Selecting a power cable for a deep well submersible pump involves more than matching a conductor to the motor’s rated power.
The cable may run from a transformer or control panel across the site, down the complete depth of the well and through a permanently submerged connection to the motor leads. Its resistance creates voltage drop, while the underwater section must withstand water, pressure, temperature and mechanical stress.
An undersized or excessively long cable can cause low voltage at the motor terminals. Possible results include difficult starting, excessive current, overheating, nuisance tripping, reduced torque and shortened motor life.
An oversized cable may reduce voltage drop, but it increases cost, outside diameter, weight and installation difficulty. It must also fit inside the well beside the rising main, cable guards, couplings and pump assembly.
Reliable cable sizing requires the motor nameplate data, actual cable route, supply voltage, starting method, installation conditions and applicable electrical standard.
A surface motor is normally located close to its control panel and remains accessible for inspection. A borehole pump motor may operate tens or hundreds of metres below ground.
The electrical route can include:
Transformer-to-panel cable
Panel-to-wellhead cable
Cable down the borehole
Factory motor leads
Underwater splice
Terminal and connection resistance
Every section contributes to the total voltage drop.
The submerged cable must also operate in a restrictive environment. It may be exposed to:
Continuous immersion
Hydrostatic pressure
Water temperature
Water chemistry
Abrasion against the casing
Cable-clamp pressure
Pump vibration
Mechanical loads during installation
Long-term insulation ageing
A cable that is suitable for a dry industrial building is not automatically suitable for a submerged borehole installation.
Begin with the exact motor rather than the pump series name.
Record:
Rated motor power
Rated voltage
Frequency
Single-phase or three-phase supply
Rated current
Full-load or maximum operating current
Power factor
Efficiency
Starting method
Number of motor leads
Insulation class
Permitted voltage tolerance
Manufacturer’s maximum cable-length data
SLAPK submersible pumps can be configured for different voltages and frequencies, including project-specific 50 Hz and 60 Hz requirements. Available configurations depend on the selected motor and pump model.
Do not assume that two motors with the same kilowatt rating have the same current. Rated current changes with voltage, phase, efficiency, power factor and motor design.
Use the confirmed motor data sheet for the exact order.
Do not use well depth alone as cable length.
The complete electrical route may include:
Distance from transformer to control panel
Distance from control panel to wellhead
Additional cable inside the panel
Depth from wellhead to the motor connection
Service loop at the wellhead
Cable required for termination
Routing around structures
Planned maintenance allowance
If the well is 120 m deep but the control panel is 45 m from the wellhead, the electrical route is already substantially longer than the downhole section alone.
Use the actual one-way route length when consulting the applicable motor cable table or performing the voltage-drop calculation. Apply the correct formula for the phase arrangement; do not manually double or multiply lengths unless the selected calculation method requires it.
The factory motor lead must also be included if the manufacturer’s sizing method does not already account for it.
The cable’s current-carrying requirement is normally based on the motor’s confirmed current and the applicable electrical rules.
Do not calculate cable size from kilowatts alone when a rated current is available.
The design review should consider:
Normal operating current
Motor service factor, if applicable
Starting current
Starting duration
Frequency of starts
Ambient temperature
Cable grouping
Installation method
Harmonic content from a VFD
Required protective-device coordination
Starting current does not usually mean that the cable must carry locked-rotor current continuously. However, the cable must maintain enough voltage during starting for the motor to develop adequate torque.
A long, undersized cable can create a large voltage drop during startup even when its continuous ampacity appears acceptable.
Ampacity is the continuous current a cable can carry under specified conditions without exceeding its allowable conductor or insulation temperature.
The published ampacity depends on:
Conductor material
Conductor cross-sectional area
Insulation material
Number of loaded conductors
Cable construction
Ambient temperature
Installation in air, conduit, ground or water
Grouping with other cables
Local electrical regulations
A cable that passes the voltage-drop calculation must still satisfy ampacity requirements.
Conversely, a cable that can safely carry the current may still be too small because of excessive voltage drop over a long distance. Both checks are necessary.
Voltage drop occurs because every conductor has electrical resistance and impedance.
