For a three-phase 415 V pump, size the flat cable on both current and length. Up to 50 m, 1.5 sq mm suits pumps up to 5 HP; at 100 m a 5 HP pump needs about 4 sq mm and a 10 HP pump 6 sq mm. Longer runs need a bigger cable, or the motor gets low voltage and runs hot.
Cable size chart (three-phase, 415 V, copper flat cable)
| Pump | Up to 50 m | Up to 100 m | Up to 200 m |
|---|---|---|---|
| 1 HP | 1.5 sq mm | 1.5 sq mm | 1.5 sq mm |
| 2 HP | 1.5 sq mm | 1.5 sq mm | 4 sq mm |
| 3 HP | 1.5 sq mm | 2.5 sq mm | 4 sq mm |
| 5 HP | 1.5 sq mm | 4 sq mm | 6 sq mm |
| 7.5 HP | 2.5 sq mm | 6 sq mm | 10 sq mm |
| 10 HP | 4 sq mm | 6 sq mm | 16 sq mm |
| 12.5 HP | 4 sq mm | 10 sq mm | 16 sq mm |
| 15 HP | 6 sq mm | 10 sq mm | 16 sq mm |
| 20 HP | 10 sq mm | 16 sq mm | 25 sq mm |
The length is the cable run from the starter to the pump, including the depth of the borewell. The chart keeps the voltage drop near 3% at full load, allowing for submersible motors drawing a little more current than surface motors. Where the pump maker publishes its own cable chart, follow it.
Why length matters
Every metre of cable has resistance, so the voltage at the motor is lower than at the starter. Too much drop makes the motor draw more current, run hot and wear out early, and it may fail to start. The drop is roughly 1.73 × current × length (km) × cable resistance (Ω/km). Keep it under about 3% (12 V on a 415 V supply) for long pump life.
Single-phase pumps
Single-phase pumps on 230 V draw more current for the same power, so they need a larger cable for the same length. Tell us the pump HP and the depth, and we will suggest the size.
Good practice
- Use proper submersible flat cable, made to run in water, not ordinary cable.
- Joint the cable to the pump lead with a proper waterproof joint kit.
- Protect the pump with a starter or controller that has single-phasing protection.
Products
- Polycab submersible flat cable
- L&T MU-G submersible pump controller
- Single-phase pump controller
- All motor starters
Need help choosing?
Send us the rating, the load or a photo of the nameplate on WhatsApp, and we will confirm the right model, availability and rate.
Values are typical guidance for Indian 230 V single-phase and 415 V three-phase supplies. Always follow the equipment nameplate, the manufacturer's instructions and your licensed electrician, who is responsible for the final selection and installation.