Optical fiber cables can be installed in ducts using pulling or blowing methods, following strict guidelines for tension, bend radius, innerduct fill, and safety to ensure cable integrity and performance.

Cable Handling and Specifications

• Maximum Pulling Tension: Each cable type has a specified maximum pulling tension, typically around 600 lbF (2,700 N) for stranded loose tube and ribbon cables, but always refer to the cable datasheet for exact limits .
• Minimum Bend Radius: During installation, the cable must not be bent below its minimum bend radius. A common guideline is 15 times the cable diameter for working bend radius, and twice that for pull wheels or rollers .
• Crush and Strain Limits: Avoid exceeding the cable's maximum crush load and fiber strain limits (usually <0.5%) to prevent permanent damage .
• Innerduct Fill Ratio: The innerduct should have sufficient diameter to reduce pulling tension. Fill ratios are calculated by comparing the cable cross-sectional area to the innerduct area; lower fill ratios reduce stress during installation .

Installation Methods

1. Pulling Method: Suitable for short distances (typically <200–300 meters). The cable is pulled manually or with a puller machine using a pre-installed rope. Coiling in manholes may be required at intervals .
2. Blowing (Air Jetting) Method: Preferred for longer ducts with multiple bends. Compressed air is injected to float the cable inside the duct, often combined with mechanical pushing near the inlet. This reduces friction and allows longer continuous runs .

Equipment and Preparation

• Cable Reels: Must be inspected for damage and oriented to allow smooth payoff from the top of the reel .
• Pulling Grips and Swivels: Used to prevent twisting and kinking during installation .
• Innerduct: Can be smooth, ribbed, or corrugated; proper installation and slack in manholes are critical to maintain bend radius and reduce tension .
• Lubricants: Cable pulling lubricants may be used to reduce friction in ducts .
• Safety Measures: Barricades, flagmen, ventilation in manholes, and inspection for harmful gases are required before installation .

Best Practices

• Avoid pulling new cables over existing ones to prevent entanglement .
• Use figure-eight coiling for cable storage to prevent kinking, especially for lengths over 30 meters .
• Perform a crash test for blowing installations to determine the maximum safe pushing force without damaging the cable .
• Plan for extra slack in ducts and manholes to accommodate innerduct stretch and cable relaxation .
• Follow all local safety regulations and FOA standards for fiber optic installations .

By adhering to these requirements and best practices, optical fiber cables can be installed safely and efficiently in ducts, ensuring long-term reliability and performance.