relay Q so that it falls back at the end of the impulse. The third impulse causes the re-operation of relay P and the release of relay R, and the cycle is repeated for further impulses. Relay 3 completes the interrupting circuit for magnet RM over 3 (4), 2 (5), 1 (72), 6 (82), 1(71), 3 (P) or 2 (Q) or 2 (R), 3 (3). Relay 5 is connected over front contact 1 (Q) to the first terminal of the 1st, 4th, 7th and 10th groups in bank 10, over front contact 1 (R) to the first terminal of the 2nd, 5th and 8th groups and over front contact 1 (P) to the first terminal of the 3rd, 6th, and 9th groups, so that this relay energizes to ground at contact 3 (3) and stops the marking switch on the first line of each group until its circuit is opened on the receipt of the next impulse by relays P, Q, R. At the end of the train, relay 5 remains operated, and relay 3 falls back, releasing the last of relays P, Q, R to be operated. Change-over relay 2 now energizes over off-normal contacts, and relay 5 falls back, closing a fresh stepping circuit for magnet RM over contacts 5 (2), 9 (4), and connecting test relays 71, 72 to wipers 6, 5. Assuming wiper 6 finds an idle trunk, relay 71 pulls up and connects up relay 81, which switches through the talking wires via wires 1, 4 to the succeeding switch and grounds test wiper 6. Relay 3 re-energizes, closing a circuit for magnet R over 1 (5), 6 (3), 4 (81) for stepping the selector to the marked trunk, when relay 5 energizes over wipers M, 7 and cuts the drive. Switching relay H energizes and locks, and release relay 4, which is held over 2 (1), 1 (5), 6 (3), 4 (81) after the relapse of line relay 1, falls back and closes a restoring circuit for magnet RM, relay Q being energized to prevent seizure of the marking switch during this movement. If wiper 5 finds an idle trunk, relay 72 connects up relay 82 with similar results. If all the trunks of the group are busy, relay 5 energizes over 9 (82), 8 (81), 2 (2), wiper 10, 9 (4) and connects up relay O which operates slowly to allow the last trunk to be seized if it is idle and applies busy tone. If no impulses are received by the marking switch, ground impulses over wire TP energize relays 9, O in turn, and magnet R operates to drive the selector to a position marked in the normal position by the marking switch, when relay 5 energizes and cuts the drive. Switching relay H energizes and locks over an alarm wire connected to the test terminal. Connector, Figs. 2, 3, 4. Relays K, P energize as in the case of the group selector, and line and release relays AA, 4 are connected up. Impulses are repeated at contact 2 (AA) to the set of relays P, Q, R in parallel with relay 3, and magnet RM steps the marking switch under control of relay 5 to the first line of the group determined by the tens digit as described with reference to Fig. 1. Release of relay 3 connects up change-over relay 2, which disconnects relay 5 and re-energizes relay P. The first impulse of the units train energizes relay 3, which connects up relay Q, and relays P, Q, R operate in turn in response to further impulses as before with the difference that each time relay R is unlocked following the energization of relay P, relay Q energizes' at once over 2 (R), 2 (P), 1 (2), 1(3) and releases P. Relays P, R are therefore momentarily operated at the same time during the 3rd, 5th, 7th and 9th impulses, and an impulse is sent over 4 (2), 5 (R), 6 (P) to magnet RM to advance the marking switch one step, and relay Q or R remains operated at the end of the train according as the digit is odd or even to connect up the correct set of the wipers. If the wanted line is busy, relay 6 energizes over test wiper T1 or T2 and connects up busy relay GA to apply busy tone, and relay HA energizes to release the marking switch, which restores as in Fig. 1. If the wanted line is idle, relay 7 energizes over 2 (6), ( 0), 6 (3), 5 (2) to test wiper T1 or T2, locks, releases relay 2, applies ring- back tone at contact 8 (7), contacts ground to marking wiper W1 or W2 and closes a circuit for magnet R of the connector over 4 (HA), 3 (2). 2 (7), 2 (5), which is opened by energization of relay 5 over wiper C when the marked line is reached. Relay HA pulls up, releasing the marking switch and applying ringing current through ring-trip relay FA, which energizes on reply of the called party and connects up relays B, BB, which release relay K, connect in feed relays A, D and ground the test wire. If no impulses are received by the marking switch, relays 9, 6 energize in turn to give an alarm after an interval, substantially as in Fig. 1. P.B.X. hunting. If the line selected in response to impulses is the first of a P.B.X. group, and if this is busy, relay 6 energizes over test wiper T1 or T2, and relay 8 energizes to battery on wiper XI or X2, closing a fresh circuit for magnet RM and connecting up relav O, which connects relay 5 to wiper X1 or X2. If all the P.B.X, lines are busy, relay 5 energizes on the last line, cutting the drive and releasing relay O, and busv relay GA energizes to apply busy tone. If an idle line is found, relay 7 energizes over test wiper T1 or T2 and the connection is completed as in the case of an ordinary line. Multiplying arrangements. The connectors served by a single marking switch are divided into two sub-groups which are associated with two relay groups HA, GA, AA, I'A and HB, GB, AB, FB. While one relay group in use with a particular connector is engaged in ringing or giving a busy signal, the marking switch is released by relay HA or HB and may be seized for use with a connector of the other sub-group which is associated with the other relay group.