How Deep Do You Bury Electrical Wire? UF-B Burial Depths and Code Rules
The answer depends on the wiring method: 24 inches for direct-buried UF-B cable, 18 inches in PVC conduit, 12 inches for a GFCI-protected residential circuit. Here's the full table and what inspectors actually check.
The 24 / 18 / 12 rule
NEC Table 300.5 sets minimum cover — and "cover" has a specific meaning: the shortest distance measured from the top surface of the cable or conduit to the top surface of finished grade. Not the bottom of the trench, the top of the cable. Dig to the depth, then the cable sits at that depth.
| Wiring method | Minimum cover | Notes |
|---|---|---|
| UF-B or other cable, direct buried | 24 inches | The gray UF-B cable laid straight in the earth |
| Conductors in PVC (nonmetallic) conduit | 18 inches | Individual THWN-2 conductors inside listed PVC conduit |
| Residential branch circuit, 120V or less, GFCI-protected, max 20A breaker | 12 inches | UF-B or conduit — the GFCI is what earns the reduction |
| Conductors in rigid metal conduit | 6 inches | Metal raceway is the toughest option, so it gets the shallowest depth |
A few things the table doesn't say out loud: under streets, driveways, and parking lots, the general rule stays at 24 inches regardless of column. And the 12-inch GFCI column applies to one- and two-family dwelling circuits rated 120 volts or less with a maximum 20-amp breaker — a 240V run to the garage doesn't qualify. When in doubt, dig deeper: these are minimums, and your local inspector is the final word.
How a GFCI buys you 12 inches
The 12-inch depth isn't a shortcut — it's a trade the Code makes deliberately. A ground-fault circuit interrupter trips on tiny current leaks, which is exactly the hazard a shallow cable faces: a shovel or aerator nicking the cable in damp soil. With GFCI protection on the circuit, the Code accepts 12 inches of cover.
The conditions are specific: one- and two-family dwelling, 120 volts or less, GFCI protection, and an overcurrent device rated 20 amps or less. Miss any one of those — a 30-amp circuit, a 240-volt run, no GFCI — and you're back to 24 inches for direct burial or 18 in conduit. GFCI protection can be a GFCI breaker in the panel or a GFCI receptacle feeding the underground run; either satisfies the Code as long as the whole underground portion is protected.
The ribbon above the cable
For underground service conductors, the NEC requires a warning ribbon at least 12 inches above the burial depth (300.5(D)(3)) — so the next person who digs hits bright tape before they hit copper. For branch circuits and feeders, the Code doesn't require it, but it's cheap insurance and plenty of inspectors like seeing it. Lay it in the trench above the cable before you backfill: six inches of soil over the cable, tape, then the rest of the backfill.
Two more backfill rules that fail inspections: no large rocks, cinders, or sharply angular material against the cable — it has to be clean fill or sand around the cable so nothing punctures the jacket. And the trench bottom should be reasonably smooth, not a jagged pile of broken concrete.
Running power to the shed
The classic project: a detached shed or garage 40–60 feet from the house, one 20-amp 120V circuit for lights and outlets. Here's how the Code-compliant version goes:
1. Feed it from a GFCI. Put the underground run on a 20-amp GFCI breaker (or feed it from a GFCI receptacle). This unlocks the 12-inch depth and protects the whole run.
2. Use UF-B cable. 12-2 UF-B with ground is the standard for a 20-amp circuit. It's the gray cable rated for direct burial — sunlight resistant where it emerges, wet-location rated underground. (Why the gray cable and not Romex: NM-B vs. UF-B, explained.)
3. Trench 12 inches of cover. Dig so the top of the cable sits 12 inches below finished grade. Where the cable rises out of the ground at each end, sleeve it in conduit for physical protection — the Code requires protection where direct-buried cable emerges from grade.
4. Warning tape, then backfill. A few inches of clean soil over the cable, tape, then fill the rest. Keep rocks away from the jacket.
5. Disconnect at the shed. A detached structure needs a disconnecting means — for a single circuit, a simple switch or the breaker back at the house can serve, but check with your inspector on what's acceptable locally. A subpanel with two circuits changes the rules; here's the subpanel wire sizing guide.
Chicago-area note: the NEC doesn't require burial below the frost line — the 24/18/12 table is about physical protection, not freezing. That said, freeze-thaw heaving is real in Illinois soil, and some local amendments add requirements. Check with your village or city inspector before you dig, and call JULIE (811) to mark utilities. That's not optional.
Bought a 250-foot roll for a 60-foot trench? If the rest is still good and on the roll, we buy usable leftover wire — anywhere in the country. Fast, free quote.
More from the Wire Guide
- NM-B vs. UF-B: Why Your Outdoor Project Needs the Gray Cable — the cable comparison behind this article.
- What Size Wire for a Subpanel? — when the shed needs more than one circuit.
- How to Read the Printing on Electrical Wire — confirm the jacket says UF-B before you bury it.
Burial depth questions, answered.
How deep do you bury UF-B cable?
24 inches of cover for direct burial. If the UF-B run is on a GFCI-protected 120V circuit with a 20-amp (or smaller) breaker, the Code allows 12 inches. In PVC conduit, 18 inches.
Can I bury Romex (NM-B) underground?
No. NM-B is not rated for wet locations or direct burial — and underground is always a wet location. Use UF-B for direct burial, or individual THWN-2 conductors in conduit.
Does the GFCI have to be at the panel for the 12-inch depth?
No — the requirement is that the underground portion of the circuit is GFCI-protected. A GFCI breaker in the panel or a GFCI receptacle upstream of the buried run both work.
Is warning tape required over buried wire?
The NEC requires a warning ribbon above underground service conductors. For branch circuits and feeders it isn't required, but it's cheap protection against the next person with a shovel — and inspectors like it.
Do I have to bury below the frost line in Illinois?
The NEC's burial depths are about physical protection, not frost — nothing in Table 300.5 references the frost line. But freeze-thaw movement is real in Chicago-area soil, and local amendments can add requirements, so check with your local inspector.
Can I run UF-B through conduit instead of direct burying it?
Yes. UF-B in PVC conduit gets the 18-inch conduit depth, and the conduit adds protection. One caution: UF-B's flat, stiff jacket makes it harder to pull through conduit than round cable — upsize the conduit or use individual THWN-2 conductors instead.
What does the inspector check on an underground run?
Depth of cover (measured to the top of the cable), the right cable type for the location, conduit sleeves where cable emerges from grade, GFCI protection if you claimed the 12-inch depth, clean backfill, and a disconnect at the detached structure.
I know wire. That's how I know what it's worth.
The jacket tells us whether a roll is direct-burial UF-B or indoor-only NM-B — and that difference is the difference between resale inventory and scrap. That's also how we know when usable wire is worth more than the yard pays for it.