Regulations on Reserved Length of Communication Optical Cables

Reserved length of optical cables is required to ensure proper installation, maintenance, and future modifications, with specific guidelines provided by national and international standards.

General Principles

Reserved cable length, often called service loop or slack, is the extra length of optical fiber left during installation to accommodate future moves, terminations, or repairs. This practice prevents strain on the fiber, allows for re-termination, and ensures compliance with performance standards. The amount of reserved length depends on the installation environment, cable type, and applicable standards.

Chinese Standards (GB/T 50312-2016)In China, GB/T 50312-2016 specifies that during the construction of generic cabling systems, extra cable length must be reserved at connection points, distribution frames, and termination boxes to facilitate maintenance and testing. The standard emphasizes that: Slack should be sufficient for on-site testing and future re-routing. Reserved lengths are typically installed in loops or coils within telecommunications rooms or equipment rooms.

The installation must comply with mechanical and bending radius requirements to avoid fiber damage. International Recommendations (ITU-T L. 104)The ITU-T L.

104 Recommendation provides guidance for small count optical fiber cables, particularly for indoor applications. Key points include: Slack loops should be provided at both ends of the cable to allow for termination, splicing, and future reconfiguration. The exact length of reserved fiber should be agreed between the user and supplier based on the installation environment.

Compliance ensures that the cable maintains signal integrity and performance under operational conditions.

European Union Regulations

In the EU, communication cables, including optical fibers, must comply with the Construction Products Regulation (CPR) and relevant harmonized standards such as EN 50575.

While CP

R primarily addresses reaction to fire and safety, installation practices, including reserved lengths, are guided by national wiring codes and best practices.

C

E marking indicates that the cable meets essential performance requirements, but the specific slack length is determined by installation standards and manufacturer recommendations.

Practical Guidelines

Telecommunications rooms: Reserve 1–2 meters of slack per termination point. Wall or floor conduits: Leave enough slack to allow for future moves or repairs without exceeding the minimum bend radius. Patch panels and distribution frames: Coiled loops should be neat and secured to prevent microbending or macrobending losses.

Outdoor installations: Slack should account for thermal expansion, contraction, and potential rerouting.

Summary

Reserved length of optical cables is a mandatory practice in structured cabling to ensure operational reliability, maintenance flexibility, and compliance with standards. While GB/T 50312-2016 and ITU-T L. 104 provide explicit guidance on slack loops and termination points, EU regulations focus on safety and performance, leaving slack length to be determined by installation best practices and manufacturer guidance.

Properly implemented reserved lengths prevent signal degradation and facilitate future network modifications.