THE LOCALISATION OF BREAKS AND FAULTS. 



439 



which is the same algebraically as (3), but in a convenient form 

 to use if B is greater than A. 



The values of P for various current ratios are given in 

 Table III. 



The last term to be deducted is not eliminated in single- 

 ended tests and must be estimated. The formula shows that 

 the correction to deduct is something less than the resistance of 

 the fault (/— (IF), and in experienced hands this allowance can 

 be estimated very closely. As pointed out by Dr. Kennelly, 

 there is less resistance to be allowed for the break than in any 

 other test except Lumsden's in particular instances. The same 

 applies when localising a small fault by this method by tests 

 from one end only. 



Table III. — Coefficients in Mance's Test. 



The test is only to be taken to true zero ; it is not applic- 

 able to false zero. 



It is not worth while spending time to get the ratio of 

 currents exactly 2 to 1. Any ratio approximately near that 

 will do, and the corresponding value of P found from 

 Table III. 



Taking three pairs of observations with the milammeter in 



