Riser Vs. Plenum Rated Bundled Cables
By Rudy Hanecak
One-Pull Wire and Cable Solutions
There are some crucial distinctions between riser and plenum rated cable bundles. Most commercial spaces will have to use either plenum or riser rated cables to meet fire safety codes.
Plenum rated cables are used in plenum areas meant for use in commercial and residential spaces. Plenum spaces are the spaces between the ceilings and the floors above it (drop ceiling) that are used for creating pathways for heated/air conditioned or return air flows. The importance of these spaces for air circulation create a greater hazard if a fire were to occur, both in regards to the growth of the fire and the spread of smoke from the materials burning in the space which may contain toxic chemicals under high heat that are carried in the smoke.
Plenum cables have a higher fire rating and are designed with fire-retardant plastic jackets of either a low-smoke PVC or a fluorinated ethylene polymer (FEP). This decreases the likelihood that the cables burn quickly, thereby spreading toxic air through the building during a fire as people try to evacuate.
To be rated as plenum, the outer jacket of the cable needs a specially treated jacket insulating the wire to meet NFPA and NEC standards. Plenum cables are usually designated with the letter CMP where the “P” stands for plenum.
Riser cables, sometimes referred to as “backbone” cables, are the cables run vertically from floor to floor in a structure. They “rise” through cable spaces or in elevator shafts in non-plenum areas. The riser space is the term given to any vertical shaft or series of rooms within a building that allow primary utilities such as electrical conduits, water supply lines, and communications cabling to be distributed vertically.
For communications cabling, the riser could be a separate room on each floor, or a room shared with the electrical gear. In either case, the room is self-contained and not used for recirculating air to the HVAC system. Thus, the fire safety requirements for materials installed within these rooms is less stringent than those of plenum spaces. Like plenum, the riser must also meet certain NFPA standards. These cables must self-extinguish if caught on fire by a spark in order to prevent the flame from traveling up the cable.
The Cost Difference Between Riser and Plenum Bundled Cable
Since the requirements for riser space and plenum space are different (with those requirements for riser cables being less strict compared to plenum ones), plenum cable can replace riser cables as they meet the minimum safety specifications.
We would not recommend bundling plain PVC cables that do not meet either riser or plenum requirements but would suggest having them printed and labeled if the customer requires organized cables that can be easily identified.
We would also suggest spending the little extra for peace of mind and adding a level of safety to the install.
To summarize the difference between PVC and plenum and riser rated cables are cost and fire protection. While the cost is a major factor, it boils down to a matter of how fire-resistant you want your bundled cables to be and how much smoke is emitted if they do burn. And in many instances the code decides for you.