Solar Cable Size Calculator

Size for voltage drop: required area (mm²) = 2 × 0.0175 × current × one-way length ÷ allowed volt-drop, then round up to the next standard gauge. 30 A over 16 ft (5 m) on a 12 V system at 3% (0.36 V allowed) needs about 14.6 mm² — so 6 AWG (16 mm²) wire. The calculator handles the arithmetic and the standard-size rounding.

Because the allowed drop is tiny: 3% of 12 V is just 0.36 V, versus 3.6 V on a 120 V circuit. The same power also means far more current at low voltage. A wire that would be laughably oversized on 120/240 V AC is often the minimum on a 12 V battery run — and doubling the system voltage to 48 V quarters the current and slashes the copper needed.

Common practice: up to 3% on panel-to-controller runs, but only 1–2% between battery and inverter, where high currents flow and every volt of sag hits the inverter’s low-voltage cutoff early. Keep battery-to-inverter cables as short and fat as practical — that run is where systems most often disappoint.

No — it sizes purely on volt-drop, and you must also confirm the wire’s ampacity (the NEC tables) and fusing. At solar currents the volt-drop size is usually the larger of the two, but always fuse battery cables at the battery end, use proper DC-rated wire (double-insulated PV wire on the roof), and crimped lugs — DC arcs don’t self-extinguish like AC.

One-way — the route distance from source to load, in feet (m). The formula already doubles it for the return conductor, so measuring the loop would size the wire twice as heavy as needed.