441,736. Automatic exchange systems. GENERAL ELECTRIC CO., Ltd., Magnet House, Kingsway, London, and CARPENTER, O. 1., and MOSS, B. F., c/o General Electric Co., Ltd., Stoke, Coventry. Dec. 19, 1934, No. 36409. [Class 40 (iv)] The existence of a faulty line at an unattended exchange is signalled to an operator at an attended exchange, and means is provided whereby the operator may ascertain the number of the line to which she may attempt to speak or apply tone. If standstill conditions arise in the normal line finder, a special finder connects the line to common apparatus which signals the operator. The common apparatus has a stepping switch cross-connected to the banks of the special finders in order to identify the lines, the switch being moved in single steps by the operator until a tone signal is removed from the junction whereby the operator ascertains the digits of the line number in turn. The initiation of a call operates A which makes marking and starting circuits for a line finder, B and C pulling up when the line is found. Standstill conditions cause the finder to remove ground from P releasing B, while C remains held over the loop. The finder also grounds lead 20 to operate relay ST of the special finder, Fig. 2, serving the line group in question. The unattended exchange is assumed to have 200 lines, and four 50-point special finders are used, the contacts in the dotted rectangles, Fig. 2, being those of relays in the other finder serving the same 100's group. Only one special finder at a time can be in use. Relay ST operates G in series with H which remains inert, but G interacts with LF to step the finder which, on reaching the faulty line, finds ground on lead M to the normal finder, whereupon H pulls up followed by switching relay HA in series with common relay R if no other switching relay is operated. H grounds lead 21 to release the normal finder and HA short-circuits a winding to prevent operation of another HA relay and connects ground over banks LF5, 6 of the special finder to banks of a common switch DS according to the number of the line. G re-operates. A delay circuit applies pulses in turn to XA, XB, XC and if XC operates on the third pulse, the pulses are connected over lead 15 to a repeater (not shown) which sends signals over the junction, and a buzzer relay BZ provides tone on one of the junction wires 14. The operator plugs in, whereupon the repeater causes A to operate follower by B and RA which locks and makes HA and R dependent on B. The operator then proceeds to send single impulses which are repeated by A to C and the back stroke magnet DS. The first and second 100 subscribers are represented by a ground on the second and third contacts respectively of DS2 and as the finder LF shown belongs to the first hundred, SZ pulls up after one impulse, locks on the relapse of C, and removes tone from the junction to inform the operator that the first digit is 1, DS proceeding by selfinterruption to contact 4. The operator proceeds with impulsing, and if the second digit as marked over bank LF5 is 1, SZ remains operated and tone is not re-applied to the junction. If the second digit is other than 1, SZ relapses and re-applies tone which is again removed when SZ re-operates over the contact of DS2 marked over LF5. The 5th to 14th contacts of DS2 are taken to tens mutiples in the banks of the LF switches. The operation of SZ sends DS by self-interruption to contact 15 and in response to further impulses DS is stepped to a contact marked over LF6 according to the units digit, tone being re-applied and removed as before. After the units digit, SZ remains operated and DS goes home. The operator may now test or attempt to speak to the faulty line and when she withdraws, all the operated relays in Figs. 2 and 3 fall back, the faulty line being locked out by relay C in its line circuit. Should the fault disappear while the operator is on the line, C, Fig. 1, relapses and releases the finder LF.