Page:Popular Science Monthly Volume 56.djvu/582

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times cover the tracks and fill the conduits, hence the securing of perfect insulation presents great difficulties. The manner in which inventors have sought to surmount the obstacles can be made clear by the aid of a few illustrations of typical designs.

PSM V56 D0582 Shielded underground electrical conduit rail.png

Fig. 25.—Underground Conduit with Protecting Shield for the Conductor.

Fig. 25 shows one of the forms of a class of underground conduits belonging to the inclosed conductor type. The track rails are supported upon the outer ends of large castings, F F, commonly called yokes. These are made of such size that the portion below the opening which incloses the conduit may be of sufficient depth to afford the requisite strength to properly support the track. The conductor that carries the current is located at f and is insulated from the casing j, which forms the lower half of the conduit, by the stands g. From the car a bar, P, which is called a plow, projects downward through the slot between the rails, k k, and on its end is spread out into a fork, d, which carries a pulley, e. When this pulley is in contact with the conductor f the current passes through the plow P to the motors upon the car, and thence to the track rails and back to the power house.

As the yokes F F and the conduit casing j are made of iron and are in metallic connection with the track rails, it is evident that if the conduits should fill with water to the depth of the wire f the current would pass directly to the rails, and thus would avoid the longer path through the motors. To prevent this occurrence, the sides of the conduit are inclosed with the sheet-iron covers c c, which nominally are in the position shown by the dotted lines i i.