Railway optical fiber cables typically use loose tubes with diameters up to 1.5 mm, containing 6–12 fibers, installed in corrugated ducts made of HDPE with diameters ranging from 25 mm to over 50 mm depending on structural requirements.

Optical Fiber Cable Specifications

For railway communication, optical fiber cables are designed to withstand mechanical stress, environmental conditions, and long-distance transmission requirements. A common example is the K209B LSZH armoured cable, which features:

• Loose tube diameter: maximum 1.5 mm
• Number of fibers per tube: 6 or 12 singlemode (G.652) or multimode fibers
• Central strength member: steel wire strand or glass yarn reinforcement
• Armour: corrugated steel tape for mechanical protection
• Outer jacket: UV-stabilized LSZH (low smoke zero halogen) for fire safety and environmental resistance These cables are suitable for installation in ducts, tunnels, or on hooks, and are designed to be pulled through corrugated conduits without damage .

Corrugated Duct Dimensions

Corrugated ducts provide mechanical protection and flexibility for optical fiber cables. Typical characteristics include:

• Material: high-density polyethylene (HDPE), often UV-stabilized
• Standard diameters: 25 mm, 32 mm, 40 mm, 50 mm, and larger depending on load and soil pressure
• Construction: single-layer for indoor or shallow burial, double-layer or reinforced with steel wire for underground or high-pressure environments
• Length: supplied in coils of 255–300 meters, flexible for bends and turns The duct diameter is chosen to allow easy installation of the cable while maintaining sufficient space for thermal expansion, bending, and future cable upgrades.

Standards and Recommendations

• ITU-T L.100 (2024) provides guidelines for optical fiber cables in ducts and tunnels, including fiber dimensions, mechanical characteristics, and test methods .
• EN 61386 regulates conduit dimensions and structural strength for telecom applications, ensuring compatibility with standard optical fiber cables .

Summary

For railway communication:

• Fiber tube diameter: up to 1.5 mm
• Fibers per tube: 6–12
• Duct diameter: typically 25–50 mm or larger depending on installation conditions
• Duct material: HDPE, optionally reinforced for high mechanical stress
• Cable protection: corrugated steel tape armour and LSZH jacket This combination ensures mechanical protection, flexibility, and long-term reliability for optical fiber networks in railway environments.