New York City Subway

opposite the panel which carries the switch belonging to the corresponding circuit. This plan will effectually prevent damage to other parts of the switchboard equipment when circuit-breakers open automatically under conditions of short-circuit. It also tends to eliminate risk to the operator, and, therefore, to increase his confidence and accuracy in manipulating the hand-operated switches. [Illustration: ASSEMBLY OF CONTACT RAIL AND PROTECTION] The three conductor cables which convey tri-phase currents from the power house are carried through tile ducts from the manholes located in the street directly in front of each sub-station to the back of the station where the end of the cable is connected directly beneath its oil switch. The three conductors, now well separated, extend vertically to the fixed terminals of the switch. In each sub-station but one set of high-potential alternating current bus bars is installed and between each incoming cable and these bus bars is connected an oil switch. In like manner, between each converter unit and the bus bars an oil switch is connected into the high potential circuit. The bus bars are so arranged that they may be divided into any number of sections not exceeding the number of converter units, by means of movable links which, in their normal condition, constitute a part of the bus bars. Each of the oil switches between incoming circuits and bus bars is arranged for automatic operation and is equipped with a reversed current relay, which, in the case of a short-circuit in its alternating current feeder cable opens the switch and so disconnects the cable from the sub-station without interference with the operation of the other cables or the converting machinery. [Illustration: CONTACT RAIL INSULATOR] [Sidenote: _Direct Current Distribution from Sub-Stations_] The organization of electrical conductors provided to convey direct current from the sub-stations to the moving trains can be described most conveniently by beginning with the contact, or so-called third rail. South of 96th Street the average distance between sub-stat