XHHW
Wire spec for high heat and water, such as PV. Compared to THHN -
Whether you can use XHHW cable on a roof without conduit depends on the specific cable type (XHHW vs. XHHW-2) and the local electrical codes, which often prioritize mechanical protection for exposed wiring.
Standard XHHW: Standard XHHW wire is generally not rated for long-term direct sun exposure and typically requires installation in a conduit or raceway when used outdoors to protect it from UV degradation and physical damage. XHHW-2: XHHW-2 is a premium variant with enhanced UV stabilization and is rated as "Sunlight Resistant" (SR). It is designed for use in harsh outdoor conditions and is suitable for exposed runs in PV systems under specific National Electrical Code (NEC) articles (e.g., NEC Article 690.31(C)).
Mechanical Protection: Even if the cable is UV-resistant (like XHHW-2), the NEC and local building codes may still require it to be in a conduit for mechanical protection if it is in an area prone to physical damage (e.g., high-traffic areas, or areas where it could be abraded or impacted). Laying bare cables directly on the roof without a raceway would likely not pass inspection in most jurisdictions.
Can i run THHN in conduit for solar on roof?
XHHW-2 wire is suitable for use in rooftop solar applications because it is specifically designed to be resistant to high heat, moisture, and UV radiation, and it complies with National Electrical Code (NEC) standards for such installations. Standard XHHW wire, however, may require conduit for protection if it lacks a "sunlight resistant" rating.