CM vs. CMR vs. CMP: What's the Difference?
Lots of customers have found the letters “CM”, “CMR” and CMP” in the product description when purchasing copper cables like Cat5e cable and Cat6 cable. These terms are the most common cable jacket ratings specified by the National Electric Code (NEC). Ethernet cable jacket rating comes in a variety of different types and materials. It's important to know the differences between cm, cmr and cmp cables because each different type is used is difference locations. Let’s see the difference between CMR vs. CMP in their applications.
What Is a CM Cable?
The CM or “Communications Multipurpose” rating is the minimum standard for Ethernet cables installed within the walls of single-story commercial buildings. To be CM-rated, cables must pass a standardized flammability test. CM cable jackets are made from polyvinyl chloride (PVC), which is cost-effective and flexible but can produce thick smoke and release dangerous gases in a fire.
What Is a CMR Cable?
CMR cable stands for “Communications Multipurpose Cable, Riser” and is a higher rating than CM. CMR-rated cables are designed for installation in the risers, or vertical shafts, between the floors of a building. CMR-rated cables go through stricter testing to show that they are sufficiently flame retardant to prevent a fire from spreading from one floor to another.
Riser-rated cable jackets may be made from either low-smoke PVC or fluorinated ethylene polymer (FEP). Although CM-rated cables may not be used where CMR-rated cables are required, CMR-rated cables can replace CM-rated cables. Therefore, CMR-rated cables are generally recommended because they can be used to meet multiple cabling needs.
What Is a CMP Cable?
The CMP rating, which stands for “Communications Multipurpose, Plenum,” is the strictest of the cable jacket ratings. It designates Ethernet cables that may be used in a building’s plenum, such as a dropped ceiling, raised floor, and other air spaces. Non-air-handling dropped ceilings may also be considered plenums if the ducts aren’t sealed properly.
Plenum-rated cables must limit flame propagation to five feet or less and minimize the amount of smoke emitted. Therefore, cables designed for installation in plenum spaces must use a jacket material that burns cleanly and self-extinguishes easily. Because air travels through the plenum, CMP-rated cables must not give off toxic fumes in a fire. CMP cables may be used in any application, but are generally reserved for plenum spaces due to their higher cost.
CM vs. CMR vs. CMP: What's the Difference?
CM is the most basic cable jacket rated for general use. CMP is higher rated than CMR. The most significant difference is that they are suitable for different situations with various types of airspace. Both CM and CMR cable jackets are made from relatively inexpensive polyvinyl chloride (PVC). Price and flexibility are the upsides of PVC, but the PVC material can release thick smoke and dangerous gases like hydrogen chloride in a fire. While the CMP cable jacket is made from either a low-smoke polyvinyl chloride (PVC) or a fluorinated ethylene polymer (FEP).
Note:
Since the jacket material requirement for CMP is stricter than that of CM and CMR, their fire resistance and application ranges are different.
CM cable for general use can not replace CMR and CMP cables but both CMP and CMR Ethernet cables can be substitutes for CM Ethernet cables.
Ethernet cables with CMP jacket can always replace cables with CMR jacket, but CMR cable cannot replace CMP cable in plenum spaces.
The practical application of CM vs CMP vs CMR can show their differences clearly. No one can explain better than a direct graphic presented below.
CM vs. CMR vs. CMP: Which to Choose?
To maximize cabling performance, it's important to ensure that the type of cable selected meets the standards outlined for your particular project. Generally speaking, CMP cable is more commonly recommended, since it can be used for any type of cable needs. The safer CMP cable can allow peace of mind that if a house fire were to occur, and there would be less risk of toxic fumes being inhaled. However, CMR cable can also be a great choice if you are not required to run cables through air ducts. Since many homeowners are able to run cables without the use of air ducts, CMR cable is already enough for most home runs.
