When planning a fiber optic installation, choosing the right cable jacket type is critical for both safety and code compliance. The two most common indoor ratings are plenum-rated (OFNP) and riser-rated (OFNR). Each is designed for a specific installation environment and fire safety requirement, and understanding their differences will help you make the correct choice for your project.
Plenum and riser-rated jackets are designed to limit flame spread and smoke generation in the event of a fire, but they serve different purposes based on where the cables are installed.
Plenum-rated (OFNP) fiber cables are made for air-handling spaces, such as above suspended ceilings or below raised floors that circulate heating and cooling air. These spaces can rapidly spread smoke and flames, so plenum cables use special low-smoke, fire-resistant materials—typically fluoropolymers—to minimize risk. Plenum cables meet the highest fire safety standards required by building codes.
Riser-rated (OFNR) fiber cables, on the other hand, are designed for vertical pathways that run between floors, such as riser shafts or conduits. They use flame-retardant PVC jackets that prevent fire from moving up through a building but do not have the same low-smoke performance as plenum cables. Riser cables are suitable for most non-air-handling areas within a building.
Both plenum and riser cable ratings are defined by their fire safety performance, as required by building and electrical codes. These ratings ensure that the right type of cable is used for the environment, reducing the risk of fire spreading through air or structural spaces.
Plenum spaces always require OFNP-rated cable because of the increased risk of air circulation carrying flames or smoke. Riser spaces can safely use OFNR-rated cable. However, plenum-rated cable can always substitute for riser-rated cable, while riser-rated cable cannot be used in plenum spaces under any circumstances.
In situations where a single cable run passes through both plenum and riser spaces, it’s best practice to use plenum-rated cable throughout. This ensures compliance with all applicable codes and simplifies installation.
Plenum-rated fiber cables should be installed in areas where air moves freely for ventilation or HVAC systems—most often in drop ceilings or under raised floors used for air return. These cables are specifically tested to prevent the spread of smoke and toxic gases in such spaces.
Riser-rated fiber cables are designed for vertical installations, such as between floors or in walls that connect one story to another. They are not meant for air-handling spaces but are fully compliant for general and riser use throughout most of a building’s interior.
In most cases, the choice between plenum and riser cable comes down to where the cable will be installed. If your pathway includes any plenum areas, use plenum-rated (OFNP) cable. If the pathway is confined to vertical shafts or general spaces without air circulation, riser-rated (OFNR) cable is acceptable and more cost-effective.
While plenum cable is typically more expensive due to the higher-grade materials used, it provides greater flexibility and ensures compliance in all indoor spaces. Many installers choose to standardize on plenum cable to simplify installation and inspection.
Plenum and riser fiber cable jackets are not interchangeable. Plenum-rated (OFNP) cables are required in air-handling spaces because of their superior fire and smoke resistance. Riser-rated (OFNR) cables are intended for vertical runs between floors, where they effectively contain flame spread but are not safe for air-handling use. Always follow local building codes when selecting cable types, and when in doubt, choose the higher-rated plenum cable for maximum safety and compliance.