What is the difference between UF cable and Romex?

UF cable is rated for direct burial and wet locations, while standard NM cable, often called Romex, is for dry interior spaces. UF also has a tougher molded jacket and is harder to strip.

Can UF cable be buried without conduit?

Often yes, because that is one of its main uses, but the burial depth still has to meet code. Some portions of the run, especially where the cable emerges from the ground, may still need conduit protection.

Why is UF cable so hard to work with?

Its jacket is thicker and molded tightly around the conductors for durability in wet or buried conditions. That makes it stiffer and more difficult to strip than indoor NM cable.

Do I need a permit to run UF cable to a shed?

Usually yes. Exterior feeder or branch-circuit work commonly requires a permit and inspection to verify wire sizing, trench depth, grounding, and protection.

How do I know if buried UF cable has failed?

Tripped breakers, dead outdoor circuits, nuisance GFCI trips, or visible damage where the cable enters or leaves the ground are common clues. Locating the exact failure often requires electrical testing.

UF Cable (Underground Feeder Cable) — Buried Wiring

A UF cable is a nonmetallic electrical cable rated for direct burial and wet locations without requiring conduit around the conductors.

UF Cable diagram — labeled parts and installation context

What It Is

UF stands for underground feeder. Unlike standard indoor NM cable (Romex), which has a paper-wrapped, loosely jacketed construction, UF cable has a solid thermoplastic outer sheath molded tightly around each insulated conductor in a flat, integral package. This monolithic jacket resists moisture, soil chemicals, and fungal growth, allowing the cable to be buried directly in the earth without conduit when installed at the code-required depth.

Homeowners most often encounter UF cable on exterior branch circuits that run to sheds, detached garages, yard lighting, well pumps, and other outdoor loads. NEC Article 340 governs UF cable installations, and the minimum burial depth for a 120-volt, 20-amp GFCI-protected branch circuit is 12 inches. Without GFCI protection, the required depth increases to 24 inches. Where the cable transitions from underground to above-ground at a building wall or post, it must be protected by conduit from at least 18 inches below grade to the point of entry.

Types

UF-B cable with two insulated conductors and a bare equipment ground is the standard residential product, available in sizes from 14 AWG (15-amp circuits) through 6 AWG (60-amp feeders). The most common residential sizes are 14/2, 12/2, and 10/2 for branch circuits serving outdoor receptacles, lighting, and small equipment.

Larger multi-conductor UF cables, such as 6/3, are used for feeder circuits supplying subpanels in detached garages and workshops. Copper is the standard conductor material for residential direct-burial applications because aluminum requires larger conduit and special termination hardware that complicates underground work. Some manufacturers produce UF cable with a sunlight-resistant jacket for exposed outdoor runs along building exteriors.

Where It Is Used

UF cable is used for direct-buried outdoor branch circuits and feeders, and in any location that may be damp or wet where NM cable is not permitted. It commonly serves landscape lighting transformers, detached structures such as sheds and pool houses, outdoor receptacles on patios and decks, irrigation control valves, well pump circuits, and sign lighting.

In addition to underground use, UF cable is permitted inside buildings as a substitute for NM cable in damp locations such as basements, crawl spaces, and agricultural buildings where moisture exposure would degrade standard NM cable sheathing. It is not permitted in conduit embedded in concrete, in hazardous locations, or as service entrance cable.

How to Identify One

UF cable is usually gray (compared to the white or yellow jacket of NM cable) and feels noticeably flatter and stiffer because the thermoplastic sheath is molded tightly around each conductor rather than loosely wrapping them. Stripping UF cable requires a sharp knife or a specialized stripping tool because the jacket does not peel away the way NM sheathing does.

The jacket is printed at regular intervals with markings that identify it as UF or UF-B along with the conductor gauge, number of conductors, voltage rating (typically 600V), and UL listing. At the point where UF cable emerges from the ground and enters conduit, the transition fitting and conduit riser are visible on the exterior of the building.

Replacement

Replacement is needed when the cable jacket is nicked or crushed by excavation equipment, the conductors are undersized for an increased load, the installation depth does not meet current code, or the cable has suffered insulation breakdown causing nuisance GFCI trips on the circuit. Locating a buried cable failure often requires a cable locator or tone generator to trace the run and identify the approximate fault location before digging.

Exterior wiring work involving UF cable replacement typically requires a permit because trench depth, GFCI protection, conduit transitions at building entries, and grounding all require inspection. When replacing, use the opportunity to upsize the cable if future load growth is anticipated, and install the new cable in a sand bed at the bottom of the trench to protect it from sharp rocks.