How Are Medium-Voltage Cable Trenches Designed for Solar?

The trench plan is drawn against the full site — roads, drainage, array blocks, substation, and future phases — so the cable routes serve the plant without creating conflicts. I keep trenches in the road corridors where the ground is already disturbed, cross drainage at designed culvert locations rather than wherever the trench happens to arrive, and hold the routes clear of tracker foundations and their grading tolerances. The plan shows every crossing of existing utilities with the verification method, because an unmapped utility found by the trencher is a schedule and safety event.

Ampacity in a shared trench is a thermal calculation, not a table lookup. I model the trench cross-section with the site's soil thermal resistivity, the burial depth, the loading of every circuit in the group, and the earth ambient temperature, then size each cable for its derated ampacity. Spare conduits are included in the thermal model as future heat sources if they will ever be loaded — an empty spare costs nothing thermally, but a spare that later carries a circuit changes the group derating. The design documents the assumptions so a future circuit addition can be checked instead of guessed.

A cable trench design is construction-ready when it clears this checklist. Buried cable is the hardest plant system to fix — the trench design has to be right before the blade hits the ground. • Routes coordinated with roads, drainage, arrays, and future expansion areas • Burial depths meeting code with extra cover at road and heavy-haul crossings • Shared-trench circuits thermally modeled with mutual heating derating applied • Bedding, backfill, compaction, and warning tape specified and detailed • Directional bores designed for crossings with verified utility clearances