Generally a 12 inch to 24 inch soil separation is recommended as a safety barrier and for locating purposes. The Fiber Optic Association, Inc. (FOA) was founded in 1995 to help develop the workforce to build the fiber optic networks to support a rapid expansion in communications and the Internet. Underground Cable Construction. It is recommended to record the data provided on the labeling tags of all the reels in case of any subsequent issues. Sub-ducts are often referred to as innerducts. FO-VC2 JOINT USE - VERICAL MIDSPAN CLEARANCES 48. FO-RI JOINT USE RISER. Aerial Cable Installation Pathway Separation When placing, installing, or rearranging communication cables and service drops, including optical fiber, copper and coax, the proper clearance requirements must be maintained.