Laying optical cables for overhead lines

Overhead fiber optic cables are installed using self-supporting or messenger-supported methods, with careful attention to pole spacing, sag, and environmental protection to ensure durability and performance.Cable Types and SupportOverhead optical cables are typically self-supporting (ADSS) or messenger-supported, both relying on steel wire strands for suspension. Self-supporting cables carry their own weight, while messenger-supported cables use a separate steel strand to bear mechanical loads. The suspension wire is usually galvanized steel, with specifications such as 7/2.2mm for standard cables and 7/2.0mm or 1.8mm for light-armored cables . Proper tensioning during installation is critical to prevent excessive sag and mechanical stress.Pole Selection and SpacingPoles are chosen based on terrain and environmental conditions, with heights ranging from 7m to 9m and tip diameters around 150mm. Pole spacing varies: 25–40m in urban areas, 40–50m in suburban/rural areas, and up to 67m in extreme environments with reinforced structures . Poles must be vertical, with corner poles slightly tilted inward or outward to maintain tension and alignment .Cable Laying and Sag ManagementCables are hung using hooks or clamps, typically spaced 50cm apart, with allowable deviation of ±3cm. Expansion bends are reserved every 3 poles, and protective corrugated tubes are used where cables contact poles. At junctions, 8–10 meters of slack is reserved before and after the joint box, and 20 meters at entry and exit points . Sag must account for elongation during erection and under maximum load, ensuring the cable remains properly tensioned without overstressing the fiber.Environmental and Safety ConsiderationsOverhead cables must withstand wind, ice, temperature fluctuations, and natural disasters. Grounding is essential: the cable reinforcement core should connect to the ODF frame lightning protection and then to the outdoor ground wire using a 16mm² conductor . Special sections, such as river or bridge crossings, require additional protective measures, including steel pipes and drip bends to prevent water ingress .Construction StepsThe installation process generally follows these steps:Preparation: Verify design, materials, tools, and team readiness.Routing Survey: Measure the route accurately, avoiding obstacles and planning for reserved lengths.Pole Installation: Erect poles according to design, ensuring proper depth and vertical alignment.Cable Laying: Hang or bundle the cable along the suspension wire, managing sag and expansion bends.Splicing and Termination: Leave sufficient slack for splicing and connect to ODF frames.Inspection and Acceptance: Check tension, alignment, grounding, and optical performance before commissioning . By following these guidelines, overhead fiber optic cables can be installed efficiently, safely, and with long-term reliability, minimizing failures and ensuring optimal network performance.