20 BELL SYSTEM TECHNICAL JOURNAL 



even 26 A.W.G. wire with little breaking of the conductors. Fig. 10 

 shows the stripping characteristics of typical pulp insulation on 24 

 A.W.G. conductors impregnated with compounds of different pro- 

 portions of parafhn wax and oil. The pull required to strip the 

 insulation from a few inches of wire is plotted against atmospheric tem- 

 perature and shows the benefit of the higher percentage of oil par- 

 ticularly at the lower temperatures. There is, of course, with pulp 

 no raveling of the insulation, and the cotton sleeves which are used to 

 insulate the joint slip over the ends of the wires rather more readily 

 than for the spirally applied paper. Thus the overall time required for 

 joining a given number of pairs is practically the same for the two 

 types of insulation. 



An unbleached pulp is used and the natural brownish color of the 

 Kraft stock results in less sharp color distinction for the different 

 groupings of pairs than where ribbon insulation is used. However, by 

 simplifying the color code so as to require only red, blue, and green, 

 besides the natural color, sufficient contrast in the shades is obtained 

 so that there is no difificulty in distinguishing colors in the splicing 

 operation. 



Possible Applications 



This work was undertaken primarily to develop an insulation for 

 use in exchange area cables and efforts have been confined largely to 

 this phase of the study. It is possible to vary the characteristics 

 widely by changes in the raw materials, process and subsequent treat- 

 ment and other fields of use are being considered. 



Pulp insulation is being used as sleeving for lead-in wires in some 

 apparatus at the present time. For this purpose the insulation is 

 made on 19 A.W.G. wire, stripped from the wire and cut in short 

 lengths. It has proved quite superior to the old paper sleeves rolled 

 by hand over mandrels. 



Preliminary tests have indicated that there may be a field for use 

 for this type of insulation with certain modifications for switchboard 

 wiring, terminating cables and some kinds of coils. 



Economies 

 Preliminary cost figures indicated that this process offered the 

 possibility of a considerable saving over the ribbon process. These 

 predictions have been verified by actual machine operation extending 

 over a period of more than three years. The savings are made possible 

 by the low cost of Kraft pulp as compared with manila paper and by 

 the elimination of the intermediate paper making, paper slitting and 

 handling operations. 



