21S BRLL SYSTEM TECIIXICAL JOi'RXAL 



Power Distribution and Telepho}ic Circuits. Inductive and Physical 

 Relations. H. M. Trueblood and D. I. C^oxeJ Consideration of 

 the relation between power distribution and telephone systems is 

 naturally involved in the comprehensive review of the problems of 

 the rapidly expanding power distribution networks in this country. 

 Pending the completion of studies now being actively carried on in 

 this comprehensive re\'iew, a preliminary and qualitative discussion 

 is given. 



Situations of exposure fall into three groups determined by the 

 character of the area served. (1) "downtown" districts; (2) residential 

 urban districts; (3) rural districts. The major problems arise in the 

 second group. A wide variety of arrangements characterize both 

 systems, and require consideration. 



Among technical features, coei^cients of induction for close ex- 

 posures, shielding action of metallic cable sheaths for both power 

 and telephone circuits, and "ground potential" effects, are distinctive 

 problems. Where both classes of circuits are in cable with suitable 

 precautions as to grounding, interference is rarely to be anticipated. 



Noise induction from power-distribution circuits is chiefly from 

 residuals, which occur on single-phase branches of polyphase circuits, 

 or where triple harmonics or load-current unbalances are introduced 

 by grounding neutrals, or where admittances to ground of phase 

 wires are unequal. Residual currents are largest in systems having 

 multiple-grounded neutrals, both load currents and triple harmonics 

 occurring. Approximate resonance at triple harmonic frequencies 

 between the inductance of station apparatus and power cable capaci- 

 tance has characterized several situations. Various single, two and 

 three-phase arrangements are compared from the induction standpoint. 



The closely related matter of unbalances in the telephone plant is 

 briefly discussed. 



■> Journal of the A. I. E. E., Vol. XLIV, No. 12, Dec, 1925. 



