Direct burial cable is a type of electrical cable designed to withstand direct exposure to soil and moisture, and it is rated for wet, dry, and damp environments. That rating allows the cable to be buried in a trench underground without the extra protection of a conduit. The individual conducting wires inside the cable are encased in a solid thermoplastic sheath that seals out moisture and shields the conductors within. Homeowners use this wiring for outdoor lighting, detached garages, sheds, well pumps, and landscape power, while contractors rely on it for service entrances and feeder circuits. Before planning a run, check the utility service pipe and cable burial depths rules that apply in your region, because required depths change with voltage, cable type, and the utility involved.
This article explains how direct burial cable is built, which types are rated for underground service, the trench depths codes require, and the installation steps that produce a safe, long-lasting circuit.
What Direct Burial Cable Is
A direct burial cable is a factory-assembled bundle of insulated conductors wrapped in a tough outer jacket that can sit in contact with soil for decades. Ordinary NM cable, the type used inside wall cavities, is not rated for wet locations and breaks down quickly when buried. Direct burial cable differs in three ways: the insulation on each conductor is rated for wet conditions, the outer jacket resists moisture, soil chemicals, and abrasion, and the whole assembly is listed for direct contact with the earth.
How the cable is constructed
Every direct burial cable shares the same basic anatomy:
- Copper or aluminum conductors carry the current.
- A layer of insulation rated for wet locations surrounds each conductor.
- A thermoplastic jacket binds the bundle and seals out groundwater.
- Some types add metallic armor or a second jacket for rodent and shovel resistance.
The jacket is the component that earns the direct burial label, because it is the barrier between the energized conductors and the surrounding soil. When you lay out a run across a yard, establish the distances between the panel, the trench, and the termination point with the same care a survey crew applies to direct methods of linear measurement in surveying. A measured route prevents ordering too little cable and keeps the trench on the intended line instead of wandering around trees, beds, and paving.
Wet, damp, and dry ratings
Cable listings state the environments a product can tolerate. A wet rating means the insulation keeps working while immersed or in continuous contact with moisture. A damp rating covers protected outdoor locations such as a porch ceiling. A dry rating applies only inside buildings. UF-B cable carries a wet rating and is the common choice for residential direct burial, while USE-2 is used where higher conductor temperatures are expected.
Temperature and sunlight ratings
The jacket also carries a temperature rating, typically 60, 75, or 90 degrees Celsius at the conductor, and a sunlight rating when sections of the cable will sit above grade. A cable that is not sunlight rated will chalk, crack, and shed its jacket within a few seasons of exposure, so verify both numbers on the reel label before you buy.
Types of Underground Cable
Not every cable sold for outdoor use can be buried directly. The label on the reel tells you which listings the product carries. The three families below cover most residential and light commercial underground work.
UF-B cable
Underground feeder cable with a B insulation rating is the workhorse of residential direct burial. It carries a wet rating, resists sunlight, and comes in the common branch circuit sizes from 14 AWG up through larger feeder sizes. UF-B can feed outdoor receptacles, post lights, and small subpanels.
USE-2 cable
Underground service entrance cable rated for 90 degrees Celsius conductors is a common choice for service drops and feeder runs from the utility point to the main panel. Its insulation handles higher operating temperatures, which matters on long, heavily loaded runs where voltage drop is a real concern.
Wires in conduit
Where a run passes under a driveway, through rock, or into a building, install individual THWN-2 conductors inside conduit instead of burying a cable. The conduit adds mechanical protection and makes future wire replacement possible without digging up the yard.
Other terms you will see on outdoor wiring products:
- MC cable with a wet-rated jacket for exposed outdoor runs.
- Service entrance cable for overhead and underground utility connections.
- Landscape lighting cable for low-voltage path and accent lighting.
