Outdoor Outlet Wiring: Wire Types, Code Requirements, and Installation
Adding or upgrading outdoor electrical outlets is one of the most common residential electrical projects, and it involves two different wire types depending on whether the wiring runs through walls or underground. Getting the wire selection right matters both for code compliance and long-term reliability because outdoor wiring is exposed to moisture, temperature cycles, and physical damage that indoor wiring never encounters. Here is the complete guide to outdoor outlet wire selection.
NEC Requirements for Outdoor Outlets
The NEC requires at least one GFCI-protected outdoor receptacle accessible at the front and rear of every one-family and two-family dwelling. These receptacles must be located not more than 6.5 feet above grade. All outdoor receptacles require GFCI protection per NEC Section 210.8(A)(3) and must be installed in weatherproof enclosures. In-use weatherproof covers (the kind with a hinged plastic flap that stays closed over a plugged-in cord) are required when the receptacle location indicates exposure to weather while in use.
Wire Type for Indoor Wall Runs
The portion of the outdoor outlet circuit that runs inside your home through walls, floors, or ceilings uses standard 12/2 NM-B (Romex). Because outdoor receptacles must be on a 20-amp circuit, 12 AWG is the minimum wire size. Run 12/2 NM-B from the panel or junction point through the interior wall path to the exterior outlet box location. NM-B is appropriate for this portion because it remains in a dry, protected environment throughout its run inside the structure.
Wire Type for Underground Runs
If you are running power from one outdoor outlet to another, from the house to a detached structure, or along an outdoor path that requires burying the cable, 12/2 UF-B is required. NM-B cannot be buried underground because its plastic jacket is not waterproof and will fail from moisture infiltration. UF-B has a solid-core waterproof jacket construction specifically designed for direct earth burial without conduit. Minimum burial depth for UF-B is 24 inches per the NEC. For runs in conduit (which provides additional physical protection), the minimum depth drops to 12 inches.
GFCI Protection Requirements
Every outdoor receptacle must have GFCI protection. This can be achieved with a GFCI outlet at the first receptacle in the outdoor circuit, with any additional outdoor outlets wired through the LOAD terminals to receive downstream GFCI protection. A GFCI breaker in the panel is an alternative that protects the entire circuit. Outdoor GFCI outlets should carry a weatherproof rating for outdoor installation. Standard indoor GFCI outlets are not rated for outdoor enclosures exposed to weather.
Weatherproof and In-Use Cover Requirements
Outdoor outlet boxes require weatherproof covers at minimum. In locations where cords will remain plugged in while the cover is closed (such as holiday lighting receptacles, tool outlets on a patio, or any outlet used with a plugged-in appliance in the rain), in-use covers with a hinged flap are required. Standard flat weatherproof covers are not adequate for in-use applications because they do not seal around a plugged-in cord.
Circuit Sharing
Outdoor receptacles may share a circuit with other outdoor receptacles but must be GFCI-protected. They may also share a circuit with garage receptacles in some code interpretations, though many jurisdictions and electricians prefer dedicated outdoor circuits to avoid tripping issues when multiple outdoor tools run simultaneously. A dedicated 20-amp outdoor circuit with 12/2 NM-B is the cleanest approach for a single-family home.
IB Lighting carries 12/2 NM-B and 12/2 UF-B from Southwire in all standard spool sizes with free freight insurance. Browse our wire and cable selection or call (800) 674-9019 for contractor pricing. Both cable types ship together on one order for complete outdoor circuit projects.