For a simplified resistive calculation, voltage drop increases with:
Cable length
Motor current
Conductor resistivity
It decreases as conductor cross-sectional area increases.
For a copper conductor, a simplified relationship is:
Voltage drop is proportional to current * cable length ÷ conductor area
A complete AC calculation may also account for:
Power factor
Conductor reactance
Cable configuration
Operating temperature
Three-phase or single-phase supply
For a balanced three-phase motor, use a three-phase voltage-drop formula or an approved manufacturer cable table. For a single-phase motor, use the correct single-phase method.
Do not mix the two calculations.
The calculated voltage at the motor terminals should remain within the motor manufacturer’s permitted range under both running and starting conditions.
The same voltage loss represents different percentages at different system voltages.
For example, a fixed voltage loss is more significant in a lower-voltage system than in a higher-voltage system.
Excessive voltage drop can cause:
Reduced starting torque
Extended acceleration time
Higher motor current
Contactor chatter
Repeated overload trips
Motor overheating
Unstable VFD operation
Failure to start under hydraulic load
Reduced service life
SLAPK troubleshooting information identifies low voltage, an excessively thin wire and an overly long cable as possible reasons a submersible motor may fail to start.
Cable selection must therefore be coordinated with the actual voltage available at the site, not only the nominal system voltage.
A motor draws substantially more current during direct-on-line starting than during normal operation.
Because voltage drop is related to current, the temporary drop during startup can be much larger than the running drop.
The starting review should consider:
Available transformer capacity
Generator capacity
Supply-system impedance
Cable length and conductor size
Motor locked-rotor current
Pump starting torque
Wellhead and panel connections
Starting method
Acceleration time
A motor may operate normally after reaching speed but still fail to start because the terminal voltage collapses during acceleration.
Possible starting methods include:
Direct-on-line starting
Star-delta starting
Autotransformer starting
Soft starter
Variable-frequency drive
The selected method must be compatible with the motor leads, voltage, control panel and project requirements.
Do not assume that installing a soft starter or VFD automatically permits a smaller cable. The complete manufacturer instructions and electrical design still apply.
Copper is commonly used for submersible pump cables because of its conductivity, connection reliability and availability.
If aluminium conductors are considered for a surface section, the designer must account for:
Larger required conductor area
Termination compatibility
Oxidation control
Mechanical strength
Thermal expansion
Connector ratings
Transition to copper motor leads
Do not make an underwater copper-to-aluminium connection unless the complete splice system is specifically designed and approved for that purpose.
The conductor material used in the voltage-drop calculation must match the actual cable.
The downhole portion should be a cable specifically rated for continuous immersion and the expected water conditions.
Selection factors include:
Fresh water or saline water
Maximum water temperature
Hydrostatic pressure
Chemical exposure
Oil or hydrocarbon exposure
Flat or round construction
Cable outside diameter
Flexibility
Abrasion resistance
Voltage rating
Insulation and jacket material
Drinking-water approval, where required
A standard flexible cable may appear physically similar but may not be designed for continuous underwater service.
Confirm both the insulation and the outer jacket. A waterproof jacket does not compensate for conductor insulation that is unsuitable for the voltage, temperature or immersion period.
Submersible pump cables are available in flat and round constructions.
Flat cable may be useful where the clearance between the pump, rising main and casing is limited. It can sit more closely against the pipe or cable guard.
Round cable may be preferred for certain glands, seals, cable clamps and mechanical protection systems.
The correct choice depends on:
Motor connection
Well casing clearance
Cable gland design
Cable-clamping method
Splice kit
Installation equipment
Manufacturer approval
Cable shape does not determine conductor capacity. Confirm the conductor area, insulation, voltage rating and dimensional drawing.
Cable selection also affects whether the pump assembly can pass through the borehole.
Check the combined envelope of:
Pump and motor
Rising main
Cable
Cable guard
Cable clamps
Underwater splice
Check valves
Pipe couplings
Centralizers
The splice may be thicker than the cable itself and can become the controlling installation dimension.
Verify the minimum casing internal diameter along the complete installation path. Allow practical clearance for casing deviation, joints, deposits and retrieval.
For related dimensional guidance, see 6-Inch vs 8-Inch Borehole Pumps: How to Choose.
