What Is UF Wire? | Underground Feeder Explained

UF wire, or Underground Feeder cable, is a moisture-resistant, sunlight-resistant cable rated for direct burial in soil and outdoor wet locations.

UF wire—short for Underground Feeder—is an electrical cable built to survive continuous exposure to moisture, sunlight, and soil contact that would quickly destroy standard indoor wiring. Its solid PVC jacket resists water, fungus, and corrosion, making it the NEC-approved choice for outdoor feeders, landscape lighting, pumps, electric gates, and any branch circuit that runs through wet earth or direct burial. UF-B is the current standard type, rated 600 volts with a system temperature rating of 60°C for most configurations.

What UF Wire Is Used For

UF cable carries power from a service panel or junction box to outdoor equipment that standard NM cable cannot safely serve. Common applications include floodlights, well and sewer pumps, dock power pedestals, irrigation controllers, electric gates, detached-garage subpanels, and outdoor receptacles. It is also the standard conductor for landscape lighting where the cable passes through soil. The cable may be buried directly at code-required depth or installed in conduit in wet locations for extra mechanical protection.

Conductor sizes range from #14 AWG through #4/0 AWG for UF-B products, with solid conductors from #18 to #8 AWG and stranded from #6 to #2 AWG depending on the product line. Packaging is typically on reels of 500, 1000, or 2500 feet. Two-conductor cables use black/white insulation; three-conductor cables add a red conductor.

UF Wire vs. NM Cable: What’s the Difference?

NM cable (often called Romex) is designed exclusively for dry indoor wall and ceiling cavities. It has a paper wrapping and thin PVC jacket that degrades rapidly when exposed to moisture, sunlight, or soil. UF cable uses a dense, homogeneous PVC outer jacket that is flame-retardant, moisture-resistant, fungus-resistant, and corrosion-resistant, and each conductor also carries moisture-resistant insulation. You cannot substitute NM for UF in wet or buried locations, but UF may replace NM indoors provided the conductor insulation is rated 90°C.

UF Wire Code Requirements and Installation Rules

Direct burial of UF-B is permitted under the NEC. Minimum burial depth is typically 24 inches for 120V circuits with GFCI protection on the feeder, though local amendments may differ. The bending radius of the inner edge of any bend must be at least five times the cable’s diameter. Where UF enters a building or transitions to conduit, it must be protected from physical damage, typically with conduit or an approved fitting.

Ampacity for standard UF-B is determined using the 60°C column of the NEC tables unless the cable jacket is specifically marked for a higher rating—some UF-B2 products list 90°C conductors, but the system ampacity may still be restricted by the product listing and code rules. A common mistake is assuming the conductor’s higher insulation temperature automatically allows higher ampacity; always check the cable’s own marking and the NEC. For a 50-amp subpanel or large outdoor equipment, 6/3 UF-B is a typical size—you can compare vetted 6/3 UF-B cable options in our roundup for specific product recommendations.

Never confuse UF with NM or assume all “underground” cables are identical. Different product lines (UF-B, UF/TWU, UF-B2) carry different temperature ratings, conductor counts, and UL listings; the datasheet and jacket marking always control. The NEC also requires that where UF substitutes for NM indoors, the conductor insulation must be rated 90°C.