460 SUBMAKINE CABLE LAYING AND EEPAIEING. 



are such as to place the fault electrically in the centre of the 

 line, when by Fig. 256. 



whence a^=k±Lz3, (5) 



where 



R = the greater resistance added to end nearer fault. 

 r = the lesser ,, „ end further from fault. 



X = distance of fault from end nearer fault. 

 L = true CE, of line. 



For example, let A be the end nearer the fault and B the other 

 end. Preliminary balances to false zero gave 



2,164 ohms from the A end, 

 6,886 „ B end. 



Both stations arranged to balance to 5 per cent, above 

 6,686 = 7,230 ohms, and after testing alternately for a given 

 number of times the added resistances when this balance was 

 obtained at both ends were 



R= 5,065 ohms at the A end, 

 r--265 „ Bend. 



The true CR being 8,200, the distance to fault from the 

 A end was — • 



8,200 + 265-5,065 , ^^^ , 

 x = =1,/00 ohms. 



If during the first period of tests the observations have not 

 come out quite uniform, a second set should be taken for a 

 similar period, balancing to a lower resistance and reducing 

 the added resistances at both ends accordingly. 



This test is taken to false zero with zinc current to line 

 and the same even bridge arms at both ends. The battery 

 power must be the same at both ends, and a milammeter may 

 be used as in the previous test to show the equality of the 

 testing currents. 



If there is known to be a low insulation at any particular 

 place in the cable the N.R.F. correction should be applied. 

 For instance, in the above example, suppose there is known to 

 be a low place of 0-8 megohm situated 1,500 ohms from the 



