What do the acronyms mean?

  • CM = Communications Multipurpose
  • CMR = Communications Multipurpose Riser
  • CMP = Communications Multipurpose Plenum

So what is a “Riser”?

A riser is usually a space that runs between floors in an office or a commercial building. Think of it as an elevator shaft without the elevator… If you have a large building with multiple floors, each floor will house one or more “rooms” the are dedicated to distributing network to that floor. Each one of those rooms are usually placed on top of each other, and are connected to each other via a “riser” shaft.

The riser is then used to run all the network cables (copper, fiber, coax, etc.) to interconnect all the floors.

What is Plenum, or a Plenum Space?

A Plenum Space is the part of a building that is used as part of the air conditioning and heating system. This usually is the area above a suspended ceiling that is used as a forced air return. Unlike a riser, the flow of air is greater and distributed around the entire floor that the area services.

Why is this Important?

As you can tell by the above descriptions the differences between the two are the amount of airflow and the distribution of that flow around a given area. This means that any combustible material (such as a network cable) would cause smoke and fumes that would be distributed very quickly in the event of a fire.

In the case of a Plenum space, the speed and distribution would be much greater than in a riser.

CM Rated Jacket

CM stands for “Communications Multipurpose.” This rating is the minimum standard that is suitable for in-wall installation and is only appropriate for installation inside a residence or a single-story commercial building. In-wall rated cables are designed to prevent fire from traveling along a cable from one part of a building to another.

CM rating is NOT suitable for running between floors, typically risers run vertically between floors of buildings. Excessive would be generated by CM rated cable in a fire situation which would be easily distributed through an entire building in a short space of time.

Pre made patch cables are generally constructed from CM Rated cable and should not be used in riser or plenum areas.

CMR Rated Jacket

CMR cable stands for “Communications Multipurpose Riser”. CMR rated cable has better flame-retardant properties than CM which can prevent the spread of fire from one floor to another. When the cable burns it also produces les smoke than its CM Rated counterpart.
CMR rated cable is usually more expensive than CM cable.

CMP Rated Jacket

CMP cable stands for “Communications Multipurpose Plenum”, commonly referred to as “plenum-rated cable”. It is constructed to restrict flame propagation to no more than five feet and limit the amount of smoke and toxins emitted during a fire.

Air travels throughout a building via plenum spaces, so it is critical (and a matter of building regulation and compliance) that cables installed in these spaces are CMP rated.

CM vs. CMR vs. CMP: What’s the Difference?

Both CM and CMR cable jackets are made from relatively inexpensive polyvinyl chloride (PVC). With CMR being less flammable and producing less hazardous fumes when burned
CMP cable is made from either a low-smoke polyvinyl chloride (PVC) or a fluorinated ethylene polymer (FEP). Some plenum applications may dictate which of these jacket types must be used, please check your local fire regulations to find out what type of CMP jacket you need to use.

What Is LSZH?

LSZH (Low Smoke Zero Halogen) cables are manufactured with a jacket material free from halogenic materials such as chlorine and fluorine. LSZH cables are slightly inferior to the Plenum type and mostly available in Europe. When burned, LSZH cables produce very little smoke and do not produce toxic halogenic gasses that PVC or FEP cables do.