Solar DC Cable Size Calculator

A solar panel cable size calculator mm2 for 12v 24v DC wiring showing voltage drop per cable size and distance. Use the free Solar DC Cable Size Calculator below — enter your values and get instant results, right in your browser. Voltage drop (V) = 2 × distance (m) × current (A) × resistance per meter (4mm² = 0.0046, 6mm² = 0.0031, 10mm² = 0.0019 Ω/m). Drop % = drop volts ÷ system voltage × 100. Keep total DC drop under 3% (under 1.5% is ideal). On 12V systems the same cable gives 4× the percentage drop of 48V — size up aggressively.

How to use the Solar DC Cable Size Calculator

Thin DC cables silently steal your solar power as heat — a 5% voltage drop on a long panel run can cost you hundreds of watts every sunny day. This solar panel cable size calculator mm2 for 12v 24v DC wiring generates a voltage-drop table for 4mm², 6mm², and 10mm² copper cables at your actual current and distance. Find your cable length in the table, pick the first size whose drop stays under 3%, and your panels will deliver what they promise.

  1. Enter your string current in amps in the input box (a 550W panel at ~42V gives about 13A; add strings in parallel).
  2. Set the number of rows to cover your longest cable run in meters (one-way distance from panels to inverter).
  3. Click Generate to build the voltage-drop table for 4mm², 6mm², and 10mm² cables.
  4. Find your distance row and choose the smallest cable size whose drop is under 3%.
  5. If even 10mm² exceeds 3%, shorten the run or split into two parallel strings.

Formula

Voltage drop (V) = 2 × distance (m) × current (A) × resistance per meter (4mm² = 0.0046, 6mm² = 0.0031, 10mm² = 0.0019 Ω/m). Drop % = drop volts ÷ system voltage × 100. Keep total DC drop under 3% (under 1.5% is ideal). On 12V systems the same cable gives 4× the percentage drop of 48V — size up aggressively.

Worked example

A 15A string runs 10 meters to a 48V inverter. From the table: 4mm² drops (2 × 10 × 15 × 0.0046) ÷ 48 × 100 = 2.88% — just under the 3% limit, so 4mm² is acceptable but 6mm² (1.94%) is the safer pick. On a 12V system the same run would lose 11.5% — completely unacceptable.

Frequently asked questions

4mm² solar cable suits most single strings up to ~15A over short runs. For runs over 10–15 meters or higher currents, step up to 6mm² or 10mm². Use the table above with your real current and distance instead of guessing.

No. AC house wire insulation is not rated for sustained outdoor DC voltage and UV exposure, and DC arcs are harder to extinguish. Use proper UV-rated solar DC cable (usually black, marked 1.5kV DC) for panel runs.

Drop percentage = lost volts ÷ system volts. Losing 1.4V on a 12V system is 11.7%, but the same 1.4V on 48V is only 2.9%. That is why long cable runs should use 24V or 48V systems, or much thicker cable.

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