Conduit Network Pulling

In the telephone and electrical utility industries, the underground plant is often
comprised of a network of3”,4”, and6”conduit banks. These "rigid” conduits are
composed of clay tile, cement conduit, or more recently, PVC constructions. They
are usually separated by manhole vaults or buried pull-boxes. Distances between,
and placement of manholes and pull-boxes is largely a function of the following
constraints:
1. Location of branch circuit intersections
2. Lengths of cables (or innerducts) available on reels
3. Access to, or limited by physical obstructions
4. Path difficulty for placement of cable or innerducts
5. Surface environment
6. Method of cable placement (mid-assist access)
In addition, Department of Transportation (DOT) regulations often require
additional protection and support structure for buried conduits in road bores and
traffic areas. Although steel casings have been used in the past, it is becoming more
prevalent to horizontally bore under roadways (or waterways) and pull back an PE
casing into which PE innerducts are installed.
Pull placement of innerducts has obvious similarity to traditional cable placement
methods. Several good references on this subject exist, including Guide For Installation
of Extruded Dielectric Insulated Power Cable Systems Rated 69KV Through 138KV,
Chapter 14
Duct and Conduit
485
Underground Extruded Power Cable Pulling Guide, AEIC Task Group 28 and IEEE Guide
Distribution Cable Installation Methods In Duct Systems.
There are a number of variables that influence loading and selection of innerducts
when pulling into conduit structures:
• Diameter of conduit and innerduct, and number of innerducts to be
installed – clearance fit
• Length and direction changes of conduit run, sweeps
• Composition of conduit and coefficient of friction
• Jam combinations
• Pull speed and temperature
• Elevation and innerduct weight