What does laying optical cables in ducts mean

Optical cables in ducts are primarily installed using two methods: pulling and blowing, each suited to specific distances, duct conditions, and cable types.

Pulling Method

The pulling method involves manually or mechanically pulling the cable through a pre-installed duct, often using a rope or pull line already placed inside the duct . This method is commonly used in short-distance installations, typically up to 200–300 meters, such as in access networks. Key considerations include:

• Cable handling: Avoid excessive pulling tension, bending, or crushing forces to prevent damage to the optical fibers .
• Bend radius: Maintain the minimum bend radius during installation, often specified as 15 times the cable diameter for working radius .
• Coiling: Use figure-eight coiling for cable storage at manholes to prevent kinking or twisting, with loops generally 5–8 feet in diameter .
• Limitations: Pulling is less efficient for long ducts with multiple bends, as friction and stress on the cable increase.

Blowing (Air Jetting) Method

The blowing method, also called air jetting, uses compressed air combined with a mechanical pushing force to install the cable inside the duct . This method is preferred for longer ducts or routes with multiple bends and undulations. Key features include:

• Mechanism: A few hundred meters of cable are initially pushed into the duct using a tractor or rollers, then high-speed air is injected to float the cable, reducing friction against the duct walls .
• Cable types: Suitable for standard optical cables (uni-tube, multi-tube, armored/unarmored) and microduct cables .
• Advantages: Reduces installation time, manpower, and mechanical stress on the cable; allows continuous installation over distances exceeding 1,000 meters depending on duct conditions .
• Cable stiffness: Stiffer cables perform better in straight ducts, while more flexible cables navigate complex routes more effectively .
• Pre-installation testing: Conduct a crash test to determine the maximum pushing force to avoid cable buckling or sheath damage .

General Best Practices

• Pre-installation preparation: Identify manholes, loops, and duct conditions; clean and drain ducts if necessary .
• Cable protection: Handle cables in their drum, box, or coil to prevent damage before and during installation .
• Supervision and safety: Ensure trained personnel supervise the laying process, follow cable datasheets for maximum tensile load, and maintain safety measures around manholes .
• Environmental considerations: Follow local regulations and environmental measures during installation .

Summary

• Pulling method: Best for short distances, simple duct routes, and limited manpower; requires careful tension and bend management.
• Blowing method: Ideal for long ducts, complex routes, and microduct applications; reduces friction and stress, allowing faster and more efficient installation.
• Key factors: Cable type, duct length, bends, and installation equipment determine the optimal method. Proper preparation, handling, and adherence to specifications are critical for reliable optical network performance.