What Is Cat6 Plenum Cable And Why It Is More Expensive Than Cat6 Riser Cable?

Updated on Sep 29, 2021

For safety concerns, many users tend to buy flame-retardant cables, of which plenum cable and riser cable are the top two flame retardant classes that they may prefer. Cat6 cables are widely applied in these two classes among the Ethernet cable categories. So, what is the Cat6 plenum cable? What is Cat6 riser cable? Cat6 plenum cable vs Cat6 riser cable, why is the former more expensive than the latter?

Flame Retardant Ethernet Cable Jacket Coatings

Before knowing what Cat6 plenum cables and Cat6 riser cables are, you should figure out the flame retardant Ethernet cable jacket coatings in the first place. At present, there are two widely used flame retardant cable types, namely PVC Underwriters Laboratories cable (UL cable, US fire protection standards) and Low Smoke Zero Halogen cable (LSZH cable, European national fire protection standards).

Cat6 plenum cables vs Cat6 riser cables belong to "UL cable type"—including a series of cables that are divided into five classes according to their safety standards and using environments: CMP cable, CMR cable, CM cable, CMG cable, and CMX cable.

Cat6 Ethernet Bulk Cable (PVC CMR)

What Is Cat6 Plenum Cable?

First, the CMP cable (Communications Multipurpose Cable, Plenum) is the most demanding cable in the UL fire protection standard—the safety standard is UL910. It is designed to restrict flame propagation to no more than five feet and to limit the amount of smoke emitted during a fire. Cat6 plenum cable refers to Cat6 CMP cable, which fits for installation into air plenum spaces. Normally, a Cat6 plenum cable jacket is made up of either a low-smoke polyvinyl chloride (PVC) or a fluorinated ethylene polymer (FEP).

Where to Install Cat6 Plenum Cables?

The Cat6 plenum cables are designed to provide pathways for return airflows of buildings, facilitating air circulation for heating and air conditioning systems. These Cat6 network cables are typically deployed in the air return pressure boosting system used in ventilation ducts or air handling equipment (above a suspended ceiling or under a raised floor, for example). Since the fire and smoke can travel and spread quickly through these plenum spaces full of fresh oxygen, which may cause damage to the furniture and threaten people's lives, the Cat6 plenum cables are essential to prevent the fire from spreading out.

What Is Cat6 Riser Cable?

Cat6 riser cable, also regarded as Cat6 CMR cable (Communications Multipurpose Cable, Riser), is the commercial-grade cable in the UL standard, applicable to the UL1666 safety standard. It is constructed to prevent fires from spreading floor to floor in vertical installations. Thus, it is generally used for floor vertical wiring. Unlike a Cat6 plenum cable, a Cat6 riser cable usually has a jacket covering made up of relatively inexpensive PVC.

Where to Install Cat6 Riser Cables?

Non-plenum cables can be used anywhere except plenum space and air ducts. Thus, Cat6 riser cable is typically installed between floors in non-plenum areas. It is the primary conduit of a building's distribution system, carrying voice, data, and video into the different spaces and levels of a building from the service entrance point. In both commercial and residential buildings, Cat6 CMR cables are needed when running cable between floors through risers or vertical shafts.

NOTES for riser vs. plenum cables:

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

  • Using the wrong cable type may result in legal issues if a fire were to break out. If riser-rated cables are used in a plenum space where CMP-rated cables should've been installed, smoke and fumes from burning cables could be swept into the HVAC system and spread throughout the building, resulting in economic losses or even casualties.

  • When in doubt, consult the NFPA National Electrical Code. It will tell you which cable type can be used where.

Cat6 Plenum Cable vs Cat6 Riser Cable: Why Is Plenum Cable More Expensive?

Safety Standard

Fundamentally, Cat6 plenum cables and Cat6 riser cables differ in safety standards. The former one meets the standard of UL910, which is the strictest standard, making plenum cables the most demanding. While, the latter one meets the standard of UL1666, not as strict as the former one. As mentioned before, since the requirements for riser cables are lower, plenum cables can be usually used as an alternative to riser cables, but not vice versa. Thus, some installers may choose to keep only plenum cable on hand to reduce storage requirements and streamline inventory.

Here is a diagram of Cat6 plenum cable vs Cat6 riser cable typical applications:

CM vs CMR vs CMP Application

Cable Jacket Material

Cat6 plenum cable adopts low-smoke PVC or FEP, which has superior chemical resistance and electrical properties. It can support an operating temperature from -25 to 125 degrees Celsius and is resistant to all kinds of chemicals. Cat6 riser cable, on the other hand, uses relatively inexpensive PVC and such PVC material may release thick smoke and dangerous gases like hydrogen chloride in a fire. The operating temperature of a Cat6 riser cable is from 0 to 70 degrees Celsius. That's one of the reasons why a Cat6 plenum cable is more expensive than a riser one.

Check the chart listed below to get a clearer understanding of Cat6 CMP cable vs Cat6 CMR cable:

Cat6 Plenum Cable Cat6 Riser Cable
CMP Plenum CMR Riser
Safety Standard UL910 UL1666
Jacket Coating Low-smoke PVC or FEP PVC
Cable Price Costly than CMR Less Expensive


To sum up, both Cat6 plenum cables and Cat6 riser cables are flame retardant Cat6 Ethernet cables, the former one meets higher requirements in cable jacket material and safety standard, bringing more investment. Using CMR cable is cost-saving because it generally costs half or a third as much as CMP cable. Before you purchase, check with your insurance provider and local area building code.

If making a decision about riser vs. plenum cables is still weighing on you, just remember: When it comes to selecting the right cable rating, you won't go wrong when you put safety first. Not only will the right solution keep people safe, but it will also reduce building damage and protect against liability. Make your wise choice according to your actual needs.

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