. American telephone practice . .Over the upper layer is then laid another creosoted wood plank twoinches thick, after which the trench is filled in with earth. Thegreat point in favor of this conduit is its cheapness, this being greatly UNDERGROUND CABLE CONSTRUCTION. 839 enhanced by the fact that no concrete is employed for a foundation. Conduits of clay or terra-cotta, burned hard and with vitrifiedsurface, are being extensively used and are giving unqualified satis-faction. These are made up in a number of forms which may bedivided into two classes, namely, multiple duct and single
. American telephone practice . .Over the upper layer is then laid another creosoted wood plank twoinches thick, after which the trench is filled in with earth. Thegreat point in favor of this conduit is its cheapness, this being greatly UNDERGROUND CABLE CONSTRUCTION. 839 enhanced by the fact that no concrete is employed for a foundation. Conduits of clay or terra-cotta, burned hard and with vitrifiedsurface, are being extensively used and are giving unqualified satis-faction. These are made up in a number of forms which may bedivided into two classes, namely, multiple duct and single multiple duct conduit is made up in a variety of ways, someof which are shown in cross-section in Fig. 615, loaned by theH. B. Camp Company. For telephone purposes, the duct openingis either round and 2,2 to 4 inches in diameter, or square with roundcorners and of the same dimensions both ways. The earliest form of clay duct, which was used at all, generallywas one having a square outer form in section, about 12 by 12 inches,. FIG. 616.—SINGLE AND QUADRUPLE TILE. walls of one inch, and a horizontal shelf across the middle, one inchthick. This divided the pipe into two ducts, one above the other, eachabout zlJ inches high by 10 wide. Into each duct were drawn threecables, two side by side, and one on top of these two. Economy ofduct space was gained at a sacrifice of safety, as it was found im-possible to draw out one of three, if it became necessary, withouttearing ihe sheath off in doing so. Single-duct tile then came into existence, and still later the mul-tiple-duct type, but these latter, as Figs. 615 and 616 show, had oneduct opening for each cable. Fig. 616 is loaned by Field Clay Con-duit Company. The single-duct class of tiles possesses some advantages over themultiple-duct tiles, chief among which are the greater flexibility 840 AMERICAN TELEPHOXE PRACTICE. and the increased ease of handling. The form shown in Fig. 617has come into very wide use and has proven its
Size: 1970px × 1268px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., boo, bookcentury1900, bookdecade1900, bookidamericantelepho00mill
