First, let’s clear up a common confusion: Romex (NM or NM-B cable) is a type of non-metallic sheathed electrical cable used indoors for residential wiring. It is not designed for direct burial or outdoor use. Standard Romex has a PVC jacket, which is not waterproof and cannot withstand moisture or soil conditions.
If you need a cable for underground installations, you’ll need a cable rated for direct burial, such as UF-B cable or USE cable. These cables are manufactured to meet NEC (National Electrical Code) requirements for underground use.
Romex Direct Burial Cable
Can You Bury Romex Cable Underground?
No. Regular Romex (NM-B) is only rated for dry, indoor environments (walls, ceilings, floors). Burying it underground will cause:
Moisture penetration → Leads to short circuits and corrosion.
Physical damage → Soil pressure or digging can compromise the cable.
Code violations → Not compliant with NEC standards.
What to Use Instead of Romex for Direct Burial?
If your goal is to run wiring underground without conduit, choose one of these direct burial-rated cables:
UF-B Cable (Underground Feeder)
PVC jacket, moisture-resistant.
Common for outdoor circuits, garden lighting, and sheds.
USE-2 / RHW-2 Wire
For underground service entrance.
Tray Cable (TC-ER)
For industrial or heavy-duty applications.
Depth Requirements for Direct Burial
According to NEC:
UF-B or USE cable without conduit → Minimum 24 inches deep.
Cable inside conduit → Minimum 18 inches deep.
GFCI protection may allow for shallower depth in certain cases.
Installation Tips
Mark the Route → Use warning tape above the cable.
Protect Entry Points → Use proper connectors where cable enters the house.
Avoid Rocky Soil → Can damage insulation over time.
Check Local Codes → Some states require conduit even for UF-B.
Romex vs UF-B Cable
| Feature | Romex (NM-B) | UF-B Cable |
|---|---|---|
| Indoor Use | ✅ Yes | ✅ Yes |
| Outdoor Use | ❌ No | ✅ Yes |
| Direct Burial | ❌ No | ✅ Yes |
FAQ
Q: Can I put Romex in conduit underground?
Yes, if properly rated conduit (PVC Schedule 40 or 80) is used and sealed. However, pulling NM-B cable through long conduit runs is difficult and not recommended; THWN-2 wires are better for this purpose.
Q: Is UF-B the same as Romex?
No. UF-B looks similar but has a solid outer jacket that makes it waterproof and suitable for direct burial.
✅ Summary:
Romex (NM-B) cannot be buried directly. For underground wiring, use UF-B or USE cable, following NEC depth requirements and local codes.
