When installing Ethernet cable in walls or ceilings, you may encounter terms like CM, CMR, CMP, or PVC and LSZH. Do you know what these terms really mean and which one is fit for your project? CM, CMR, and CMP are the most common Ethernet cable ratings specified by the National Electric Code (NEC), which are named to distinguish the different levels of ability to resist fire. An explicit analysis of CM vs CMR vs CMP Ethernet cable jacket ratings will be provided in this article, which may help you choose the right rated cable to ensure safety when cabling.
CM stands for "Communications Multipurpose." It is a cable jacket fire resistance rating defined in Article 800 of the NEC. In the case of CM, the standard outlines general use, or use in cases where the fire code does not place any restrictions on cable type.
The CM cables are generally the minimum jacket ratings suitable for in-wall installation of Ethernet cables and are appropriate for installation inside a residence or a single-story commercial building. As with any in-wall rated cable, the goal is to prevent fire from traveling along a cable from one part of a building to another. The Ethernet cables labeled "Type CM" must pass a standardized flammability test before the cables are put into use.
CMR cable stands for "Communications Multipurpose Cable, Riser". It is a cable jacket fire resistance rating defined in Article 800 of the NEC. CMR cable is also referred to as "riser-rated cable" and designed to prevent fires from spreading between floors through risers or vertical shafts.
The goal of CMR cable is to be flame-retardant enough to prevent the spread of fire from one floor to another. The fire resistance requirements for CMR are much stricter than that of CM. And CMR cable is more flame-retardant and consequently more expensive than CM cable.
CMP cable stands for "Communications Multipurpose Cable, Plenum". It is a cable jacket fire resistance rating defined in Article 800 of the NEC. CMP cable is also 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 emitted during a fire.
CMP or plenum-rated cables adopt materials that burn more cleanly and self-extinguish more easily. Air travels throughout a building via plenum spaces, so it is critical that cables installed in such spaces use this kind of material in the construction — won't give off toxic fumes if burned.
Thus, a CMP cable is suitable for installation into air plenum spaces. An example of the most common types of plenum spaces would be a dropped ceiling or raised floor.
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.
As mentioned above, PVC is the material that makes up the Ethernet cable jackets with CM, CMR, and CMP ratings. Ethernet cables labeled PVC CM, PVC CMR, or PVC CMP on the jackets are often seen in the market. And LSZH (Low Smoke Zero Halogen) cables are built with a jacket material free from halogen for different applications. The LSZH cable is slightly inferior to the Plenum type and commercialized mostly in Europe.
Another confusion: OFNR (Optical Fiber Non-conductive Riser) with a jacket for riser airspace and OFNP (Optical Fiber Non-conductive Plenum) with a jacket suitable for plenum airspace. Compared with the copper-made CMR and CMP Ethernet cables, OFNR and OFNP are more superior and flame-retardant since they're fiber optic cables constructed of materials that do not conduct electricity.
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.
FROM: FS Community