Why is the U-Shaped Installation Method for OPGW Cable Slack Storage Becoming More Common?
The U-shaped installation method for OPGW Cable Slack Storage is a newly developed installation practice. It helps reduce installation difficulty, significantly improves the pass rate of Cable Slack Storage installation, enhances the overall appearance of the splice box tower configuration, and effectively avoids interference with tower-climbing work during routine line maintenance. In addition, it greatly reduces torsional stress at the end of the fiber splice box, thereby preventing water or air leakage caused by long-term twisting force.
Why Can U-Shaped Cable Slack Storage Installation Improve the Pass Rate?
Common issues with traditional Cable Slack Storage racks include: cable winding, crossing, insufficient bending radius, friction against tower steel, torsion applied to the splice box, and interference with maintenance tower climbing.
In contrast, the advantages of U-shaped Cable Slack Storage installation are mainly reflected in the following aspects:
Installation difficulty is greatly reduced due to a clear and straightforward routing path.
Clamp placement follows a regular and standardized pattern.
Cable crossing and stress superposition are avoided, preventing overlapping tension buildup.
The number of binding points is not less than 4, improving stability and control.
The cable is routed along the inner side of the main tower members, reducing interference with step bolts and improving safety for maintenance personnel.
With U-shaped downlead routing + fixation at key points, torsion on the splice box can be significantly reduced, lowering the risk of leakage.
Installation Requirements
The OPGW shall be routed along the main tower members and follow the line direction to form a U-shaped downlead (cables from different circuits/lines must not cross each other).
Install downlead clamps at intervals of 1.5 to 2 meters along the downlead route.
The downlead cable shall be smooth and neat, with no winding or sharp bending permitted.
After the OPGW is routed down to ground level, reserve a slack length of 10 to 15 meters.
The splice box shall be mounted vertically on the tower. A downlead clamp or parallel groove clamp shall be installed 50 cm below the splice box to fix two OPGW cables, so as to prevent torsion.
Common Problem Points
Non-uniform clamp spacing
Insufficient bending radius, especially at tower-top turning points where hard bends are most likely to occur
Friction between the cable and tower steel: wind-induced movement can damage the outer layer within half a year
Splice box torsion: long-term stress on sealing surfaces increases the risk of water/air leakage
Insufficient reserved slack length: makes future re-splicing impossible
Crossing or winding of slack loops: maintenance becomes messier over time and may introduce micro-bending loss
FAQ
Is the U-shaped installation suitable for all tower types?
It is suitable for most transmission towers, but it should be evaluated together with:
Tower structure (angle-steel tower / tubular steel tower / compact tower)
OPGW incoming and outgoing directions
Whether there is sufficient installation space for the splice box location
Why is the clamp spacing required to be 1.5–2 m? Can it be larger?
A larger spacing is not recommended. Excessive spacing may cause:
Larger cable swing amplitude, increasing the risk of abrasion against tower steel and hardware fittings
Uneven sag and localized stress concentration, resulting in poor appearance and potential reliability issues
How to control the bending radius for U-shaped downlead routing?
Core principle: it is better to make the route "more rounded" than to create any hard bends.
Acceptance criteria:
All turning points must form a smooth curve
Dead bends or sharp angles are not allowed
A larger bending radius is always safer, especially near the tower-top downlead point where sufficient space must be reserved
Why install a clamp/parallel groove clamp 50 cm below the splice box?
This action forms an anti-torsion structure. Adding a fixation point below the splice box works like a "rotation stopper," significantly reducing:
Torsional force transmitted to the splice box end due to wind swing
Long-term pulling stress on the splice box caused by the cable's self-weight