420 SUBMABINE CABLE LAYING AND REPAIRING. 



rent, for the reason already explained. That is, with a posi- 

 tive earth current the correction which is originally additive, 

 as in (7) and (8), becomes subtractive when combined with the 

 correction for the break resistance in the Schaefer equation 

 (10). 



In equations (1) and (2) the earth current corrections - and 

 — may be subtracted at once from the readings A and B re- 

 spectively when the earth current opposes the testing current 

 or added to them when the earth current is in the same direction. 

 The final formula is then simpler. 



Let Ai=:A— -orA+- (for negative or positive earth current). 



„ Bi = B — — orB+— „ ,, „ 



nc nc 



Then for a negative earth current — 



£r = Ai-(A,-Bi)P; ..... (11) 



and for a positive earth current — 



£^ = Ai + (Bi-Ai)P (12) 



When the corrections are made in this way the factor M is 

 not required, and the working out is somewhat simpler. 

 Taking the last example this way we have : — 



Correction for first pair -=^^^——=937. 

 ^ c 2-5 



Correction for last two pairs - — ^ — = 1.308. 



c 2*5 ' 



« 3,270_ 

 nc 6-41 



Working out the first pair we have : — 

 Ai=8,070- 937 = 7,133, 

 Bi=7,310- 365=6,945, 

 ^=Ai-(Ai-Bi)P 

 =7,133 - (188 X l-943)=6,768 ohms. 



