Requirements for laying optical cables at high altitudes

High-altitude optical cable installation requires reinforced structures, precise tensioning, environmental load considerations, and adherence to international standards for safety and reliability.

Cable Selection and Environmental Considerations

For high-altitude or extreme environments, cable type and construction are critical. Aerial cables such as ADSS (All-Dielectric Self-Supporting) cables are preferred due to their ability to withstand ice loading up to 50 mm, wind speeds up to 320 km/h, and temperature fluctuations. Cable selection should consider fiber count, tensile strength, and UV resistance.

In remote or mountainous areas, ITU-T L. 163 recommends evaluating cable tension, temperature effects, bend protection, and pilot testing to mitigate risks during installation and operation.

Pole and Support Structures

Pole spacing: Maximum 67 m for reinforced poles (steel lattice structures) in extreme environments. Pole types: Concrete dead-end poles with guy wires at 45° angles provide stability; wooden poles require concrete footings and deeper burial (≈2 m) for high-altitude conditions. Sag control: Maintain sag at 1–2% of span length to prevent excessive tension or ice-induced stress (e.g., 50 m span = 0.

5–1 m sag),. Messenger wire: Galvanized steel with tensile strength ≥41,000 N; tension set to 15–20% of breaking strength to allow thermal expansion.

Installation and Tensioning

Pulling tension: Should not exceed 0. 5% of cable breaking strength to avoid fiber damage. Lashing techniques: Self-lashing for ADSS cables or polyester lashing with UV protection for messenger-supported cables ensures uniform tension and durability.

Clearance requirements: Maintain vertical clearances based on voltage exposure: