To be honest, when many people first encounter the term "double-tension assembly," they assume it simply means "two tension clamps strapped together." In reality, it is far more complex than that. The fundamental difference between double-tension and single-tension assemblies lies in their load-bearing capacity and application scenarios - one handles "heavy-duty" tasks, while the other handles "light-duty" ones.
Single-tension assemblies suffice for standard lines
Single-layer tension clamps are typically used in short-span scenarios where the span length does not exceed 100 meters and the rated tensile strength of the optical cable is no more than 15 kN. For instance, at terminal towers where the optical cable only needs to be anchored and tensioned on one side, a single-tension assembly is perfectly adequate; a single set of clamps secures that end, while the other end is either suspended or spliced, completing the installation.
However, there are situations where a single-tension assembly simply cannot handle the load.
When is a double-tension assembly mandatory?
First, lines with long spans and high tension loads. This is the classic application scenario for double-tension assemblies. Double-tension assemblies are mandatory for ADSS optical cables with spans exceeding 200 meters or OPGW cables with a breaking strength exceeding 160 kN. Furthermore, double-tension assemblies utilize a three-layer structure (inner, middle, and outer preformed rods), offering significantly higher gripping force than single- or double-layer versions, and their tensile strength is not limited by line angle conditions. Simply put, the longer the span and the heavier the conductor, the greater the required gripping force - a single layer of rods simply cannot provide a secure enough grip.
Second, towers situated at sharp angles or locations with significant elevation differences. Where a line changes direction, the optical cable is subjected not only to longitudinal tension but also to lateral force components. At tower locations with large elevation differences, the optical cable also experiences greater vertical loads. In these complex loading scenarios, a single-tension assembly lacks sufficient gripping margin; only a double-tension assembly provides the necessary safety redundancy.
Third, critical crossing sections. Locations directly above railways, expressways, or major power transmission lines - known as "three-crossing" sections - carry catastrophic consequences in the event of a failure. At these locations, tension insulator strings often require retrofitting from single-tension to double-tension configurations. The dual-tension configuration effectively secures the conductor at the exit of the hydraulic tension clamp, preventing line breakage and detachment, thereby providing a double layer of safety for the infrastructure or terrain below.
In short:
A single-tension setup is merely "sufficient," whereas a dual-tension setup guarantees "absolute reliability." For long spans, sharp angles, significant elevation changes, or critical crossings, do not hesitate - opt for the dual-tension configuration. This is not a matter of cost; it is a matter of the fundamental safety baseline.