DC Cable Sizer
Copper cross-section for <2% voltage drop
Free · No sign-up · Computed instantly on your device
Circuit Parameters
Size the DC run from array junction to inverter. Distance is one-way cable route length — the return path is accounted for automatically.
Formula: A = (2 × L × I × ρ) ÷ (V × 2%), copper ρ = 0.0186 Ω·mm²/m at operating temperature, rounded up to the next standard size. Verify ampacity and derating per IS 694 / cable manufacturer tables for the final BOM.
Required copper cross-section
2.5mm²
Calculated minimum 1.61 mm² → rounded up to the standard 2.5 mm² size
Actual voltage drop
1.29%
7.7 V lost end-to-end
Conductor length
80 m
out + return path
Resistive loss
101 W
dissipated in the cable
Standard size ladder
About This Calculator
Every metre of undersized cable is a permanent, invisible tax on generation. This calculator applies the standard voltage-drop formula — A = (2 × L × I × ρ) ÷ (V × 2%) — to return the minimum copper cross-section for a DC run, rounded up to the next standard size (4 mm², 6 mm², 10 mm²…), along with the actual voltage drop and watts dissipated in the cable.
The 2% DC voltage-drop ceiling is the design norm for quality Indian installations. The tool accounts for the out-and-return conductor path automatically — you enter the one-way route length. Always cross-check the chosen size against ampacity and derating tables (IS 694 / manufacturer data) for the final bill of materials.
How the Calculation Works
Voltage drop in a cable is V = 2 × L × I × ρ ÷ A, where L is the one-way length (the 2 covers the return conductor), I the current, ρ the resistivity of copper at operating temperature (about 0.0186 Ω·mm²/m) and A the cross-section in mm². The calculator solves for A so the drop stays under 2% of array voltage, then rounds up to the next standard size.
It also reports the actual drop and the power lost as heat. Many installers commonly use 4 mm² solar DC cable as a minimum for mechanical strength and current rating, so treat the calculated size as the electrical minimum, not the only rule. The relevant IS/IEC codes are listed in our standards reference.
Worked example (the calculator’s defaults)
- Array voltage 600 V, string current 13 A, one-way run 40 m.
- Required area: 2 × 40 × 13 × 0.0186 ÷ (600 × 0.02) = 1.61 mm², so the next standard size is 2.5 mm².
- Actual drop with 2.5 mm²: about 1.29% (7.7 V), with roughly 100 W lost as heat in the run.
- Stepping up to 4 mm² cuts the drop to about 0.8% and the heat loss to about 63 W.
Go Deeper
Frequently Asked Questions
- Why 2% and Not More?
- Voltage drop is energy converted to heat in the cable — every day, for 25 years. The industry norm caps DC drop at 2% (and total system drop at ~3%) because beyond that, the lifetime energy loss outweighs the cost of thicker copper.
- Copper or Aluminium for Solar DC Cables?
- Copper for rooftop DC runs — better conductivity, smaller cross-sections, and compatible with standard MC4 ecosystems. Aluminium appears mainly in large ground-mount AC transmission where its cost advantage justifies the larger sizes.
More Free Solar Calculators
Found this useful? Send it to someone planning solar.