Solar
Solar Cable Voltage Drop Calculator
Solar cable voltage drop equals current multiplied by round-trip cable resistance. Power lost in the cable equals current multiplied by that voltage drop.
Calculate resistive DC voltage drop and cable power loss between solar-system components.
Calculated result
Solar cable loss
Calculating…
Calculated locally in your browser
Planning math only. Verify equipment specifications and installation requirements separately.
Data provenance: NLR PVWatts v8 grid awaiting its first private-key refresh; the visible peak-sun-hours fallback is active. EIA residential state averages updated 2026-08-13. ZIP centroids use the 2025 Census Gazetteer. No ZIP or calculator input is sent to those sources. Read the solar data provenance and limitations.
What this calculator returns
Use the result for cable-loss planning only, then verify PV equipment limits and installation requirements.
Formula and variables
The calculation runs entirely in your browser. Static formulas, definitions, examples, and tables remain readable without JavaScript.
Vdrop = I × (2ρL/A); Ploss = I × Vdrop.
- Vdrop
- Voltage lost across the conductor path, in volts.
- I
- Current through the conductor, in amperes.
- R
- Electrical resistance of the modeled conductor path, in ohms.
- ρ
- Material resistivity at the modeled temperature, in ohm-metres.
- L
- Conductor length used by the selected path model.
- A
- Metal cross-sectional area of the conductor.
L is one-way cable length; the DC return path is included.
Worked example
| Input | Value |
|---|---|
| Circuit voltage | 48 V |
| Current | 20 A |
| One-way cable length | 30 ft |
| Conductor material | Copper |
At 48 V and 20 A, the tool calculates delivered voltage and watts lost for the selected two-conductor path.
Reference table
| AWG | Cu 20°C Ω/1000 ft | Cu 75°C Ω/1000 ft | Al 20°C Ω/1000 ft | Al 75°C Ω/1000 ft | Cu 20°C Ω/km | Al 20°C Ω/km |
|---|---|---|---|---|---|---|
| 14 | 2.5254 | 3.0712 | 4.1400 | 5.0576 | 8.2853 | 13.5825 |
| 12 | 1.5882 | 1.9315 | 2.6036 | 3.1807 | 5.2107 | 8.5421 |
| 10 | 0.9988 | 1.2147 | 1.6374 | 2.0004 | 3.2770 | 5.3722 |
| 8 | 0.6282 | 0.7640 | 1.0298 | 1.2581 | 2.0609 | 3.3786 |
| 6 | 0.3951 | 0.4805 | 0.6476 | 0.7912 | 1.2961 | 2.1248 |
| 4 | 0.2485 | 0.3022 | 0.4073 | 0.4976 | 0.8152 | 1.3363 |
Frequently asked questions
Does solar cable length include both conductors?
Enter one-way length; the calculator includes the DC return path in its resistance calculation.
Why does cable loss rise with current?
Voltage drop rises with current, and resistive heat loss follows current squared times resistance.
Assumptions and limitations
- No PV code, ampacity, overcurrent, temperature-derating, connector, or protection sizing.
- Steady DC resistance model.
Method and sources
Review the solar data sources, calculation methodology, and electrical formulas for the references most relevant to this calculation. The broader technical sources index records source scope and verification. Last reviewed .