To determine the size of conduit you need in order to fit your chosen cable, enter your Belden cable part number or the diameter of your cable. "However, Outside Plant, also known as OSP fiber optic jackets, are suitable to be buried directly underground as the jacket material will be made with a polyethylene jacket. Installing armored fiber through a. First thing you need to do is find the minimum bending radius for the fiber, and then make sure that conduit bend have a radius larger than that. Then, under Conduit Size, select the size of your conduit and hit "Calculate. Fiber optic conduits are a massive.