What is the difference between CMP (Plenum cable), CMR, CM?

CMP cables are plenum cables; these cables are used if networking must be done in air ducts. They can be used for commercial or residential spaces. They will not combust and cannot actually cause fires. If the cable is in the path of a fire, it melts and emits very little toxic fumes.

CMR cables are riser cables. These are used for regular networking from room to room, as long as the cable does not need to pass through an air duct. For example, if you drill a small hole in the living room floor, you can run a CMR cable into the basement.

CM/CMG are the most commonly used commercial grade communication cable.

CMX is a residential grade cable. Such cables are limited to residential or other small applications where the number of communication cables used is very little.


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Plenum cable /ˈplɛnəm/ is electrical cable that is laid in the plenum spaces of buildings. In the United States, plastics used in the construction of plenum cable are regulated under the National Fire Protection Association standard NFPA 90A: Standard for the Installation of Air Conditioning and Ventilating Systems. All materials intended for use on wire and cables to be placed in plenum spaces are designed to meet rigorous fire safety test standards in accordance with NFPA 262 and outlined in NFPA 90A.

Plenum cable is jacketed with a fire-retardant plastic jacket of either a low-smoke polyvinyl chloride (PVC) or a fluorinated ethylene polymer (FEP). Polyolefin formulations, specifically based on polyethylene compounding had been developed by at least two companies in the early to mid-1990s; however, these were never commercialized, and development efforts continue in these yet-untapped product potentials. Development efforts on a non-halogen plenum compound were announced in 2007 citing new flame-retardant synergist packages that may provide an answer for a yet-underdeveloped plenum cable market outside the United States.

In 2006, significant concern developed over the potential toxicity of FEP and related fluorochemicals including the process aid perfluorooctanoic acid (PFOA) or C8 such that California has proposed some of these materials as potential human carcinogens. The NFPA Technical Committee on Air Conditioning, in response to public comment, has referred the issue of toxicity of cabling materials to the NFPA Committee on Toxicity for review before 2008.

In 2007, a development program specifically targeting the production of a non-halogen plenum cable compound was announced to specifically address lingering toxicity concerns presented by halogenated compounds for use in European and other global markets.
Riser cable

Cable that is run between floors in non-plenum areas is rated as riser cable.The fire requirements on riser cable are not as strict. Thus, plenum cable can always replace riser cable, but riser cable cannot replace plenum cable in plenum spaces.

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.

WHAT DOES "PLENUM" MEAN?

 
plenum

The word "plenum" gets used a lot in cabling circles but what does it mean? Let's look up some definitions, shall we? One definition of plenum is "a full assembly, as a joint legislative assembly." That can't be right, here's another definition with the meaning of plenum that we need:

Plenum — a space, usually above a ceiling or below a floor, that can serve as a receiving chamber for air that has been heated or cooled, to be distributed to inhabited areas.
 

 

At its root, plenum refers to "full space" and most of its varying definitions pertain to a separate enclosed space that is set apart from surrounding areas. It's the space above a building's dropped ceilings or below a raised flooring system, that gets used for heating, ventilation or air conditioning (often shortened to "HVAC").
WHAT DOES THAT HAVE TO DO WITH CABLING?

 

How do cables factor into all of this? In addition to being utilized for routing air, plenum spaces are often used to house telephone and network communication cables being run from one location to another. These cables are appropriately referred to as plenum cables. What sets these wires and cords apart from regular cables? The answer is they need to adhere to special fire-safety standards.

According to Article 800 of the National Electrical Code (NEC), plenum cables must comply with the specifications for flammability and smoke density outlined in Underwriters Laboratories (UL) and National Fire Protection Association (NFPA) testing methods.

To accomplish this greater resistance to fire, plenum-rated cables use special types of plastics in their jacket coverings. Flame-retardant, low smoke materials such as polyvinyl chloride (PVC), fluorinated ethylene polymer (FEP) or polyolefin, offer good resistance against fire. In the event they do begin to burn, they will not emit large quantities of harmful fumes.
WHY USE PLENUM?

 

Since plenum cables are routed through air circulation spaces which often contain very few fire barriers, they need to be coated in material that won't contribute to the spreading of flames. As network and communications cabling runs also typically spread throughout buildings, that increases the chances that if one ignited, flames and smoke could spread quicker.

