Evening star., 1902-01-29
A GREAT ELECTRIC CABLE
HAS SINGLE SPAN Of NEARLY A
MILE.
1t is Used to Garry Electric Power
Across the Straits of Car
quinez i'm California.

From the Scientific American.
The longest span in any electric power
transmission line operated on the American
continent, If not indeed anywhere in the
world, is that across the Straits of Car
quinez, comparatively narrow waterway
separating Solano and Contra Costa coun-
ties of California, and connecting San
Pablo and Suisun bays, which latter form
the northerly extremity of San Francisco
bay. The swinging Of the electric cables,
which cover the horizontal distance of 4.42I
feet in single span that has a clearance
of 206 feet above extreme high tide, consti-
tutes one of the most remarkable engineering
achievements of the age; and how greatly
1t exceeded all previous performances
of the kind will be appreciated when it is
stated that. previous to the construction OF
the Carquinez span, the most notapie eX-
ample of such construction was found in
sheer stretch of 1900 feet Of cable across
the Columbia river in British Columbia.
At the point on the Straits of Carquinez
selected for the spanning of the cables the
water is about 2, $50 feet wide, with depth
ranging up to 100 feet, and through this
gap flow the waters of the Sacramento and
San Joaquin rivers. There is also an ocean
tide of about five feet. There is thus pro-
duced constantly a heavy and dangerous
current-a current so strong, in fact, as to
render impra acticable the laying or opera
Far Above the River.
On one side Of the straits where the
crossing is made is bluff, rising to a
height of 162 feet above extreme high tide
On the opposite side there is hill rising
about 100 feet from the waters edge, and
back Of this a gradual incline, eliminating
at an elevation Of 400 feet about half
mile back from the waters edge. The Car
quinez span extends from the 4O0-foot ele-
%h4 vii Of fha
bluff on the opposite shore, passing directly
over the town of Eckley. In planning the
span numerous exactions had to be Kept
in mind, one of which was the provision
imposed by the United States government
to the effect that clear headroom of at
least 200 feet should be allowed for vessels
The cables are supported In the great
span by two steel towers. The one on the
bluff known as the main tower, is 223
feet in height, and the one on the gradually
rising ground opposite is sXty-four feet
high, the latter structure being known as
the south" tower, The south tower is
located SO high on the hillside that it's top
is fully eighty feet higher than the top Of
the lofty main tower, and thus the low
est point of sag in the span Is thrown off
the lineal center between the two towers In
order to bring the cables down to anchor
ages, only 1,70O feet back Of the main
tower, there was constructed third
structure, known as the leaning tower.
and which has an inclination of thirteen
degrees from the perpendicular.
Steel and iron have been used almost ex-
clusively in the construction of all these
towers. Estimating the maximum wind
pressure at forty pounds a square foot, each
Of the four corner posts of the main tower
is subject to a maximum compressive strain
of 132,510 pounds.
The AnchOrages.
The support Of the cables from the tow
ers represents an achievement Of no incon-
siderable magnitude, since each cable ex-
erts pull of twelve tons on its anchorages
The insulators weigh about fifty pounds
each, and every insulator was subjected,
previous to installation, to long-continued
tests of 100 900 volts. There is an extreme
variation in temperature of sixty degrees
at CarquineZ, so that there may be a uiffer-
ence during the year Of five feet in the sag
Of the cables, difference which will cause
travel of fully two inches to occur in the
cables running over the sheaves Of the
main tower.
Each cable has an individual anchorage,
consisting of mass Of concrete nine by
ten feet in size and five feet high, set
into the bedrock. The cables are dead
ended at the anchorages, power being de-
lfvered to or taken from them by means Of
taps. Only three cables are ever in use
at one time. the fourth invariably being
held in reserve. The provision of this extra
cable also makes 1t possible to overhaul or
repair any cable at anv time
When the four cables, each 6,400 feet
long, were in readiness the ends were
hauled up to the south anchorage by wind
lass and secured to the anchorage system.
The reels, one at time, were then carried
across the straits on a self-propellng steam
barge, paying out the cable as they went.
On the north shore the donkey hosting en-
gine for pulling up the cables was located
near the leaning tower previously men
toned, or some ], 800 feet from the landing.
Leading from the engine through a block
in the anchorage and over both the leaning
and main towers was run a hemp line,
hi ioh 11ti1 rad tn null <to clo o1y
end Of the cable. The four cables were
raised In five days. Some idea of the power
required to pull up the cables may be
gained from the fact that when the sag of
a cable was such that it touched the sur
face Of the water it's length was 1895 feet
and the strain was 1900 pounds: when 120
feet above the surface the length of the
span was 4,4S2 feet and the strain 12,7 $50
pounds, and when in final position the
length was 4,44S feet and the strain %, 500
pounds.