A deep-well pump commonly requires a connection between the factory motor leads and the extended drop cable.
This connection must provide:
Reliable electrical continuity
Low connection resistance
Mechanical strength
Electrical insulation
A permanent water barrier
Compatibility with the cable insulation
A smooth outside profile
Resistance to installation stress
The SLAPK cable-connection instructions show preparation of the conductor ends, mechanical joining, insulation wrapping and multiple sealing layers. The approved method and materials should be followed for the actual cable supplied.
A splice that is electrically insulated but not water-tight can fail after immersion.
Water entering a cable or joint can lead to:
Low insulation resistance
Ground faults
Phase-to-phase faults
Corrosion of conductors
Protection trips
Motor winding damage
Use a manufacturer-approved submersible splice kit or documented connection procedure.
Removing insulation carelessly can reduce the effective conductor area and weaken the connection.
The connector and sealing system must accommodate both conductors and remain mechanically secure.
Sharp conductor ends or connector edges can penetrate the insulation during wrapping or installation.
A few layers of general-purpose tape do not necessarily form a reliable deep-water seal.
Cable ends and connection materials must be clean and dry before sealing.
An oversized joint can catch on casing joints or become damaged during lowering.
The splice should not carry the suspended cable load or remain sharply bent against a coupling.
The power cable should be supported along the rising main so that it does not hang freely, rub against the casing or move excessively during operation.
Cable supports should:
Hold the cable without crushing it
Resist the water and installation environment
Avoid sharp edges
Accommodate thermal and mechanical movement
Remain secure during pump starting
Permit safe removal of the assembly
Cable guards should be used where required around the pump and coupling sections.
Do not use metallic fastening materials that can cut into the cable jacket or create an unsuitable galvanic condition.
The fastening interval and material should follow the pump, cable and installer requirements.
Cable selection cannot be separated from the motor protection system.
The control panel may include:
Short-circuit protection
Motor overload protection
Phase-loss protection
Phase-sequence protection
Under-voltage and over-voltage protection
Ground-fault protection
Dry-running protection
Temperature monitoring
Level control
Soft starter
Variable-frequency drive
Protection settings should be based on the confirmed motor and manufacturer instructions.
An overload relay should not be set higher merely to prevent nuisance trips caused by low voltage or a damaged cable. Find and correct the electrical or hydraulic cause.
A VFD changes the electrical waveform supplied to the motor.
Long motor cables can increase reflected-wave effects, voltage stress, leakage current and electromagnetic interference. The allowable cable length may depend on:
Drive model
Carrier frequency
Output voltage
Motor insulation
Cable construction
Grounding
Output reactor
dV/dt filter
Sine-wave filter
Follow the VFD and motor manufacturer’s maximum cable-length instructions.
The cable must also be suitable for the drive output and installed with the required grounding and shielding arrangement.
Do not apply a standard direct-on-line cable table to a VFD system without checking the drive documentation.
The pump installation must include the grounding or protective conductor required by the applicable electrical code and equipment design.
Grounding helps protective devices respond to insulation failure and reduces shock risk.
Do not use the rising main, safety cable or well casing as an unverified substitute for the required protective conductor.
The grounding arrangement should include:
Motor grounding connection
Control-panel grounding
Cable protective conductor
Bonding of required metallic components
Correct termination
Continuity testing
Local electrical regulations and site conditions determine the final design.
Before lowering the pump, inspect and test the cable and motor assembly.
Recommended checks may include:
Visual inspection of the cable jacket
Verification of conductor continuity
Phase-to-phase resistance comparison
Insulation-resistance testing
Ground-conductor continuity
Splice inspection
Motor winding-resistance comparison
Confirmation of phase identification
Verification of cable length
Use the test voltage and procedure specified by the motor and cable manufacturer.
Disconnect sensitive electronic equipment, including a VFD, before performing insulation-resistance tests when required by its instructions.
Record the results before installation. These baseline values help diagnose future problems.
Repeat the required electrical checks after lowering the pump but before normal operation.
