Understanding Fiber Optic Cable Jacket & Fire Rating
Fiber optic cable is constructed from the inside core, cladding, coating, strengthen member to the outside cable jacket. As the bare fiber is easily broken, fiber optic cable jacket is needed to provide protection for the shielding and conductors within the cable. The cable jacket is the first line of moisture, mechanical, flame and chemical defense for a fiber cable.
Fiber cable jacket is made of various types of materials. It’s important to consider the jacket type when selecting the compatibility with the application’s connectors and environment. The table below contains some of the most common fiber cable jacket material types used both indoor and outdoor cables:
|Jacket Material||Benefit of Jacket Material|
|PE (Polyethylene)||PE has excellent properties of moisture and weather resistance, and has the good electrical properties over a wide temperature range. It's also abrasion resistant. So PE is the standard jacket material for outdoor fiber optic cables.|
|PVC (Polyvinyl Chloride )||PVC is usually low-cost, flexible, fairly rugged, and a flame/oil-resistant material, so it can be formulated to function in a variety of environments and applications. In other words, it can be used as the jacket materials for both indoor and outdoor cables.|
|PVDF (Polyvinyl Difluoride)||PVDF is used for plenum cables, because it has better fire-retardant properties than PE and produces little smoke.|
|LSZH (Low Smoke Zero Halogen)||LSZH jacket is free of halogenated materials which can be transformed into toxic and corrosive matte during combustion. LSZH materials are used to make a special cable called LSZH cable, which is a good choice for inner installations. But it is the most expensive jacket material.|
According to EIA/TIA-598, the fiber optic cable color code defines the jacket color codes for different fiber types (SMF or MMF). For single mode fiber, the jacket color is typically yellow. While for multimode cable, the jacket color can be orange (OM1 & OM2 cable), aqua (OM3 cable) and purple (OM4 cable). For outside plant cables, the standard jacket color is black. For more information about fiber optic cable color code, please refer to How to Identify the Fiber Optic Cable Color Code?
Typically, there are eight levels of fire resistance for both non-conductive and conductive cables specified by NEC (National Electrical Code). All indoor fiber optic cables must be marked and installed properly for its intended use: plenums, risers and general purpose areas.
(1) A Plenum area is a building space used for air flow or air distribution system (drop ceiling and raised floors).
(2) A Riser area is a floor opening, shaft or duct that runs vertically through one or more floors.
(3) A general purpose area is all other area that is not plenum or riser and on the same floor.
|NEC Code||Description||Cable Application||Possible Substitute|
|OFNP||Optical Fiber Non-conductive Plenum Cable||Plenum, overhead, fiber only||/|
|OFCP||Optical Fiber Conductive Plenum Cable||Plenum, overhead, hybrid (fiber/wire)||/|
|OFNR||Optical Fiber Nonconductive Rise Cable||Riser, backbone, fiber only||OFNP|
|OFCR||Optical Fiber Conductive Rise Cable||Riser, backbone, hybrid||OFCP|
|OFNG||Optical Fiber Nonconductive General-Purpose||General purpose, horizontal||OFNP, OFNR|
|OFCG||Optical Fiber Conductive General-Purpose||General purpose||/|
|OFN||Optical Fiber Nonconductive||General purpose, horizontal, fiber only||OFNP, OFNR|
|OFC||Optical Fiber Conductive||General purpose, horizontal, hybrid||OFCP, OFCR|
As mentioned above, OFNP and OFNR are two types of fiber optic cables that are used in buildings. OFNP cables have fire-resistance and low smoke production characteristics. This is the highest fire rating fiber cable and no other cable types can be used as substitutes. So these cables are mostly installed in plenum areas. Whereas, the fiber-resistance and low smoke of OFNR cables are not good as OFNP. OFNP plenum cables can be used as substitutes for OFNR cables. Through OFNR vs. OFNP, it is worth noticing that OFNR fiber optic cable cannot be used in plenum areas to replace OFNP cables, however, the latter can be used in the riser areas. Both OFNP and OFNR can be used in general purpose areas.
In the nutshell, plenum rated and riser rated cables are generally deployed within the buildings. Choosing the right type of rated cables can effectively reduce loss when the cables are burning. If your cabling application requires materials that are flame-retardant or compliant with strict safety standards, please always opt for plenum-rated cables. FS.com provides a full line of plenum and riser fiber optic cables, including MTP plenum trunk cables, MTP-LC plenum harness cables, tight-buffered distribution plenum cables, armored tight-buffered plenum cables, and tight-buffered distribution / breakout riser cables.
Related Article: Tight-Buffered Fiber Distribution Cable for Indoor and Outdoor Use