644 



BELL SYSTEM TECHNICAL JOURNAL 



conductivity of 5.0 X 10~^^ for the lower stratum and a thickness of 130 

 feet for the upper stratum an excellent agreement could be found 

 between calculated and observed values for all frequencies. The agree- 

 ment extended not only to the magnitudes of the mutual impedances, 

 but to the components as well. 



Because of the simplifying assumption that the disturbing circuit is 

 so long that the effects due to the ground connections at its ends can 

 be neglected, the theory which we have been discussing is obviously in- 

 adequate to explain the phenomena in the neighborhood of the ground- 

 ing electrode. 



Practical Methods for Predeterminixg Coupling between 

 Power and Telephone Lines 



The ultimate purpose of the work of the committee is to develop 

 simple methods to enable the calculation of the mutual impedance be- 

 tween power and telephone circuits before they are built. It is evident 

 from the foregoing discussion that the use of any formula for the mutual 

 impedance of ground-return circuits requires a knowledge of the con- 

 ductivity of the earth or of the depth of the equivalent ground-plane. 

 In the relatively few places in which tests have been made, a range of 

 earth conductivity from 10^^- to 10~^^ abmhos per cm. cube has been 

 observed, and reference to Fig. 12 indicates that within this range of 

 earth conductivity a variation in mutual impedances of 20 to 1 or more 

 may exist. Therefore, other experimental work has been done with 

 the object of developing relatively simple testing schemes, the results 



TO SPIER J> 

 FALLS ^ 



tJO GLENS 



FALLS 



SARATOGA- ^(^/^ ^nV^ 

 GLENS FALLS -i^^^ I ^°-^ 



^ SARATOGA— MONTREAL" ' 



TO WHITEHALL 



SEE DETAIL A 

 DETAIL "A" 



TWO TOLL LEADS 

 AT ROADWAY 

 SEPARATION SCALE IN 

 KILOFEET 

 I 



L . 



EXPLORING 

 WIRES 



SCALE IN 

 KILOFEET 

 12 34 



Tower 99 



Circuit 



Height 



Frequency 



I 



Fig. 15 — Glens Falls tests. 



Circuit arrangements 



3-Phase conductors 



Power 



50 ft. 



60 cycles 



Grounded 



Telephone 



20 ft. 



I 



