Fig. 74. Contact Plow.
Current Leakage. The leakage on an underground conduit road is considerable, because the insulators are necessarily located in a damp, dirty place, which causes leakage over the surface of the insulators. This leakage, however, is not prohibitive so long as the conductor rails are not under water. If on account of poor drainage the conductor rails become submerged, the leakage becomes so great that it is impossible to operate the road.
It will be noticed that the conduit system as illustrated here employs two conductor rails—one for the positive side of the circuit and the other for the negative. The track rails, therefore, are not used as conductors, and one side of the circuit is not grounded as in the ordinary trolley system, although the leakage to ground may be considerable from one or both conductor rails.
TRACK CONSTRUCTION.
Girder Rail. A great variety of track rails are used in electric railways. The most common at one time was the girder, a typical section of which, with joint, is illustrated in [Fig. 75]. This is an outgrowth of the old tram rail used on horse railways. It has a tram alongside of the head, on which vehicles may be driven. Its chief advantage from the standpoint of the railway company is that there is plenty of room for dirt and snow to be pushed away by the flanges of the cars. If the company maintains the paving, it may be to its advantage to have teams use the steel track rather than the paving, although this advantage in maintenance is probably more than compensated for by the delay of cars through the regular use of the track by teams.
Fig. 75. Girder Rail.
Trilby Groove Rail. A modification of the girder rail, known as the Trilby, and sometimes as the grooved girder, is shown in [Fig. 76]. A rail similar to this is used in several large cities of the United States. It has a groove of such a shape that the flanges of the car wheels will force snow and dirt out of it instead of packing it into the bottom of the groove, as in the case of the regular European narrow-grooved rail. A narrow-grooved rail in which the grooves correspond closely to the shape of the car-wheel flanges is sure to make trouble in localities where there is snow and ice, as the grooves become packed and derail the cars.
Shanghai T-Rail. In some systems a T-rail is used. Where the T-rail is to be used with paving, the popular form is the Shanghai T, shown in [Fig. 77]. This rail is high enough to permit the use of high paving blocks around it.