Plenum-rated fiber cable is used in spaces such as ceiling cavities that carry return air. Riser-rated fiber cable is used for permitted vertical runs between floors or in shafts. Choosing between them starts with the actual building route, including every space the cable passes through.
For U.S. installations, follow the locally adopted National Electrical Code (NEC), local amendments, and project specifications. Have the designer or authority having jurisdiction (AHJ) confirm uncertain space classifications and installation methods before ordering.
Read the plenum and riser designations
Fiber cable markings identify both construction and fire rating. Nonconductive types contain no metallic or other electrically conductive members. Conductive types can contain metal strength members, armor, or similar components.
| Rating | Nonconductive cable | Conductive cable | Fire-performance evaluation |
|---|---|---|---|
| Plenum | OFNP | OFCP | NFPA 262: flame spread and smoke |
| Riser | OFNR | OFCR | UL 1666: vertical flame propagation |
Select singlemode, OM3, or OM4 fiber separately to meet the link's optical requirements. The plenum or riser classification addresses fire performance and permitted installation locations.
Confirm whether ceiling and floor spaces handle air
A suspended ceiling or raised floor does not automatically create a plenum. Review the HVAC design to determine whether the space itself carries environmental air, such as return air moving through a ceiling cavity. For exposed fiber cable in these spaces, select the permitted plenum-rated type.
In a ceiling void that is not used for environmental air, riser cable may be acceptable when the applicable code and project specifications allow it. Confirm the entire route, including any floor penetrations or sections that enter an air-handling space.
Use riser cable for the right vertical route
Riser-rated fiber cable is evaluated for vertical flame propagation. OFNR or OFCR can be appropriate for a shaft or floor-to-floor run outside environmental-air spaces when the installation meets the applicable requirements.
A corresponding plenum type can satisfy a riser fire-rating requirement: OFNP can replace OFNR, and OFCP can replace OFCR. Other requirements, including cable construction and environmental suitability, still apply. A riser rating alone does not qualify cable for exposed use in a plenum.
For example, a run that rises between telecommunications rooms and then crosses a return-air ceiling cavity needs a cable and pathway permitted in both locations. An appropriately listed plenum cable can simplify that continuous route.
Check pathways, penetrations, and installation limits
A plenum-rated plastic innerduct does not, by itself, make riser cable acceptable inside a plenum. Certain raceway arrangements permit different cable selections, but the complete installation must meet the applicable code provisions. Fabricated HVAC ducts have separate restrictions; a plenum marking alone does not authorize routing ordinary network cable inside them.
Where the route penetrates a fire-rated wall or floor, use an approved firestop system that matches the construction, opening, and cable configuration. The cable's fire rating does not replace the penetration's firestopping requirements.
Follow the manufacturer's pulling-tension, bend-radius, and vertical-support limits. Check applicable bonding and grounding requirements when the cable contains metallic components.
Verify cable details before ordering
Match the exact part number and manufacturer specification to the cable markings and certification label. Retain the reel or carton label with the project records. Jacket color and a low-smoke zero-halogen (LSZH) description alone do not establish the required plenum or riser listing.
For cable entering from outdoors, confirm the approved entrance and transition method. An indoor/outdoor cable must carry the classification required for the indoor portion of its route.
- Approved route and environmental-air space classifications
- Required cable listing: OFNP, OFNR, OFCP, or OFCR
- Fiber type, strand count, and termination requirements
- Run length, cable diameter, and approved pathway
- Support, firestopping, and applicable bonding details
- Manufacturer data sheet and certification documentation
Plan your next order
Send Telecom Specialties your approved route, required cable rating, fiber type, strand count, and length so the correct configuration can be reviewed before ordering. Explore indoor fiber optic cable, or contact Telecom Specialties about your building installation.
