, 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.
Pages:
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132