Indoor vs. Outdoor Electrical Wire Selection
Using the correct wire type for the installation environment is a fundamental NEC requirement. Wire rated only for indoor use will degrade when exposed to moisture, sunlight, or direct burial conditions, creating serious safety hazards over time.
Indoor (Dry Location) Wire
NM-B cable (Romex) is the standard indoor residential wiring product. Its outer jacket provides physical protection for the conductors inside but is not rated for moisture or UV exposure. NM-B should only be installed in dry, protected locations such as interior walls, ceilings, attics, and crawl spaces that are not subject to persistent moisture.
Outdoor and Wet Location Options
For outdoor installations, you have several options depending on the specific application. UF-B (Underground Feeder) cable has a solid, moisture-resistant jacket and is approved for direct burial in the ground and for use in wet locations. It is the go-to product for running power to outbuildings, landscape lighting, and other outdoor circuits. THWN/THWN-2 individual conductors in weatherproof conduit (PVC or rigid metal) are the standard for exposed outdoor runs, such as wiring from a meter to a panel on the exterior of a building, generator connections, and outdoor sub-panel feeds. USE-2 (Underground Service Entrance) wire is specifically rated for direct burial service entrance applications.
Conduit Considerations
When running wire outdoors in conduit, the conduit itself must be rated for the environment. PVC (Schedule 40 or 80) is the most common choice for outdoor and underground conduit runs. Rigid metal conduit (RMC) and intermediate metal conduit (IMC) are also options, particularly where physical protection from damage is a priority. All outdoor conduit runs must include proper drainage provisions and waterproof fittings.
IB Lighting stocks UF-B cable, THWN conductors, and related supplies for outdoor electrical projects. Call (800) 674-9019 to discuss your project requirements.