What is Electric Cable Tensioning?

Electric cable tensioning refers to applying and managing tension when installing or pulling electrical cables through conduits, ducts, or raceways. This process is crucial for ensuring proper cable installation and preventing damage to the cables during and after the installation process.

Cable pulling tension is the primary parameter evaluated during cable installation. It is essential to understand and control the pulling tension for several reasons:

1. To plan the cable laying process effectively
2. To assess the suitability of the cable design
3. To evaluate the route design
4. To determine appropriate installation methodologies

The highest tension typically occurs at the end of the pull, although this may vary in cases with significant downhill sections or when using Push/Pull devices.

Every cable has a maximum permissible tension, which is determined by its construction and specified by the manufacturer. In the absence of manufacturer data, there are equations to estimate the maximum allowable pulling tension. For example:

• A single-core cable can typically withstand a nominal pulling tension of 22,250N
• A three-core cable can withstand up to 44,500N due to unevenly distributed forces when bending

Sidewall pressure is another critical factor in cable tensioning. It refers to the force exerted on the cable as it bends around corners or pulleys. The Maximum Allowable Sidewall Pressure (MASP) varies depending on the cable type:

• For single conductors, multiple conductors, triplexed power, and multi-conductor control or power cables: 4380 N/m to 7300 N/m of bend radius
• For armoured cables: typically 4380 N/m of bend radius or lower

Calculating tension and sidewall pressure involves complex equations that consider various factors such as:

• Straight or horizontal sections
• Sloped sections (up/down)
• Horizontal bends
• Downward or upward bends
• Large radius bends
• Rollers
• Push/pull machines

Proper cable tensioning is crucial for several reasons:

1. Prevent Cable Damage: Excessive tension can lead to cable stretching, insulation damage, or conductor breakage.
2. Ensure Proper Installation: Correct tension helps maintain the cable’s integrity and performance characteristics.
3. Optimize Cable Life: Proper installation with appropriate tension can extend the service life of the cable.
4. Comply with Regulations: Many electrical codes and standards specify maximum pulling tensions and sidewall pressures (refer to below for specific details).

1. Route Inspection: Thoroughly inspect the cable route before installation to avoid bends and pulling tensions that exceed specified limits.
2. Use of Lubricants: Applying suitable lubricants can significantly reduce pulling tension. It can sometimes decrease total tension by up to 67%.
3. Pulling Direction: Choose the optimal pulling direction. For example, pulling from the end with the most bends or the uphill side of a cable run generally results in lower pulling tensions.
4. Tension Monitoring: Use dynamometers or tension meters to monitor pulling tension during installation.
5. Respect Bending Radii: Adhere to the minimum bending radius specified for the cable to prevent damage and maintain performance.

Installers can ensure safe, efficient, and long-lasting cable installations by understanding and properly managing electric cable tensioning.

Cable tension plays a significant role in determining the lifespan of electrical cables. Proper tensioning is crucial for ensuring optimal performance and longevity, while improper tension can lead to premature failure and reduced cable life.

1. Damage to insulation and conductors: Overly tight cables can experience increased mechanical stress, potentially damaging the insulation or breaking internal wires.
2. Accelerated wear: High tension increases friction, leading to faster degradation of cable components.
3. Reduced flexibility: Excessive tension can make cables more prone to kinking and twisting, further compromising their integrity.

1. Improper functioning: Loose cables may not operate correctly, leading to handling issues in applications like two-wheelers.
2. Increased risk of physical damage: Under-tensioned cables are more likely to experience kinking, twisting, or exposure to sharp objects, potentially damaging the insulation and internal components. This can be particularly hazardous in installations such as overhead power lines.

The electrical codes in Australia provide specific guidelines for cable tensioning, particularly for wire barriers and balustrades. Here are the key points regarding cable tensioning in Australian electrical standards:

1. For wire barriers, the National Construction Code (NCC) specifies required tension values based on wire diameter, spacing, and post distance [1]. For example:
   1. 2.5 mm wire with 80 mm spacing: 145 N tension
   2. 3.0 mm wire with 100 mm spacing: 310 N tension
   3. 4.0 mm wire with 110 mm spacing: 610 N tension
2. The NCC provides tables for continuous wire barrier construction, detailing required tensions for vertical or near-vertical stainless steel wires [1].
3. Tension measurements should be taken using a strain indicator [1].
4. For vertical wires in balustrades, specific tension requirements are provided for wire spacings of 80 mm, 100 mm, and 110 mm.
5. The AS/NZS 3000 Wiring Rules Standard includes requirements for the protection and installation of electrical cables:
   1. Cables in roof spaces that can be stood on must have suitable covering to prevent damage.
   2. Cables within walls and ceilings may require additional mechanical protection if not installed with RCD protection.
6. For underground electrical cable installation, trenches should typically be 750 mm deep, though this may vary based on local regulations.
7. Voltage drop calculations are required to ensure proper cable sizing in DC circuits, with specific maximum voltage drop percentages for different parts of the system.

It’s important to note that these standards are regularly updated, and professionals should always refer to the most current version of the relevant codes and standards when planning and executing electrical installations.

Citations:[1] https://ncc.abcb.gov.au/editions/2019-a1/ncc-2019-volume-two-amendment-1/part-39-safe-movement-and-access/part-392-barriers