In areas prone to lightning strikes, the lightning protection design of outdoor optical cables requires systematic protective measures to prevent surges from damaging fiber optic equipment. The core of this design lies in blocking the path of lightning current intrusion, reducing induced voltage, and improving the lightning resistance of the cable structure. Since optical fibers themselves are non-conductive, the risk of lightning strikes is mainly concentrated in the metal components of the cable, such as the reinforcing core, armor layer, and metal sheath. During a lightning strike, these components may generate arcs due to potential differences, leading to sheath breakdown, metal layer erosion, or even fiber breakage. Therefore, lightning protection design requires a comprehensive approach encompassing route planning, structural optimization, grounding protection, and surge suppression.
Route selection is a fundamental aspect of lightning protection design. When planning optical cable routes, priority should be given to avoiding areas with frequent lightning activity, such as isolated trees, towers, tall buildings, and mountaintops—all potential lightning attractants. If avoidance is not possible, the horizontal distance to lightning attractants should be reduced by adjusting the cable's route, ensuring that the clearance between the cable and isolated trees, towers, or other lightning attractants meets safety requirements. Furthermore, when crossing high-voltage power lines, a perpendicular crossing method should be used. In difficult cases, the crossing angle should not be less than 45° to reduce the risk of induced voltage superposition. Scientific route planning can reduce the probability of optical cables being exposed to lightning strikes from the source.
Optimizing the optical cable structure is key to improving lightning resistance. In areas prone to lightning strikes, non-metallic optical cables or non-metallic reinforced core optical cables are recommended. These cables completely block the lightning current conduction path by eliminating metal components, making them suitable for scenarios with severe lightning damage and complex maintenance conditions. If optical cables containing metal components must be used, insulation performance must be improved by enhancing the dielectric strength of the outer sheath and increasing the thickness of the armor layer. For example, directly buried optical cables can use a PE sheath combined with steel tape armor, which can prevent moisture intrusion and disperse lightning current energy through the armor layer, reducing the risk of local overheating. In addition, the metal components at the optical cable joints must be electrically disconnected to prevent the accumulation of induced current at the joint and the formation of an arc.
The grounding protection system is the core component of lightning protection design. For optical cables containing metal components, lightning current must be conducted to the ground via lightning protection wires (drainage wires). These lightning protection wires are typically made of galvanized steel stranded wire, laid parallel to the optical cable at a height of 30 cm, and reliably connected to the ground via a grounding device. In areas with frequent thunderstorms or severe lightning damage, the cross-sectional area of the lightning protection wire can be appropriately increased, or a double-wire layout can be used to enhance the discharge capacity. Simultaneously, the suspension wires of overhead optical cables should be electrically connected and grounded at regular intervals to form a continuous overhead ground wire protection network. For terminal equipment, such as ODF racks and optical cable junction boxes, they must be connected to the grounding busbar via copper core power cables of sufficient cross-sectional area to ensure rapid discharge of lightning current.
The application of surge protectors is the last line of defense in lightning protection design. When optical cables enter buildings or equipment rooms, surge protectors (SPDs) must be installed at the entry point. Their nonlinear elements rapidly break down and discharge when overvoltage occurs, limiting the surge voltage to within the equipment's tolerance range. The selection of SPDs (Sustainable Power Distribution Devices) must be matched based on the type of optical cable, transmission rate, and equipment interface characteristics to ensure that parameters such as response time and current carrying capacity meet protection requirements. Furthermore, the grounding wire of the SPD should be as short and straight as possible to reduce the impact of lead inductance on the protection effect.
Special scenario protection requires customized solutions based on environmental characteristics. For example, in optical cable laying across rivers or bridges, the impact of water conductivity on lightning current distribution must be considered, and the protection effect can be improved by increasing the number of lightning protection wires or optimizing the grounding device layout. In optical cable lines in mountainous areas, it is necessary to prevent lateral arcing caused by lightning strikes on hillsides, and the risk can be reduced by adjusting the burial depth of the optical cable or adding lightning rods. For existing optical cable lines, potential hazards can be identified and repaired in a timely manner by regularly inspecting grounding resistance, outer sheath integrity, and the insulation performance of metal components.
Lightning protection design for outdoor optical cables in lightning-prone areas requires a comprehensive approach, including route optimization, structural improvement, grounding enhancement, and surge suppression, to construct a multi-layered protection system. Through scientific planning, precise construction, and regular maintenance, the risk of damage to fiber optic equipment from lightning strikes can be significantly reduced, ensuring the stable operation of communication networks under extreme weather conditions.
