THE LOCALISATIOX OF BREAKS AND FAULTS. 



449 



•Society of Telegraph Engineers, Vol. V., 1876) is applicable 



where the leakage as in a cable, is approximately uniformly 



distributed, viz. : — 



/■ 1 p \ 

 True conductor resistance = R ( 1 + . — ; , 



^ 3 Rj/' 



where R is the apparent resistance of conductor and R^ is the 

 apparent resistance of insulator. 



In using this correction for the observed metallic resistance 

 we may write it 



Where R = observed metallic circuit resistance, j' = observed 

 insulation resistance between cables and L = the true CR of 

 the loop. 



\ 



{A 



M. 



^|i{i{i{i{iP 



■-c^- 



Faully Cable. 

 } 



Good Cable. 



Loop 

 Conaection. 



Fia. 252, — Murray Loop. 



Murray's Loop Test. — In Murray's method the cable ends are 

 connected direct to the bridge ratios without an added resis- 

 tance. One of the bridge ratio arms is usually fixed and the 

 other adjusted to balance. The connections are as in Fig. 252, 

 the fixed arm a being a low resistance (usually the 10 ohm 

 coil) on account of being next the shorter length of cable to 

 the fault. If na is the resistance unplugged to balance, we 



have 



a _ a- 



na L — ?; 



•whence 



,v= , 



7? + 1 



G G 



