A submersible sewage pump cable is part of the pump's sealing and electrical protection system.
Cable failure can be caused by:
- Lifting the pump by its cable
- Abrasion against the wet-well wall
- Sharp bends or crushing
- Poor cable support
- Damaged cable gland
- Incorrect field joints or splices
- Chemical attack
- Ageing insulation
- Repeated flexing
- Loose electrical terminations
- Water travelling through a damaged cable toward the motor
Warning signs include:
- Intermittent pump operation
- Earth leakage trips
- Low insulation resistance
- Visible cracks or swelling
- Moisture at terminations
- Burnt or discoloured connections
- Pump trips when the cable moves
A cable problem should be repaired correctly rather than covered with temporary tape inside a wet environment.
Why the Cable Matters So Much on a Submersible Pump
A normal surface motor is installed in a dry environment.
A submersible sewage pump operates directly inside wastewater.
Its power cable must therefore perform several jobs at the same time:
- Carry electrical power
- Resist water exposure
- Resist mechanical damage
- Remain sealed where it enters the motor
- Tolerate installation and removal
Damage to the cable can create both electrical and water-ingress risks.
A pump with perfect mechanical seals can still suffer motor damage if water enters through the cable or cable gland.
Cable Gland vs Mechanical Seal
These are different sealing systems.
Mechanical Seal
Protects the motor around the rotating shaft.
Cable Gland
Protects the motor where the electrical cable enters the pump housing.
When water is found inside a motor, both entry paths should be investigated.
Do not automatically conclude that every water-ingress failure came from the mechanical seal.
1. Lifting the Pump by the Electrical Cable
This is one of the most damaging handling mistakes.
A submersible pump should be lifted using the approved:
- Lifting chain
- Lifting eye
- Lifting cable or certified arrangement specified by the manufacturer
The electrical cable is not a lifting device.
Pulling the pump by its cable can damage:
- Internal conductors
- Insulation
- Cable gland
- Terminal connections
- Motor sealing
The damage may not be immediately visible.
The pump can fail weeks later because water gradually enters through the stressed cable entry.
2. Cable Abrasion Against Concrete or Metal
Submersible cables often travel from the pump to the control panel through a wet well containing:
- Concrete walls
- Steel brackets
- Guide rails
- Pipes
- Covers
If the cable repeatedly rubs against a sharp or rough surface, the outer insulation can wear away.
Vibration from pump operation can make the problem worse.
During inspection, pay particular attention to cable sections that touch:
- Pit edges
- Guide rails
- Pipe supports
- Metal covers
- Cable clamps
Good cable routing prevents movement against abrasive surfaces.
3. Excessively Tight Cable Ties or Clamps
Cable support is necessary, but over-tightening can crush the cable.
This can deform:
- Outer insulation
- Internal insulation
- Conductors
Use suitable cable supports that prevent uncontrolled movement without damaging the cable structure.
Do not use sharp metal ties directly against the cable jacket.
4. Sharp Bends
Electrical cables have minimum bending requirements.
A tight bend can stress:
- Copper conductors
- Insulation
- Internal fillers
Repeated bending at the same point can eventually cause conductor breakage or cracking.
Cable routing should avoid unnecessary sharp changes in direction, particularly near:
- Pump entry
- Wet-well cover
- Panel entry
5. Damaged Cable Gland
The cable gland provides a sealed transition into the motor housing.
Failure can occur because of:
- Incorrect assembly
- Damaged elastomer
- Loose gland components
- Cable pulled sideways
- Corrosion
- Ageing
- Incorrect cable diameter
A gland that no longer seals correctly can allow moisture to migrate toward the motor.
Cable-gland condition should be checked during major pump overhaul.
6. Field Cable Joints in Wet Locations
Sometimes the original cable is too short and a field joint is added.
A poor joint can become the weakest part of the electrical system.
Risks include:
- Water entry
- Corrosion
- Increased resistance
- Intermittent contact
- Earth leakage
Any cable joint used in a wet or submerged environment must be designed and installed specifically for that service.
Ordinary indoor electrical jointing methods are not suitable for permanent immersion.
7. Chemical Attack on Cable Insulation
Industrial wastewater may contain substances that degrade standard cable materials.
Examples include:
- Oils
- Solvents
- Acids
- Alkalis
- Cleaning chemicals
- Process chemicals
The cable material should be checked against the actual wastewater chemistry.
A cable that performs well in municipal sewage may deteriorate more quickly in chemically aggressive industrial effluent.
8. Heat and Ageing
Cable insulation changes with age and temperature.
Repeated exposure to:
- High motor temperature
- Hot wastewater
- Electrical overload
- Sunlight on exposed cable sections
can contribute to hardening, cracking or loss of flexibility.
Old cable should be inspected more carefully even if it has not suffered obvious mechanical damage.
9. Water Can Travel Inside a Damaged Cable
One dangerous feature of cable damage is that water does not always stay at the visible defect.
Moisture can migrate along cable materials toward:
- Termination points
- Junction boxes
- Motor entry
This means a pump may show electrical problems at a location far from the original external cable damage.
When water ingress is suspected, inspect the complete cable run.
Warning Signs of Cable Failure
Look for:
- Cracked outer jacket
- Cuts
- Flattened sections
- Swelling
- Soft or brittle insulation
- Burn marks
- Exposed conductor
- Corrosion near terminations
- Moisture inside junction box
- Pump trips when cable position changes
- Low insulation resistance
- Repeated earth leakage
Any visible damage should be taken seriously in a submerged electrical application.
Intermittent Pump Operation Can Be a Cable Problem
An intermittent fault can be difficult to diagnose.
