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BELL SYSTEM TECHNICAL JOURNAL 



also practically zero. For loaded lines, the inductance is efifectually 

 that of the loading coils, and for the frequencies usually employed in 

 open location tests it can be considered as being uniformly distributed. 

 For non-loaded lines, the equation of line impedance is reduced to 

 one of series resistance and capacitance to ground. These constants 

 can be determined by the measurement of short lengths of cable. In 

 making capacitance measurements, the remaining three wires of the 

 quad should be grounded to eliminate their capacitances to ground. 

 When the other three wires of the quad are left free, the capacitance 

 to ground of the faulty wire increases as the length of good wire 

 beyond the break increases. This effect is shown in Fig. 1. 



The values of R and C obtained by measuring short lengths of 

 cable are used to calculate P and Zq. Where the lines are loaded, the 

 nominal inductance and resistance of the loading coils are used and 

 the characteristic constants R and C are, if possible, determined from 

 non-loaded conductors. These constants for one particular cable are 

 listed as follows: 



TABLE 1 



Constant 

 per Mile 



Grade of Loading 



Non-Loaded 



H-44-25 



H-174-106 



H-245-155 



R 

 L 

 C 



R 

 L 

 C 



42.90 

 .000 + 

 .100 



44.00 

 .000- 

 .110 



19-Gauge Inner Layer Conductors 



44.65 

 .015 

 .100 



47.78 

 .062 

 .100 



19-Gauge Outer Layer Conductors 



45.75 

 .015 

 .110 



48.88 

 .062 

 .110 



50.34 

 .089 

 .100 



51.44 

 .089 

 .110 



These constants represent values per single-wire mile, R being in ohms, L in 

 henries and C in microfarads. 



In making an open location, two impedance measurements are 

 made. One measurement is made on the faulty wire. The other 

 measurement is made on a good wire which follows the same route 

 as the faulty wire. The input impedance of the open conductor 

 divided by the input impedance of the good wire gives an indication 

 of the location of the fault. For short cables, the impedance measured 

 to ground may be regarded as identical with the capacitance com- 



