The Drop Cable Demystified: Structure, Types, and Why It’s Perfect for FTTH
When it comes to Fiber-to-the-Home (FTTH) installations, a specialized cable is the unsung hero of the final connection—the Drop Cable . Officially known as a Butterfly or Figure-8 Introduciton Cable , this unique design is engineered for one purpose: to bridge the gap between the external network and your living room reliably and efficiently.
Its common nicknames— Butterfly Cable or Figure-8 Cable —come from its distinctive cross-section, which resembles a butterfly or the number “8”. This isn’t just an aesthetic choice; it’s a clever engineering solution for indoor/outdoor connectivity.
The Core: The “Figure-8” Structure
The standard drop cable features a simple yet effective two-part “figure-8” profile:
- The Top Loop (Signal): This section contains the optical fibers—typically 1 to 4 cores. These fibers are often of the bend-insensitive G.657 type, ensuring minimal signal loss even when routed around tight corners.
- The Bottom Loop (Strength): This part houses two parallel strength members, which can be made of metal (like steel wire) or non-metallic materials (like FRP or aramid yarn) . These members provide the crucial tensile strength needed for installation.
- The Outer Jacket: The entire structure is sheathed in a protective coating, usually made of flexible PVC for general use or Low-Smoke Zero-Halogen (LSZH) material for enhanced safety in enclosed public spaces.
This bifurcated design brilliantly separates the delicate fiber from the mechanical stress-bearing components, making the cable both robust and highly flexible .
Main Types and Their Applications
Not all drop cables are the same. They are tailored for different segments of the “last mile” journey:Type Key Characteristics Typical Application Scenario
Standard Indoor Drop Cable Lightweight, highly flexible, with excellent bend performance (minimum bend radius can be as low as 20mm). Easy to route through conduits and secure along walls.In-home or office wiring: for wall mounting, running in cable ducts, or embedding in internal pipes.
Self-Supporting / Aerial Drop Cable Integrates a metallic messenger wire (or high-strength yarn) into the “figure-8” structure, providing high tensile strength for overhead suspension. Short-distance aerial entry: from a utility pole or cable strand to the customer’s building.
Armored / Duct Drop Cable Features an extra-hardened external layer (armor) for superior mechanical and environmental protection. Often includes water-blocking materials.Outdoor duct installation or for the entry segment where higher rodent/crush resistance is required.
Why This Design Wins for FTTH
The drop cable’s success lies in solving several critical FTTH challenges:
Ease of Installation: Its flat, flexible profile allows installers to easily route it under carpets, along baseboards, through existing conduits, or neatly secure it to walls.
Space Efficiency: The compact, flat design is ideal for crowded spaces like in-wall cavities or multi-dwelling unit (MDU) entry points.
Durability: The dedicated strength members absorb pulling and tension forces during installation and over time, protecting the fragile glass fibers inside.
Versatility: With its range of types—from simple indoor cables to ruggedized aerial and armored versions—a single cable family can handle almost every step of the FTTH drop, ensuring consistency and reliability.