Submersible Pump Cable

Submersible pump cable is the round, waterproof flexible cable that runs down the borehole from the control box to the pump motor. It is made to SANS 1574-3, rated 600/1000 V, with class 5 flexible copper cores and a PVC sheath that stays watertight for years under water. We stock 3 core (blue) for single-phase pumps and 4 core (green) for three-phase pumps, in 1.5 mm², 4 mm² and 6 mm², currently on special as short drums of 100 m to 450 m.

What this cable is, and which one you need

A submersible pump hangs in water, often 50 to 200 metres down, and the only thing connecting it to the surface is its cable. Ordinary house wire or welding cable is not made for that: the insulation absorbs water, the sheath cracks where it rubs on the casing, and the motor eventually earths out through the borehole. Submersible pump cable has a thick waterproof PVC sheath over individually insulated flexible cores, so it survives years of immersion and the flexing of installation and removal.

• 3 core blue – for single-phase 230 V pumps. Cores red, yellow and blue: two are the run and start windings, one is common. No earth core.
• 4 core green – for three-phase 380 V pumps. Cores red, yellow, blue and black: three phases plus one spare that is normally used as the earth conductor.

Both are round cable. Round cable is easier to strap to the rising main, passes through a well seal cleanly and is the standard for pump installations in South Africa.

Short drums explained: a full drum is 500 m. The drums on this page are ends of production runs – 100 m to 450 m – sold complete at a lower price per metre. Pick a drum at least as long as your borehole depth plus the run to the control box, and keep the balance for the next job.

Cable construction and specifications

All sizes share the same construction: class 5 annealed copper conductors, PVC core insulation, PVC bedding and a tough PVC outer sheath. The table gives the figures per size for 3 core and 4 core.

Sizes 2.5 mm², 10 mm² and 16 mm² are available to order. Volt drop figures are at 220 V single-phase and 380 V three-phase.

How to size submersible pump cable

1. Find the pump motor’s full-load current on the nameplate or datasheet (amps, not kW).
2. Measure the total cable run: borehole depth to the pump plus the distance from the wellhead to the control box.
3. Check the current rating: the cable’s maximum current must exceed the motor’s full-load current.
4. Check the volt drop: keep it under 5% of supply voltage (11 V on 230 V, 19 V on 380 V). Volt drop = mV/A/m × amps × metres ÷ 1000. A pump starved of voltage draws more current, runs hot and fails early.
5. Go up a size if in doubt. The next size costs a little more and runs cooler for the life of the pump.

A worked example: a 1.1 kW single-phase borehole pump draws about 7.5 A. The pump sits at 90 m and the control box is 20 m from the wellhead, so the run is 110 m. On 1.5 mm² the drop is 29 × 7.5 × 110 ÷ 1000 = 24 V – far too much. On 4 mm² it is 11 × 7.5 × 110 ÷ 1000 = 9 V, inside the 11 V limit. Use the 4 mm² blue 150 m drum.

Maximum cable run at 5% volt drop

Read across from your motor current to the cable size. The figure is the longest total run (down and back is already allowed for) that keeps volt drop under 5%.

Single-phase 230 V (3 core blue)

Three-phase 380 V (4 core green)

Dashes mark where the motor current exceeds the cable’s rating. Typical full-load currents: 0.37 kW 1-ph 3.2 A; 0.55 kW 4.4 A; 0.75 kW 5.5 A; 1.1 kW 7.5 A; 1.5 kW 10 A; 2.2 kW 14 A; 3 kW 19 A; 4 kW 25 A; 5.5 kW 34 A. Three-phase motors draw roughly 40% of the single-phase figure. Always use the nameplate value.

Installation guidelines

• Splice with a heat-shrink or resin submersible joint kit where the drum cable meets the motor lead. Tape alone will not stay watertight under pressure.
• Strap the cable to the rising main every 3 m with cable ties or stainless straps, leaving a little slack so it is not carrying the pump’s weight.
• Protect it at the wellhead – a sharp casing edge or a tight well seal will cut the sheath over time.
• Insulation-test the cable and motor together before lowering: a reading below 1 MΩ means a fault that will only get worse under water.
• Earth the installation at the control box; the 4 core black conductor or a separate earth lead can be used for the motor earth.

Typical applications

• Domestic and farm borehole pumps, 0.37 kW to 5.5 kW
• Solar borehole pump systems (DC) – use the volt-drop table with the pump’s DC current
• Dewatering, sump and sewage pumps on long cable runs
• Replacement of damaged or undersized cable on existing installations

Frequently asked questions

Pricing

Each drum is sold complete. Prices include VAT and are subject to change; the online store always carries the current price. Stock is limited to the drums listed – once a drum is sold it is gone.

Full 500 m drums, 2.5 mm², 10 mm² and 16 mm² sizes and cut lengths are available to order – send us your pump size and borehole depth and we will quote the right cable.