TELEPHONE LINE WIRE SPACING PROBLEMS 225 



2. A rod-type insulating spacer used to bridge the wires of a pair in 

 the approximate center of the span was somewhat more effective 

 than one disc, increasing the normal wind velocities at which 

 swinging contacts began by about 10 to 30 miles per hour over 

 those for the same arrangements unequipped. 

 In general, the higher the threshold velocity, the less frequent will 

 be the occurrence of those winds which will cause contacting. There- 

 fore, if the threshold velocity of a wire arrangement is increased 5 or 

 10 miles per hour or more by the addition of an anti-contacting device 

 there will be a decrease in the amount of contacting occurring de- 

 pendent upon the original threshold velocity and the amount of the 

 increase. For example, in the vicinity of Chester, New Jersey, an 

 increase in the threshold velocity of a wire arrangement from 40 to 

 45 miles per hour results in a reduction of about 50 per cent in the 

 number of five-minute intervals during which winds of sufficient 

 velocity to cause contacts will occur. At higher wind velocities an 

 increase of five miles per hour in the threshold velocity will produce a 

 greater per cent reduction in the number of five-minute intervals 

 during which winds of sufficient velocity to cause contacts will occur. 

 In regard to the field installations with a spacing of 8 inches between 

 the wires of a pair, referred to at the beginning of this article, no 

 serious difficulties have been encountered except in certain sleet 

 areas where there has been some wrapping and freezing together of 

 the wires. In these locations insulating spacers have been installed 

 on a few pairs and their behavior is being followed. The installations 

 in which a 6-inch spacing has been used have been confined to the 

 warmer sections of the country and no serious trouble has yet been 

 encountered. 



APPENDIX I 

 The expression for determining the angle of deflection or equilibrium 

 position of a suspended wire in a steady transverse wind as given in 

 the theory ^ is 



tan a = , (1) 



mg cos 7 '^ ^ ^ 



where a = Angle between the plane of the suspended wire and a 

 vertical plane through the supports, 

 V = Steady transverse wind velocity (miles per hour), 

 m = Mass of unit length of wire (slugs), 

 g = Acceleration of gravity (feet per second per second), 

 k = Ratio of wind pressure per unit length of wire to square of 



velocity, and 

 7 = Angle of inclination of line through supports to the hori- 

 zontal. 



