320,905. Standard Telephones & Cables, Ltd., Wright, E. P. G., Baker, J. H. E., and Colebrook, C. M. July 25, 1928. Automatic exchange systems; party lines.-A bi-directional connector is controlled by common apparatus multipled to a group of connectors and including a bi-directional switch which moves in unison with the connector. In the rotary connector, Fig. 1, the control switch has a test wiper Te which moves over terminals multipled to the test terminals of the connectors, and a discriminating wiper Di which moves over terminals which are marked to distinguish between ordinary lines and private branch exchange lines. and over the tenth level to main exchange trunks, and the wipers of the control switch serve to connect up the ringing current appropriate to the wanted party. Rotary connector, Fig. 1. Relay K energizes over the incoming test wire in series with relay 2 and associates the common control apparatus with the connector. Line relay 1 and release relav 9 energize, and incoming impulses are repeated to the vertical magnet V1 of the connector, and to the vertical magnet V2 of the control switch, parallel relay 3 being operated throughout the train, and then falling back to connect up the rotary magnets R1, R2, which respond to the final train of impulses. Relays 7, 4 are operated at the first impulse, and fall back in turn at the end of the train, test relay 8 being then connected to test wiper Te. If the switches are standing on an ordinary subscriber's line, and this is idle, relay 8 energizes, grounds wiper Te, and when relay 4 has relapsed, applies ringing current RI through ring cut-off relay F to the wanted line and ring-back tone to the calling line through line relav 1. Relay F operates on the reply of the called party and energizes switching relay B in the connector, which connects feed relays A, D to the calling and called lines, the feed of the calling line being reversed to effect metering. Relay K is disconnected, and the relapse of relays 1, 9 initiates the release of the control apparatus. Release of the connector is controlled by relay B, which is held at contacts of both relays A, D. If the switches are standing on the first line. of a P.B.X. group, and this is busy, relay 8 does not operate, and a circuit is closed from battery at discriminating wiper Di for relay 6 which connects up relav 3 and interacts with the rotary magnets R1, R2 to step the switches over the group until an idle line is reached, when the test relay 8 energizes, or until the last line is reached, when wiper Di finds no ground for the further operation of relay 6. If after the numerical movement, the switches are standing on a P.B.X. line other than the first of the group, relay 6 does not operate, since wiper Di is connected to ground, and the line is tested by relay 8. In the case of an ordinary subscriber's line or the last line of a P.B.X. group being found busy, both relays 8, 6 fail to operate, and busy relay 5 energizes and connects up busy tone BT to line relay 1. Hanging up by the calling party then effects the release of both the connector and the control apparatus. Connector giving access to party lines and main exchange trunks, Fig. 2. Line relay A energizes over the calling loop, and relay K over the incoming test wire, applying dialling tone DT. Release relay 2 pulls up. Impulses are repeated by relay A through relay 1 to the vertical magnet VI of the connector and to the vertical magnet V2 of the control switch, parallel relay 3 being operated throughout the train, and then falling back to connect up the rotary magnets R1, R2, which respond to the second train of impulses. Relays 4, 6 are operated at the first impulse, and fall back in turn at the end of the train, test relay H being then connected to test wiper T. A separate number is provided for each partyline subscriber, so that each line has several numbers, which determine the code or harmonic ringing supply to 'be used. If the wanted line is idle, relay H pulls up, and connects ring-back tone RT to the calling line, and when relay 6 has relapsed, the appropriate ringing circuit is completed from,the wipers of the control switch through ring cut-off relay F, which operates on the reply of the called party and energizes switching relay B in the connector. Back-bridge relay D energizes and effects metering, and relay K falls back, disconnecting relay 2 to initiate release of the control apparatus. If the wanted line is busy, test relay H does not operate, and busy relay 7 energizes and connects up busy tone BT. The tenth level is reserved for main exchange calls, and when the switches are raised to this level, relay JC energizes over shaft springs NP, opening the normal circuits of the rotary magnets R1, R2 and connecting up relay 5, which interacts with the magnet R1 to rotate the connector until an idle trunk is reached, when test relay H operates, and energizes switching relay B. No ringing takes place from the control switch. If all the main exchange trunks are busy, the connector moves to the 11th position, when busy relay 7 energizes over springs S, and connects up busy tone BT. If no impulses are received within a given time, successive earth impulses over wire TPL operate relay TP, B, and the latter disconnects relay K to release the control apparatus.