. The Street railway journal . e is agreat temptation, when a particularly difficult crossing is en-countered, to use iron pipes because of the ease with whichthese pipes may be sandwiched between other undergroundstructures. It is a mistake to employ iron pipe in these cases,if by digging a deeper trench and going under the obstruc-tions its use can be avoided. The shape of the manholes is an important item in the con-struction of a conduit. They should be designed so that the 270 STREET RAILWAY JOURNAL. [Vol. XXVI. No. 8. cables will have to be bent as little as possible, although it isessen
. The Street railway journal . e is agreat temptation, when a particularly difficult crossing is en-countered, to use iron pipes because of the ease with whichthese pipes may be sandwiched between other undergroundstructures. It is a mistake to employ iron pipe in these cases,if by digging a deeper trench and going under the obstruc-tions its use can be avoided. The shape of the manholes is an important item in the con-struction of a conduit. They should be designed so that the 270 STREET RAILWAY JOURNAL. [Vol. XXVI. No. 8. cables will have to be bent as little as possible, although it isessential that the cables be bent to some extent in order toplace them in a position where they are least subject to me-chanical injury. An elliptical shape, such as is shown in Fig. 2, seems to bewell adapted to fulfil these requirements. Intersections wheretwo conduits cross at right angles and enter the same man-holes have always been troublesome. An approximately squarehole set diagonally is well adapted to these location. (See. FIG. 2.—PLAN OF ELLIPTICAL MANHOLE Fig. 3.) Cables entering the corners can be formed aroundthe walls and splices can be made without excessive bending. The distance between manholes should be made as great asis practical for drawing in the cables. A good standard oflength between manholes is 500 ft. It is often necessary toplace manholes at shorter intervals, however, on account ofsudden changes in grade. Ducts should be laid at such gradesas to drain themselves into the manhole. HIGH-TENSION CABLESThe insulating material for high-tension cables has been thesubject of a great deal of discussion and experiment. In thiscountry, manila paper, thoroughly impregnated with a good
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectstreetr, bookyear1884
