Underground Installations — Burial Depth

Table 300.5 sets the numbers: deeper for direct burial, less for rigid conduit, and more under driveways and roadways. The depth is measured to the top of the wiring method.

I always lay a warning tape above the run. Cover depth protects against the shovel; the tape gives the operator a chance to stop before the blade reaches the pipe.

When it applies

This section governs anything buried underground, whether it is direct-buried cable, PVC, or metal raceway. The minimum cover depth depends on the wiring method and what sits above it. A run under a driveway is treated differently from one crossing an open yard, and residential branch circuits at reduced voltage get their own allowances.

Common mistakes

• Measuring cover from the wrong reference. Cover is measured from the top of the conduit to the finished grade, not from the trench bottom.
• Ignoring frost depth in cold regions, so heave stresses the run over a few winters.
• Backfilling with sharp rock directly against the conductors instead of clean fill or protection where required.

In the field

Before I close a trench I photograph the tape measure against the conduit at grade. If a question comes up months later, that image settles it precisely.