Introduction — The Hidden Risk Beneath the Ground

Across the globe, utilities are racing to expand high-voltage power lines and fiber-optic communication networks. Yet, beneath the headline excitement of “smart grid rollout” or “high-speed telecom deployment,” one silent threat keeps engineers awake: over-tension during long-distance cable pulling.

When underground cable installation stretches across tunnels, ducts, bridges, or mountainous terrain, maintaining safe pulling force becomes critical. Excessive tension can lead to conductor elongation, sheath cracking, micro-bending in optical fibers, or catastrophic failure during haul-in. A single mistake may scrap kilometers of costly cable and delay commissioning for months.

This is why modern project teams now incorporate cable hauling equipment with tension-monitoring systems, intelligent winch control, and optimized route planning. Managing pulling loads has become not only a technical requirement but a decisive factor in installation economics.

This article breaks down how over-tension occurs, why it’s so dangerous, and how power and telecom engineers can mitigate it during long-set underground works.

Understanding Over-Tension in Cable Hauling

Cable pulling tension is the combined result of friction, bend radius, duct surface conditions, lubricant properties, and route angle changes. Underground cable paths often introduce unpredictable forces, especially when run through multiple manholes, elevation profiles, or congested ducts.

Even the strongest cable hauling equipment cannot save a poorly controlled installation. A smart operator focuses on reducing accumulated drag and real-time monitoring to keep load under manufacturer tension limits.

Key contributing factors

1. Long Pulling Distance
   The longer the cable is dragged through ducting, the more friction compounds. Tension is cumulative.

2. Bend Radius & Alignment
   Sharp turns or poorly aligned ducts significantly add directional force.

3. Elevated Running Surface Resistance
   Aged ducts, corrosion, debris, or uneven conduit interior worsen friction.

4. Insufficient Lubrication
   Low-grade or insufficient lubricant results in friction spikes mid-pull.

5. Improper Winch Selection
   Winches without proper torque control and calibration pose higher tension risk.

6. Lack of Real-Time Load Sensing
   Without feedback systems, crews cannot respond to overload conditions quickly.

Why Over-Tension Is Dangerous

A cable is engineered to withstand both elastic and limited plastic deformation. Over-tension forces the conductor and insulation beyond design yield, creating irreversible defects.

Power Cable Damage

• Conductor elongation

• Insulation cracking

• Shield layer buckling

• Compromised dielectric performance

• Reduced long-term reliability

Optical Cable Damage

• Micro-bending

• Signal attenuation

• Fiber breakage

• Loss of bandwidth performance

Damage may not appear at installation; failure may occur months later, leading to costly post-commission repairs.

Safe Tension Limits

Manufacturers specify Maximum Pulling Tension (MPT). For power cable, MPT often falls around:

• Copper conductor: ~50–60 N/mm²

• Aluminum conductor: ~30–35 N/mm²

For fiber-optic cable, safe pulling forces may be as low as 600–2700 N depending on construction.

Always consult the manufacturer datasheet before deployment.

How Cable Hauling Equipment Protects Against Over-Tension

Modern underground installation relies on automated components to ensure stable pulling force:

1) Tension-Limiting Winch

A variable-speed winch with adjustable torque prevents abrupt spikes.

2) Load Indicators & Monitoring

Digital readings allow operators to monitor every second of pulling.

3) Capstan-Assist System

Multi-capstan systems distribute load over stages, reducing single-point tension.

4) Signal Coordination

Push-pull coordination prevents jam-point stress.

These systems balance pulling force, lowering cumulative strain.

Strategies to Avoid Over-Tension

Avoiding over-tension requires comprehensive planning before a cable touches the ground.

1) Route Planning & Duct Evaluation

Survey the entire pulling path — including angle, elevation, duct size, and potential obstruction. More bends = more friction.

Recommendation: Bore scope ducts in advance and map hot spots.

2) Reduce Bending Angles

Where possible, route smoothing and roller positioning will greatly reduce drag.

Minimum bending radius should be ≥ 12× cable diameter for power cable and ≥ 20× cable diameter for fiber cable.

Tighter bends dramatically increase pulling tension — avoid them unless absolutely necessary.

3) Use Proper Cable Lubrication

High-performance lubricant reduces friction up to 80%.

Best practice:

• Apply generously in entry and intermediate pulls

• Re-apply after manholes

• Choose lubricant compatible with insulation

Lubricant grade significantly influences coefficient of friction — never compromise here.

4) Segment the Pull

For long sets (hundreds of meters to multiple km), break the job into segments using intermediate pulling points.

Advantages:

• Pressure recovery

• Lower cumulative tension

• Easier monitoring

• Safer handling during unexpected events

5) Push-Pull Method

Using pushers near the feed end while winching from the far end reduces peak force. This dual-support architecture prevents load concentration.

Modern cable hauling equipment with synchronized control improves efficiency and eliminates sudden tension waves.

6) Select the Right Winch

Choosing the wrong pulling machine is where many projects fail.

Selection criteria:

• Rated pulling force

• Speed control resolution

• Remote monitoring options

• Recording capability

• Brake system reliability

Intelligent winches with tension feedback dramatically reduce risk.

7) Real-Time Tension Monitoring

Use load cells and electronic recorders to generate a pulling log.

Crew must stop if load approaches 90% MPT.
This protects both equipment and cable assets.

8) Intermediate Manhole Assist

Rollers or capstan support at manholes can isolate frictional torque.

This prevents runaway overload states halfway through installation.

Common Failure Modes

Knowing typical failure patterns aids preventive action:

Early detection = long-term reliability.

Case Reference — Tension Risk in Long-Tunnel Power Cable

In a 110kV tunnel power installation, a 2.4-km pulling run through multiple 45° bends caused tension spike beyond 75% safe load at mid-route.

Mitigation:

• Installed additional rollers

• Added lubrication injection points

• Reduced pulling speed

• Conducted dual-capstan segmentation

Result:
Pull completed below controllable maximum, avoiding conductor deformation.

Role of Experienced Manufacturers

Engineering and equipment partners with automation integration experience can provide:

• Tension-feedback systems

• Stable capstan and winch units

• Route assessment services

• Customized solutions for complex terrains

Dongguan Dongxin (DOSING) Automation Technology Co., Ltd., founded in 2009, has decades of innovation in cable systems. With nearly 30 years of R&D experience from founder Lin Huazhong, the company revolutionized automation by introducing PLC-based control systems in stranding machinery. The same philosophy drives development of more intelligent hauling interfaces for stable pulling performance in both power and communication cable installation.

Their engineering ecosystem — from R&D to manufacturing to after-sales support — ensures that cable factory and field contractors can build reliable long-set deployment capability with one-stop service.

Conclusion

Over-tension during long-distance underground installation is not a trivial inconvenience — it is a serious threat to cable integrity, service life, and project cost.

By combining:

• Professional route assessment

• Proper lubrication

• Push-pull methodology

• Correct cable hauling equipment selection

• Real-time tension monitoring

— project engineers can minimize risk while ensuring smooth pull-through, especially in ducted or multi-bend infrastructure.

As utilities expand toward higher capacity and denser digital networks, the demand for safe, intelligent underground cable pulling will grow. Investment in modern hauling systems and technical expertise not only prevents damage but also ensures that cables live out their full operational life.

In today’s underground cable era, tension control is more than a specification — it is a discipline of engineering precision.