THE LOCALISATION OF BREAKS AND FAULTS. 499 



Identification of Cable Lengths in Tank.— The following 

 ingenious and useful methods for identifying cable ends, and 

 the relative position of the lengths coiled in tank, have been 

 devised by Mr. H. W. Sullivan, and were described in The Elec- 

 trician of May 14, and the Electrical Review of June 11, 1897. 



When splicing lengths together in tank ready for paying out, 

 it is most important that no mistake is made between top and 

 bottom ends, or the relative position of coils, and this test is 

 of great value if any doubt exists as to the marking on labels 

 or where labels have become lost or obliterated. 



A simple continuity test is first applied to the ends of all 

 lengths with a battery of a few cells and a detector. This 

 settles which pair of ends belong to which coil, and these pairs 

 are then labelled or tied together ready for the identification 

 tests. 



A shunted galvanometer, key and battery are connected in 

 circuit with the uppermost or No. 1 coil, the top end of which 

 is put in connection with, say, the left-hand terminal of the 

 galvanometer. The key is tapped and the direction of the 

 deflection observed. The galvanometer is then changed over 

 to any one of the other coils, leaving the battery and key in the 

 circuit of No. 1, as at A, Fig. 278. On closing the key the cur- 

 rent in No. 1 induces a current in the oj^posite direction in the 

 coil or coils next to it, and the induced current will be seen by 

 a swing or throw on the galvanometer. This swing must be 

 observed when all other cable ends are free, and also when the 

 pair of ends to each coil are connected together. If the swing 

 is greater when the other cable ends are free than when they 

 are looped, it shows that there is at least one intervening coil 

 acting as a screen to the induction between No. 1 coil and that 

 under test. The galvanometer must then be changed over to 

 another coil and the tests repeated in the same way. When 

 a coil is found in which the induced swing is the same, whether 

 the other ends are free or looped, this will obviously be No. 2 

 coil next in order to No. 1. Also, if the swing observed on 

 No. 2 is in the opposite direction to that observed on No. 1, 

 then it is evident tiiat the end in connection with the left- 

 hand terminal of the galvanometer is the top end of No. 2 coil. 



When labels have been pat on this coil indicating its top 

 -and bottom ends and its number, it is in turn treated as the 



K k2 



