The practical telephone handbook and guide to the telephonic exchange (1906)
Poole, Joseph · New York, Macmillan Co. · leaf 163
extension and main instruments are in the same building. A push button is used to actuate the bell and so call the i38b PRACTICAL TELEPHONE HANDBOOK extension. On the latter operating the switch the main isentirely cut off from the exchange line. The supervisory signalis always in circuit and is… … Fig. 1526.—C.B. Pedestal Instrument with 3 Instrument Jacks may be connected as shown in Fig. 152a so that the extensioninstrument may be connected to either line. Speaking between main and extension cannot be donewith this arrangement, and no overhearing need be feared. Private House…
Telephone
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