Improper tensioning during electric cable installation can lead to safety hazards and system failures.
Incorrect tension forces can damage cables, reduce performance, and create dangerous situations.

Understand the fundamentals and methods of electric cable tensioning to ensure safe, reliable, and efficient cable installations.

Electric Cable Tensioning

What is Electric Cable Tensioning

Electric cable tensioning is a critical process in the installation and maintenance of electrical cable systems. It involves applying the proper amount of tension to cables as they are pulled through conduits, raceways, and other pathways. The goal is to ensure cables are installed safely, securely, and in compliance with relevant codes and standards.

Fundamentals of Electric Cable Tensioning

Two key forces come into play during cable tensioning:

  1. Tensioning force: This is the force applied to the cable as it is pulled through a conduit or raceway during installation. The appropriate tensioning force must be applied to prevent damage to the cable insulation and conductors while ensuring the cable is installed correctly.
  2. Sidewall pressure: This is the force exerted on the cable as it passes around bends, corners, or pulleys within a conduit or raceway system. Excessive sidewall pressure can cause damage to the cable insulation, leading to premature failure or reduced performance.

Methods of Electric Cable Tensioning

Several methods can be employed to optimize electric cable tensioning and minimize the risk of damage during installation:

  1. Lubrication: Applying a suitable lubricant to the cable can significantly reduce friction between the cable and the conduit wall. This can reduce the required tensioning force by as much as 67%, making installation easier and reducing the risk of damage to the cable. Lubricants specifically designed for electrical applications should be used to ensure compatibility with cable insulation materials.
  2. Tension direction: Selecting the optimal direction for applying tension can help minimize the force required. For example, pulling the cable from the end of the conduit with the most bends or where the cable is being pulled uphill will generally result in lower tension compared to pulling from the opposite end. This is because the cable will encounter less resistance when being pulled through the straighter sections of the conduit first.
  3. Tensioning wire methods: In overhead line installations, tensioning wire methods are used to maintain proper tension on the conductor and prevent it from contacting live circuits or obstructing traffic at road crossings. This typically involves using a lightweight synthetic guide rope, followed by a heavier pull rope, to pull the conductor into place. Specialized equipment such as tensioners and wire pullers are often used to ensure the appropriate tension is maintained throughout the installation process.
  4. Fixed reel method: For rural distribution line construction, the fixed reel method may be more suitable. In this method, a tractor is used to drag the conductor along the ground, allowing for a more controlled and gradual application of tension. This method is particularly useful in areas where access for larger equipment may be limited.

Types of Electric Cable Tensioning Systems

Manual Tensioning

The simplest type of tensioning is done manually using come-alongs, ratchet pullers and similar hand-operated devices. While inexpensive, this is only practical for shorter pulls with lighter cables. Consistent tension is difficult to maintain, and the manual effort required can be substantial.

Automatic Tensioning (often called Auto-Tensioning or AT) Systems

AT systems use sensors to monitor the cable tension and automatically adjust the pulleys or capstans to maintain a constant tension within a pre-set range. This allows for much longer and heavier pulls while protecting the cable from over-tensioning. AT systems provide better tension consistency than manual methods.

Hydraulic Tensioning Systems

For the highest pulling forces, hydraulic systems are used. These employ hydraulic motors, pumps and cylinders to generate massive, consistent tension. Hydraulic systems are capable of tensioning the largest and heaviest cables over the longest distances. They are frequently truck or trailer-mounted for portability.

Electric Tensioning Systems

Electric systems use variable-speed electric motors to drive the pulling capstans or drums. They provide good control and consistency and are capable of long, heavy pulls. However, they generally aren’t as powerful as hydraulic pullers. Electric systems are powered by on-board generators or external power sources.

Pneumatic Tensioning Systems

Pneumatic or air-powered tensioners are sometimes used for lighter-duty pulls. They employ compressed air motors to drive the pull wheels and are simple and economical. However, their tension capacity is limited compared to hydraulic or electric systems. Pneumatic systems are often used where power sources are limited.

Here is an expansion of the specified sections:

Components of Electric Cable Tensioning Systems

  • Tensioners: These devices, either manual or powered, maintain a constant pulling force on the cable. They prevent cable slack and ensure the cable is pulled through the conduit at a consistent tension.
  • Tractors: In some installations, especially for power distribution lines, tractors are used to pull the conductor along its path.
  • Dynamometers and Tension Meters: Dynamometers measure the pulling force exerted on the cable, while tension meters measure the tension within the cable itself.
  • Reel Stands: Cable reels must be supported on stands that allow the reel to spin freely as cable is pulled off. Reel stands are designed to handle the substantial weight of loaded cable reels and permit smooth unspooling under tension.
  • Winches: Winches are used to pull cables, especially in applications requiring substantial force, such as pulling through long conduit runs with multiple bends. Modern winches are available in electric, hydraulic, and pneumatic models. They often incorporate sensors and controls to monitor and adjust pulling force as needed.

Advantages of Electric Cable Tensioning

  • Reduced Manual Labor: Tensioning systems, especially powered ones, minimize the need for manual pulling and feeding of cables.
  • Consistent Tension Control: Tensioning equipment maintains steady tension on the cable throughout the pull.
  • Faster Installation: The automation and power provided by tensioning systems can dramatically speed up cable installation compared to manual methods.
  • Longer Pull Distances: With appropriate tensioning equipment, cables can be successfully installed through longer conduit runs and over more complex paths than would be feasible manually.
  • Improved Safety: By reducing manual handling of cables under tension and providing greater control over the pulling process, tensioning systems create a safer working environment.
  • Better Cable Integrity: Proper tensioning helps avoid stretching or other damage to the cable during installation.