How Moisture Affects XLPE Power Cables
Created on 08.27
How Moisture Affects XLPE Power Cables
XLPE insulated power cables are widely used in electrical distribution systems because of their excellent electrical insulation, thermal performance, and long service life. However, moisture can become a serious concern when cables are installed underground, in wet environments, or in areas exposed to water.
Although the outer sheath provides an important barrier against moisture, damage to the sheath, poorly sealed cable ends, defective joints, or unsuitable cable construction can allow water to reach the cable's internal layers.
Understanding how moisture affects XLPE power cables can help engineers, contractors, and cable buyers select the right cable construction and reduce the risk of premature failure.
Why Is Moisture a Concern for XLPE Cables?
XLPE itself has good moisture resistance compared with many traditional insulation materials. However, the overall performance of a power cable depends on the complete cable construction, including the conductor, insulation, screen, armour, sheath, joints, and terminations.
When water enters a cable system and remains there for a long period, it can contribute to deterioration of electrical insulation and other cable components.
The risk is particularly important for medium-voltage cables because the electrical stress inside the insulation system is much higher than in typical low-voltage applications.
How Can Moisture Enter a Power Cable?
Water can enter or reach a cable through several paths.
1. Damaged Outer Sheath
The outer sheath is the primary protective barrier against the external environment.
During transportation, installation, or subsequent construction work, the sheath may be damaged by:
- Sharp objects
- Improper pulling
- Excessive bending
- Excavation equipment
- Stones or rough surfaces
- Incorrect handling
Even a small sheath defect can provide a pathway for moisture.
2. Poorly Sealed Cable Ends
Cable ends should remain properly sealed during transportation and storage.
If the ends are left exposed for an extended period, moisture may enter the cable, particularly in humid or rainy environments.
This is especially important for cables that are stored before installation.
3. Cable Joints and Terminations
Cable joints and terminations are potential weak points in an electrical installation.
Poor workmanship, unsuitable accessories, or inadequate sealing may allow water to penetrate the cable system.
Correct installation procedures and compatible accessories are therefore essential.
4. Underground Installation
Underground cables may be exposed to:
- Groundwater
- Rainwater
- Wet soil
- Flooding
- Seasonal changes in soil moisture
For projects in areas with high groundwater levels or frequent flooding, cable construction should be selected according to the actual site conditions.
What Happens When Moisture Enters an XLPE Cable?
The effects depend on the cable design, voltage level, amount of moisture, and duration of exposure.
1. Insulation Resistance May Decrease
Water and moisture can affect the electrical properties of the insulation system.
If moisture reaches sensitive internal components, insulation resistance may decrease.
A significant reduction in insulation performance can increase the risk of electrical faults.
2. Water Treeing Can Develop in Medium-Voltage Cables
One of the most important moisture-related phenomena in XLPE insulated medium-voltage cables is water treeing.
Water treeing refers to the gradual development of microscopic, tree-like structures within polymeric insulation when moisture and electrical stress are present over an extended period.
These structures can progressively weaken the insulation.
Water treeing is generally a long-term degradation mechanism rather than an immediate result of a single exposure to water.
3. Electrical Strength Can Deteriorate
As insulation degradation progresses, the cable's ability to withstand electrical stress may decrease.
In severe cases, deterioration can eventually contribute to insulation breakdown.
This is why moisture control is particularly important for medium-voltage power cables.
4. Metallic Components May Be Affected
Depending on the cable construction, moisture can also affect metallic components such as screens, armour, or other conductive elements.
Long-term exposure to water can increase the risk of corrosion when suitable protection is not provided.
5. Cable Service Life May Be Reduced
A cable exposed to moisture over a long period may experience accelerated deterioration.
Even when the cable continues to operate normally, internal degradation may already be taking place.
Preventing water ingress is therefore generally more effective than attempting to repair moisture-related damage after it has occurred.
Are XLPE Cables Waterproof?
This is an important question for cable buyers.
XLPE insulation is moisture-resistant, but "XLPE cable" does not automatically mean that the complete cable is waterproof or longitudinally water-blocked.
The moisture resistance of a cable depends on its complete construction.
