5 Critical Mistakes to Avoid When Installing Medium Voltage Cables

Medium voltage (MV) cable installation requires careful planning, specialized tools, and strict compliance with technical standards. Even minor installation errors can lead to insulation failure, safety hazards, costly downtime, and premature cable replacement. Understanding and avoiding the most common installation mistakes is essential to ensure long-term system reliability and operational safety.

The most common installation mistakes include:

• Improper cable terminations that damage insulation or create weak electrical connections.

• Exposed conductors that allow moisture ingress and corrosion.

• Incorrect cable routing near energized equipment.

• Excessive slack or bending beyond the recommended bend radius.

• Poor shield cutback alignment, leading to insulation stress and partial discharge.

Using proper installation procedures, approved accessories, and professional handling methods significantly reduces the risk of system failure.

Medium Voltage Cable NA2XS2Y/NA2XS(F)2Y/NA2XS(FL)2Y

1. Improper Cable Terminations

Cable terminations are among the most critical points in any medium voltage system. Incorrect termination techniques can weaken insulation, introduce moisture, and create unreliable electrical connections.

One common mistake is removing the semi-conductive insulation layer using standard knives instead of specialized scoring tools. This can create microscopic cuts in XLPE insulation, reducing dielectric strength and creating stress concentration points that may eventually cause failure.

Crimping errors also present serious risks. Using incorrect crimping dies or mismatched connectors can lead to loose connections, overheating, and electrical arcing. Over-compression can deform connectors and create hotspots, while under-compression results in poor conductivity. Always use compatible lugs and crimping tools from the same manufacturer and verify proper conductor insertion before crimping.

Moisture intrusion is another major concern. If heat-shrink tubing or termination components are applied over uneven insulation surfaces, voids may form where moisture can accumulate. Proper surface preparation, smoothing insulation, and sealing termination points are essential to prevent long-term damage.

2. Leaving Conductors Exposed

Exposed medium voltage conductors present serious operational and safety hazards. When conductors are not properly sealed, moisture can enter the cable through capillary action, leading to corrosion of the conductor and metallic shield.

Water accumulation inside the conductor strands can create internal pressure, potentially damaging termination components or causing system failure. In colder climates, trapped moisture may freeze and expand, resulting in insulation cracking or mechanical damage.

To prevent these issues:

• Seal cable ends immediately using heat-shrink end caps.

• Use proper termination kits designed for medium voltage applications.

• Avoid temporary sealing methods such as PVC tape.

• Perform sheath integrity testing before commissioning.

Proper sealing ensures long-term protection against environmental exposure.

3. Improper Cable Routing Near Energized Equipment

Incorrect routing of medium voltage cables near energized components can result in electrical faults, overheating, and insulation failure. Even without direct contact, electromagnetic fields and improper grounding can create hazardous electrical conditions.

Poor routing may also expose cables to mechanical stress or accidental damage during equipment maintenance.

Best practices include:

• Maintaining safe clearance from energized busbars and equipment.

• Using cable trays, ducts, or protective troughs for secure routing.

• Properly grounding cable shields to prevent induced voltage buildup.

• Securing cables with rated cleats and supports.

Careful routing reduces both electrical and mechanical risks while improving system reliability.

4. Excessive Slack and Incorrect Bend Radius

Improper slack management and tight bending are common causes of medium voltage cable damage. Excessive slack may force installers to bend cables beyond the recommended limits, while overly tight bends can damage internal insulation layers.

Exceeding the minimum bend radius may cause:

• Insulation cracking or deformation

• Separation of internal shielding layers

• Partial discharge and insulation breakdown

• Reduced cable lifespan

As a general guideline, the minimum bending radius should be at least 12–15 times the cable’s overall diameter during installation. Installation should also be avoided in extremely cold temperatures unless cables are properly pre-conditioned to prevent brittleness.

5. Incorrect Shield Cutback and Alignment

Shield cutback refers to the precise removal of insulation and shielding layers during cable termination preparation. Incorrect cutback dimensions or misalignment can create localized electrical stress points, increasing the risk of partial discharge and premature insulation failure.

Proper alignment ensures that stress control components function correctly and distribute electrical stress evenly along the cable termination.

To ensure correct shield preparation:

• Follow manufacturer-specified cutback measurements.

• Use precision scoring tools designed for MV cables.

• Clean insulation surfaces thoroughly before termination.

• Ensure proper bonding and grounding of the metallic shield.

Accurate shield preparation significantly improves termination reliability and system safety.

Conclusion

Most medium voltage cable failures can be traced back to installation errors rather than manufacturing defects. Avoiding common mistakes such as improper terminations, exposed conductors, poor routing, excessive bending, and incorrect shield preparation is essential for ensuring reliable operation.

Following manufacturer guidelines, using certified installation tools, and performing proper testing procedures can extend cable service life beyond 30–40 years while minimizing safety risks and maintenance costs.

A well-installed medium voltage cable system ensures efficient power distribution, protects critical infrastructure, and delivers long-term operational reliability.

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