This can reveal damage caused by:
Pulling the cable
Contact with casing edges
Crushed insulation
A damaged splice
Incorrect termination
Water entering the connection
During commissioning, record:
Supply voltage
Motor terminal or panel voltage
Phase-to-phase voltage balance
Running current on each phase
Starting behavior
Insulation resistance
Protection settings
Pump flow and discharge pressure
Current imbalance may indicate voltage imbalance, a connection problem, cable damage or a motor fault.
Assume a three-phase borehole pump will be installed 150 m below the wellhead, while the control panel is 35 m from the well.
The motor nameplate and supplier data provide the rated voltage, current, starting method and permitted cable length.
The engineer should:
Add the downhole cable, surface route, service allowance and factory motor leads as required by the selected calculation method.
Identify the rated and starting current.
Select a submersible-rated copper cable with suitable insulation.
Check its ampacity under the actual installation conditions.
Calculate running voltage drop.
Check the available motor voltage during startup.
Compare the result with the manufacturer’s permitted range.
Increase the conductor size if either voltage-drop or ampacity requirements are not met.
Check the cable and splice outside dimensions against the casing clearance.
Confirm the cable with the control-panel, starter or VFD supplier.
Document the final conductor area, length, splice method and protection settings.
The final cable cannot be selected from installation depth alone.
Selecting conductor size from motor kilowatts alone
Ignoring the surface cable between the panel and wellhead
Using nominal well depth as total cable length
Checking ampacity but not voltage drop
Checking running voltage but not starting conditions
Using single-phase calculations for a three-phase motor
Using ordinary cable for continuous immersion
Ignoring water temperature and chemistry
Installing an unapproved underwater splice
Allowing the cable to rub against the casing
Failing to include the splice in the clearance check
Ignoring VFD maximum motor-cable length
Increasing overload settings instead of correcting low voltage
Failing to test insulation before and after installation
Send the following information to the motor, cable and control-panel supplier:
Complete pump and motor model
Rated motor power
Rated voltage and frequency
Single-phase or three-phase supply
Rated current
Starting method
Transformer or generator capacity
Distance from supply to control panel
Distance from panel to wellhead
Pump installation depth
Factory motor-lead length and size
Proposed cable material and cross-sectional area
Flat or round cable requirement
Water temperature and chemistry
Minimum casing internal diameter
VFD model and operating frequency range
Required local electrical standard
Grounding arrangement
Expected starts per hour
Continuous or intermittent operating duty
The answer depends on motor current, voltage, phase, complete cable length, voltage-drop limit, starting method, installation conditions and local regulations. Motor power and well depth alone are not sufficient.
Often yes, provided it is compatible with the terminals, splice, control equipment and well clearance. A larger conductor reduces voltage drop but increases cost, weight and outside diameter.
Yes. All electrical sections that contribute to voltage drop must be included according to the chosen calculation method.
Only if it is specifically rated for continuous immersion, the required voltage, temperature, pressure and water conditions. General flexible cable should not be assumed suitable.
Not automatically. The cable must still meet ampacity, voltage-drop, insulation, grounding and drive-manufacturer requirements. Long VFD output cables may require additional filters or reactors.
The voltage may fall substantially during starting because of cable resistance, weak supply capacity or high starting current. Measure and evaluate the voltage under starting conditions.
This is often impractical in a deep-well installation. When the splice is submerged, it must use an approved permanent underwater sealing method.
Perform the specified continuity, winding-resistance and insulation-resistance tests before and after lowering the pump. Compare the results with the recorded baseline.
A deep-well pump cable must be selected through both an electrical and an installation review.
The final selection should:
Carry the required current safely.
Limit running and starting voltage drop.
Use the complete electrical route length.
Match the voltage, phase and starting method.
Withstand continuous submersion.
Use a reliable underwater splice.
Fit inside the casing with the complete assembly.
Coordinate with the control panel and protection system.
Meet applicable electrical regulations.
Do not order a cable from motor power or well depth alone. Confirm the exact motor current, total cable length, voltage-drop calculation, conductor area, insulation system and installation environment before production.
Send SLAPK your required flow and head, well depth, pump setting depth, motor power, voltage, frequency, phase, total cable route, starting method, water temperature and casing internal diameter.
Our engineers can recommend a suitable QJ or SP borehole pump and provide the motor data, rated current, factory lead information and cable-length guidance required for your project.
