How to calculate the number of fused cores in a fiber distribution box

The total number of fused fiber cores in a distribution box is calculated by multiplying the number of fibers by the number of splices or branches, considering any redundancy or direct fusion points.

Step-by-Step Calculation

1. Identify the Fiber Cable Cores Determine the number of cores in each incoming fiber optic cable. Common cable types include 6, 12, 24, 48, 72, 96, 144, or 288 cores .
2. Determine the Number of Splice Trays or Fusion Points Each FDB may contain multiple splice trays. If fibers are directly fused without adapters or pigtails, count the number of fibers entering and leaving the tray. For example, a 24-core FDB with direct fusion at both ends would have 24 cores at the start and 24 at the terminal, totaling 48 cores .
3. Account for Branching or Multiplication If the FDB splits fibers to multiple branches, multiply the number of cores per branch by the number of branches. For instance, a trunk cable with 4 branches and 8 cores per branch results in 32 cores (4 × 8) .
4. Include Redundancy or Spare Cores It is common to add 10–20% spare cores for future expansion or redundancy. For example, if 24 cores are required, adding 20% spare results in 24 × 1.2 = 28.8, rounded to 29 cores .
5. Sum All Contributions Add the cores from all cables, splice trays, and branches to get the total number of fused cores in the FDB. If multiple FDBs are connected in series, include the cores from each box.

Example Calculation

• A building has a 24-core fiber cable entering an FDB.
• The FDB has 2 splice trays, each handling 12 cores.
• Fibers are directly fused at both ends. Calculation:
• Start cores: 24
• Terminal cores: 24
• Total fused cores: 24 + 24 = 48 If branching occurs with 2 branches of 12 cores each, multiply 12 × 2 = 24 cores per branch, then sum with the main line cores.

Practical Considerations

• Direct Fusion vs. Adapter-Based Connections: Direct fusion splicing counts each fused fiber individually, while adapter-based connections may not require additional splicing.
• Device Interfaces: Each device typically requires 2 cores (send and receive), so plan the FDB capacity accordingly .
• Future Expansion: Always consider spare cores to accommodate network growth without replacing cables or FDBs . By following these steps, you can accurately calculate the number of fused fiber cores in a fiber distribution box, ensuring proper network design and scalability.