There are several parts that make up a fiber optic cable; starting with the core, to the cladding, followed by the coating, the strength member and lastly the outer jacket. The outer jacket is the cover that gives protection and shielding, especially to the optical fibers. Whether it is meant to be indoor/outdoor, UV rated or armored, the jacket is what keeps the fiber protected and useful. Above all of these, the outer jacket is the first layer of protection to the fiber so it can withstand different conditions such as fire, moisture, chemicals, and stress during installations and maneuvering.
The National Electrical Code (NEC) has a classification system for optical fiber cables. The system specifies the requirements regarding how the fiber cables will endure under fire conditions. These requirements concentrate on how these cables can add a dangerous amount of fuel and smoke and transmit fire from one place to another.
Plenum
OFNP - Optical Fiber Non-conductive Plenum - refers to the specific fire code rating of cable that is flame resistant and emits the least toxic fumes or smoke when burned. Plenum rated cables have a higher fire rating and are for both commercial and residential use. They are considered the safest rated cable among jacket types. These cables are primarily used in ducts or pathways for heated and cooled return airflows. These spaces are usually above a ceiling or below a floor that serves as heated or cooled inhabited areas.
Plenum cables are purposely built with a jacket that gives off low amounts of smoke and that is flame retardant. Being able to deter the spread of flames and toxic fumes are the main uses for this jacket rating. The word plenum refers to the space in which air is circulated by a HVAC system. Drop ceilings and raised floors are perfect for the application. Plenum cables still use PVC (Polyvinyl Chloride) in the construction of the plenum jacket but special additives are put into the jacket material in order to make it more flame retardant. The NEC defines plenum cables by the airspace they are put into. Plenum rated cables are often used in building construction, typically they are used as communication cables for the building’s computer and telephone networks. Use of plenum areas for cable does pose some hazard in the event of a fire. This is because there are fewer barriers to contain smoke and flames.
Riser
OFNR - Optical Fiber Non-conductive Riser - is constructed of PVC and will emit toxic fumes when burned. Riser cables are to be run only in non-plenum areas. Plenum can usually replace riser but riser cannot replace plenum. Riser rated cables are typically used in the riser areas of buildings and in vertical telecommunications infrastructures. They connect from one floor to another and are used within shafts in accordance with section 800.53(B) of the NEC (National Electrical Code). They typically have load bearing strength members since they need to be upright without placing added stress on the fiber.
OFNR cable is resistant to oxidation and degradation but still gives off heavy black smoke and toxic gases when it is burned. Yet it is perfectly fine to use as a patch cord or for single in-wall runs. If you want to use it in a building, the building must feature a contained ventilation system and have good fire exits. Location is extremely important for these types of cables.
LSZH – Low Smoke Zero Halogen
These types of cables are made with halogen free materials and although they still emit smoke it is a much safer alternative. This type of cable jacket has superior safety characteristics. This rating offers low smoke, low toxicity and low corrosion standards. Tunnels, enclosed rooms, aircraft, and other minimum-ventilation areas are prime spots for the use of LSZH cables because areas like these are more difficult to escape from quickly. There are many different types of LSZH jacketed fiber optic cables provided for many different uses. The primary use for these types of cables is to satisfy the need for safety and environmental protection. Hospitals, schools and airports are good examples of where these cables should be installed. Due to the amount of people and the serious need for the protection of those people and equipment from toxic matter and gases should a fire ever occur. These cables are especially popular outside the United States, specifically for plenum spaces. Although it may seem as if you can replace plenum with LSZH cables, that’s not really the case. The difference is that while there is a lower smoke rating for LSZH, plenum cables have higher fire spread rating.
Cable tray rated
Tray cables are designed for just that, installation in cable trays. Primarily they are used in industrial control systems, factories, wind turbines and other severe environments. They can be rated for use indoors, outdoors, and in corrosive areas, for hazardous locations or high electrical noise areas. This cable was first introduced in order to combat failures in power and communication applications. There are several different kinds of cables to choose from, these include: Tray Cable (TC), Power Limited Tray Cable (PLTC), Instrumentation Tray Cable (ITC), Exposed Run (ER), and Wind Turbine Tray Cable (WTTC). Effective in direct sunlight as well as underground, these types of cables are extremely versatile in their application. Although cable in tray is viewed as being exposed to a greater risk of mechanical damage and it can be a potential ignition source or fuel load in a fire scenario. Due to this the NEC has a specific requirement in order to ensure the safety and quality of these fiber runs.
When choosing a jacket rating it is important to understand the placement and application where the cables will be run. It is pivotal that the cables meet local code requirements for the installations as well. These ratings are designed to prevent hazards and reduce risks to human and environmental health. We put on a jacket to prevent uncertainties from happening to our body, such as a cold or the flu. Fiber optic cable jacketing is very similar in the sense that we apply a certain compound to prevent a dangerous mishap, or if it does happen in the environment of the application.
Winter is coming… be sure to put on the appropriate jacket! .
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