Solar cable size: mm² and AWG table by current and length

Cable size is what people undersize the most. A gauge that looks 'good enough' loses 5% of your yield every day, every year, and heats to fire risk. Here's the right table and the formula.

Why it matters more in DC than AC

At 12 V DC, a 1000 W load pulls 83 A. The same load at 240 V AC pulls 4 A. Cable losses scale with current squared. That's why a poorly wired 12 V system burns 20% of its energy as heat.

Acceptable voltage drop per run

Panel→controller: 3% max. Controller→battery: 1%. Battery→inverter: 1%. Inverter→AC panel: 3%. DC loads (12 V lights): 5%. Go over and you bought extra panels for nothing.

The real formula

Area (mm²) = (2 × L × I × 0.0175) ÷ ΔV, where L is the length of ONE cable in meters, I is amps, ΔV is allowed drop in volts. Example: 33 A at 24 V over 8 m with 3% drop → 13 mm² → buy 16 mm² (next commercial size, 6 AWG).

Quick table 12/24/48 V (≤3% drop)

5 A, 16 ft: 14 AWG. 10 A, 16 ft: 12 AWG. 20 A, 16 ft: 10 AWG. 40 A, 16 ft: 8 AWG. 60 A, 16 ft: 6 AWG. 100 A, 16 ft: 4 AWG. 200 A, 6 ft: 2 AWG.

AWG ↔ mm² equivalence

14 AWG = 2.5 mm². 12 AWG = 4 mm². 10 AWG = 6 mm². 8 AWG = 10 mm². 6 AWG = 16 mm². 4 AWG = 25 mm². 2 AWG = 35 mm². 1/0 AWG = 50 mm². 2/0 = 70 mm². 4/0 = 95 mm².

Cable type: PV1-F / USE-2, not building wire

Panel-to-controller requires PV1-F (EU) or USE-2/PV (US): double insulated, UV-resistant, 1500 V DC, 90-120 °C. Indoor wire degrades in sun in 2 years. For battery-inverter use flexible class 5 (silicone or EPDM).

Pair it with the right fuses and review the typical install mistakes.