Commonly Used Optical Cables in Ducts

Optical cables in ducts are installed using pulling or blowing methods, with careful attention to cable type, duct material, and mechanical stress to ensure long-term reliability.

Duct Fiber Optic Cables

Duct fiber optic cables are designed to be installed inside pre-existing conduits rather than directly buried or aerially mounted, providing protection, flexibility, and scalability for urban and long-haul networks. Common duct materials include: Plastic Ducts (PVC/HDPE): Cost-effective, corrosion-resistant, and flexible; HDPE adds impact resistance and is ideal for areas with soil movement. Steel Ducts: Used in industrial or high-security zones for maximum physical protection.

Concrete/

Asbestos Cement Ducts: Durable but heavy and rigid, often found in legacy networks.

Fiberglass-

Reinforced Plastic (FRP) Ducts: Lightweight, non-conductive, and chemical-resistant, suitable for coastal or high-lightning-risk areas.

Installation Methods

Pulling Method

The traditional method involves physically drawing the cable through the duct. While simple, it can generate high friction, especially in ducts with bends or debris, potentially stressing the cable and affecting optical performance. Maximum pulling tension and minimum bend radius must be observed according to the cable datasheet to prevent damage.

Blowing (Jetting) MethodBlowing uses compressed air combined with a mechanical pushing force to move the cable through the duct. This method reduces friction, allows longer continuous cable runs, and minimizes mechanical stress on the cable. Key points include: Initial pushing of a few hundred meters of cable into the duct.

High-speed airflow keeps the cable in a floating condition, reducing contact with the duct wall. Cable stiffness affects performance: stiffer cables blow faster through straight sections, while flexible cables navigate multiple bends more effectively. Pre-installation crash tests determine the maximum pushing force to avoid sheath damage or buckling.

Best Practices

Always consult the cable specification sheet for maximum tensile load and minimum bend radius.

Use HDP

E or other high-quality duct materials to reduce friction and protect the cable. Consider microcables and microducts for long-distance installations, as smaller diameters reduce weight and tensile stress, allowing easier installation without a pulling rope. Maintain proper safety measures in manholes and work areas to prevent accidents and cable damage.

Advantages of Duct Installation

Protection: Shields cables from environmental hazards and mechanical damage. Maintenance and Upgrades: Allows easy replacement or expansion without excavation. Efficiency: Blowing methods reduce manpower and installation time, especially in long or complex duct routes.

By carefully selecting duct materials, cable types, and installation methods, optical cables can be reliably deployed in ducts, ensuring both mechanical and optical performance over the cable's lifetime.