Selecting Fiber Cable Ratings: Riser vs. Plenum

Fiber cables are installed inside different types of buildings and often deployed in risers and plenum areas. Some fiber cables are denoted with riser and plenum ratings. Is there any differences in the use of these two fiber cable ratings?

Riser-Rated Cable
A riser is the vertical shaft, area or series of rooms between 2 floors inside a building. These spaces allow primary utilities to be distributed vertically. A good example of a riser area is elevator shafts and pipes from one floor to another. Riser cable can be a building’s backbone that transmits data, audio and video signal.

Fiber Cable with riser rating are self-extinguishing to prevent flames from travelling up the cable and jumping floors in a building. However, this type of fiber cable is not as strict as Plenum-Rated Cable.

Plenum-Rated Cable
A plenum is the pathway or space used to circulate air as part of a building’s HVAC system. It is usually above a ceiling or below a floor that can serve as a receiving chamber for air that has been heated or cooled to be distributed to inhabited area. As the plenum spaces contain few fire barriers and forced-air circulation, the cables deployed here need a higher fire resistance than cables used in riser spaces.

Fiber Cable with plenum rating are with fire-retardant plastic jackets such as PVC or FEP. Even if a fire were to ignite, fewer toxic fumes are emitted as the jacket melts.

Here are some notes for your consideration between riser and plenum cables.

  • A plenum cable can be used in a riser space, but a riser cable generally cannot be used in a plenum space.

  • In the event of a fire, using the wrong cable type may cause legal issues.

Using the correct cable type can not only ensure personal safety, but also reduce building damage and avoid liability.