THE LOCALISATION OF BREAKS AND FAULTS. 513 



steady during a pair of observations and, therefore, when trying 

 to get an exact measurement such as this the most favourable 

 natural conditions should be looked for. 



After carefully arriving at a mean of several uniform observa- 

 tions with both currents, duly corrected for earth current and 

 temperature, this must be further corrected for the N.R.F. The 

 position of the N.R.F. is conveniently found from the difference 

 of the CE's at both ends and the insulation of the line at the 

 first minute by formula (7) or (8) (p. 442). 



Taking the same cable as given on p. 444 the CE's corrected 

 for earth current and temperature are 



CR observed from A end 8,320 



„ ,, ,, B ,, 8,485 



Mean of the two 8,402 



Difference 165 



Insulation first minute 0*24 megohm. 



Taking the above mean as the nearest approximation to L 

 the position of the N.R.F. is found by formula (7), p. 442, thus : 



^ / Q2_165x240^0N 33Q ohms. 

 ^V 8,402 ) 



This gives the approximate distance of the N.E.F. from the A 

 end. The distance from B is then 



8,402-1,850=6,552 ohms. 



That is approximately 



^=1,850 



(?=6,552. 



The N.R.F. correction can now be applied to the CR's by 

 formula (12), p. 445. 



=8,320 + ^^'^^^■^ =8.320 + 178 = 8,498, 

 0"24 



19 



