Here’s a practical, engineering-grade cable selection chart to help you choose 4-core submersible cable for borehole pump installs. It shows the maximum recommended cable length (meters) for common copper cable sizes to keep voltage drop ≤ 5% at 50 Hz. Use the single-phase (230 V) table for 0.37–2.2 kW and the three-phase (400 V) table for 0.37–45 kW.
Assumptions (conservative & field-ready)
- Copper cable; resistance adjusted for operating temperature.
- Typical running load:
- 1-Ph motors: PF≈0.90, η≈0.75
- 3-Ph motors: PF≈0.85, η≈0.90
- Voltage drop target: ≤5% of supply (SANS-aligned rule of thumb).
- “4-core” usage:
- 1-Ph: you’ll typically use 3 conductors (L, N, E) and keep one spare/aux.
- 3-Ph: use 3 phase cores + earth.
- If your actual motor nameplate current is higher, or your start/run gear adds extra loss, choose the next cable size up.
Single-phase 230 V (50 Hz), 0.37 kW → 2.2 kW
Cells = Max cable length (m) for ≤5% drop.
| kW | Nominal A | 1.5 mm² | 2.5 mm² | 4 mm² | 6 mm² | 10 mm² | 16 mm² | 25 mm² | 35 mm² | 50 mm² |
|---|---|---|---|---|---|---|---|---|---|---|
| 0.37 | 2.4 | 174 | 291 | 466 | 699 | 1166 | 1865 | 2915 | 4081 | 5831 |
| 0.55 | 3.5 | 117 | 196 | 314 | 471 | 786 | 1258 | 1962 | 2747 | 3925 |
| 0.75 | 4.8 | 86 | 144 | 230 | 345 | 575 | 919 | 1433 | 2007 | 2866 |
| 1.10 | 7.0 | 59 | 100 | 160 | 240 | 400 | 640 | 997 | 1396 | 1995 |
| 1.50 | 9.7 | 43 | 72 | 116 | 174 | 290 | 464 | 723 | 1012 | 1446 |
| 2.20 | 14.2 | 29 | 49 | 78 | 117 | 196 | 313 | 490 | 686 | 980 |
Tip: Many 1-Ph submersible installs in the 1.1–1.5 kW range at 60–100 m do well with 6 mm²; at >100 m, step to 10 mm².
Three-phase 400 V (50 Hz), 0.37 kW → 45 kW cable selection
Cells = Max cable length (m) for ≤5% drop.
| kW | Nominal A | 1.5 mm² | 2.5 mm² | 4 mm² | 6 mm² | 10 mm² | 16 mm² | 25 mm² | 35 mm² | 50 mm² |
|---|---|---|---|---|---|---|---|---|---|---|
| 0.37 | 1.4 | 591 | 986 | 1577 | 2366 | 3944 | 6310 | 9860 | 13805 | 19721 |
| 0.55 | 2.1 | 394 | 657 | 1051 | 1577 | 2628 | 4205 | 6570 | 9200 | 13150 |
| 0.75 | 2.8 | 295 | 492 | 787 | 1180 | 1970 | 3150 | 4927 | 6911 | 9880 |
| 1.10 | 4.1 | 201 | 335 | 536 | 804 | 1340 | 2140 | 3350 | 4700 | 6723 |
| 1.50 | 5.5 | 150 | 250 | 400 | 600 | 1000 | 1600 | 2500 | 3500 | 5000 |
| 2.20 | 8.0 | 103 | 172 | 275 | 412 | 687 | 1100 | 1720 | 2410 | 3440 |
| 3.00 | 10.8 | 76 | 127 | 203 | 304 | 506 | 810 | 1275 | 1790 | 2550 |
| 4.00 | 14.3 | 58 | 99 | 158 | 237 | 395 | 632 | 996 | 1400 | 1990 |
| 5.50 | 19.6 | 42 | 71 | 114 | 171 | 285 | 456 | 718 | 1000 | 1425 |
| 7.50 | 26.7 | 31 | 52 | 83 | 124 | 207 | 331 | 521 | 731 | 1039 |
| 11.0 | 38.9 | 21 | 33 | 54 | 81 | 134 | 215 | 338 | 474 | 672 |
| 15.0 | 53.0 | 15 | 25 | 40 | 60 | 99 | 159 | 251 | 352 | 499 |
| 18.5 | 65.4 | 12 | 20 | 32 | 48 | 79 | 128 | 201 | 282 | 399 |
| 22.0 | 77.7 | 10 | 17 | 27 | 41 | 67 | 108 | 170 | 239 | 339 |
| 30.0 | 106.0 | 7 | 12 | 20 | 30 | 47 | 75 | 118 | 166 | 235 |
| 37.0 | 130.6 | 6 | 10 | 16 | 24 | 38 | 61 | 95 | 134 | 190 |
| 45.0 | 84.9* | 9 | 16 | 26 | 39 | 65 | 105 | 164 | 230 | 328 |
*For 45 kW the nominal current shown is for η≈90%, PF≈0.85 at 400 V; your nameplate may vary by manufacturer.
How to use this cable selection chart (quick method)
- Find motor kW and check the Nominal A is close to your nameplate (if it’s higher, upsize cable).
- Pick your planned cable length (depth + horizontal run + panel distance).
- Choose the smallest mm² that gives a max length ≥ your run.
- If starting is “hard” (weak supply, DOL on long runs, high static head), go one size larger.
Practical notes for boreholes cable selection
- Cable type: Use submersible pump cable 600/1000 V (flat or round), UV-resistant for the rising main and above-ground section.
- Splices & joints: Every joint adds resistance — if you have multiple splices, treat your run as longer or upsize.
- Earth continuity: Always run a dedicated earth core to the motor frame/ground lug.
- Protection: Size breakers/overloads to motor FLA (per nameplate) and cable’s current-carrying capacity (installation method).
- Standards: South Africa’s SANS 10142-1 generally targets ≤5% voltage drop on final circuits; many pump OEMs prefer even tighter for reliable starting.