The practical telephone handbook and guide to the telephonic exchange (1906) (14756182265)

Identifier: practicaltelepho00pool (find matches)

Title: The practical telephone handbook and guide to the telephonic exchange

Year: 1906 (1900s)

Authors: Poole, Joseph

Subjects: Telephone

Publisher: New York, Macmillan Co.

Contributing Library: Northeastern University, Snell Library

Digitizing Sponsor: Boston Library Consortium Member Libraries

Text Appearing Before Image:

Fig. 290.—Plain Scale £ 286 PRACTICAL TELEPHONE HANDBOOK silver strips, riveted on the thick iron bar, which forms thesupport for the whole strip. The resistance of the heat coil is 375 ohms. All thebars are connected to earth, and thus the line wire becomesdirectly earthed when the fuse operates. The current throughthe line is at once strengthened, and the line fuse (fitted at thepoint where the lead joins the outside line) melts, and introducesa gap in the line circuit, cutting off the high voltage from everypart of the internal circuit. Latest Practice.—In the latest exchanges the line fuses arecombined with the arrester strips as in Fig. 291a, which gives

Text Appearing After Image:

Fig. 291.—Scale \ two views of the combination. The lines are connected firstto the line fuses, then to the arresters, then by jumper wire tothe horizontal frame and next to the I.D.F. When a heat coil fuses, the corresponding line inside isearthed, and its lamp is lit on the switch-board ; but as nocommunication can be obtained, the operator reports the lineto the fault clerk. For convenience of connecting the twin jumper wires, theclamping screw a is connected to one of the inner-line springs,but is otherwise insulated, and is furnished with a soldering tabon the opposite side of the frame plate, so that both jumperwires can be connected on one side. Resetting Heat Coils.—In some recent forms of protector usedin America the heat coils are so constructed that they can beused over and over again without repairs. In the Kaisling protector this is accomplished by making the heat coilsymmetrical, so as to be reversible. When the coil has operated,and the pin has been pressed inward,

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1906

Northeastern University, Snell Library

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public domain