THE LOCALISATION OF BREAKS AND FAULTS. 



503 



— Core 



resistance, so that should 

 there be any slight leakage 

 from the wire to earth the 

 conditions would be the same 

 in the case of both the high 

 resistance and the cable. 



Connections for doing this 

 are shown in the diagram. 

 The battery and galvanometer 

 can be plugged over to the 

 cable or resistance, while the 

 guard wire remains on the 

 core for both observations. 



The device is specially 

 effectual when testing cable in 

 tank where both ends are avail- 

 able, the guard wire then being 

 wound round the tapers of 

 both core ends in the manner 

 described . 



Another device for the same 

 purpose is the insulating 

 guard ring, designed by Mr. 

 J. Eymer-Joues, chief elec- 

 trician of the Submarine 

 Department of the Silvertown 

 Telegraph Company {Electri- 

 cal Beview, March 22, 1907). 

 This is a hollow cup insulator 

 of polished ebonite with a bore 

 slightly taper and large 

 enough to permit of its being 

 drawn over any size core likely 

 to be tested (Fig. 281). At a 

 point about 8 in. from the end 

 the core should be cleaned for 

 1 in. or 2 in. by scraping or 

 washing with naphtha on a 

 clean rag, lamped and then 

 coated with paraffin wax, 



Fig. 281. — Rymer-Jones' Guard-Ring 

 for Preventing Surface Leakage. 



