When using lightning protection drainage lines, lay them 30 cm above the optical cables, with single or double drainage lines. Underground cables are pulled in conduit that is buried underground, usually 1-1. 2 meters (3-4 feet) deep to reduce the likelihood of accidentally being dug up. Note that Recommendation ITU-T L. When optical cables are dug out after backfilling and relaying, strictly check for. Q1: How Deep Should Fiber Optic Cables Be Buried? A1: Underground fiber optic cables are typically buried 18–36 inches, depending on local regulations, soil type, and site conditions. In urban areas, 12–24 inches is common, while rural or high-traffic zones may require 24–48 inches to provide.