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Three-wire twisted conductors, each of No. 18 B. & S. gage rubber-covered wire, join the binding posts 1, 3, and 5 on the rack to the respective binding posts 1, 3, and 5 on the telephone stand. The magneto box may be connected to the line wires either
Fig. 49.—The Wiring and Connections for a Desk Set
with straight or twisted conductors of No. 18 B. & S. gage rubber-covered wire.
Modifications of the Bridging Connections are numerous. One of the commonest is that in which the bell and generator, instead of being in parallel with each other across the line, are joined in series and bridged across the line as in Fig. 50. The
generator g is then provided with an automatic shunt, Fig. 29, and consequently offers no resistance to the incoming signaling current when not in service. The magneto bell b being constructed the same as in Fig. 44, presents sufficient impedance, however, to prevent the talking current being shunted through this path.
Fig. 50.—Bridging Connection with the Bell and Gen
erator in Series
Other modifications are shown in Fig. 51, where o is the battery, i the transmitter, p the primary of the induction coil, s the secondary of the induction coil, r the receiver, g the magneto generator, b the ringer, m and n the line terminals, and e the ground terminal. At A are given the connections for a bridging station in which the bell and generator are automatically disconnected during conversation.
Although the bell and generator are here shown in series connection across the line, they may be joined in parallel with each other if an open-circuit generator is used, and operated as in Fig. 44. As
Fig. 51.—Modifications of the Bridging Connection
in previous cases, either a grounded or a complete metallic line circuit can be used. At B is shown an arrangement in which the talking circuit is metallic, and the signaling circuit is grounded, the talking circuit or the signaling circuit
being automatically introduced by the action of the hook switch. When the receiver is on the hook the signaling apparatus is in circuit, and when it is off the hook the signaling apparatus is entirely disconnected. At C is given a plan of wiring for a wall set, somewhat different from that in Fig. 47, and at D is a different form of wiring from that in Fig. 49 for a desk set. The ringers are all of the bridged type. The generators in cases A and B are provided with automaticshunts, but in the cases C and D they are of the opencircuit type.
The Op ration of the Bridging Station. - Bridging stations when operated on a grounded system are connected together as shown in Fig. 52, and when operated on a complete metallic sys
Fig. 52.—Method of Wiring Bridging Telephone Sets on a Grounded Circuit
tem are connected together as in Fig. 53. As previously noted, disturbances are more frequent in grounded systems, but only half as much line wire is required as with complete metallic circuits. The ordinary operation of bridging stations is practically the same as already described for series stations, a party ringing once to signal one station, twice to signal another, and so on, or by a predetermined code of long and short rings accomplishing the same results. As, in the previous case, the line is serviceable for but two parties at a time, there is no privacy afforded the conversation, and the ringing of all the bells simultaneously. is somewhat annoying. Notwithstanding these dis
Fig. 53.—Method of Wiring Bridging Telephone Sets on a Complete Metallic Circuit