. American telephone practice . PRACTICE. The lightning arresters found on nearly all telephone instrumentsup to within a few years ago, were of the saw tooth type, and usuallyof the general form shown in Fig. 421. This was an adaptation ofthe lightning arrester frequently used on single telegraph lines atintermediate stations where the two wires, which looped into theoffice, terminated respectively in the binding posts on the plates,Aand B, between which posts the local instruments were also plate, C, was connected directly with earth. By inserting aconducting plug in the hole, e,
. American telephone practice . PRACTICE. The lightning arresters found on nearly all telephone instrumentsup to within a few years ago, were of the saw tooth type, and usuallyof the general form shown in Fig. 421. This was an adaptation ofthe lightning arrester frequently used on single telegraph lines atintermediate stations where the two wires, which looped into theoffice, terminated respectively in the binding posts on the plates,Aand B, between which posts the local instruments were also plate, C, was connected directly with earth. By inserting aconducting plug in the hole, e, the local instrument would be short-circuited and the line left connected through. If the plug wereinserted in the hole, g, that end of the line terminating in plate Awould be grounded, while the local instruments would be connectedin circuit with that end of the line terminating in plate B. Simi-larly, inserting the plug in hole, /, would ground the end of the lineconnected with the plate B, and leave the instruments connected. FIG. 421.—SAW-TOOTH ARRESTER. in operative relation with the end of the line terminating in theplate A. When applied to a telephone instrument, or more properly, to asub-station equipment, the plates A and B form the terminals of theinstrument and also the terminals of the line, the plate C, as before,being grounded. When telephone instruments are connected in seriesin a party line, as was the common practice in the early days,either end of the line could be cut off and grounded, leaving theinstrument in operative relation with the other end in exactly thesame manner as described in connection with the telegraph formed a convenient means of cutting out a defective end ofthe line when comunication was desired with the other end. On atelegraph line, or on a series telephone line this device, therefore,served admirably as a switch, in addition to its functions as a light-ning arrester. The latter functions may be described as follows:When the l
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