The pump may:
- Run normally when cold
- Stop after vibration moves the cable
- Restart later
- Trip only occasionally
Possible causes include:
- Broken conductor strands
- Loose termination
- Water inside a joint
- Damaged insulation
Do not assume intermittent operation means the motor itself must be defective.
Insulation Resistance Testing
Insulation resistance testing can help identify deterioration in the motor-cable system.
Testing should be performed by qualified electrical personnel using the correct procedure for the pump and connected equipment.
Important considerations include:
- Isolate the pump correctly
- Follow the motor manufacturer's test-voltage guidance
- Disconnect sensitive electronic equipment where required
- Record readings consistently
- Compare trends over time
A single reading is useful.
A series of readings recorded during maintenance is even more useful because it shows deterioration trends.
Do Not Test Through a VFD Without Checking the Procedure
If the pump is connected to a Variable Frequency Drive or electronic protection equipment, insulation testing should follow the equipment manufacturer's instructions.
Applying an insulation test voltage through sensitive electronics can damage equipment.
The motor and cable may need to be electrically isolated from the VFD before testing.
This work should be performed by qualified personnel.
Three-Phase Current Imbalance Can Point to Connections
During operation, compare current on all phases.
An abnormal phase can indicate:
- Loose terminal
- Damaged conductor
- Poor contactor contact
- Supply imbalance
- Motor winding issue
Current imbalance alone does not prove the cable is faulty, but it provides a useful diagnostic clue.
Check the Cable After Every Pump Removal
Pump removal creates a good opportunity to inspect the cable.
Before lowering the pump back into the wet well, check:
- Full visible cable length
- Gland area
- Cable support
- Cable bends
- Abrasion points
- Termination condition
Do not reinstall a pump with known cable damage simply because the motor still runs.
Cable Routing in a Wet Well
Good routing should achieve several goals:
- Keep cable away from pump suction
- Keep cable away from floats
- Prevent cable from wrapping around guide rails
- Avoid sharp edges
- Provide enough slack for pump removal
- Prevent excessive uncontrolled movement
Poor cable routing can also interfere with float switches, creating level-control problems.
Flow Chem's Submersible Sewage Pump Installation Guide covers installation planning in more detail.
Cable Problems After Pump Maintenance
If a pump fails immediately after being removed and reinstalled, inspect:
- Cable pulled during lifting
- Gland disturbed
- Cable pinched under cover
- Termination not tightened correctly
- Phase connection changed
- Cable damaged against pit edge
Maintenance activity can create a new electrical fault even when the original pump problem was mechanical.
Cable Failure Troubleshooting Table
| Symptom | Possible Cause | What to Check |
|---|---|---|
| Earth leakage trip | Insulation damage | Cable, gland, motor |
| Pump stops when cable moves | Broken conductor | Cable continuity and condition |
| Low insulation resistance | Moisture or damaged insulation | Cable and motor |
| Cable hot near terminal | Loose/high-resistance connection | Terminal and contactor |
| Visible swelling | Water or chemical damage | Cable jacket |
| Motor has water but shaft seal looks healthy | Cable-entry leak | Gland and cable |
| Fault after pump removal | Handling damage | Cable and gland |
| One phase current abnormal | Connection or supply issue | Terminals, cable, supply |
Common Cable Maintenance Mistakes
1. Pulling the Pump by the Cable
Always use the approved lifting arrangement.
2. Using Temporary Tape as a Permanent Submerged Repair
A wet-environment cable repair requires a suitable engineered method.
3. Ignoring Small Cuts
Moisture can enter through apparently minor damage.
4. Over-Tightening Cable Clamps
The support itself can damage the cable.
5. Ignoring Cable Chemistry
Industrial effluent can attack unsuitable insulation materials.
6. Failing to Record Insulation Resistance
Trend data can reveal deterioration before a complete fault develops.
Preventing Cable and Gland Failure
Use these practices:
- Never lift a pump by its electrical cable
- Route cable away from sharp surfaces
- Protect cable at wet-well edges
- Use suitable cable supports
- Avoid tight bends
- Inspect cable after pump removal
- Maintain correct cable glands
- Use suitable submerged joints only where unavoidable
- Check chemical compatibility
- Record insulation resistance
- Investigate earth leakage trips immediately
Frequently Asked Questions
Can a damaged sewage pump cable cause motor failure?
Yes. Cable damage can create short circuits, earth leakage, phase problems and water-ingress paths that may eventually damage the motor.
Can water enter a submersible pump through the cable?
Yes. Damage to the cable, gland or cable entry can allow moisture to migrate toward the motor.
Should I lift a submersible pump by its cable?
No. Use the approved lifting eye, chain or manufacturer-specified lifting arrangement.
What causes a submersible pump cable to swell?
Possible causes include water ingress, chemical attack, heat or insulation deterioration. The cable should be inspected by qualified personnel.
Why does my pump trip when the cable moves?
A damaged conductor, loose connection or insulation fault may change as the cable flexes.
Can cable damage cause low insulation resistance?
Yes. Moisture ingress or damaged insulation anywhere in the motor-cable system can reduce insulation resistance.
Is every water-ingress failure caused by the mechanical seal?
No. Cable glands and cable-entry systems are another possible path into a submersible motor.
Need Help Selecting a Pump for Harsh Wastewater Service?
Reliable submersible pump operation depends on more than hydraulics.
The application should also consider:
- Wastewater chemistry
- Cable exposure
- Installation depth
- Pump removal method
- Control panel
- Motor protection
- Solids and ragging risk
For STP, ETP and industrial wastewater applications, share these details with Flow Chem Pumps.
Explore the Submersible Sewage and Sludge Pump range for sewage and sludge transfer duties.