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 additional mechanical protection. The methods described are intended for guideline use only, as it is impossible to cover all the various conditions that may arise during an installation. Individual. on except for lengths of 100 ft (30 m) or less. The preferred size of the igure-eight coils is about 15 ft (4. However, care must be taken during installation to observe the cable's minimum recommended bend diameter and maximum rated cable load (MRCL). In extreme cold climates, cables may need to be buried at greater depths where there temperatures are colder and frost penetrates to. The width of the artificially excavated ditch bottom should be 400mm.