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Abstract

A duct for transmission cable including a polymeric tubing having an inner and an outer wall. Spiral ribs having peaks and valleys are located on the inner wall. The valleys are adapted to receive lubrication and the peaks form a surface over which cable may travel at reduced friction. The spiral makes one revolution from about one to six linear feet, at rib heights from about 0.005 to 0.125 inch, and the spacing between the ribs is about 0.025 to 0.500 inch. The duct may be located in an outer duct which is normally buried underground, or directly buried or plowed. There may be a plurality of ducts placed in the ground with an outer duct. Longitudinal ribbing on the external walls prevents rotation. This invention also includes the process of laying a cable which includes pulling the ducts through the outer ducts over the longitudinal ribs and subsequently pulling the cable through the ducts along the spiral ribs, thus reducing the friction and increasing the length of pull that may be done without exceeding the tension strength of the cable.

First Claim