How the calculator works
- It finds your motor's row in Franklin Electric's 4-inch single-phase cable table (AIM 2026, p.50) and returns the smallest copper size whose maximum length covers your total cable length: power supply to motor (panel to well head + pump depth).
- 3% voltage drop = table length × 0.6. Aluminum = two sizes larger than copper.
- Two sections: each length ÷ the maximum for its size; the fractions must add to 1.00 or less (Franklin, p.50).
- Shaded cells (3 hp on 14 AWG, 5 hp on 12 AWG) are skipped for jacketed cable.
Well pump wire size chart (4-inch, single-phase, copper)
Maximum total cable length in feet, power supply to motor, 75 °C copper, 5% voltage drop. From AIM 2026, p.50. Multiply by 0.6 for 3%.
| Volts | HP | 14 | 12 | 10 | 8 | 6 | 4 | 3 | 2 | 1 | 0 | 00 | 000 | 0000 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 115 | 1/2 | 100 | 160 | 250 | 390 | 620 | 960 | 1,190 | 1,460 | 1,780 | 2,160 | 2,630 | 3,140 | 3,770 |
| 230 | 1/2 | 400 | 650 | 1,020 | 1,610 | 2,510 | 3,880 | 4,810 | 5,880 | 7,170 | 8,720 | – | – | – |
| 230 | 3/4 | 300 | 480 | 760 | 1,200 | 1,870 | 2,890 | 3,580 | 4,370 | 5,330 | 6,470 | 7,870 | 9,380 | – |
| 230 | 1 | 250 | 400 | 630 | 990 | 1,540 | 2,380 | 2,960 | 3,610 | 4,410 | 5,360 | 6,520 | 7,780 | 9,350 |
| 230 | 1.5 | 190 | 310 | 480 | 770 | 1,200 | 1,870 | 2,320 | 2,850 | 3,500 | 4,280 | 5,240 | 6,300 | 7,620 |
| 230 | 2 | 150 | 250 | 390 | 620 | 970 | 1,530 | 1,910 | 2,360 | 2,930 | 3,620 | 4,480 | 5,470 | 6,700 |
| 230 | 3 | 120* | 190 | 300 | 470 | 750 | 1,190 | 1,490 | 1,850 | 2,320 | 2,890 | 3,610 | 4,470 | 5,550 |
| 230 | 5 | 0 | 110* | 180 | 280 | 450 | 710 | 890 | 1,110 | 1,390 | 1,740 | 2,170 | 2,680 | 3,330 |
0, 00, 000, 0000 = 1/0, 2/0, 3/0, 4/0. * Shaded in the manual: individual conductors only. 0 = printed as 0; "–" = no value printed. The table is titled '2-Lead and 3-Lead' and gives one row per voltage and horsepower, so a 1 hp 230 V 2-wire motor and a 1 hp 230 V 3-wire motor get the same lengths. A table from another motor maker may give different numbers; use the one for the motor actually installed.
Worked examples
One size: 1.5 hp, 230 V, pump at 260 ft, well head 120 ft from the panel → 380 ft total. 12 AWG allows 310 ft (too short), 10 AWG 480 ft, so 10 AWG. At 3% drop: 8 AWG (462 ft).
Two sizes (Franklin's example): 160 ft of existing #10 copper, new 3 hp 230 V motor at 310 ft.
| Section | Length (ft) | Max for size (ft) | Fraction | Total | Result |
|---|---|---|---|---|---|
| #10 buried | 160 | 300 | 0.533 | — | — |
| + #8 drop cable | 310 | 470 | 0.660 | 1.193 | Over 1.00: too small |
| + #6 drop cable | 310 | 750 | 0.413 | 0.946 | Meets the limit |
When this chart does not apply
- Other motor makers: amps differ; use the table in their manual.
- Variable-speed (constant-pressure) drives: follow the drive's manual. Franklin's SubDrive Connect says not to use aluminum wire for VFD connections.
- Three-phase, 6-inch motors, 60 °C or 90 °C cable: other tables in the manual.
- Breaker, ampacity and grounding still have to meet the NEC and local code.
Related
- Still choosing the pump? Well pump size calculator.
- Pressure tank size calculator.
- Pump trips the breaker or runs weak? Well pump troubleshooting.
- Running the pump on backup power: Generator size for a well pump.
Frequently asked questions
What size wire do I need for a 1 hp well pump?
For a 1 hp, 230 V single-phase 4-inch motor, Franklin's table allows up to 400 ft of 12 AWG copper, 630 ft of 10 AWG and 990 ft of 8 AWG, from the power supply to the motor.
Can I use aluminum wire for a well pump?
Franklin allows it only two sizes larger than the copper size in the table, with oxidation inhibitor on every connection. Where the table calls for 12 AWG copper, you need 10 AWG aluminum.
Do I measure wire length from the panel or the well head?
From the power supply. Add the run from the panel to the well head and the drop cable down to the pump, not just the pump depth.
Sources
- Franklin Electric, AIM Manual 60 Hz Submersible Systems, 2026 edition (M1311 06-26): Equipment Grounding p.10, Cable Selection p.49, Cable Size Combinations p.50, 4-inch single-phase Motor Specifications pp.39–41, "4-inch/1-Phase/2-Lead and 3-Lead/75 °C Cable" p.50 · checked October 5, 2026
- Franklin Electric, SubDrive Connect Owner's Manual 226203103 (©2024): Wiring Guidelines p.21, Input (Power) Wire and Fuse Sizing p.22, Output (Motor) Wire Sizing p.23 · checked October 5, 2026
Method: Maximum lengths are copied from the '4-inch/1-Phase/2-Lead and 3-Lead/75 °C Cable' table of the Franklin Electric AIM Manual (2026 edition, p.50) and checked cell by cell against the PDF; the 3% option, aluminum rule, line-contactor limit and two-size method are the manual's own rules on pp.49–50. We have not installed or measured any pump wiring.