Running power out to a shed, a pump, or a detached garage means choosing a cable rated to live in the ground, and getting that choice wrong can be both a code violation and a fire hazard. 10 2 underground wire usually refers to UF-B direct-burial cable with two 10-gauge conductors plus a ground, a common pick for 30-amp circuits that need to travel outdoors and underground. This guide covers what the cable is, how deep to bury it, where it gets used, and the safety and permit rules that should never be skipped.
What 10/2 Underground Cable Means
The labeling breaks down into two parts. The “10” is the wire gauge, 10 AWG, which is rated to carry roughly 30 amps on a typical residential circuit. The “2” refers to two current-carrying conductors, a hot and a neutral, and there is also a separate equipment grounding conductor that the numbering does not count. So a 10/2 cable actually contains three wires total: black, white, and a bare or green ground.
For underground use, the cable type matters as much as the gauge. UF-B (underground feeder) cable is built with the conductors molded into a solid, moisture-resistant jacket so it can be buried directly in the earth. Standard indoor NM-B (Romex) is not rated for burial and must never be put in the ground.
Common Uses for 10/2 UF-B
A 30-amp underground circuit handles a range of outdoor and outbuilding loads. Typical applications include:
- Feeding a subpanel or single circuit in a detached garage or shed
- Wiring a well pump or other 240-volt equipment within its amperage rating
- Powering outdoor equipment that the manufacturer specs at 30 amps
- Dedicated circuits where the run length and load justify 10-gauge wire
Matching wire size to the load and the circuit breaker is critical. A 10-gauge cable belongs on a 30-amp breaker, not a larger one, and the actual load plus the distance of the run should be checked against current code tables, since long runs may require upsizing for voltage drop.
How Deep to Bury the Cable
Burial depth is set by the National Electrical Code (NEC) and depends on the installation method and protection. The exact figure varies, so treat these as general references and confirm the current code and your local amendments before digging:
- Direct-buried UF-B cable: often around 24 inches deep for a standard residential circuit.
- Circuits with GFCI protection at lower voltage: the NEC allows shallower depths in some cases, sometimes about 12 inches, under specific conditions.
- Cable in rigid or intermediate metal conduit: can typically be buried shallower than direct burial.
Because depth requirements hinge on voltage, conduit type, and GFCI protection, the only safe approach is to verify the applicable NEC table and any local rules for your exact setup rather than relying on a single remembered number.
Direct Burial Versus Conduit
You have two broad ways to run the circuit. Direct burial uses UF-B cable laid straight into the trench, which is simpler and cheaper but offers less mechanical protection. The alternative is running individual THWN/THWN-2 conductors inside conduit, which adds protection, allows for future wire pulls, and is often required where the cable transitions above ground or passes through areas at risk of physical damage.
Where a cable emerges from the ground, it generally must be protected in conduit up to a required height to guard against shovels, mowers, and impacts. Many installers use conduit for the vulnerable sections even on an otherwise direct-buried run.
Safety Steps That Cannot Be Skipped
Underground electrical work carries real shock and fire risk, so the safety basics are non-negotiable. Before touching any wiring, turn off the breaker for the circuit and verify it is dead with a tester. Before digging, call 811 to have underground utilities located so you do not strike a gas, water, or existing power line.
Use the correct cable type and gauge for the load, protect the cable where it exits the ground, and make sure outdoor circuits have the required GFCI protection. Use weatherproof outdoor-rated boxes and fittings, and seal entries to keep moisture out. Cutting corners on any of these is how underground circuits become hazards years down the line.
Planning the Run and Voltage Drop
Distance matters more than people expect on outdoor circuits. Over a long run, electrical resistance causes voltage to drop, and too much drop means equipment runs poorly and wiring runs warm. As a rule of thumb, the longer the distance from the panel to the load, the more likely you are to need a larger conductor than the load alone would suggest.
A 30-amp circuit on 10-gauge wire is fine over modest distances, but a run of a hundred feet or more out to a detached structure may push you toward 8-gauge or larger to keep voltage drop within acceptable limits. Calculate this before you buy cable, because pulling an undersized conductor and discovering the problem later means trenching and rewiring all over again.
Tools and Materials You’ll Need
A proper underground circuit involves more than just the cable. Plan for the full materials list before you start so the job is not stalled halfway through.
- UF-B cable in the correct gauge, or THWN conductors plus conduit
- Conduit, fittings, and sweeps for above-ground transitions and protected sections
- Weatherproof outdoor-rated junction boxes and covers
- A correctly sized circuit breaker matched to the wire gauge
- GFCI protection where required by code
- A voltage tester to confirm circuits are dead before work
- A trenching shovel or rented trencher for the burial run
Buying the right components up front, all rated for wet and outdoor use, is part of doing the job safely and to code.
Permits and Hiring a Professional
Outdoor and underground circuits almost always require an electrical permit and an inspection, and that process exists to keep the work safe. The inspector confirms depth, cable type, breaker sizing, grounding, and GFCI protection before the trench gets backfilled, so do not cover anything until it has been checked.
While experienced DIYers handle some wiring, running a new underground feeder, sizing a subpanel, or working at 240 volts is squarely in the territory where hiring a licensed electrician is the smart call. A pro pulls the permit, sizes everything to current code, and stands behind the work. The cost of doing it right once is far lower than the cost of an electrical fire or a failed inspection that forces you to dig the whole run back up.
