222 BELL SYSTEM TECHNICAL JOURNAL 



of the pair to the windward side of the Une. When two discs were 

 used they were placed on the windward wire at one-third of the 

 distance from each support. The three-disc arrangement comprised 

 the two-disc arrangement with the third disc placed at the center of 

 the span on the other wire of the pair. 



Fig. 15 — Insulating spacer. 



In selecting the disc and these sizes, various shapes and sizes of 

 insulators (one of which is shown in Fig. 13) were tested using the 

 accelerated method of test referred to above. The circular type was 

 found to give as good results as any other shape and had the advantage 

 of being simple in design. 



The insulating spacers were used one per span per pair of wires 

 located at the approximate center of the span. Any insulating spacer 

 bridging the wires of a pair constitutes an additional line leakage 

 path and from this standpoint is undesirable. In this respect the 

 discs have a distinct advantage over the spacers. As stated above, 

 they are not normally in contact with both wires and when such 

 contacts take place they are generally of short duration. Then too, 

 in a long line with wires equipped with discs it is improbable that 

 more than a short section would be affected at one time. The thought 

 was that owing to the additional line leakage provided by the spacers, 

 their use would be confined to the occasional long span and the use 

 of discs to the shorter spans. For this reason the tests involving 

 discs were confined to spans of 160 feet and less and those involving 

 spacers to spans of 160 and 260 feet. The dimensional characteristics 



