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What Is Plenum Cable? OFNP Cable Explained
Sep
When wiring and buying fiber optic cables, we will see OFNP, OFNR, and so on signs; how to choose is a big question. So, it is important to know when to use them. In this article, we will introduce plenum cable, riser cable, and OFNP cable and their application scenarios.
Table of contents
What is a Plenum Space
Plenum space is a separate space for ventilation, heating, and air circulation for air conditioning. It is located between suspended and structural ceilings or underneath a movable floor. However, some suspended ceilings are designed to be tightly sealed and not allow air circulation, the resulting space cannot be characterized as a plenum space.
Plenum space is often used to house communication cables that connect equipment such as computers in a building. Since plenum space is responsible for air circulation in the building, cables with higher fire ratings are needed to prevent the fire from spreading and toxic fumes from becoming airborne in the event of a fire.
What is Plenum Cable?
Plenum cables are constructed in plenum space. Flame retardant cables are sheathed in low-smoke polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), or fluorinated ethylene polymer (FEP) jackets. These jackets emit less smoke and are less flammable. Because of its enhanced safety features, booster wiring is commonly used in hospitals and schools.
What is a Riser
The riser is a vertical space within a building that extends between multiple floors, such as an elevator shaft, water supply line, or any other vertical pipe. It can also be a separate room for special purposes, such as storing fire suppression equipment.
These areas enable the vertical distribution of utilities such as water pipes and communication wiring. In contrast to plenum space, risers are not part of a building’s Heating, Ventilation, and Air Conditioning (HVAC) system, meaning cables used for these applications do not need a strict fire rating.
What is Riser Cable?
Riser cable is a type of cable that meets the requirements for use in vertical risers and other non-flame retardant environments. It meets the fire safety standards for these environments. Riser cables are suitable for use in confined areas to prevent the spread of toxic fumes from burning cables in the event of a fire.
Riser cable has lower fire safety requirements and is therefore well suited to non-pressurized environments where smoke toxicity and exposure pose less of a hazard or a fire is unlikely. Despite the lower standards, it still has fire safety features that enable the user to be safe.
The Difference Between Plenum and Riser Cabling
| Plenum cable | Riser cable | |
| Fire rating | Plenum cables require higher fire ratings due to their use in HVAC systems | Riser cables are used at a riser due to their lower fire ratings |
| Burn emissions | Fewer emissions are released into the air and enable a slower burn | Basic fire safety properties |
| Location | Riser cabling can be placed in non-plenum environments like elevator shafts | Plenum cabling is used for areas with high air circulation, like plenum space |
| Versatility | You can install them in both plenums and risers | However, riser cables can only be employed in riser spaces. |
| Cost | Plenum non-fiber cables tend to be more costly than riser cables | plenum fiber optic cables may be closer in price to riser cables, as these additional materials aren’t needed |
What is OFNP
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 correctly for their intended use: plenums, risers, and general-purpose areas:
| NEC Code | Description | Cable Application | Possible Substitute |
| OFNP | Optical Fiber Non-conductive Plenum Cable | Plenum | / |
| OFCP | Optical Fiber Conductive Plenum Cable | Plenum | / |
| OFNR | Optical Fiber Nonconductive Riser Cable | Riser | OFNP |
| OFCR | Optical Fiber Conductive Riser Cable | Riser | OFCP |
| OFNG | Optical Fiber Nonconductive General-Purpose | General purpose | OFNP, OFNR |
| OFCG | Optical Fiber Conductive General-Purpose | General purpose | OFCP， OFCR |
| OFN | Optical Fiber Nonconductive | General purpose | OFNP, OFNR |
| OFC | Optical Fiber Conductive | General purpose | OFCP, OFCR |
What is OFNP Cable
OFNP is the highest-rated fiber optic cable. It will self-extinguish within 5 meters of flame spread and emits no or very little toxic fumes. OFNP cables are typically installed in pressurized spaces or HVAC systems in communication cabling applications. They are also flexible, easy to install, and heat—and moisture-resistant.
Conclusion
Hopefully, reading this article will help the reader choose the right cable. If you see something like OFNP, OFNR, LSZH, or OFNR LSZH in your cables (or no LSZH), you should know what that means.
FAQ
Q. What is the difference between OFNP and OFNR cables?
A. The application’s location is different. OFNR is used in riser areas, while OFNP is used in plenum areas. OFNP flame retardant cables can be used instead of OFNR cables, while OFNR cables cannot be used the other way around. Both OFNP and OFNR can be used in general-purpose areas.
Q. What is the difference between plenum, riser, and general purpose areas in a building?
A. Their difference is as follows:
- Plenum Area: A separate building space used for ventilation, heating, and air conditioning airflow.
- For Riser Zone: A vertical space in a building that extends between multiple floors, such as an elevator shaft, water supply pipe, or any other vertical duct.
- For General Purpose Areas: Other areas on the same floor except for pressurized zones and risers.
Q. How do I choose the right fiber optic cable jacket for my application?
A. Suggestions are as follows:
- For Plenum Areas, select pressurized zone sheathing labeled “OFNP” or “OFCP.”
- For Riser Areas, use riser grade jacketing labeled “OFNR,” “OFCR,” “OFNP,” or “OFCP.” “ for the riser grade sheathing.
- For General Purpose Areas, if budget is a concern, general-purpose cables labeled “OFNG” or “OFCG” are sufficient. Cables suitable for the previous two zones can also be used as alternatives when budget is not a concern.
Q. What is the difference between OFNP and OFCP cables?
A. OFNP cable sheath is conductive, and OGCP cable sheath is non-conductive.
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