Air-insulated fiber optic cables are “charged” or installed using air-assisted techniques such as blowing or jetting, which use compressed air to float the cable through a duct while minimizing friction and stress on the fibers.

Air-Assisted Installation Techniques

1. Blowing: Compressed air is introduced into the duct to create fluid drag along the cable, pushing it forward. No reaction head is used; the cable is propelled by the air flow distributed along its length . 2. Jetting: A reaction head or “parachute” is attached to the cable end. Differential air pressure across the head generates a pulling force, helping the cable move through the duct . Both methods reduce sidewall friction and allow longer cable lengths to be installed compared to traditional pulling.

Equipment and Setup

• Tractor or air-assisted device: Pushes the cable while air is blown into the duct.
• Cable bullet: A protective tip matching the cable diameter is attached to the leading end to prevent damage .
• Duct fill ratio: Maintain a cable-to-duct fill ratio of 50%–80% for optimal performance. Too high a ratio can hinder bending through turns, while too low a ratio may require careful monitoring of air pressure .

Installation Precautions

• Bend radius: Never bend the cable below its minimum radius (typically 15×D unloaded, 20×D under load, where D is cable diameter) to avoid fiber breakage .
• Tensile stress: Avoid excessive pulling or twisting; air-assisted methods help distribute forces along the cable length .
• Slack and splice length: Include extra cable length for splicing and maintenance to prevent tension on fibers .
• Mid-assist devices: For very long runs, additional air-assisted devices can be placed along the duct to extend installation distance .

Summary

To charge an air-insulated fiber optic cable:

1. Attach a cable bullet to the leading end.
2. Use a tractor or air-assisted device to push the cable.
3. Introduce compressed air into the duct to float the cable.
4. Monitor fill ratio, bend radius, and tensile stress throughout the installation.
5. Use mid-assist devices for long runs to maintain safe installation forces. Following these steps ensures the cable is installed efficiently while protecting the fibers from damage and maintaining optimal performance .