TELEPHONE LINE WIRE SPACING PROBLEMS 219 



In order to narrow the scope of the test in natural winds to the most 

 representative and promising of the various proposed arrangements, 

 an accelerated method of test was used for characterizing the proposals 

 in a preliminary way. 



This accelerated method was suggested by the above mentioned 

 theory concerning the equilibrium position of a span of wire in wind. 

 From this theory it was conceived that the relative merits of a type 

 of wire arrangement could be determined by successively deflecting 

 one wire of a pair outward and upward and releasing it to swing 

 towards the other wire through an increasing series of known angles 

 until the two contacted. The theoretical wind velocity corresponding 

 to this minimum angular displacement producing contacts would 

 then be determinable through the use of equation (1). 



While it was realized that such a procedure does not simulate the 

 contacting of wires in natural winds, it was thought that from a relative 

 point of view the arrangement requiring the greater angular displace- 

 ment and therefore the higher theoretical velocity to produce con- 

 tacting might also require a higher natural wind velocity. Further, 

 it was felt that there was a possibility of being able to determine not 

 only the relative merits of types of arrangements but also their natural 

 wind threshold velocities by correlating the data obtained by the 

 accelerated method with those obtained in the natural wind tests. 



Accordingly, a number of tests were made using arrangements on 

 which considerable natural wind data were available. The test set-up 

 comprised a pair of 0.165-inch diameter hard drawn copper wires 

 installed in proximity to the ground with suitable means for changing 

 spacings and sags at will. In order that the deflection of the wire 

 might be accurately controlled and the results reproducible, a series 

 of rods used as guides were mounted rigidly on a vertical support at 

 the center of the span in a plane at right angles to and in proximity 

 to the wires. The points of these rods were positioned in the arc of 

 a circle with a radius equal to the sag in the manually deflected wire. 

 The intervals between the points of the rods in terms of theoretical 

 wind velocity were five miles per hour. The arrangement of rods 

 represented a range of 20 to 80 miles per hour. The test apparatus 

 is shown in the accompanying Fig. 13. 



In the first stages of these tests it was found that a pair of wires 

 would not always contact for the same minimum angle of deflection. 

 Experiments showed, however, that during the absence of any natural 

 wind there was a minimum angle for a given wire arrangement which 

 would produce contacting five times in five consecutive trials. This 

 refinement of the method was then adopted and the theoretical 



