UF-B vs NM-B: indoor cable or underground cable
Published Sep 30, 2026
NM-B and UF-B look alike on the spool: the same gauges, the same 2 and 3 conductor builds, the same bare ground. They are not interchangeable. NM-B is for dry spaces inside a building. UF-B is built for wet locations and direct burial.
How they are built
NM-B (NEC Article 334) has individually insulated THHN-type conductors and a paper-wrapped bare ground inside a loose PVC jacket. You can peel the jacket off by hand, which is what makes it quick to work with indoors.
UF-B (NEC Article 340) has its conductors molded solid into the PVC jacket. There is no air space for water to travel along, which is what lets it go in the ground. It is harder to strip: you usually split the jacket with a knife or a UF stripper.
Side by side
| NM-B | UF-B | |
|---|---|---|
| NEC article | 334 | 340 |
| Dry locations | Yes | Yes |
| Damp and wet locations | No | Yes |
| Direct burial | No | Yes |
| Exposed to sunlight | No | Only if the jacket is marked sunlight resistant |
| Ampacity column | 60 °C (334.80) | 60 °C (340.80) |
| Common jacket color | By gauge: white, yellow, orange, black | Gray |
| Stripping | Easy | Slower; the jacket is solid |
| Price | Lower | Higher per foot |
Both are limited to the 60 °C column of NEC Table 310.16, so a 12 AWG circuit is 20 A in either cable. See NM-B wire size by circuit for the full table.
Where UF-B is the right call
- Direct-buried circuits to a detached garage, shed, well pump, gate opener or landscape feed.
- Outdoor runs along a wall, where the jacket is marked for sunlight.
- Wet or damp interior spaces such as some barns and wash areas.
Burial depth
NEC Table 300.5 sets the minimum cover. For UF-B buried directly in the earth under the general condition (column 1), that is 24 in. Two common reductions:
- 12 in. for a residential branch circuit of 120 V or less with GFCI protection and overcurrent protection of 20 A or less (column 4).
- Less cover where the cable is under a concrete slab or in a raceway, per the other columns and notes of Table 300.5.
Where the cable comes up out of the ground, NEC 300.5(D) requires protection from physical damage, usually a conduit sleeve from the required depth up to at least 8 ft above grade, or up to the enclosure.
Where NM-B still wins
Inside the walls, floors and ceilings of a dry building, NM-B is cheaper and faster to install. There is no benefit to running UF-B through a dry stud wall, and the solid jacket makes box work slower.
Common mistakes
- Pulling NM-B through underground conduit. Conduit below grade counts as a wet location, so NM-B is not permitted there even inside a pipe.
- Running NM-B on an exterior wall or under a deck exposed to rain.
- Using UF-B as a service entrance cable. It is not listed for that. Use USE-2 or SE cable instead.
- Forgetting the depth reduction only applies to 120 V, 20 A, GFCI circuits. A 240 V well pump feed needs the full 24 in. when direct buried.
Shop the cable
- 12/2 UF-B, 10/2 UF-B and 12/3 UF-B
- 12/2 NM-B and 14/2 NM-B
- For larger underground feeders, URD aluminum cable and USE-2 aluminum wire
Verify with your local code. Burial depth, GFCI rules and permitted wiring methods vary by NEC edition and by local amendment. Ask your inspector before you dig.