TELEPHONE LINE WIRE SPACING PROBLEMS 199 



crossarms at alternate poles. Later another line (Line 2) was erected. 

 This line consisted of three spans, one each of 100, 160 and 260 feet. 



Special steel crossarms were mounted on each pole with a vertical 

 separation between them somewhat greater than the two feet usually 

 used in the Bell System. This was to lessen the effect of wind shielding 

 on the test results. These steel crossarms were slotted so as to 

 accommodate steel insulator pins and make it possible to vary the 

 spacing at will. On each pole of Line 1 were mounted five of these 

 crossarms each carrying eight pins, two pairs on each side of the pole. 

 The line wires used were hard drawn copper, 0.104 inch and 0.165 inch 

 in diameter. These sizes comprise the two extremes of the three sizes 

 of copper line wire most frequently used in the Bell System, the 

 intermediate size being 0.128 inch in diameter. As the results obtained 

 during the first two years indicated that the size of wire, within the 

 range of interest, did not appreciably affect the contacting tendency, 

 later tests were confined to the 0.165-inch diameter wire which was 

 selected because of its relatively greater use for important circuits. 

 On Line 2, one crossarm with four pairs of 0.165-inch diameter wire 

 was mounted in the 260-foot span and two crossarms of the same size 

 wire in the 100- and 160-foot spans. 



The spacings used in the tests between the wires of a pair comprised 

 3, 4, 6, 8 and 12 inches, a range which starts with as small a horizontal 

 spacing as appeared to offer possibilities, with the present type of 

 construction, and extends up to the previous standard of 12 inches. 

 The sags used conformed to Bell System Practices and ranged from 

 4 inches to 45 inches depending upon temperature and span length. 

 In certain of the tests sag inequalities between the wires of a pair 

 were introduced to simulate chance conditions. In referring to the 

 results unless otherwise noted it is to be understood that the two 

 wires of a pair were at equal sags. When the sags in the wires were 

 unequal it is so stated. The amount of the inequahty used in spans 

 of 100, 130 and 160 feet was 3 inches at 60° F., while that used in 

 260-foot spans was 6 inches at 60° F. In these tests the greater sag 

 was always placed in the windward wire while the sag in the leeward 

 wire was maintained so as to conform to Bell System Practices. 



In the later stages of the tests certain anti-contacting devices as 

 hereafter described were applied to the wires in the narrow spaced 

 arrangements to raise the velocities at which contacting began. 



Recording Apparatus 

 Apparatus was installed in a building adjacent to one end of the 

 line to record graphically the number and time of occurrence of the 



