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Ethernet Jacket and Fire Rating: CM CMR CMP CMX

Author Yana

Date 12/29/2021

The wiring installers must take the fire rating of jacket material into consideration for different wiring projects. CM CMR CMP CMX are four common Ethernet jacket materials. How to sort their fire ratings, let us find out below.

Communication systems using twisted-pair wiring should keep in step with the cable protection rule specified in Article 800, Communication Circuits of NEC by the National Fire Protection Agency. Hence, When deploying Ethernet copper cabling in residential or commercial usage, choosing the right fire rating of the Ethernet jacket is significant. CM, CMR, CMP, and CMX are the four major Ethernet jacket types in the market. This post provides a brief introduction to each Ethernet jacket type and guides to choose from.




What is CM, CM Cable (General)?

Communications Multipurpose (CM) is the most basic Ethernet jacket fire rating, which retards flame by halogenated chemicals. It is specified by the industry burn test standard UL 1581. The standard defines an 8 feet long vertical tray flame test for 20 minutes, over which the flame of the cable should not spread to the top of the tray before self-extinguishing.


CM jacket is sheathed with PVC and insulated with high-density PE, which will release thick smoke with high toxicity.


CM cable is designed for general use and found commonly as standard Ethernet patch cable running direct connection between two devices, such as from a  wall plate to desktop, or switch to the server.


What is CMR, Riser Rated Cable?

Communications Multipurpose Cable, Riser (CMR) is a flame-resistant Ethernet jacket standard, defined in UL 1666. The standard specified a vertical chamber test in a 12 feet long shaft. At the bottom, a 145kW propane burner ignites the cable for 30 minutes. Tests will pass only if the flame does not reach 12 feet.


CMR jacket is sheathed with high fire-resistant PVC material and insulated with high-density PE. When the cable catches fire, it will emit toxic gas containing halogenated material. As a strong oxidizer, the halogen (Chlorine) will support combustion to run out of oxygen. Oxygen is exhausted, the flame will go out.


It is designed for vertical wiring applications to prevent fire from spreading between floors or a shaft. Riser cable has more strict requirements than CM cable. Generally speaking, it can be applied in any place except for the plenum areas.


CMR cable is also known as CMR riser cable, riser-rated cable. Currently, the most commonly used CMR cables are PVC CMR Cat6 riser cable and Cat5e riser cable, seen commonly in the form of bulk Ethernet cable rolls. 


What is CMP, Plenum Rated Cable?

Communications Multipurpose Cable, Plenum (CMP) is the highest grade of fire rating Ethernet jacket. CMP complies with the UL 910 Plenum test. Under the flame test, a bundle of 24-foot cables running through an isometric Stein tunnel test furnace is being ignited using an 88 kW methane burner. It must extinguish within 5 feet when burned in ventilated spaces with air flowing for 20 minutes. 


Plenum Ethernet cable is made of fluorinated ethylene polymer (FEP) insulation and low smoke polyvinyl chloride (PVC) outer sheath. FEP has high fireproof features and its ignition point is up to 800°C. Besides, the plenum cable is coated with Teflon, which prevents flames from spreading and decreases the emission of smoke and toxic gas in combustion. 


Therefore, the plenum-rated cable is very suitable for making cables that transmit high-speed data in a ventilated environment. It is designed to be installed through plenum spaces of the HVAC system, typically above the dropped ceiling or below raised floors in commercial buildings.


PVC CMP plenum rated Cat6 is the most popular plenum rated cable in the market, found commonly as bulk Ethernet cable Cat6 plenum 1000ft.


What is CMX, CMX Cable (Outdoor)?

CMX stands for Communications Limited Purpose. It meets the lowest fire rating requirements. CMX is standardized by UL 1581 VW-1 test. CMR-rated cable is often granted with an optional UL rating for outdoor use, exposed in the open air, or direct burial underground. Consequently, considerations come first for choosing jacket material is UV resistance. CMX cable utilizes a non-PVC Linear Low-Density Polyethylene (LLDPE) jacket, ensuring UV- and weather-proof.


Outdoor vs General vs Plenum vs Riser Cable, What's the Difference?


Now that you already have a picture of each Ethernet cable jacket type and its fire rating. Let's sum up the differences in the table below.


Jacket Material outer sheath: PVC
insulation: PE
outer sheath: PVC
insulation: PE
outer sheath: PVC
insulation: FEP
Fireproof additive / oxidizer Chlorine coating Teflon /
Fire rating CMX<CM<CMR<CMP
Test standard UL-1581 UL-1666 UL-910 UL-1581
Product Form Patch cables Bulk Ethernet cables Bulk Ethernet cables /
Typical Application Scenarios general usage for residential;
direct connection from the wall plate to CPs for commercial
in wall;
vertical cabling between floors of non-plenum spaces
Plenum area of HVAC system drop ceiling and raised floors in commercial building outdoor;
direct burial
Price CMP is much expensive than the others
Interchangeability CM cannot replace CMR and CMP, CMP can alternate all except CMX, CMR can be used in any non-plenum spaces indoor.


Plenum vs Riser Cable, Plenum vs Non Plenum Opotion

Previously we mentioned the fire rating and Interchangeability of the four jacket type. Fire rating CMX<CM<CMR<CMP and the latter can be applied in almost any areas that CMR and other rated cables can do. Here comes the question, Plenum vs riser cable option, should I buy CMP for best fire rating? I suggest one should choose according to your needs without excessive consumption. To choose between CMP vs CMR is just a matter of plenum vs non-plenum. If your wiring project must be done in plenum space, pick CMP. If not, pick CMR. For example, DCs that with the condition to wire without air ducts or vents, picking riser cable will save you a fortune and meet just-right fireproof requirements. 


CM vs CMR vs CMP vs CMX: When to Choose Which?


General Riser Plenum Outdoor
Residential general use for direct connection
Comercial in-wall; between floors (non-plenum areas)
Comercial air plenum spaces
Outdoor in the air, direct burial, etc

Check the following buying guide tips:

CM — a direct connection between devices within a short distance

CMR — vertical wiring project in walls or between floors in non-plenum spaces (no need to run through an air duct)

CMP — wiring installation required for running cables in Plenum areas of HVAC system

CMX — outdoor wiring project