512 SUBMARINE CABLE LAYIXG AND REPAIRING. 



and P (by Table m.) = l'714 



L=A-(A-B)P, 

 = 2,555-5 - (324 x l-71'i) = 2,000 ohms. 



which is the correct CR of the cable. As will be seen, the- 

 formula eliminates the earth current effect. 



Now, consider a positive earth current is acting. This will be 

 in the same direction as the testing current (Fig. 286), and the 



, , I Cable 2000^ 



Hi|i|i I — =^ I 



^Testing current " StV^^; 



Zinc to line 



Fig. 286. — Good Cable with Positive Earth Current. 



effect will be that the balance obtained will be less than the 

 true CR. 



The balance A will be 



c 

 that is, 2,000 - ^ill^ = 1,444-5 ohms. 



The balance B will be 



2,000=^^=1,768-5 ohms. 



L=A + (B-A)P, 

 = 1,444-5 + (324 X 1-714) = 2,000 ohms, 



which is the correct CR of the cable. 



As will be seen, the earth current effect is eliminated in this 

 case also. 



Conductor Resistance Correction for N.R.F. — The CR's 

 from both ends are duly corrected for earth current (as explained 

 in the preceding paragraph) and the proper temperature cor- 

 rection applied (as explained in the next paragraph following), 

 A time must be chosen when the earth current is fairly steady. 

 It should be borne in mind that correction methods and 

 formulae are based on the assumption that the earth current is 



