Why Is a Deep Well Submersible Pump Drawing Too Much Current?

A deep well submersible pump drawing excessive current signals an electrical, hydraulic or mechanical problem. The overload relay may trip, or one phase may read higher than the others.

Do not repeatedly reset the protection device. Excessive current produces heat and can damage the cable, motor windings, bearings and control equipment. First record the operating data, then identify the cause.

Starting Current or Running Overcurrent?

Motor current normally rises briefly during starting. Its value and duration depend on motor size, supply capacity and starting method.

The important question is whether current returns to its normal running range after the pump reaches speed. A brief starting peak is not the same as current that remains above the motor nameplate value.

Measure every phase at stable flow with a suitable meter.

1. The Pump Is Delivering Too Much Flow

A centrifugal borehole pump can draw excessive power when it operates at a much higher flow and lower head than its intended duty point. This can happen when:

• A discharge valve is opened too far.

• Actual system resistance is lower than calculated.

• A bypass line remains open.

• The selected pump has too much capacity.

• A VFD is running above the approved frequency.

Compare measured flow and pressure with the exact pump curve. Calculate total dynamic head from pumping water level, delivery elevation, outlet pressure and pipe losses.

For many radial-flow borehole pumps, carefully reducing flow with the discharge valve reduces load. Confirm this on the exact curve and monitor current. Never throttle the suction side.

2. Supply Voltage Is Too Low

Low voltage can prevent the motor from producing the required torque efficiently and may increase current and heating. The voltage may look acceptable when the pump is stopped but fall significantly during starting or operation.

Possible causes include:

• An undersized transformer or generator

• A long or undersized power cable

• Loose, corroded or overheated terminals

• A damaged underwater splice

• Excessive voltage drop in the surface supply

• Other large loads operating on the same system

Measure all line-to-line voltages while the pump runs and compare them with the manufacturer’s range. If voltage falls under load, inspect the complete supply route instead of changing the overload setting.

3. Voltage or Current Is Unbalanced

In a three-phase motor, even a relatively small supply imbalance can create a larger current imbalance and additional heating. Record voltage and current on all three phases, not only one.

Unequal readings may result from a fuse, contactor, connection, cable, splice, transformer or winding fault. Phase loss is especially dangerous.

Stop the pump if one phase is missing or substantially different. A qualified electrician should test the supply, protection equipment, cable and motor. Use the motor manufacturer’s allowable imbalance limits; do not rely on a universal percentage.

4. Cable Size or Connections Are Incorrect

A long or undersized cable can create excessive voltage drop. Include both surface and downhole sections in the calculation.

Check for:

• Correct conductor size and material

• Continuous-submersion rating

• Sound panel terminals

• A dry and properly sealed underwater splice

• Undamaged insulation

• Correct motor lead connections

Discolored terminals, melted insulation or a burnt smell require immediate attention. Never compensate by raising the overload setting.

5. The Pump Contains Sand or Debris

Sand wears impellers, diffusers, guide bearings and thrust components. Larger particles may partially jam the rotating assembly, raising current.

Look for declining flow, vibration, noise, sandy water or unstable amperage. Test the water if excessive solids are suspected.

If the pump is mechanically tight, stop it. Continued operation can damage the shaft, bearings and motor. The well may need cleaning or development, while the pump may require inspection and replacement of worn components.

6. Bearings, Shaft or Impellers Are Damaged

Mechanical resistance directly increases motor load. Common causes include worn rubber or graphite bearings, damaged bushings, a failed thrust bearing, a bent shaft, misaligned bearings, or an impeller rubbing against a diffuser.

Mechanical trouble is more likely with vibration, abnormal sound or a swinging ammeter. If voltage and operating point are correct, qualified technicians may need to retrieve and inspect the pump.

7. Motor, Pump or Fluid Does Not Match the Duty

The motor must have enough rated power for the complete pump curve and the actual operating conditions. Installing additional pump stages, using the wrong impeller, or pairing a pump with an undersized motor can cause continuous overload.

A clean-water pump should not automatically handle heavy solids or liquids with different properties. Confirm temperature, chemistry and solids content.

8. Starter or VFD Settings Are Wrong

Protection equipment must match the motor’s voltage, frequency, current, phase and starting method.

For a VFD installation, verify:

• Minimum and maximum frequency

• Acceleration and deceleration time

• Motor nameplate data entered in the drive

• Current limit and overload parameters

• Required output reactor or filter for a long cable

• Cooling requirements at reduced speed

Increasing the frequency above the approved value can raise pump speed, flow, head and power demand. Changing parameters without reviewing the pump curve can overload the motor.

A Safe Troubleshooting Sequence

Use the following order to avoid unnecessary pump removal:

1. Stop the unit if current exceeds the permitted value, a phase is missing, or there is severe vibration or noise.

2. Confirm the ammeter and measurement method are suitable.

3. Record current and voltage on every phase during starting and stable operation.

4. Record flow, discharge pressure, pumping water level, valve position and VFD frequency.

5. Compare the operating point with the pump curve and motor nameplate.

6. Inspect fuses, contactors, terminals, cable and accessible connections.

7. Check the water for sand and observe vibration or unusual sound.

8. Perform insulation-resistance and winding-resistance tests according to the motor instructions.

9. Retrieve the pump only when measurements indicate an internal mechanical or motor problem.

Before testing, isolate power and follow lockout procedures. Use trained personnel for electrical work.

Common Mistakes

• Resetting the overload relay repeatedly

• Measuring only one phase

• Checking voltage only when the motor is stopped

• Raising the overload setting to prevent trips

• Assuming high current always means a damaged motor

• Ignoring excessive flow and low system head

• Ignoring cable voltage drop and underwater connections

• Continuing to run a noisy or vibrating pump

• Operating a clean-water pump in excessive sand

• Removing the pump before recording electrical and hydraulic data

Frequently Asked Questions

Why is one phase drawing more current?

Possible causes include voltage imbalance, a poor contactor or terminal, cable or splice damage, and a motor winding fault. Measure all three voltages and currents under load and have the circuit tested.

Can low voltage cause high current?

Yes. Low voltage can reduce available motor torque and increase heating or current under load. Check voltage while the pump is starting and running, not only when it is stopped.

Will Partially Closing the Discharge Valve Reduce Current?

It often reduces power demand on a radial-flow centrifugal borehole pump, but the exact response depends on the pump curve. Adjust slowly, monitor current and keep the pump within its approved operating range.

Should I Increase the Overload Setting?

No, not simply to stop nuisance trips. Confirm that the setting matches the motor instructions, then correct the voltage, flow, cable, connection or mechanical problem causing the overload.

Conclusion

High current is a symptom, not a diagnosis. Separate starting current from continuous overcurrent, then check phase readings, the operating point, cable, connections, sand and mechanical resistance.

SLAPK troubleshooting guidance identifies excessive flow at low head, worn bearings, thrust-component problems, shaft misalignment, low voltage, phase loss and long-term overload as important causes to investigate. The exact limits and protection settings must come from the selected motor and pump data.

Request Technical Support

Send SLAPK the pump and motor model, rated voltage and current, measured voltage and current on each phase, flow, discharge pressure, pumping water level, cable size and length, VFD frequency, water temperature and sand condition.

Our engineers can compare the operating data with the pump curve and help determine whether the problem is electrical, hydraulic or mechanical.

Contact SLAPK for deep well pump troubleshooting