BiRKS AND Webb. — Resistance of Earth Connections. 



479 



A comparison of these two sets of values (Taltles VII and VIII) indicates 

 that the bare pipe salted is more efficient than the pipe packed with coke 

 and costing twice as much to place. The more elaborate earth, however, 

 will probably tend to retain its efficiency longer. 



A number of sample values (A.C. bridge method) of the resistances of 

 pipes in various parts of the transmission-line are indicated in curve No. 4. 

 The initial resistance of individual pipes ranges from 12 ohms to 4,000 ohms, 

 and averages several hundred ohms. Immediately after salting, the range 

 is 7 ohms to 560 ohms. 



Pipes are now being placed at each pole on the transmission-fine. "Where 

 there is nothing heavier than ordinary gravel, pipes can easily be started 

 Avith a crowbar, and then driven to 6 ft. or 7 ft. with a hammer. The lower 

 end of the pipe is flattened and closed, while the top is protected for driving 

 by a loosely fitting cap turned from mild steel. In heavy shingle ground 

 it is sometimes necessary to make an excavation in depth almost equal 

 to the length of the pipe, and this very considerably increases the cost of 

 placing. The lead from the pipe, as before, is 1 in. galvanized-iron strip, 

 riveted round and bolted through by ^m. bolt to the pipe, and riveted 

 on to the earth -strip running up the pole. Bolting and riveting were 

 resorted to after it was fourd that the sweated joint broke away while 

 driving. Particulars of some samples of these earths are given below (sum 

 of two resistances in series values equivalent to A.C. bridge test) :• — 



For salting these pipes, ordinary coarse salt is best for the initial charge, 

 as it readily dissolves, while rock salt is better for filling and leaving about 

 the pipe, on account of its taking a considerable time to dissolve. At 

 present refuse rock salt from tanneries is being used, and found equal to 

 ordinary salt for the purpose, and much cheaper. 



