Motion of Telephone Wires in Wind 



By D. A. QUARLES 



This paper deals with the position of equilibrium of a loop of wire in a 

 steady transverse wind and with the swinging of such a loop in one or more 

 gusts of wind. In the first part, the loop is assumed to be inelastic and to 

 swing as a rigid body. Under these conditions, nomograms are given from 

 which may be read the deflection of loops of wire .104" or .165" in diameter 

 as a function of steady wind velocity. The maximum additional swing of 

 such a loop with a single gust and with a succession of gusts of given peak 

 velocities may also be read from the nomograms. A chart is also included 

 giving the effect of wind velocity on the sag of .104" and .165" hard drawn 

 copper wires at tensions and span lengths common in the telephone plant. 



UNTIL recent years, most of the important open wire toll circuits 

 of the Bell System had the two wires of a pair spaced 12 inches 

 apart. This wide spacing, with the consequent high mutual induct- 

 ance between the several pairs on a pole line, limited the use of the 

 lines for multiplex transmission with high frequency or "carrier" 

 currents. A reduction in the separation of the wires of a pair with 

 the retention of the present center-to-center spacing of the pairs was 

 one of the measures which offered the opportunity of increasing the 

 message carrying capacity of a pole line. The controlling factor in 

 limiting such a reduction in spacing was the hazard of the wires of a 

 pair swinging together in the wind thus interrupting or impairing 

 the transmitted messages. 



About two years ago the 12-inch spacing was reduced to 8 inches in 

 some cases. This was considered to be as great a change as could be 

 safely taken from a mechanical point of view, based on the available 

 data. These data consisted in part of experiments made on an 

 experimental line and in part of an analysis of the performance of 

 certain working wires in the telephone plant which, for various reasons, 

 had been installed on a close spaced basis. 



It was realized that if the wires of pairs could be placed even closer 

 together, materially lower crosstalk between the circuits would result, 

 thus increasing the circuit capacity of open wire lines, and therefore 

 effecting economies. Accordingly, a comprehensive investigation of 

 the wire spacing problem was begun. As some of the factors involved 

 in a theoretical determination of the chance of two parallel wires 

 swinging together in the wind were rather obscure and difficult of 

 evaluation, it was decided to attack the problem experimentally. A 

 field site was selected some distance from New York, where the terrain 

 and weather conditions were suitable for such an investigation, and 

 an experimental station was constructed and appropriately equipped. 



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