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BELL SYSTEM TECHNICAL JOURNAL 



nected to them. The voltage to ground at either end of the exposure 

 is equal to the longitudinal current times the impedance-to-ground 

 seen looking away from the exposure at that end. Figure 10-C 

 illustrates how the voltages may distribute due to the distribution of 

 impedances between the wires and ground along the line and in the 

 central office equipment. Of course, in practice, the variety of im- 

 pedance distributions encountered is almost infinite and the corre- 

 sponding voltage distributions vary over a wide range. 



If voltage-to-ground at any point where protectors are located 

 exceeds the operating voltage of the protector, the protector operates 

 and three things happen : 



{a) The voltage-to-ground at the place where the protector operates 

 is reduced to a low value. This makes the longitudinal voltage 

 pile up at the protectors at the opposite end, and in most cases, 

 they will also operate. 



{h) The operation of the protectors at the two ends completes a loop 

 consisting of the telephone circuit and ground so that the in- 

 duced voltage will cause current to flow through both pro- 

 tectors. 



(c) The voltages-to-ground on the circuits on which protectors have 

 operated are changed and redistributed and the voltages on the 

 other telephone circuits are also changed and redistributed due 

 to shielding, as discussed later. 



Fig. 1 1 — Demonstration showing effect of terminal impedance on voltage distribut ion . 



All of these effects take place within a very short time after the longi- 

 tudinal voltage is applied so that for all practical purposes they can 

 usually be considered as being instantaneous. 



In order to illustrate these phenomena, the demonstration shown in 

 Fig. 11 can be used. In this demonstration the longitudinal voltage 