Selecting a power cable for a deep well submersible pump involves more than matching a conductor to the motor’s rated power.
The cable may run from a transformer or control panel across the site, down the complete depth of the well and through a permanently submerged connection to the motor leads. Its resistance creates voltage drop, while the underwater section must withstand water, pressure, temperature and mechanical stress.
An undersized or excessively long cable can cause low voltage at the motor terminals. Possible results include difficult starting, excessive current, overheating, nuisance tripping, reduced torque and shortened motor life.
An oversized cable may reduce voltage drop, but it increases cost, outside diameter, weight and installation difficulty. It must also fit inside the well beside the rising main, cable guards, couplings and pump assembly.
Reliable cable sizing requires the motor nameplate data, actual cable route, supply voltage, starting method, installation conditions and applicable electrical standard.
A surface motor is normally located close to its control panel and remains accessible for inspection. A borehole pump motor may operate tens or hundreds of metres below ground.
The electrical route can include:
Transformer-to-panel cable
Panel-to-wellhead cable
Cable down the borehole
Factory motor leads
Underwater splice
Terminal and connection resistance
Every section contributes to the total voltage drop.
The submerged cable must also operate in a restrictive environment. It may be exposed to:
Continuous immersion
Hydrostatic pressure
Water temperature
Water chemistry
Abrasion against the casing
Cable-clamp pressure
Pump vibration
Mechanical loads during installation
Long-term insulation ageing
A cable that is suitable for a dry industrial building is not automatically suitable for a submerged borehole installation.
Begin with the exact motor rather than the pump series name.
Record:
Rated motor power
Rated voltage
Frequency
Single-phase or three-phase supply
Rated current
Full-load or maximum operating current
Power factor
Efficiency
Starting method
Number of motor leads
Insulation class
Permitted voltage tolerance
Manufacturer’s maximum cable-length data
SLAPK submersible pumps can be configured for different voltages and frequencies, including project-specific 50 Hz and 60 Hz requirements. Available configurations depend on the selected motor and pump model.
Do not assume that two motors with the same kilowatt rating have the same current. Rated current changes with voltage, phase, efficiency, power factor and motor design.
Use the confirmed motor data sheet for the exact order.
Do not use well depth alone as cable length.
The complete electrical route may include:
Distance from transformer to control panel
Distance from control panel to wellhead
Additional cable inside the panel
Depth from wellhead to the motor connection
Service loop at the wellhead
Cable required for termination
Routing around structures
Planned maintenance allowance
If the well is 120 m deep but the control panel is 45 m from the wellhead, the electrical route is already substantially longer than the downhole section alone.
Use the actual one-way route length when consulting the applicable motor cable table or performing the voltage-drop calculation. Apply the correct formula for the phase arrangement; do not manually double or multiply lengths unless the selected calculation method requires it.
The factory motor lead must also be included if the manufacturer’s sizing method does not already account for it.
The cable’s current-carrying requirement is normally based on the motor’s confirmed current and the applicable electrical rules.
Do not calculate cable size from kilowatts alone when a rated current is available.
The design review should consider:
Normal operating current
Motor service factor, if applicable
Starting current
Starting duration
Frequency of starts
Ambient temperature
Cable grouping
Installation method
Harmonic content from a VFD
Required protective-device coordination
Starting current does not usually mean that the cable must carry locked-rotor current continuously. However, the cable must maintain enough voltage during starting for the motor to develop adequate torque.
A long, undersized cable can create a large voltage drop during startup even when its continuous ampacity appears acceptable.
Ampacity is the continuous current a cable can carry under specified conditions without exceeding its allowable conductor or insulation temperature.
The published ampacity depends on:
Conductor material
Conductor cross-sectional area
Insulation material
Number of loaded conductors
Cable construction
Ambient temperature
Installation in air, conduit, ground or water
Grouping with other cables
Local electrical regulations
A cable that passes the voltage-drop calculation must still satisfy ampacity requirements.
Conversely, a cable that can safely carry the current may still be too small because of excessive voltage drop over a long distance. Both checks are necessary.
Voltage drop occurs because every conductor has electrical resistance and impedance.
