682 ELECTRICAL MEASUREMENTS 



Loop Z and W and measure the resistance, ft, of the loop. 

 Loop (x + y) and W and measure the resistance, ft, of this loop. 

 Finally, connect Z and (x -h y) in parallel and loop the combina- 

 tion with W and measure the resistance, ft. 



ft = Z + W. 



ft = (x + y) + TF. 



p w . S(* + ^ 

 M '* 7!. i -.\ i v 



(x + y) = (ft - ft) + V(ft - ft) (R* - ft) (11) 

 Or, 



Z = (ft - ft) + \/(ft - ft) (ft - ft). 



To be strictly accurate, the ratio of the resistance up to 

 the fault to the total resistance of the wire should be the same 

 for both defective conductors, for then there will be no flow of 

 current through the faults. 





v 



N r 



FIG. 426. Connections for Fisher loop test for fault location. 



Fisher Loop Test. In order to make this test there must be 

 two unfaulted wires which run from the testing station to the 

 far end of the line. The result obtained is the same as that given 

 by the above methods where two perfect conductors are available 

 and both the resistance up to the fault and the total resistance 

 of the faulty line are measured. 



