You might be thinking about 300.5(D)(1) that says direct buried conductors emerging from grade shall be protected by a raceway or enclosure from the minimum cover distance to a point at least 8 feet above finished grade. Also take a lok at 334.15(B) for protection of NM cable.
There may be local amendments to the NEC, such as this one in Oregon:
(3) Amend Section 334.15(B) Protection from Physical Damage by adding: "Exposed nonmetallic sheathed cable shall be protected where it is installed horizontally below 8 feet above the floor. Exposed nonmetallic sheathed cable below 8 feet above the floor that enters the top or bottom of a panelboard shall be protected from physical damage by conduit, raceway, 1/2" plywood or 1/2" drywall."