Guide from Superior Essex explains how numbers and sizes of cables, plus number of conduit bends, determines fill ratio. It also provides two examples.
A technical document available for direct download from Superior Essex takes users through a step-by-step process for calculating conduit fill. “When sizing conduit, there are three factors that must be taken into account,” the document says. “The number of cables being placed in the conduit, the cross-sectional area of the cable or cables being placed in the conduit, and the number of conduit bends.”
Superior Essex then explains each of those three factors as a step in the calculation process. The first step (number of cables) is straightforward. But the second step involves more mathematical calculation. Specifically, the cross-sectional area (A) is equal to 0.79D2, where D is the cable’s diameter. This calculation is made for each cable being pulled into the conduit. Then step three requires a 15-percent subtraction from the total cross-sectional area for each 90-degree conduit bend.
The document provides two examples—one calculating the conduit fill for two RG-6 quad-shield coaxial cables and two four-pair unshielded twisted-pair cables pulled into a conduit with no bends, and the other for the same cables pulled into a conduit with two 90-degree bends.