Contractors check the grade along the trench with surveying techniques such as the direct levelling methods used to establish elevations on construction sites. A consistent grade keeps water from pooling around the cable and makes backfill compaction predictable.
| Cable type | Wet rating | Typical use | Notes |
|---|---|---|---|
| UF-B | Yes | Branch circuits and feeders | Common residential direct burial choice |
| USE-2 | Yes | Service and feeder runs | 90 degree C conductor rating |
| THWN-2 in conduit | Yes | Driveway and building crossings | Wire can be replaced later |
| MC cable | Yes | Exposed outdoor runs | Metal armor adds protection |
Trench Depths and Code Requirements
The National Electrical Code sets minimum cover depths in Table 300.5, and local amendments can go deeper. Cover is measured from the top of the cable or conduit to finished grade, not from the trench floor. A 24 inch trench for direct burial cable is the standard residential figure, but the number changes with the wiring method and the location.
Minimum cover depths
Compare the common scenarios in the table below. When two numbers conflict, the deeper one wins.
| Installation location | UF-B direct burial | Rigid metal conduit | PVC conduit |
|---|---|---|---|
| Residential branch circuits | 24 inches | 6 inches | 18 inches |
| Service laterals | 24 inches | 6 inches | 18 inches |
| Under driveways and parking areas | 24 inches | 6 inches | 18 inches |
Check the local code before digging. Many jurisdictions require 24 inches for 120 and 240 volt residential circuits and more for higher voltages or for crossings under driveways.
Soil conditions and excavation
Soil type changes how you dig and how deep the trench must be. Sandy soil drains well but collapses easily, clay holds moisture against the jacket, and rock can make the full depth impractical. Excavation methods used for deep foundations, including pile foundation installation using the direct mud circulation method, show how much support unstable ground can demand. For a residential trench, sloping the walls or using a trench box is usually enough.
Frost line and trench width
In cold climates, bury cable below the local frost line where practical so freeze and thaw cycles do not heave the soil and stress the cable. A trench 6 to 12 inches wide gives you room to lay cable without sharp bends and to place warning tape above it.
Step-by-Step Installation
A safe underground circuit is the product of a sequence of small decisions. Work through the steps in order and inspect each stage before covering it.
- Confirm the circuit design, conductor size, and breaker rating against the load you plan to feed.
- Pull the permit and schedule the inspections your jurisdiction requires for buried wiring.
- Call the one-call utility locating service a few days before digging so existing lines are marked.
- Lay out the route and measure it, adding 10 percent for bends, terminations, and mistakes.
- Dig the trench to the required depth and width, keeping the walls stable.
- Place a 2 inch bed of sand or screenings to cushion the cable.
- Lay the cable without kinking, coiling extra length at each end for the termination.
- Backfill in shallow lifts, removing rocks and debris that could damage the jacket.
- Install warning tape 12 inches above the cable so future diggers find it first.
- Terminate at both ends, test the circuit, and close out the inspection before final grading.
Before you dig
Utility locates are not optional. Striking a buried gas line or water main turns a small wiring job into an emergency repair, and the property owner usually carries the cost. Mark the route with paint or flags, then re-check the marks the locator leaves before any machine enters the yard.
Budgeting the project
The direct and indirect costs of an underground wiring project include cable and fittings as direct costs, plus permits, equipment rental, and inspection fees as indirect costs. Writing both groups down before you start keeps the estimate realistic and prevents surprises when the trench turns out longer than planned.
Protection, Splicing, and Repairs
Once the cable is buried, the risks shift from weather to digging, settling, and the occasional fault. A few habits keep an underground circuit healthy for its full service life.
Splices below grade
Splices belong in accessible boxes, not buried in the soil. Use listed underground splice kits rated for direct burial, or bring the cable up into a handhole or junction box where the connection can be inspected. A buried splice is the most common source of intermittent faults on yard circuits.
Concrete encasement
Where cables cross driveways, parking areas, or equipment yards, a concrete-encased duct bank adds mechanical protection. The same logic behind the direct design of concrete pipes for sewer and sanitary lines applies here: the rigid envelope carries the load so the cable inside survives traffic and settling.
When to call a professional
Panel terminations, service entrances, and fault tracing are work for a licensed electrician. If a yard circuit trips repeatedly or a GFCI will not reset, the cause is usually a damaged jacket or a wet splice, and locating it requires test equipment most homeowners do not own.
Every underground circuit touches excavation, electrical, and restoration work, so the types of construction project costs involved include materials, labor, permits, and site repair. A written breakdown of those categories helps you compare contractor quotes and keeps the whole job on schedule.