[Sidenote:  Conduit
System for
Distribution]

From the power house to the subway at 58th Street and Broadway two lines of conduit, each comprising thirty-two ducts, have been constructed.  These conduits are located on opposite sides of the street.  The arrangement of ducts is 8 x 4, as shown in the section on page 96.

[Illustration:  EXTERIOR OF SUB-STATION NO. 11]

The location and arrangement of ducts along the line of the subway are illustrated in photographs on pages 98 and 99, which show respectively a section of ducts on one side of the subway, between passenger stations, and a section of ducts and one side of the subway, beneath the platform of a passenger station.  From City Hall to 96th Street (except through the Park Avenue Tunnel) sixty-four ducts are provided on each side of the subway.  North of 96th Street sixty-four ducts are provided for the West-side lines and an equal number for the East-side lines.  Between passenger stations these ducts help to form the side walls of the subway, and are arranged thirty-two ducts high and two ducts wide.  Beneath the platform of passenger stations the arrangement is somewhat varied because of local obstructions, such as pipes, sewers, etc., of which it was necessary to take account in the construction of the stations.  The plan shown on page 98, however, is typical.

The necessity of passing the cables from the 32 x 2 arrangement of ducts along the side of the tunnel to 8 x 8 and 16 x 4 arrangements of ducts beneath the passenger platforms involves serious difficulties in the proper support and protection of cables in manholes at the ends of the station platforms.  In order to minimize the risk of interruption of service due to possible damage to a considerable number of cables in one of these manholes, resulting from short circuit in a single cable, all cables except at the joints are covered with two layers of asbestos aggregating a full 1/4-inch in thickness.  This asbestos is specially prepared and is applied by wrapping the cable with two strips each 3 inches in width, the outer strip covering the line of junction between adjacent spirals of the inner strip, the whole when in place being impregnated with a solution of silicate of soda.  The joints themselves are covered with two layers of asbestos held in place by steel tape applied spirally.  To distribute the strains upon the cables in manholes, radical supports of various curvatures, and made of malleable cast iron, are used.  The photograph on page 100 illustrates the arrangement of cables in one of these manholes.

[Illustration:  OPERATING BOARD—­SUB-STATION NO. 11]

In order to further diminish the risk of interruption of the service due to failure of power supply, each sub-station south of 96th Street receives its alternating current from the power house through cables carried on opposite sides of the subway.  To protect the lead sheaths of the cables against damage by electrolysis, rubber insulating pieces 1/6 of an inch in thickness are placed between the sheaths and the iron bracket supports in the manholes.