Existing suspension cable expansion for overhead optical cable

Overhead optical cables can be expanded using specialized suspension clamps and U-shaped frames that attach to existing support cables, ensuring mechanical stability and protection against stress.

Suspension System Overview

For retrofitting optical cables onto existing overhead lines, a garland-style suspension is commonly used. The aerial cable is attached to the existing support cable via a U-shaped frame that encloses the carrying cable. A longitudinally divided sliding insert surrounds the support cable, allowing the frame to slide slightly and absorb mechanical and thermal stresses. The optical cable is then secured in a carrying clamp with a U-shaped cross-section, fastened with clamping strips, and bolt-shaped attachments engage corresponding holes in the frame for a secure fit .

Installation Considerations

• Mechanical Protection: The suspension system protects the optical cable from bending, crushing, and excessive tension, which could degrade signal quality .
• Thermal Stress: Sliding inserts and flexible clamps allow the cable to expand and contract with temperature changes without damage .
• Splicing and Storage: Coils of spare cable should be stored near splice closures, with at least 4 inches of central tube exposed inside the closure. Minimum bend radius (MBR) must be respected, typically 10 times the cable's outer diameter .
• Retrofit Advantages: Using this suspension method avoids the need for new masts or poles, allowing optical cables to be added to existing high-voltage lines efficiently .

Standards and Best Practices

• Fittings: Use line-mounted or structure-mounted fittings compatible with ADSS (All-Dielectric Self-Supporting) cables .
• Clearances: Maintain proper vertical and horizontal clearances from power lines and other utilities, following local construction standards .
• Environmental Adaptation: Overhead line teams must adapt to local conditions such as soft soil, high groundwater, or flowing water, ensuring that cable supports are stable and safe .

Practical Example

In Switzerland, optical fiber expansion was successfully implemented on overhead lines without installing new masts. The cable was spliced in a UCN closure at a shaft, then routed a few meters underground to the existing mast, demonstrating the flexibility of suspension-based retrofits .

Summary

Expanding overhead optical cables on existing suspension lines involves using U-shaped frames, sliding inserts, and carrying clamps to secure the cable while protecting it from mechanical and thermal stresses. Proper installation respects bend radius, clearance, and environmental conditions, allowing efficient retrofitting without new infrastructure. This approach is widely used in modern fiber optic network expansions .