For a simplified resistive calculation, voltage drop increases with:
Cable length
Motor current
Conductor resistivity
It decreases as conductor cross-sectional area increases.
For a copper conductor, a simplified relationship is:
Voltage drop is proportional to current * cable length ÷ conductor area
A complete AC calculation may also account for:
Power factor
Conductor reactance
Cable configuration
Operating temperature
Three-phase or single-phase supply
For a balanced three-phase motor, use a three-phase voltage-drop formula or an approved manufacturer cable table. For a single-phase motor, use the correct single-phase method.
Do not mix the two calculations.
The calculated voltage at the motor terminals should remain within the motor manufacturer’s permitted range under both running and starting conditions.
The same voltage loss represents different percentages at different system voltages.
For example, a fixed voltage loss is more significant in a lower-voltage system than in a higher-voltage system.
Excessive voltage drop can cause:
Reduced starting torque
Extended acceleration time
Higher motor current
Contactor chatter
Repeated overload trips
Motor overheating
Unstable VFD operation
Failure to start under hydraulic load
Reduced service life
SLAPK troubleshooting information identifies low voltage, an excessively thin wire and an overly long cable as possible reasons a submersible motor may fail to start.
Cable selection must therefore be coordinated with the actual voltage available at the site, not only the nominal system voltage.
A motor draws substantially more current during direct-on-line starting than during normal operation.
Because voltage drop is related to current, the temporary drop during startup can be much larger than the running drop.
The starting review should consider:
Available transformer capacity
Generator capacity
Supply-system impedance
Cable length and conductor size
Motor locked-rotor current
Pump starting torque
Wellhead and panel connections
Starting method
Acceleration time
A motor may operate normally after reaching speed but still fail to start because the terminal voltage collapses during acceleration.
Possible starting methods include:
Direct-on-line starting
Star-delta starting
Autotransformer starting
Soft starter
Variable-frequency drive
The selected method must be compatible with the motor leads, voltage, control panel and project requirements.
Do not assume that installing a soft starter or VFD automatically permits a smaller cable. The complete manufacturer instructions and electrical design still apply.
Copper is commonly used for submersible pump cables because of its conductivity, connection reliability and availability.
If aluminium conductors are considered for a surface section, the designer must account for:
Larger required conductor area
Termination compatibility
Oxidation control
Mechanical strength
Thermal expansion
Connector ratings
Transition to copper motor leads
Do not make an underwater copper-to-aluminium connection unless the complete splice system is specifically designed and approved for that purpose.
The conductor material used in the voltage-drop calculation must match the actual cable.
The downhole portion should be a cable specifically rated for continuous immersion and the expected water conditions.
Selection factors include:
Fresh water or saline water
Maximum water temperature
Hydrostatic pressure
Chemical exposure
Oil or hydrocarbon exposure
Flat or round construction
Cable outside diameter
Flexibility
Abrasion resistance
Voltage rating
Insulation and jacket material
Drinking-water approval, where required
A standard flexible cable may appear physically similar but may not be designed for continuous underwater service.
Confirm both the insulation and the outer jacket. A waterproof jacket does not compensate for conductor insulation that is unsuitable for the voltage, temperature or immersion period.
Submersible pump cables are available in flat and round constructions.
Flat cable may be useful where the clearance between the pump, rising main and casing is limited. It can sit more closely against the pipe or cable guard.
Round cable may be preferred for certain glands, seals, cable clamps and mechanical protection systems.
The correct choice depends on:
Motor connection
Well casing clearance
Cable gland design
Cable-clamping method
Splice kit
Installation equipment
Manufacturer approval
Cable shape does not determine conductor capacity. Confirm the conductor area, insulation, voltage rating and dimensional drawing.
Cable selection also affects whether the pump assembly can pass through the borehole.
Check the combined envelope of:
Pump and motor
Rising main
Cable
Cable guard
Cable clamps
Underwater splice
Check valves
Pipe couplings
Centralizers
The splice may be thicker than the cable itself and can become the controlling installation dimension.
Verify the minimum casing internal diameter along the complete installation path. Allow practical clearance for casing deviation, joints, deposits and retrieval.
For related dimensional guidance, see 6-Inch vs 8-Inch Borehole Pumps: How to Choose.
A deep-well pump commonly requires a connection between the factory motor leads and the extended drop cable.
This connection must provide:
Reliable electrical continuity
Low connection resistance
Mechanical strength
Electrical insulation
A permanent water barrier
Compatibility with the cable insulation
A smooth outside profile
Resistance to installation stress
The SLAPK cable-connection instructions show preparation of the conductor ends, mechanical joining, insulation wrapping and multiple sealing layers. The approved method and materials should be followed for the actual cable supplied.
A splice that is electrically insulated but not water-tight can fail after immersion.
Water entering a cable or joint can lead to:
Low insulation resistance
Ground faults
Phase-to-phase faults
Corrosion of conductors
Protection trips
Motor winding damage
Use a manufacturer-approved submersible splice kit or documented connection procedure.
Removing insulation carelessly can reduce the effective conductor area and weaken the connection.
The connector and sealing system must accommodate both conductors and remain mechanically secure.
Sharp conductor ends or connector edges can penetrate the insulation during wrapping or installation.
A few layers of general-purpose tape do not necessarily form a reliable deep-water seal.
Cable ends and connection materials must be clean and dry before sealing.
An oversized joint can catch on casing joints or become damaged during lowering.
The splice should not carry the suspended cable load or remain sharply bent against a coupling.
The power cable should be supported along the rising main so that it does not hang freely, rub against the casing or move excessively during operation.
Cable supports should:
Hold the cable without crushing it
Resist the water and installation environment
Avoid sharp edges
Accommodate thermal and mechanical movement
Remain secure during pump starting
Permit safe removal of the assembly
Cable guards should be used where required around the pump and coupling sections.
Do not use metallic fastening materials that can cut into the cable jacket or create an unsuitable galvanic condition.
The fastening interval and material should follow the pump, cable and installer requirements.
Cable selection cannot be separated from the motor protection system.
The control panel may include:
Short-circuit protection
Motor overload protection
Phase-loss protection
Phase-sequence protection
Under-voltage and over-voltage protection
Ground-fault protection
Dry-running protection
Temperature monitoring
Level control
Soft starter
Variable-frequency drive
Protection settings should be based on the confirmed motor and manufacturer instructions.
An overload relay should not be set higher merely to prevent nuisance trips caused by low voltage or a damaged cable. Find and correct the electrical or hydraulic cause.
A VFD changes the electrical waveform supplied to the motor.
Long motor cables can increase reflected-wave effects, voltage stress, leakage current and electromagnetic interference. The allowable cable length may depend on:
Drive model
Carrier frequency
Output voltage
Motor insulation
Cable construction
Grounding
Output reactor
dV/dt filter
Sine-wave filter
Follow the VFD and motor manufacturer’s maximum cable-length instructions.
The cable must also be suitable for the drive output and installed with the required grounding and shielding arrangement.
Do not apply a standard direct-on-line cable table to a VFD system without checking the drive documentation.
The pump installation must include the grounding or protective conductor required by the applicable electrical code and equipment design.
Grounding helps protective devices respond to insulation failure and reduces shock risk.
Do not use the rising main, safety cable or well casing as an unverified substitute for the required protective conductor.
The grounding arrangement should include:
Motor grounding connection
Control-panel grounding
Cable protective conductor
Bonding of required metallic components
Correct termination
Continuity testing
Local electrical regulations and site conditions determine the final design.
Before lowering the pump, inspect and test the cable and motor assembly.
Recommended checks may include:
Visual inspection of the cable jacket
Verification of conductor continuity
Phase-to-phase resistance comparison
Insulation-resistance testing
Ground-conductor continuity
Splice inspection
Motor winding-resistance comparison
Confirmation of phase identification
Verification of cable length
Use the test voltage and procedure specified by the motor and cable manufacturer.
Disconnect sensitive electronic equipment, including a VFD, before performing insulation-resistance tests when required by its instructions.
Record the results before installation. These baseline values help diagnose future problems.
Repeat the required electrical checks after lowering the pump but before normal operation.
