The long-term allowable tension of optical cables is typically much lower than the installation tensile strength and is designed to prevent fiber elongation beyond 0.3% to ensure a service life of 25 years.

Definition and Purpose

The long-term tensile strength of a fiber optic cable is the maximum load the cable can sustain during normal operation after installation without causing permanent damage to the fibers or degrading optical performance . Unlike the installation tensile strength, which accounts for short-term stresses during pulling or handling, the long-term tension is meant for continuous operational conditions.

Typical Values

• For self-supporting optical cables, the long-term allowable tensile load is generally at least 3 kN, though specific values vary by manufacturer and cable design .
• The relative elongation of the fiber under long-term load should not exceed 0.3%, which is about one-third of the fiber elongation during factory proof testing (typically 1%) to maintain a service life of 25 years .
• Installation tensile loads should be kept well below the manufacturer's maximum, often not exceeding 2,700 N (600 lbs) for short-term pulls .

Factors Affecting Long-Term Tension

1. Cable Construction: The number of reinforcing elements (e.g., aramid yarns, glass fiber reinforced plastic) and the type of sheath influence tensile capacity .
2. Fiber Count and Type: Higher fiber counts or specialty fibers may reduce allowable tension.
3. Environmental Conditions: Temperature fluctuations, UV exposure, and moisture can affect long-term mechanical performance .
4. Standards Compliance: IEC 60794-3-20 specifies that the fiber elongation under maximum permissible tensile load must not exceed one-third of the proof test elongation, and attenuation increase should be ≤0.05 dB .

Practical Guidelines

• Always monitor tension during installation and avoid jerking or pushing the cable .
• Use pulling grips and breakaway swivels rated for the cable's maximum tension.
• Maintain minimum bend radius under tension (typically 20× cable diameter during pulling, 10× after installation) to prevent additional stress .
• For aerial or self-supporting cables, consult manufacturer datasheets for maximum allowable tension (MAT) and long-term operating tension (TL) values . By adhering to these guidelines, the optical cable can maintain its mechanical integrity and optical performance over its expected operational life.