By TEBAOFLEX Jyen. Originally published on March 3, 2026.
A submersible pump feeder can pass through air, water and a warmer motor region. Its limiting condition may occur anywhere along that route. Cable selection must address current capacity and motor terminal voltage as well as immersion, support and compatibility with the pump assembly.
Map the route and cooling conditions
Record the highest and lowest operating water levels, temperature along the well, flow around the motor and cable, exposed surface sections, grouping and support arrangement. A submerged current rating cannot simply be used for a section hanging in stagnant air. Equally, the upper dry zone is not always the hottest location.
Use a rating or calculation applicable to each installation condition. A square-root temperature factor alone cannot translate between air and water because heat-transfer conditions also change. Generic geothermal gradients and assumed motor temperature rises are not substitutes for site and equipment data.
Check running and starting voltage separately
For a balanced three-phase sinusoidal circuit, an approximate line-to-line drop is delta_V = sqrt(3) × I × L × (R × cos(phi) + X × sin(phi)), with one-way length L in km and resistance/reactance in ohm/km. Use appropriate AC resistance at the relevant temperature. IEC 60228 DC-resistance limits are not a complete AC-impedance specification.
As a hypothetical calculation, take L = 0.40 km, running current 198 A, starting current 1,188 A, X = 0.078 ohm/km and an assumed reference resistance of 0.161 ohm/km. Ignore additional AC-resistance effects solely for this example. With copper coefficient 0.00393/°C, the assumed resistance is 0.19580015 ohm/km at 75°C and 0.17681825 ohm/km at 45°C.
Using running power factor 0.86 gives 28.56 V drop, or 7.14% of 400 V. Using starting power factor 0.35 and the assumed 45°C start gives 111.08 V, or 27.77%. A hot restart needs its actual initial temperature. These numbers demonstrate the calculation; they do not specify a cable size or validate a pump installation.
Use the motor’s allowable terminal voltage, starting-current data, load acceleration and upstream supply impedance to establish acceptance. There is no universal 3% running and 15% starting limit for every installation. Parallel feeders require current-sharing and protection design; changing to a VFD requires the drive manufacturer’s cable-length and output-waveform assessment.
Immersion class is not a depth certificate
An AD8 water-exposure description does not, on its own, approve a cable for 500 m or 50 bar. Specify water chemistry, temperature, pressure, duration and pressure cycles, and obtain evidence covering the complete cable and terminations. Longitudinal water blocking and resistance to radial water ingress are different properties.
SUBCAB is presented by Xylem as a Flygt cable product family. Its name and an unrelated datasheet cannot establish equivalent TEBAOFLEX ratings. Similarly, an armoured cable designation does not establish a universal free-hanging depth or allowable suspension load.
Downhole ESP service needs its own specification
Hot oilfield service introduces gas, chemicals, clearance and decompression conditions beyond ordinary dewatering duty. IEEE 1018 concerns EPR-insulated ESP cable and IEEE 1019 concerns polypropylene-insulated cable; IEEE lists 1017.2-2021 and 1017.3-2021 as their respective successors. Use the exact construction and contract edition rather than a generic temperature assigned to the polymer name.
Installation and acceptance
- Confirm cable and joint suitability for the medium, temperature and pressure with the motor supplier.
- Design support spacing, strain relief and wellhead anchoring for the actual cable loads; do not suspend the pump from electrical leads.
- Verify protective-earth continuity, fault protection, motor overload settings and approved drive/filter arrangements.
- Request traceable electrical routine tests and the relevant immersion/mechanical qualification.
- Keep destructive qualification, sample tests and production-drum checks distinct; no unprovided FAT results are asserted here.
Sources and further documentation
Discuss your application
Send the operating conditions, installation drawing and required acceptance evidence to TEBAOFLEX. WhatsApp: +86 185 9591 3361. Request documentation for the exact offered construction before ordering.