This can reveal damage caused by:
Pulling the cable
Contact with casing edges
Crushed insulation
A damaged splice
Incorrect termination
Water entering the connection
During commissioning, record:
Supply voltage
Motor terminal or panel voltage
Phase-to-phase voltage balance
Running current on each phase
Starting behavior
Insulation resistance
Protection settings
Pump flow and discharge pressure
Current imbalance may indicate voltage imbalance, a connection problem, cable damage or a motor fault.
Assume a three-phase borehole pump will be installed 150 m below the wellhead, while the control panel is 35 m from the well.
The motor nameplate and supplier data provide the rated voltage, current, starting method and permitted cable length.
The engineer should:
Add the downhole cable, surface route, service allowance and factory motor leads as required by the selected calculation method.
Identify the rated and starting current.
Select a submersible-rated copper cable with suitable insulation.
Check its ampacity under the actual installation conditions.
Calculate running voltage drop.
Check the available motor voltage during startup.
Compare the result with the manufacturer’s permitted range.
Increase the conductor size if either voltage-drop or ampacity requirements are not met.
Check the cable and splice outside dimensions against the casing clearance.
Confirm the cable with the control-panel, starter or VFD supplier.
Document the final conductor area, length, splice method and protection settings.
The final cable cannot be selected from installation depth alone.
Selecting conductor size from motor kilowatts alone
Ignoring the surface cable between the panel and wellhead
Using nominal well depth as total cable length
Checking ampacity but not voltage drop
Checking running voltage but not starting conditions
Using single-phase calculations for a three-phase motor
Using ordinary cable for continuous immersion
Ignoring water temperature and chemistry
Installing an unapproved underwater splice
Allowing the cable to rub against the casing
Failing to include the splice in the clearance check
Ignoring VFD maximum motor-cable length
Increasing overload settings instead of correcting low voltage
Failing to test insulation before and after installation
Send the following information to the motor, cable and control-panel supplier:
Complete pump and motor model
Rated motor power
Rated voltage and frequency
Single-phase or three-phase supply
Rated current
Starting method
Transformer or generator capacity
Distance from supply to control panel
Distance from panel to wellhead
Pump installation depth
Factory motor-lead length and size
Proposed cable material and cross-sectional area
Flat or round cable requirement
Water temperature and chemistry
Minimum casing internal diameter
VFD model and operating frequency range
Required local electrical standard
Grounding arrangement
Expected starts per hour
Continuous or intermittent operating duty
The answer depends on motor current, voltage, phase, complete cable length, voltage-drop limit, starting method, installation conditions and local regulations. Motor power and well depth alone are not sufficient.
Often yes, provided it is compatible with the terminals, splice, control equipment and well clearance. A larger conductor reduces voltage drop but increases cost, weight and outside diameter.
Yes. All electrical sections that contribute to voltage drop must be included according to the chosen calculation method.
Only if it is specifically rated for continuous immersion, the required voltage, temperature, pressure and water conditions. General flexible cable should not be assumed suitable.
Not automatically. The cable must still meet ampacity, voltage-drop, insulation, grounding and drive-manufacturer requirements. Long VFD output cables may require additional filters or reactors.
The voltage may fall substantially during starting because of cable resistance, weak supply capacity or high starting current. Measure and evaluate the voltage under starting conditions.
This is often impractical in a deep-well installation. When the splice is submerged, it must use an approved permanent underwater sealing method.
Perform the specified continuity, winding-resistance and insulation-resistance tests before and after lowering the pump. Compare the results with the recorded baseline.
A deep-well pump cable must be selected through both an electrical and an installation review.
The final selection should:
Carry the required current safely.
Limit running and starting voltage drop.
Use the complete electrical route length.
Match the voltage, phase and starting method.
Withstand continuous submersion.
Use a reliable underwater splice.
Fit inside the casing with the complete assembly.
Coordinate with the control panel and protection system.
Meet applicable electrical regulations.
Do not order a cable from motor power or well depth alone. Confirm the exact motor current, total cable length, voltage-drop calculation, conductor area, insulation system and installation environment before production.
Send SLAPK your required flow and head, well depth, pump setting depth, motor power, voltage, frequency, phase, total cable route, starting method, water temperature and casing internal diameter.
Our engineers can recommend a suitable QJ or SP borehole pump and provide the motor data, rated current, factory lead information and cable-length guidance required for your project.
