The key concept is protecting underground electrical wiring that runs under a paved surface. When an outdoor lighting circuit must pass under a driveway, the burial depth is chosen to guard the conductors from physical damage caused by vehicles and maintenance, while still being practical to install. The minimum depth you’ll most often see for this scenario is 12 inches. This depth provides enough cover to resist direct impacts and moisture, especially when the conductors are inside conduit to shield them and allow easier future pulling or replacements. Deeper depths, like 18 or 24 inches, are used in heavier-traffic areas or under different conditions, but for a typical driveway installation the 12-inch depth is the standard. A shallower depth would risk damage and noncompliance, while the choices that go deeper than necessary aren’t required for this common case.