For lines featuring sharp turns or steep elevation changes, the requirements for clamps boil down to two things: durability and stability. Standard clamps simply don't cut it in these scenarios - they either lack sufficient grip, leading to slippage, or cause stress concentrations that damage the cable. So, how should you choose? The key lies in two core metrics: the magnitude of the load and the deflection angle.
Keep this threshold in mind: 25°.
This is a practical benchmark. At tower locations where the line turns more than 25°, you must carefully consider your clamp selection.
For ADSS and OPGW cables, standard tension clamps are insufficient when the span exceeds 200 meters, the breaking strength is over 160 kN, or special conditions - such as sharp turns (>25°) or steep elevation changes - exist. In these cases, reinforced dual-tension clamp assemblies are mandatory.
Why 25°? Beyond this angle, the lateral load on the optical cable increases significantly. A single tension assembly cannot provide enough grip margin; switching to a dual-tension setup (where two assemblies work in tandem) is necessary to ensure safety.
Sharp Turns: Dual-Tension Clamps Are the Standard
Cables on angle towers are subjected not only to longitudinal tension but also to lateral force components. The sharper the turn, the greater the lateral force. Under these conditions, standard single-tension clamps are prone to issues like uneven stress distribution across the helical rods and overloading on one side.
The advantage of dual-tension clamps lies in their design: two tension assemblies use a triangular link plate to balance and distribute the load. Even with sharp turns, they transmit tension evenly, overcoming the limitations imposed by the line's geometry. Simply put, it is like two people carrying a load together - far more stable than one person shouldering it alone.
Steep Elevation Changes: Grip Strength Is the Critical Metric
The challenge with lines involving steep elevation changes is the significant vertical load. The greater the height difference between the cables on either side of the tower, the larger the suspension angle becomes, requiring the clamp to provide greater grip strength. The preformed double-tension clamp features a three-layer structure (inner, middle, and outer layers) and offers a gripping force range of 120 kN to 400 kN. It is specifically designed for demanding line sections, such as those involving long spans or significant elevation differences. Furthermore, the preformed rods distribute clamping force evenly across the entire contact length; the absence of stress concentration points ensures the optical cable is not crushed or damaged.
A note on suspension clamps: dual-support designs may also be required.
For intermediate towers on lines with significant elevation differences, attention must be paid to the suspension clamp selection: if the suspension angle exceeds 30°, a standard single-support suspension clamp is insufficient. A dual-support suspension clamp - capable of handling angles up to 60° - should be used instead to better accommodate the requirements of steep terrain.
Summary
When selecting clamps for lines with sharp turns or significant elevation differences, keep these key figures in mind:
- Turning angle > 25° → Prioritize double-tension clamps.
- Span > 200 m and breaking strength > 160 kN → Use reinforced double-tension clamps.
- Suspension angle > 30° → Switch to dual-support suspension clamps.
When it comes to selecting clamps, do not settle for the bare minimum. On specialized line sections, it is far better to build in a sufficient safety margin than to gamble on safety factors; the consequences of failure are too severe to risk regret later.