Difference Between Plenum (CMP) And Riser (CMR) Cable

The selection of Ethernet cables should be done with great care and caution. Different Ethernet cables are manufactured for different purposes. They come with different specifications and configurations. Therefore, choosing the right option for your network is the main task for network engineers. Plenum-rated (CMP) cables and riser-rated (CMR) cables are the most utilized Ethernet cables in the modern era. In this article, we will discuss some main differences between CMP VS CMR cables.

You cannot install any cable at any place on your network. Each cable is designed to be installed at specific locations and places in the networks. So, if their arrangement is compromised by any means, it negatively impacts the performance of the network. Your whole investment may get wasted by one wrong decision.

In this article, we will discuss the difference between the plenum (CMP) cables and riser (CMR) cables. What is the main purpose behind their manufacturing and where they should be installed? With that, we will also discuss some of their features.

What is Plenum?

In modern-day building structures, there is a special space left by the architects for air circulation, centralized air-conditioning, and ventilation. This space is called the plenum. Now, the question arises where this plenum space is present?

It is normally designed in the ceilings. A space is created between the structural ceiling and the drop-down ceiling. The space between the two ceilings is known as the plenum. In some buildings, it is created under the floors as well by raising them. The space between the structural floor and the raised wooden floor is also known as the plenum.

The plenum space is designed in the buildings for better air-flow purposes. Therefore, it remains full of oxygen. The cables installed in the plenum spaces must be highly fire-resistant for safety purposes. Most network engineers use this plenum space to install their networking cables. It provides them with a convenient way to complete their networking structure.   

What is Riser?

The riser is also a space left in the building structures that can be used for cable installation from one floor to its above floor. Unlike the plenum, it is in the vertical form. The spaces left with the elevator shafts or ducts installed from one floor to its above floor are all riser spaces. These spaces are used by the network engineers to install the Ethernet cables throughout the building to design their networking structure.  

The Riser spaces lie inside the building structures therefore, the requirements for the cables to be fire-retardant are almost the same as in the case of plenum spaces. Although they are not that strict but still the cables installed at the riser spaces should be fire-retardant for safety purposes. Cat6 Riser cable is the best example of it.


The Ethernet cables are manufactured in different structures and configurations. Some of them are called CMP and some are called CMR.

  • CMP: The “CMP” stands for “Communication Multipurpose Plenum”.
  • CMR: The “CMR” stands for “Communication Multipurpose Riser”.

Major Dissimilarities between CMP VS CMR Cables

Ethernet cables are distinguishable with reference to their jacket types. Similarly, when we talk about plenum and riser cables the main difference lies in their jacket type. The plenum cables are known as “CMP” or “plenum-rated” cables. Whereas, riser cables are known as “CMR” or “Riser-rated” cables.

CMP Cables

The jacket of these cables is built with a special type of material. This material is highly fire-resistant known as Polyvinyl Chloride (PVC) or Fluorinated Ethylene Polymer (FEP). This material does not catch fire quickly. Even if the fire catches the cable, it does not produce any toxic smoke that may be harmful to humans.

These plenum-rated cables are installed in the plenum spaces of the commercial and residential buildings. They are assumed as the safest cables to be installed at these places as they do not catch fire quickly. Even in case, the fire catches the cable, it does not produce any toxic smoke.    

The major advantage of using plenum cables is that they can be used in riser spaces or outdoors as well. The plenum-rated cables are more expensive than other jacket-type cables. Therefore, it depends on the budget limits of the installer whether they want to install them at all the places of the buildings or just at the plenum spaces.

CMR Cables

The Ethernet cables designed to be installed at the Riser spaces of the building structures are known as “CMR” or “Riser-Rated” cables. They are installed between the floors of the building to complete the networking structures. Network engineers use them in both commercial and residential buildings according to their needs and requirements. 

They cannot be used in the plenum spaces. They are available at cheaper prices in comparison to plenum cables. This is the only reason behind using riser-rated cables in the networking structures.


Why Plenum-rated (CMP) cables are costly in comparison to Riser-rated (CMR) cables?

The plenum-rated (CMP) cables are mandatory to be installed in the plenum spaces. There is no other cable that can be used as their replacement. On the other hand, riser-rated (CMR) cables can be replaced with plenum cables. With that, the CMP cables are manufactured by keeping in view the high standards of fire resistance as compared to CMR cables.

Why Plenum Cables are a must to use at plenum spaces?

The plenum spaces are mostly used for ventilation purposes where oxygen levels remain high all the time which increases the possibility of fire. The CMP cables are built according to the high safety standards against fire. Therefore, they are the safest option to be installed in the plenum spaces as they resist against fire process effectively. 

 Can we use CMR cables in place of CMP cables?

No, you cannot use CMR cables in place of CMP cables. On the other hand, you can use CMP cables in place of CMR cables. It is the major difference while doing CMP VS CMR cables comparison.

Conclusion: –

CMP VS CMR cables comparison in an interesting one. The network engineers need to choose the right Ethernet cable for the right places. One wrong decision will ruin their whole network. The wrong decisions not only impact negatively on the performance of the network but also makes the cabling structure vulnerable to fire. Therefore, they must install CMP cables in the plenum spaces. They cannot comprise on it at any cost. Whereas, the selection of CMR cables depends on the budget limits. If one can afford to install CMP cables in place of CMR cables then they must do it.

Related Tags: Cat6 CMP Cable, Cat6 Riser