If you have heard of riser cables, you may have heard that these are also flame retardant, but they cannot be used in plenum spaces. Riser cables are intended for non-plenum, vertical applications (between floors of a building). Though it is true they need to be fire resistant, riser cables typically incorporate load-bearing strengtheners since they need to stay upright without being stressed too hard. However, the specifications are much stricter for plenum cables; and these two cable types are not interchangeable. While plenum cables can be used in riser applications, the opposite is not true.

The bottom line is if your cabling application requires materials that are flame-retardant or compliant with strict safety standards, you should always opt for plenum-rated products.


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What is Plenum?

Plenum is an HVAC term used to identify open airspaces – usually above drop-down ceilings or below raised floors – which facilitate airflow circulation for heating and cooling. In most plenum airspaces, air ducts are used to connect the HVAC unit and the supply vents to distribute the air supply throughout a building. The return vents don't use ducting to feed the HVAC unit, creating an open airspace.

In other words, the HVAC unit pulls the return air within the open airspace and circulates it back to the supply vents. Even if both supply and return vents used ducting - a non-plenum airspace - a leaky duct can create an accidental plenum airspace.




While important for air circulation, the open airflow can quickly spread fire and smoke throughout a building. Because of this risk, any cable installed within plenum areas must be plenum-rated. Non-plenum cable will help spread the fire and introduce a higher level of toxic smoke.

What is Plenum and Non-Plenum Rated Cable?



Plenum and non-plenum cables can be any type of cable – coaxial, Ethernet, HDMI, fiber optic, etc. The term "Plenum" and "Non-Plenum" simply refers to the outer jacket/cover that protects the cable.

Plenum-rated cables, also known as CMP (Communications Multipurpose Plenum), have the highest flame rating and the highest cost. They're covered with a low-smoke polyvinyl chloride (PVC) or fluorinated ethylene polymer (FEP) fire-retardant jacket. The jacket is designed to restrict flame propagation within 5 ft, reduce the amount of smoke and toxic fumes released, and self-extinguish in the event of a fire. Thus, fire and building safety codes mandate plenum-rated cables be used in plenum spaces and air ducts. They can also be used in non-plenum areas.

Non-Plenum cables, on the other hand, are much cheaper and not as fire-resistant. When burned, they release toxic fumes such as hydrochloric acid and dioxin. Therefore, they may not be used in plenum areas. Otherwise, deadly gas will rapidly circulate through the building. The two most common non-plenum cables are riser-rated cable or CMR (Communications Multipurpose Riser) and CM (Communications Multipurpose).

CMR cables are mainly used in risers and vertical shafts to run cable through multiple floors. They are designed to prevent fires from spreading between floors. CM cable is the least fire-resistant and the cheapest. It's suited for general installations, like connecting a computer to a wall, and can also be used in areas without fire code restrictions on cable types.

Difference Between Plenum and Non-Plenum Cables
CMP   CMR   CM
Most fire resistant   Less fire resistant   Least fire resistant
Made for plenum airspaces, but can be installed anywhere   Mostly used for risers and vertical applications, but can also be used in non-riser spaces    For general use, or areas without fire code restrictions on cable types
Low-Smoke PVC or FEP Jacket   PVC Jacket    PVC Jacket
Releases a lower level of toxic fumes when burned    Releases a higher level of toxic fumes when burned   Releases a higher level of toxic fumes when burned
Most expensive    Less expensive than CMP    Cheapest
When Should Plenum Cable be Used?

Article 800 of the National Electrical Code (NEC) states that plenum cable should ALWAYS be used in plenum airspaces and air ducts to slow down the spread of flames and reduce smoke and toxic fumes from circulating throughout the building. Due to their higher safety standards, they can be freely installed inside plenum areas – no need to use a conduit. In addition, they can also be installed in non-plenum spaces.

Installing plenum cable in non-plenum spaces comes down to your budget, insurance, and building codes. For example, many commercial buildings, like schools, hospitals, and government facilities, are required to use plenum-rated cables in non-plenum areas to meet certain code requirements. Other businesses, on the other hand, choose to spend extra money on installing plenum cables in non-plenum areas to increase building safety and decrease insurance premiums.

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