Overview

Choosing a suitable Ethernet or outdoor cable can be difficult because it’s not a one-size-fits-all.
One of the difficulties you may encounter is choosing between CMP, CMR, CM/CMG, and CMX cables. The above acronyms are known as NEC (National Electric Code) types. The code is developed by the United States National Fire Protection Agency to define the type of cable jackets and their applications. A jacket is the outer sheath of an Ethernet cable whose purpose is to protect the internal wires. The acronyms have a prefix to denote the cable type and a suffix indicating the flame test passed, and their applications.
These ratings are essential for accrediting buildings by local authority fire codes, insurance requirements, or even customer requirements.
So what is the difference between all of these cables, and which does your project need to use? This article gives you an idea of these terms and a clear distinction between CMP, CMR, CM/CMG, and CMX cables.
Without much ado, let’s jump right in.

CMP (Communications Multipurpose Cable, Plenum)

Article 800 of the National Electric Code defines communications multipurpose cable plenum or CMP as a cable that has a fire-resistant rating jacket which may also be called a plenum-rated cable.
CMP is built to restrict the spread of flame from a fire to as little as five feet or less, limiting the amount of smoke in the process. The plenum is confined as a space that has higher air pressure in them than outside them. It is a separate space used for air circulation for heating, ventilation, and air conditioning. Usually, space is between the structural ceiling and drop-down ceiling or under a raised floor in a building.
The air inside buildings travels through such spaces. For this reason, the cables we use mustn’t increase toxic fumes if they get burnt.
Plenum-rated or CMP cables are made of FEP (fluorinated ethylene propylene) that melts and emits very little smoke with low toxicity when exposed to fire, also, they burn cleanly and self-extinguish easily.
Applications
These cables can be used in residential or commercial spaces in buildings, although they may be more costly than non-plenum cables.
For instance, spaces like air ducts need to use plenum-rated cables instead of plain PVC cables. In case of a fire, they will not combust.

CMR (Communications Multipurpose Cable, Riser)

In contrast to CMP cables, CMR cables are known as riser-rated cables.
CMR cable jackets are made of PVC, but Teflon coated to limit it from carrying a flame when it burns.
These cables are constructed to prevent the spread of fire between floors through vertical shafts or risers. They are usually used in conventional networking as they do not go through an air duct, unlike CMP cables.
Besides, the ultimate aim of its fire-repelling ability is to stop the spread of fires from a floor to other unaffected ones.
The fire-resistant standards for CMR cables are much higher than CM, it means CMR cables can be used as a substitute in places where CM cables are used. CMR cables are more flame-retardant and thus cost more than CM cables.
Applications
Compared with CMP, CMR cables are more preferred due to their lower cost, providing a degree of fire protection, and are less thick, thus easier to terminate. Their ideal applications are in riser ducts running vertically between floors and inside walls. They can also be used in regular networking for room-to-room applications, provided that they don’t pass through the plenum.

CM/CMG (Communications Multipurpose Cable)

CM is an abbreviation for “Communications Multipurpose.” The CM/CMG cable jackets are made of PVC but lack the Teflon coating, meaning it does not have any fire protection capabilities. In the event of a fire, the cable will burn like any other plastic, emit toxic fumes and smoke. Since it’s one of the most affordable networking cables, it is used for making short LAN connections in most residential applications. Commercial use of this cable is limited because of insurance and legal considerations.
When compared with CMR riser cables, CM/CMG cables are the less expensive option.
Applications
These are commercial-grade communication cables, and they are commonly used. Their applications are primarily in-room patch cords, for instance, from a wall plate to a computer. In the interior of any residential application, these cables can be used almost anywhere.

CMX Cable (Communications, Outdoor/Residential)

CMX rated cables are made of LLDPE (Linear Low-Density Polyethylene) due to their UV resistant and weatherproof properties. They are meant to withstand harsh sunlight, wind, rain, and extreme temperature changes. However, they are not fire-rated.
CMX rated cables are specially designed for outdoor cabling in open air or underground burial. They are often used outside in both commercial and residential properties to bring the primary network/Internet connection which can then be further distributed. Also, they can be used in areas that require few communication cables.
Applications
In effect, CMX cables have more durability and impact protection when compared with CMR, CM, or CMP cables. Whether buried underground or installed on the side of buildings, the CMX is the best pick.

So what are the Key Difference between CMP, CMR, CM/CMG, and CMX Cables?

Now we have identified what these cables are and what they are rated as we can understand their key differences. For CMP, the important thing to note is that it is a plenum cable made for plenum spaces.
Residential and commercial areas make use of CMP cables the most. A major feature and benefit to use them is their fire-retardant ability and the little fumes they produce when burnt.
CMR cables are slightly different from CMP, they shouldn’t be passed through air ducts. They are riser cables and are suitable for conventional networking from floor to floor.
CM/CMG cables have no fire-retardant abilities, compared with CMP and CMR cables. They burn like regular plastic in a fire, and they emit smoke and fumes. For this reason, they are terrible choices for plenum spaces or risers.
CMX cables on the other hand, are primarily designed for outdoor use in open-air or direct burial

Conclusion

All of the cables mentioned in this article are unique in several ways. In terms of use, they are different, and each serves a purpose according to the project you need them for.
If you’re looking for the perfect fit for your ducts, you may need CMP cables. Also, if you need something for risers, CMR will do the job while CMX cables are the ultimate outdoor/residential cables.
You can contact a networking expert from Nexer Tech Support Team to get a personalized guide for your next project.