464 



SUEJIAEINE CABLE LAYING AND REPAIRING. 



manner of the free overlap. For instance, the Kennelly and 

 Schaefer methods applied to a fault from one end only do not 

 eliminate the water column resistance, but by testing from both 

 ends with these mebhods, and working out the observations by 

 the free overlap formula, this element of the fault's resistance 

 is completely eliminated. 



Mance Partial Earth Test to True Zero.— Sir Henry Mance, 

 in his Paper previously referred to, pointed out that as a partial 

 earth fault method this test should be taken from both ends of 

 •the cable to eliminate the fault resistance. 



The test is taken to scale or true zero with two different 

 strengths of current to line in the proportion of about 2 to 1, as 

 previously described for the break test (page 437). 



Several pairs of balances are taken at each end successively, 

 and the results worked out by the Mance formulae (3) or (6) 

 given on page 438, namely 



A-(A-B)Pohms 

 or A + (B-A)Pohms 



according as to whether the reading A is greater or less than B 

 respectively and where A and B are the observed CR's to true 

 zero with the smaller and larger currents respectively, and P 

 has the values in the annexed Table : — 



Table III. — Coefficients in Mance's Test. 



