A STUDY OF TELEPHONE LINE INSULATORS 



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in Fig. 1. At the start of the rain and during the first few hours the 

 wood appears to reduce the leakage considerably but as the rain con- 

 tinues and the pin takes up moisture its effect seems to decrease to nil. 



While similar tests on this and other types of insulators give corres- 

 ponding results, still other tests indicate that at times, the wood con- 

 tinues to help out for many hours. One such test covering a period of 

 about 23 hours showed, for this same type of insulator (Fig. 1), that 

 the wood pin reduced the leakage by 30 per cent on the average. 



On the other hand, similar tests for the design of insulator shown in 

 Fig. 10, very frequently show the pin to have negligible effect. 



Fig. 10 — Experimental design (C. D.) 



While the foregoing tests have shown an advantage in favor of the 

 wood pin, that conclusion holds only for the conditions of the test; 

 namely, both wood and metal pins having the same diameter. When 

 an insulator is specifically designed for a metal pin both the pin and 

 insulator diameters can usually be made small because of the greater 

 mechanical strength of the metal pin. The advantages of the design 

 of small diameter, as previously discussed, may readily offset the slight 

 disadvantage of the metal pin and the net result may be an actual gain. 



3. Influence of Insulator Material. While the insulators are new, 

 the molecular attraction between the insulator material and water 

 plays a very important part; so important, in fact, that tests on such 

 new insulators frequently give an unreliable basis on which to make 

 decisions. On new glass insulators and particularly on those of 



