. Electric railway journal . are insulators also serve as the supports for the pro-tection proper, which is simply an inverted trough. Thedesign permits of rapid and cheap erection and at thesame time provides high insulating qualities. Special interest attaches to the thii-d-rail constructionof the Michigan Railway shown in Fig. 19, because itwas the first to be installed for a voltage of 2400. An80-lb. T-rail section of low-carbon steel especially rolledfor this road is used. The specifications provide forcarbon not over per cent, manganese not per cent, sulphur not
. Electric railway journal . are insulators also serve as the supports for the pro-tection proper, which is simply an inverted trough. Thedesign permits of rapid and cheap erection and at thesame time provides high insulating qualities. Special interest attaches to the thii-d-rail constructionof the Michigan Railway shown in Fig. 19, because itwas the first to be installed for a voltage of 2400. An80-lb. T-rail section of low-carbon steel especially rolledfor this road is used. The specifications provide forcarbon not over per cent, manganese not per cent, sulphur not over per cent and phos-phorous not over per cent. The rail is guaranteed tohave a conductivity one-eighth that of copper. The con-tact rail is carried on a three-petticoat insulator, whichin turn rests on the 10-ft. track ties. The method ofsupporting the protection board is unique and well de-signed. Here again there is a top-running system witha wooden trough 12 in. wide, with the live rail exposedin the 1148 Electric Railway Journal Vol. 53, No. 24 On continuous stretches of 1 mile or less in lengththe Michigan Railway third-rail is laid with expansionjoints one and one-half times as wide as those allowedin standard track joints. Where the stretch of thethird-rail is more than 1 mile long, twice the standardtrack expansion is provided at joints. The petticoattype insulators are tested at 5000 volts and are heldin place on the ties by square malleable lugs fastenedwith lag screws and fitted into recesses in the insulatorbases. Third-rail joints are bonded with 7-in. 500,000- use of third-rail. This is obvious since repairs can-not be carried out with the same facility. Thereforethe additional cost of upkeep might justly counter-balance the interest on the extra capital expenditure onoverhead construction.
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