BiRKS AND Webb. — Rtsistance of Earth Connections. 



469 



Some measurements of earth-resistances by D.C. and A.C. voltmeter- 

 ammeter method were made by Mr. Parry, Chief Electrical Engineer, in 

 Wellington. These were made on hemispheres Sin. and Gin. in diameter,, 

 placed in soil without addition of any salt. Kesults are tabulated below,, 

 with percentage of the D.C. value greater than the A.C. : — 



Table III. — Comparison of D.C. and A.C. Voltammeteb Methods. 



(Two Earths in Series.) 



This gives an average of D.C. values greater than the corresponding 

 A.C. values by 16 per cent. The A.C. ammeter used in these tests had a 

 very close scale, and results are not entirely satisfactory. 



Some later comparative values were obtained at Addington Substation 

 and on the transmission-line, with the following results : — 



Table IV. — Comparison of D.C. and A.C. Bridge Tests. 



(Two Pipes in Series.) 



The D.C. bridge thus gives a resistance about 33 per cent, higher than 

 the A.C. bridge. There is a considerable range in the percentage difier- 

 ence, showing that the D.C. test probably gives a rather erratic result. 

 Although results axe not sufficiently numerous to warrant a definite state- 

 ment, there is an indication that the difference unsalted is in the region 

 of 30 to 40 per cent., while salted it is from 20 to 30 per cent. 



