eeder 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_]

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-stations
approximates 12,000 feet, and north of 96th Street the average
distance is about 15,000 feet. Each track, of course, is provided with
a contact rail. There are four tracks and consequently four contact
rails from City Hall to 96th Street, three from 96th Street to