Telecom Cable Rating: CMP or CMR Cables


We usually use terms—CMP, CMR, PVC and LSZH to describe telecom cables, but do you know what these terms really mean? And, more importantly, which one does your project actually need? The article below will briefly outline many industry cable types, along with their features to help you have a better understanding of them.

Plenum Rated Cables

CMPCMP cable refers to the communication plenum cable that is laid in the plenum spaces of buildings. Plenum rated cable or just plenum cable is jacketed with a fire-retardant plastic jacket of either a flame retardant low-smoke polyvinyl chloride (PVC) or a fluorinated ethylene polymer (FEP). Owing to its material in this network cable, it doesn’t emit a toxic smoke when they burn. Plenum rated cables are slower to burn and produce less smoke than other cables.

As seen in the above image, plenum refers to the air handling space. In a standard commercial building, the plenum is the space between the drop ceiling and the structural ceiling. In residential installations, the plenum may include the space above the ceiling or under the floor when floor level air circulation is used. Plenum rated cable is mandated to be installed in any “air handling” space because of its low smoke and low flame characteristics.

Riser Rated Cables

Riser-Rated-Armored-CableCMR cable refers to the communication riser cable that is run between floors in non-plenum areas. The term ”riser” usually refers to a space that runs between floors in an office or a commercial building. The fire requirements on riser cable are not as strict as plenum cables. It will emit toxic fumes when burning. This is considered to be a slight problem, but it is not enough to warrant consideration as long as these cables are not used in ducts.

These cables can be used for both commercial and residential spaces but are generally used more for residential homes. For example, riser cables can be used from room to room, as long as it is run around baseboards, along bottoms of walls, and along the tops of walls. They can also be used to run cables from the basement to the upper floor, as long as the cable does not need to pass through an air duct.

How Do I Know Which One Should I Choose?

Many customers have asked about this question but unfortunately, we cannot help or advise you as each individual cabling details has to be evaluated. However, for those who plan to wire their house with cat 5e or cat6a cable, we do have some practical suggestions for you to choose between the plenum and riser-rated cables.

Both plenum and riser cables commonly include a rope or polymer filament with high tensile strength, which helps support the weight of the cable when it is dangling in an open chute. Cables like twisted-pair, coaxial, HDMI, and DVI are available in both plenum and riser versions. The cable cost is often significantly higher than general-use cable due to the special restricted-use flame retardant materials. Plenum cable is expensive, much more expensive than riser rated cable. Additionally, the practice of running cables in plenum spaces is becoming less popular, and therefore demand for plenum rated cable is much less than riser rated cable.

However, the plenum rated cables have a higher fire rating than riser cables. Thus, plenum cable can always replace riser cable, but riser cable cannot replace plenum cable in plenum spaces. The stiffness of CMR cable is less than that of CMP cables. This means CMR cable is easier to bend around corners of baseboards and ceilings. This can allow a tighter fit against corners to minimize the look of cables. The following pictures show the burning test of these two cables.

CMP and CMR-burn-test-result

One final tip to keep in mind is that If you will never need to run it through air-handling ducts/spaces, just get Riser rated. But, for retrofits, that’s often the easiest route from the basement to the upper floors and sometimes a few basement ceiling joist spaces are covered over with tin to use as inexpensive cold air return ducts. If you have to go through those, Plenum rating is required, too. If there’s ever a hot enough fire to melt CMR’s covering, any toxic fumes it might emit will be among the least of your worries. but the Riser rating means its fire-resistance will keep the flames from following it between floors.


Selecting the right type of cable for your home network is important; CMP cable is usually recommended as it is safer to use in case of fire, even though they are more expensive and stiffer than CMR cabling and more difficult to bend. But if you are not up to run cables through the air duct, CMR cable is actually a great choice, as this type of cable is less expensive and easy to install in a network.

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