Solar wiring involves both DC circuits (panels to inverter or charge controller) and AC circuits (inverter to panel/grid). DC wire sizing is especially critical because solar panels can be far from the inverter, creating long runs where voltage drop matters.
Panel-to-combiner box: typically 10-12 AWG USE-2 or PV wire. String wiring uses the panel's maximum series fuse rating. DC home runs to the inverter may need 6-2 AWG depending on distance and current. NEC Article 690 requires wire sizing at 125% of the short-circuit current (Isc).
Battery cables carry the highest currents in an off-grid system. A 48V battery bank powering a 5kW inverter draws over 100A — requiring 2/0 or larger cable. Keep battery cable runs as short as possible. Use welding cable or marine battery cable for flexibility and durability.
NEC recommends maximum 2% voltage drop on DC circuits (stricter than the 3% for AC). For a 100-foot run of 10 AWG copper at 8A and 48V, the voltage drop is about 0.8V (1.7%). At higher currents or longer distances, upgrade to a larger gauge.
USE-2 and PV Wire (PV1-F) are rated for direct sunlight exposure and are required for outdoor panel wiring. THWN-2 in conduit is acceptable for interior runs. For underground, use UF-B or direct-burial rated cable.
Disclaimer: This guide is for informational purposes only. Always consult a licensed electrician and follow local building codes for actual installations. Wire sizing depends on specific conditions including ambient temperature, conduit fill, and derating factors.