Fiber Optic Cable Outer Sheath Material and Fire Rating

Data center cables are intricate, converging, and dispersing into every part of the data center. Therefore, the importance of fireproof fiber optic cables to data centers is self-evident. It is possible to cause the fire to spread when the fire occurs due to improper selection, which will burn down the entire data center and cause irreparable losses.

I. Why is the outer sheath of fiber optic cable important? What are their materials?

Fiber optic cable is generally composed of fiber optic core, cladding, coating, reinforcing element and outer sheath. As the protective layer of cable, outer sheath has the functions of fire prevention and moisture proof, and has an important influence on the performance of outer sheath in case of fire in data center.

Fiber optic cable outer sheath can be divided into different material types, each type of material of outer sheath has its inherent characteristics, different (fireproof performance, suitable for use, common outer sheath material divided into PE, PVC, PVDF, LSZH, Plenum, Riser. Respectively in the following table shows the performance of the above material and application environment.

It can be seen that most of the outer sheath materials have good flame retardant performance. Is the outer sheath material the only standard to measure the fireproof performance of fiber optic cables? No, the flame retardant material used in the cables must also pass the inspection and reach a certain level of fire resistance. For example, the PVC sheath cable, to achieve the best fire performance, but also need to consider the cable as a whole to achieve what kind of fire rating.

II. What are the fire ratings for fiber optic cables?

In the NEC, the fire rating of optical fiber cables is usually divided into OFNP/OFCP, OFNR/OFCR, OFNG/OFCG and OFN/OFC.

OFNP /OFCP, flame retardant (supercharged), highest grade in NEC standard. Suppose that the flame is forced by a fan to blow to a bundle of flame retardant (supercharged) optical fiber cables, the flame on the optical fiber cable will be extinguished by itself within 5 meters, and no toxic and   corrosive gas will be generated.

OFNR /OFCR, a vertical grade (arterial grade) in the NEC standard, is the second highest. Similarly, a fan is used to force the flame to be blown into bundles of OFNR /OFCR cables. Although the flame will extinguish itself if it spreads within 5m, there is no smoke or toxicity specification.

OFNG /OFCG and OFN/OFC are of commercial grade and general grade respectively, and the fiber optic cables under these two standards are often used in environments with low requirements for fire prevention and flame retardancy.

III. What fire rating can be achieved for fiber optic cables of different sheath materials?

Although the fire rating of the fiber optic cable is not necessarily related to the material of the outer sheath, in general, if Plenum is used as an outer sheath fiber optic cable to do NEC fire rating test, its fire rating theory can reach OFNP. If PVC or Riser as the outer sheath of optical fiber cable do NEC flame retardant grade test, their level of fire prevention can theoretically reach OFNR. If LSZH is used as the fiber optic cable with outer sheath for NEC flame retardant grade test, its fire rating theory can theoretically reach OFN.

That is, using Plenum, PVC/Riser, LSZH material as the outer sheath of optical fiber cable, can satisfy the requirement of data center for fire retardant cable. UNIQUE TEL can provide the whole series of Plenum, PVC/Riser with LSZH material of fiber optic cable.

IV. How to choose fiber optic cables with different sheath materials?

In order to prevent and reduce the probability of fire in data center cabling scenario, you must know which level your data center belongs to, what purpose it is used for, what special requirements it has, etc., so as to select fiber optic cables with different sheath materials according to the standards.

V. Select fiber optic cables of different materials according to the layout area

In general, Plenum fiber optic cables are suitable for use in horizontal wiring areas and in aerated environments (delivery pipes, air handling systems), where air is circulated and fire is not easily controlled. Therefore, OFNP flame retardant fiber optic cables are the best choice. Riser/PVC material fiber optic cable is suitable for use in the region of the vertical main wiring, provide entrance equipment or computer room and the connections between different floor communications cabinet, the possibility of a large area of fire is small, flame retardant level OFNR can; LSZH fiber optic cables are often used in common areas, even in case of fire, to avoid injury to rescue workers because the smoke released by them is non-toxic.

VI. Select fiber optic cables of different materials according to the grade and size of the data center

Since the impact of a fire in a data center can vary from one size to another, the NEC standard recommends fiber optic cables for different environments. In general, Plenum fiber optic cables are suitable for use in large/very large data centers, fault-tolerant/parallel maintenance data centers; Riser/PVC material of fiber optic cable used medium data center, redundant data center, LSZH material of fiber optic cable used to small data center, general enterprise computer room.

VII. Conclusion

The outer sheath of optical fiber cable is only a part of fire prevention and control. In order to better reduce the risk and loss of fire, the planning of preliminary wiring scene and the layout of later fire warning are essential. Only comprehensive consideration can ensure the safety of data center.