For applications with a significant risk of water exposure, the project specification may require additional moisture protection, such as:
- Water-blocking tape
- Water-blocking yarn
- Water-blocking compounds
- Longitudinal water-blocking designs
- Suitable moisture-resistant sheath materials
The appropriate construction should be determined according to the installation environment and project requirements.
How to Protect XLPE Power Cables from Moisture
Use a Suitable Cable Sheath
The outer sheath should be selected according to the environment.
Common sheath materials include:
- PVC
- PE
- MDPE
- HDPE
- LSZH compounds for specific applications
For outdoor or underground applications, the required mechanical, environmental, and moisture resistance should be considered together.
Consider Water-Blocking Construction
For installations with a high risk of water penetration, a water-blocking cable construction may provide additional protection.
Water-blocking materials can help limit the longitudinal movement of water inside the cable if the outer sheath is damaged.
This can be particularly useful for:
- Underground power networks
- Wet soil conditions
- High groundwater areas
- Flood-prone locations
- Utility infrastructure
- Long cable routes
The exact water-blocking structure should be specified according to the cable design and applicable standard.
Protect Cable Ends During Storage（How to Transport and Store Power Cables）
Cable ends should be securely sealed during transportation and storage.
This simple measure helps prevent moisture from entering the cable before installation.
Cable drums should also be stored on stable, dry ground and protected from standing water.
Protect the Cable During Installation
Installation crews should avoid damaging the outer sheath.
Important precautions include:
- Use suitable cable rollers.
- Maintain the recommended bending radius.
- Avoid dragging cables over sharp surfaces.
- Control pulling tension.
- Inspect the sheath after installation.
- Repair or assess any damage before the cable is buried.
Use Proper Cable Accessories
Cable joints and terminations should be suitable for the cable construction and voltage level.
For medium-voltage applications, correct installation of accessories is particularly important because improper sealing can compromise the entire insulation system.
Moisture Protection for Different Installation Environments
The appropriate cable design depends heavily on where the cable will be installed.
Installation Environment | Key Moisture Considerations |
Indoor | Normally lower moisture risk |
Cable tray | Protect against rain and environmental exposure where applicable |
Direct burial | Consider soil moisture and groundwater |
Underground duct | Consider water accumulation inside ducts |
Flood-prone area | Additional moisture protection may be required |
Coastal area | Consider moisture and corrosion |
Mining site | Consider water, mechanical damage, and harsh environmental conditions |
There is no single cable construction that is ideal for every application.
How Should Buyers Specify Moisture Requirements?
When requesting a quotation from a cable manufacturer, buyers should provide as much information as possible about the installation environment.
Useful information includes:
- System voltage
- Conductor material
- Conductor size
- Number of cores
- Installation method
- Direct burial or duct installation
- Groundwater conditions
- Expected exposure to water
- Applicable cable standard
- Required sheath material
- Whether water-blocking construction is required
Providing these details allows the manufacturer to recommend a more suitable cable construction.
How NINGLAN Cable Addresses Cable Protection
At NINGLAN Cable, cable construction is selected according to the customer's technical specifications and intended installation environment.
Depending on project requirements, power cables can be designed with different combinations of:
- Copper or aluminum conductors
- XLPE insulation
- Metallic screens
- Armour
- PVC or PE-based sheaths
- Water-blocking components where specified
For underground and medium-voltage applications, moisture protection can be considered as part of the overall cable design rather than treated as an isolated feature.
Conclusion
Moisture is an important factor affecting the long-term reliability of XLPE power cables, particularly in underground, wet, and medium-voltage applications.
Water ingress can result from damaged sheaths, poorly sealed cable ends, defective joints, or unsuitable cable construction. Over time, moisture combined with electrical stress can contribute to insulation deterioration and water treeing.
The best approach is to consider moisture protection during the cable selection and project design stages.
By choosing an appropriate sheath, considering water-blocking construction where necessary, protecting cable ends, and using properly installed accessories, project owners and contractors can significantly reduce moisture-related risks and improve cable service life.
NINGLAN Cable supplies XLPE insulated power cables for low-voltage and medium-voltage applications, with cable constructions customized according to project requirements and installation conditions.
Related Reading：What Happens When a Cable Is Overloaded?
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