Guide to Safe Overhead Line Stringing for Efficient Construction
October 26, 2025
Overhead power lines serve as critical infrastructure in modern electrical systems, transmitting electricity from generation plants to substations and end users. With rapid socioeconomic development, reliability and efficiency requirements for power supply have intensified. The construction and maintenance of overhead lines—particularly conductor stringing—directly impact overall system performance.
Conductor stringing represents one of the most technically demanding phases in overhead line construction. Stringing blocks (also called conductor running blocks) emerge as indispensable equipment during this process, functioning both as support mechanisms and directional guides that ensure operational safety and efficiency.
Stringing blocks are specialized auxiliary devices used in overhead transmission line projects. Comprising grooved sheaves (wheel tracks) mounted within a frame, these blocks support and guide conductors, optical ground wires (OPGW), or shield wires during installation. Typically suspended from crossarms via hooks, clamps, or swivel rings, the blocks feature linings made of nylon, aluminum alloy, or polyurethane to minimize friction and prevent conductor surface damage.
- Load bearing: Supports conductor weight to prevent ground contact
- Directional control: Maintains proper alignment during installation
- Friction reduction: Rolling sheaves decrease pulling tension
- Surface protection: Lining materials prevent abrasion
- Safety enhancement: Stabilizes the stringing process
Early designs featured simple single-sheave steel units for small conductors. As transmission voltages and capacities increased, multi-sheave configurations (dual, triple, and quadruple) evolved to accommodate bundled conductors. Material advancements introduced nylon/pu-rethane linings and aluminum alloy sheaves, while specialized variants emerged for OPGW, river crossings, and angle towers.
Basic units for single conductors or pilot lines. Advantages include lightweight construction and low cost.
Designed for twin-bundle configurations, improving installation efficiency through simultaneous conductor handling.
Essential for three/four-bundle conductors in high-capacity transmission, reducing line reactance.
Compact units for initial pull rope installation prior to conductor stringing.
- OPGW blocks: Incorporate protective linings for delicate fiber optics
- River crossing blocks: Feature oversized sheaves to minimize sag
- Angle blocks: Heavy-duty designs with enhanced swivel mechanisms
Sheave groove diameter must exceed 1.5 times conductor diameter, with lining materials matched to conductor type (nylon/polyurethane for ACSR/AAC, aluminum alloy for heavy conductors).
Sheave quantity must correspond to conductor count per phase (single, twin, triple, or quad).
Rated Working Load (RWL) should surpass maximum pulling tension multiplied by safety factor (2.5-3.0).
Recommended 30-40 times conductor diameter to reduce bending stress.
Fixed frames suit tangent towers; swivel-type required for angle structures.
For ACSR 400mm² (26mm diameter) with 20kN tension: 800mm quad-sheave block with RWL >50kN and nylon lining.
Single ACSR 240mm² (20mm) crossing: 800mm single sheave with suspension frame and polyurethane lining.
15mm OPGW in mountainous terrain: 500mm sheave with fiber-protective lining and 25kN capacity.
- Regular cleaning to remove contaminants
- Bearing lubrication with manufacturer-approved grease
- Structural inspections for wear/deformation
- Timely replacement of worn components
- Proper dry storage when not in use
Future developments focus on lightweight composites, IoT-enabled condition monitoring, modular designs, multifunctional integration, and automated control systems.
Proper stringing block selection requires comprehensive evaluation of technical parameters and environmental conditions. As transmission networks expand globally, optimized stringing solutions will remain pivotal for efficient, safe power infrastructure development.