CABLE PULLING EQUATIONS
A 4,800-ft (1450 m) duct bank runs from one
campus building to another. You plan to install a
fiber optic cable in an empty conduit in the bank.
The run goes through a number of turns and
manholes. Can you safely make the installation in
a single pull, or must the cable be pulled out,
figure-eighted, and then pulled back in for the rest
of the run?
You're installing shielded, twisted-pair data cable
with a maximum pulling tension of 55 lbs (245
Newtons). Part of the run is into a 550-ft (165 m)
conduit under a concrete factory floor. It is a
straight conduit run, with a conduit stub-up at one
end. Can you make the pull with less than 55 lbs
(245 N) force? Which end of the run is it best to
feed the cable into?
There's an 8,300-foot (2530 meters) under bridge
crossing. You want to install a "preducted" fiber
optic cable (cable extruded in innerduct) into an
existing FRE conduit.
maximum load for the thick walled duct is 4,500 lbs
(20kN). Will the run be easy, hard, or impossible?
You should know before you start the pull . . .
The situations above were all real field problems.
While the cable types and specifics are quite
different, all three do have something in common!!
In all three, "Cable Pulling Theory" can answer the
questions and provide a sound basis for planning
"Cable Pulling Theory" allows us to estimate pulling
tension when cable is pulled into conduit. The
theory is based on physical laws. In this case, the
force required to move an object across a surface
is equal to the force between the surfaces times
the coefficient of friction.
In cable pulling, the cable becomes "the object"
and the conduit "the surface." The forces depend
on both gravitational weight and the "pressing"
force when pulling cable around bends. The end
result is a series of equations, which require