. Bell telephone magazine . e underground ducts to accommodate ad-ditional cables or to replace some of the cables whichnow occupy ducts in the existing conduit system withcables containing more wires. In many of these situa-tions, on account of the extent to which the space be-neath the streets is occupied by rapid transit tunnels,sewers, water and gas pipes, electric light and powercables, and other subterranean works, it would be pos-sible to provide additional telephone ducts only withgreat difficulty and at large cost. Hence the relief afforded through the ability to sub-stitute 1800-pair
. Bell telephone magazine . e underground ducts to accommodate ad-ditional cables or to replace some of the cables whichnow occupy ducts in the existing conduit system withcables containing more wires. In many of these situa-tions, on account of the extent to which the space be-neath the streets is occupied by rapid transit tunnels,sewers, water and gas pipes, electric light and powercables, and other subterranean works, it would be pos-sible to provide additional telephone ducts only withgreat difficulty and at large cost. Hence the relief afforded through the ability to sub-stitute 1800-pair cable for 1200-pair cable, or smaller,either in new w^ork or in the existing plant, is a matterof importance. Furthermore, since every underground cable occu-pies a duct and must have a metallic sheath, the ex-pense of a pair of underground wires becomes less inproportion as the cost of duct and sheath is dividedamong a larger number of pairs of wires in the where the use of 1800-pair cable, rather than 1200- [26]. 1800-Pair Cable Becomes Standard pair, is practicable, from a transmission standpoint,this will assist in keeping the cost of the telephone plantfrom mounting as rapidly as would otherwise be thecase. 1800-pair cable will also affect plant engineeringpractices, by changing the economic relation betweenthe costs of material and of labor. For example, wheregrowth is rapid, there will be cases in w^hich greatereconomy and better service will result from providingrelief by means of new 1800-pair cable than by makinga greater use of existing facilities through rearrange-ments and changes. Lest it might be assumed that the development of1800-pair cable consisted merely in substituting 26-gauge wire for the 24-gauge wire used in 1200-paircable, it seems worth while to point out that the devel-opment required the invention of a wholly new methodof forming the cable core. The type of assemblagepreviously used, consisted of layers of twisted pairs,laid up in the form
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