Short answerKeep voltage drop between the panels and the pump to about 3%. A 24V-class pump drawing 7.7 A at 36 V can run about 55 ft one way on 10 AWG copper, or about 140 ft on 6 AWG; a 12V pump at 10 A manages only about 15 ft on 10 AWG.
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Key takeaways
- Aim for 3% voltage drop or less between the panels and the pump.
- Doubling voltage halves current and halves the drop: long runs favour 48V-class pumps.
- Count the cable down the well in the run length.
The table
Distances are one way, panel to pump, and must include the cable down the well. Each column uses the pump's rated watts at its rated voltage from the VEVOR listings we link to; for another pump, use its own current.
| Copper wire | 12V pump, 120 W (10 A at 12 V) | 24V-class pump, 277 W at 36 V (7.7 A) | 48V-class pump, 369 W at 72 V (5.1 A) |
|---|---|---|---|
| 14 AWG | 5 | 22 | 67 |
| 12 AWG | 9 | 35 | 106 |
| 10 AWG | 14 | 56 | 169 |
| 8 AWG | 23 | 90 | 270 |
| 6 AWG | 36 | 142 | 429 |
| 4 AWG | 58 | 227 | 684 |
| 2 AWG | 92 | 361 | 1,086 |
Why voltage changes everything
Loss in a wire is current times resistance. Doubling the system voltage halves the current for the same watts, which quarters the loss in watts and halves the voltage drop. That is the case for a 48V-class pump at the end of a long run, covered in 12V vs 24V vs 48V.
Worked example: the 36 V pump at 7.7 A, 200 ft from its panels on 10 AWG, loses 2 x 200 x 7.7 x 1.24 / 1000 = 3.8 V, or 10.6%. On 6 AWG it loses 1.5 V (4.2%); on 4 AWG, 0.95 V (2.6%).
Other things the cable has to get right
- Ampacity. The wire must carry the current safely, including the panels' short-circuit current with the code's multipliers. Voltage drop usually forces a heavier gauge than ampacity does on pump runs.
- Where it runs. Sunlit cable needs a sunlight-resistant rating, buried cable a direct-burial rating or conduit, and cable in the well a rating for submersion. Splice drop cable with a waterproof splice kit made for it.
- Copper, not aluminium, for small pump circuits; the table is for copper.
- A 3% target is a design choice. Informational notes in the National Electrical Code suggest about 3% on a branch circuit and 5% overall. A direct-drive pump that has to start in weak morning light benefits from staying under 3%.
Questions
- What size wire do I need for a solar well pump 100 ft away?
- For a 24V-class pump drawing about 7.7 A at 36 V, 8 AWG copper keeps drop near 3% at 90 ft and 6 AWG reaches about 140 ft, so use 6 AWG for 100 ft. For a 12V pump at 10 A, even 4 AWG reaches only about 58 ft; move the panels closer or use a higher-voltage pump.
See how pump voltage changes wire size, panel strings and distance.