The instrument board is supported by iron columns and is carried at a sufficient height above the bench board to enable the operator, while facing the bench board and the instruments, to look out over the floor of the sub-station without turning his head.  The switches of the direct current circuits are hand-operated and are located upon boards at the right and left of the control board.

A novel and important feature introduced (it is believed for the first time) in these sub-stations, is the location in separate brick compartments of the automatic circuit breakers in the direct current feeder circuits.  These circuit breaker compartments are shown in the photograph on page 93, and are in a line facing the boards which carry the direct feeder switches, each circuit breaker being located in a compartment directly 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]