334,247. Standard Telephones & Cables, Ltd., and Wright, E. P. G. May 31, 1929. Automatic exchange systems.-In a district office system, first group selectors having access to main exchange junctions and to local trunks are controlled by a common circuit comprising a discriminator which responds to one or more digits and, if a local call is indicated, causes a by-path switch in the control circuit to hunt for a local trunk. The system described is identical with that described in Specification 334,248 which claims other features. A calling party S2, Fig. 5, at a district office is connected over finder switches SLF1, SLF2, to an idle group selector SGF associated with an idle control circuit SBP. The selector hunts for an idle junction and the first or first and second digits are repeated to switch R1 in the control circuit and also over the junction. If this digit or digits signifies a call to the main exchange the control circuit is released and the group selector acts merely as a repeater, but if a local call is indicated, switch R2 hunts for the group of trunks marked by R1 and for an idle one in the group. Switch R1 is then stepped on to terminals of the seized selector of its associated group which appear in the later portions of the banks of R1, and the selector is stepped on to the selected trunk under the control of the common circuit. Further digits are repeated over the by-path switch R2 to the control circuit, SFBP of the final selector SFF and the connection is completed as described in Specification 324,982. At the main exchange, mixed groups of local first group selectors such as IGF and incoming selectors JGF are associated with common control circuits such as 1BP, or incoming selectors from different district offices are grouped together under the control of the same common circuit, and connections are set up over by-path circuits as described in Specification 324,982. Local call at district office. The selectorrepeater, Fig. 1, is taken into use over non- numerical switches as described in Specification 317,821, an idle selector and control circuit being indicated by battery over home! contact in bank 1 of Rl on wire TW. Ground over K operates KS which connects up the common control circuit SBP, and line relay AS pulls up and is followed by BS and B which, at b2, holds KS. The selector steps in search of an idle junction to the main exchange, each junction being associated with a pair of relays JB, JT, of which the latter is operated in the case of a busy junction. The negative wire at the incoming selector, Fig. 3, is connected over lead 3 to battery over 2b5 and normal contacts in banks 9, C of switches 2R1, 2R2 in its common control circuit, Fig. 4, if idle. Consequently if a junction and incoming apparatus are idle, relay JB, Fig. 1, pulls up over GC which is marginal and will not energize if two district offices make simultaneous calls involving use of the same common control circuit, Fig. 4. 'When the selector arrives at an idle junction, V(ii) operates in series with JT and locks over V(i), JT being held over jt2 after JB has relapsed. Relay HS also operates in series with V(ii), grounds the test wiper, and loops the junction over IS, DS causing 2KS at the incoming selector, Fig. 3, to operate, lock, and seize the common control circuit, Fig. 4, at which relays 2A, 2B pull up. Relay AS, Fig. 1, responds to the dialled impulses, the first digit being repeated to magnet! R1 over relay C. Assuming the first digit (3 as shown) to indicate a local call, relay W pulls up over bank 4 on the relapse of C locks up over bank 3, and completes a self-interrupting circuit, over bank 3, for R1 which steps to position 12 where its circuit is open at b5 and relay W also falls back. The second digit is now repeated to R1 and, assuming it to be 5 or 6 indicative of a local call, R2 steps over m1 and bank 4 of R1 until relay M pulls up over the first contact of a group in bank CC of R2 marked over bank 7 of R1. Relay E now operates over bank 4, locks up and releases M to restore the driving circuit of R2 which hunts for an idle outlet in the group. Test relay H operates over H (ii) and TC to battery on an idle outlet, locks over H (i), grounds TC, stops R2 and completes a stepping circuit for R1 which is opened by relay T when R1 has found the selector repeater shown in Fig. 1. Relay H also releases B but is held by ground returned over wiper TC. Relay TT operates, and as HS relapsed when E operated, a circuit is completed for magnet S of the selector which hunts for the terminal marked in bank MS by battery over wiper MC of R2. When this is found, M operates over bank 6 of Rl, opens the circuit of S, and grounds the test wiper TS. When E operated, JT was made dependent on ground over V (i) and when TT operated both V and JT were released. The connection is extended to the wanted line as described in Specification 324,982, further digits being repeated over wiper - of