Fiber Optic Distribution Cable: The Complete Guide

In today’s telecommunications world, fiber optics have become the backbone of high-speed communication networks. Within the vast array of fiber optic cables available, fiber optic distribution cables play a crucial role in connecting multiple points within a building or campus. This type of cable is specifically designed for applications requiring a single termination with multiple fibers, offering an efficient and versatile solution for diverse connectivity needs.

What Exactly Is Fiber Optic Distribution Cable?

Fiber optic distribution cable is distinguished by its tight -buffered design. This construction feature allows the cable to be installed both as a backbone within buildings and in inter-building applications on campuses, eliminating the need for costly and complex transitions between different cable types. Essentially, a distribution cable is optimized to carry the fiber optic signal from a central distribution point to multiple locations within a relatively concentrated area.

The versatility of distribution cable is amplified by the variety of fiber types available. It can be found in four main categories:

• Singlemode 9/125 (SM) : Ideal for long distance, high speed transmissions where accuracy and minimal signal dispersion are crucial.
• Multimode OM1 62.5/125 : A more traditional choice for short distances and local networks, although less common in modern high-speed installations.
• OM3 50/125 Multimode : Optimized for 10 Gigabit Ethernet networks and higher over moderate distances, offering a good balance between performance and cost.
• OM4 50/125 Multimode : The highest performance multimode option, designed for 10 Gigabit, 40 Gigabit, and 100 Gigabit Ethernet speeds over longer distances than OM3.

In addition to the different fiber types, distribution cables are offered in Plenum and Riser ratings, as well as options for indoor, outdoor, or a combination of both (indoor/outdoor) installation. The number of fiber strands within a distribution cable typically ranges from 2 to 72, although in some cases it can reach up to 144, adapting to the specific needs of each project.

Common Applications of Fiber Optic Distribution Cable

The nature of the distribution cable, with its robust design and multi-fiber capability, makes it ideal for a wide range of applications, including:

• Building Backbone : Acts as the backbone of the network within a building, connecting the main equipment room to the different floors or areas.
• Inter-building Campus Networks : Facilitates the connection between different buildings within the same campus, such as universities, business parks or industrial complexes.
• Data Centers : Used to interconnect equipment within a data center, especially when a large number of fiber connections are required in a limited space.
• Local Area Networks (LANs) : Ideal for high-density LANs where multiple fiber optic connection points are required.
• Security and Surveillance Systems : In video surveillance applications or complex security systems that require the transmission of large amounts of data.

Distribution Cable Types by Fire Rating: Plenum and Riser

A key consideration when selecting a fiber optic distribution cable is its fire resistance rating, especially if the installation is indoors. The two main classifications are Plenum and Riser , defined by the National Electric Code (NEC) in the United States and adopted in similar regulations internationally.

Plenum Distribution Cable (OFNP)

Plenum cables, designated with the OFNP (Optical Fiber Nonconductive Plenum) classification , are designed to be installed in plenum spaces . According to the NEC, a plenum is defined as a “compartment or plenum to which one or more air ducts are connected and which is part of the air distribution system.” These spaces typically include spaces above acoustical ceilings and heating, ventilation, and air conditioning (HVAC) ducts.

The primary concern in plenum spaces is fire safety. Materials burning in a plenum can contaminate the air distributed throughout the building, endangering the health and safety of occupants. For this reason, regulations are very strict regarding the materials allowed in these spaces. OFNP Plenum cables are constructed of special materials that have flame-retardant and low-smoke properties . In the event of a fire, these cables do not spread the flame easily and emit minimal toxic smoke, contributing to building safety.

Types of Plenum Distribution Cable

• OFNP Indoor Plenum Cable : Designed exclusively for indoor installations in plenum spaces. Available in single-mode and multimode fiber (OM1, OM3, OM4).
• OFNP Indoor/Outdoor Plenum Cable : Versatile for installations requiring both indoor and outdoor runs in plenum environments, such as university campuses or offices. For outdoor use, they incorporate a UV-stabilized outer jacket for protection against sun exposure and resistance to degradation due to underground environmental conditions.

Riser Distribution Cable (OFNR)

Riser cables, classified as OFNR (Optical Fiber Nonconductive Riser) , are designed for vertical or “riser” installations inside buildings. These vertical sections are typically the spaces between floors where communication and power cables run.

The regulations for riser cables, although less stringent than those for plenum cables, also aim to prevent the spread of fire between floors. OFNR riser cables are designed to resist the vertical spread of flame in a fire, although they do not have the same flame-retardant and low-smoke properties as plenum cables. However, they must comply with ANSI /UL 1666-1997 , “Standard Test for Flame Propagation Height of Electrical and Optical-Fiber Cable Installed Vertically in Shafts.”

Types of Distribution Riser Cable

• OFNR Indoor Riser Cable : Ideal for vertical installations inside buildings. Available in single-mode and multimode fiber (OM1, OM3, OM4), with options up to 72 strands.
• OFNR Indoor/Outdoor Riser Cable : Offers the flexibility to be used both indoors and outdoors. It can be up to 144 strands and, for more demanding applications, can be armored for added strength in direct underground or overhead installations.

Comparison Table: Plenum Cable vs. Riser Cable

Frequently Asked Questions (FAQs)

1. What is the main difference between Plenum and Riser distribution cable?The main difference lies in their fire resistance rating and application. Plenum cables are for air handling spaces and require materials with low smoke emission and high flame resistance. Riser cables are for vertical runs and have less stringent requirements, focused on preventing the vertical spread of fire.
2. Can I use Riser Cable in a Plenum space?No, it is neither recommended nor permitted by regulations. Using riser cable in a plenum space poses a safety risk in the event of a fire, as it does not meet the requirements for low smoke and flame spread.
3. Can I use Plenum cable in a Riser space?Yes, it is technically possible and safe to use plenum cable in a riser space. Plenum cable meets more stringent requirements, so it will also meet the less demanding requirements of a riser space. However, it may be an unnecessarily more expensive option.
4. Which type of fiber (single-mode or multimode) is best for distribution cable?It depends on the application and distance. Single-mode fiber is ideal for long distances and high speeds, while multimode fiber (OM3 or OM4) is suitable for shorter distances and high-speed local networks. For very short distances within a building, OM3 or OM4 may be sufficient and more cost-effective. For campus or building interconnections, single-mode fiber is often the best choice.
5. What does the “tight buffered” design mean in distribution cable?“Tight buffered” refers to the way the optical fibers are protected within the cable. In a tight buffer design, each fiber is individually coated with a thick layer of protective material. This provides greater robustness and makes the cable easier to handle and connect, especially in indoor installations.

Conclusion

Choosing the right fiber optic distribution cable is crucial to ensuring the performance, security, and longevity of your network. Understanding the differences between fiber types, Plenum and Riser ratings, and specific applications will allow you to make informed decisions and optimize your fiber optic infrastructure. By carefully considering your project needs and applicable regulations, you can select the distribution cable that best meets your requirements and ensures reliable and secure connectivity.