R2. If the line is free, ground fed back over wiper TS, and bank 5 of R1, operates LS which locks up, operates HS and completes the ringing circuit over FS which, when the called party replies connects feed-battery over the windings of IS. Metering. This is effected over is2, ls2 and wire MW when the called party replies. Busy signal and release; normal release. If the wanted line is busy, HS does not operate and when KS falls back due to relapse of H following upon release of the control circuit of the final selector, busy tone is connected up over BT. R2 is a non-homing switch but R1, S return to normal. When the calling party replaces his receiver after a successful call, AS, BS relapse followed, by other operated relays and completes a homing circuit for S, relay CS being operated in parallel with S to open the incoming test circuit. All outlets busy in wanted group at the selector repeater. Wiper CC of R2 proceeds to last contacts of the group, relay M operates in series with G which unlocks HS and releases KS to disconnect the common control circuit and send back the busy signal. Call from district office to main exchange. The selector-repeater seizes an idle junction as previously described, but if the first digit denotes a call to the main exchange, relay Z operates over bank 4 of R1 and opens the circuit of B which releases KS and the common control circuit. If discrimination is dependent on the second digit and not the first, Z operates in a similar manner. The selector-repeater now acts merely as a repeater. When relay 2B in the common control circuit, Fig. 4, of the incoming selector, Fig. 3, operated as previously described, relay 2M energized over normal contacts of banks C, 9 of switches 2R2, 2R1 respectively. The first digit is repeated over the junction by AS at as3 and CS pulls up to complete a direct loop at cs2. Relay 2A, Fig. 4, responds and repeats the digit to 2R1 in series with 2C. At the end of the first impulse the circuit for 2M over bank 9 is opened and 2R2 steps first over 2c1 2b1 and subsequently over 2n2, 2e5 until 2M re-operates. The first contacts of groups in bank C are connected to the contacts in bank 9 so that R1 comes to rest on the first contact of the group corresponding to the setting of 2R1. Relay 2C relapses at the end of the digit and, with 2M operated, relay 2E first operates its light armature 2c10. locks up, and releases 2M so that a fresh driving circuit for 2R2 is completed over 2n2 to ground at 2b1. Switch 2R2 has two sets of wipers, and relay 2E closes the test circuits over relays 2P, 2Q. If wiper T1 finds an idle outlet, 2P operates 2H, while if T2 finds an idle outlet, 2Q operates 2J which also energizes 2H. Relays 2P or 2Q falls back and relay 2J switches in the second set of wipers. Relays 2A, 2B are released by the operation of 2H but 2E, 2T remain held by ground fed back over the test wiper. Relay 2E also completes a circuit for 2R1 which steps until 2T operates over bank 4 to the terminals of which leads such as 4 from the associated group of selectors are connected. Relay 2TT also energizes and locks 2T. Magnet 2S of the incoming selector, Fig. 3, operates over 7 to ground at 2h8 and when the selector reaches the terminals corresponding to the setting of 2R2, the ground from 2tt3 connected up over wiper 9 of 2R1 to wiper M of the selector operates 2M over the wiper M1 or M2 of 2R2 which opens the circuit of 2S and energizes 2G. Relay 2HS, Fig. 3, operates over 6 to ground at 2h8, extends this ground over 2hs5 to mark the succeeding selector in its common control circuit and switches through. The connection is further extended over group and final selectors as described in Specification 324,982. All outlets busy. Switch 2R2 steps to last contacts of the group and 2M pulls up over 2b5, 2e12, 2bl, opens the drive, and completes a circuit for slow-to-operate relay 2G which previously remained inert when 2M, 2E were operated. Busy tone is connected up over 2g8. Release of common control circuit. When the succeeding common control circuit removes ground from the test wire, relays 2T, 2TT, 2E fall back and release other operated relays, homing circuits for 2R1, 2R2 being completed. Standstill release. If the subscriber fails to dial, ground pulse over lead A and normal contact of bank 8 operates 2G which locks up and after a predetermined period a pulse over lead B and normal contact of bank 10 operates 2E which releases 2G and operates 2P over normal contact, of T1 Relay 2H operates as previously described and connects the calling loop over leads 1, 2 to the normal contacts of wipers + 1. - 1 uf 2R2 and thence back to relay 2A. The switch 2R1 is driven until 2T, 2TT operate and complete the circuit of 2S as previously described. Switch 2S is driven until it reaches terminals corresponding to the position of 2R2, that is normal, and 2M, 2G, 2HS operate as before. Relay 2G releases 2A, and opens one circuit of 2B which is final