Facts About Ethernet Cable Jacket Ratings

Written by Don Schultz, Senior Technical Marketing Specialist, Fluke Networks Certified Copper/Fiber CCTT, BICSI TECH, INSTC, INSTF Certified

An Ethernet data cable has an outer sheath (called a jacket) that protects the interior wires.  This jacket can come in many variations designed for different applications.  The choice of cable jacket affects the durability and reliability of the cable depending on the installation environment. Adding to this, the sheath and interior components will likely have some sort of fire rating printed on the jacket, so the cable must also be carefully chosen to meet strict fire safety regulations. Some cable jacket types are ideal for certain environments, but may not be legal to install indoors. All North American cable jacket fire ratings are borne from the National Fire Protection Act (NEC/NFPA 70). Let’s sort this out. Please watch our video below.

NOTE: The term “Ethernet” has become conflated over time with copper twisted pair Category cable. Many people use the terms interchangeably, since Cat5 and above copper cabling was purpose designed for Ethernet signaling. In actuality, Ethernet is a protocol that can run across fiber and coaxial as well. This blog will use the “Ethernet” interchangeably for clarity since we are referencing copper twisted pair Category cable, despite not being technically 100% accurate.

Why Fire Ratings Matter

• Fire safety: The rating reflects how the cable performs in a fire — how it burns, how much smoke it produces, and how much that smoke and flame will spread through a building via plenum and riser pathways
• Warranty: Using the wrong jacket rating can void manufacturer or installation warranties
• Code compliance: NEC/NFPA 70 dictates which ratings are legally required in which spaces; local AHJ (Authority Having Jurisdiction) enforces this
• Criminal/legal trouble: Installing the wrong rated cable in a commercial structure is a Code violation that can create real legal and liability exposure — not just a failed inspection

Key Terms and Acronyms You Should Know

When working with Ethernet cables, understanding the terminology is essential. Cable jacket fire ratings, materials, and installation guidelines are often described using specific terms and acronyms. These terms highlight critical factors like fire safety, installation environments, and material properties, while the acronyms reflect National Electric Code (NEC) standards for cable types.

Below, you’ll find an explanation of important terms and acronyms that will help you navigate the different types of Ethernet cable jackets and their applications.

General Terms

HVAC (Heating, Ventilation, and Air Conditioning)

HVAC refers to the systems responsible for circulating air within a building to maintain temperature, air quality, and comfort. These systems often include plenum spaces and air ducts, which are commonly used for running Ethernet cables.

Plenum

A plenum is an air-handling space within a building, such as the area above a dropped ceiling or below a raised floor. These spaces are often part of the HVAC system and are used for circulating air. Please note that the mere presence of a raised floor or drop ceiling does not necessarily indicate the presence of a plenum space. Always be sure you are checking with the AHJ (Authority Having Jurisdiction) like a building manager or even a local Code Inspector to be certain you know what you are dealing with to avoid costly mistakes!

Riser
A riser refers to vertical spaces within a building, such as walls or shafts, that connect different floors. A great example of riser spaces in a commercial building are the vertical conduit pathways between TRs (Telecommunication Rooms) installed in the ceiling and/or floor.

PVC (Polyvinyl Chloride)
PVC is a durable and cost-effective material used in the majority of Ethernet cable jackets. PVC serves as the base thermoplastic outer jacket material for the majority of indoor communications cable, and comes in various fire ratings.

FR-PVC (Flame Resistant Polyvinyl Chloride)

FR-PVC is essentially PVC that has additional ingredients formulated into the base thermoplastic like micronized PTFE (aka Teflon) to achieve maximum fire rating.

LLDPE (Linear Low-Density Polyethylene)
LLDPE is a material commonly used for outdoor Ethernet cable jackets due to its resistance to water, UV radiation, and physical wear. LLDPE thermoplastic is not typically formulated into indoor cable jacket types due to significant difficulty of achieving even the most basic of fire ratings.

FEP (Fluorinated Ethylene Propylene)

FEP is a material typically used in the interior construction of fire resistant and low toxicity smoke Ethernet cable such as Plenum rated. Items such as conductor insulation, spline, and even plastic wraps can all be constructed from FEP.

Common Acronyms Defined

The NEC defines several key acronyms for Ethernet cable jacket ratings, each specifying where and how the cable can be used. Here’s what you need to know:

CMP (Communications, Plenum)

Can be installed in any space, including plenum spaces. CMP cables are made with materials like FR-PVC (Flame Resistant PVC) and FEP, which resist fire and emit less smoke.

CATVP (Cable TV Plenum)

Designed specifically for plenum spaces in TV and video installations

CL3P (Class 3 Plenum)

For in-wall installations in plenum, riser, and general spaces where higher voltage may be present.

CL2P (Class 2 Plenum)
For in-wall installations in plenum, riser, and general spaces with lower voltage requirements.

CMR (Communications, Riser)
Suitable for vertical runs between floors. CMR cables are fire-resistant but not safe for plenum spaces.

CATVR (Cable TV, Riser)
Used for vertical runs in TV and video installations.

CL3R (Class 3, Riser)
For in-wall installations in riser and non-riser spaces with higher voltage.

CL2R (Class 2, Riser)
For in-wall installations in riser and non-riser spaces with lower voltage.

CM or CMG (Communications, General)
For general indoor use in non-critical areas. CM cables lack the fire resistance of plenum and riser-rated cables.

CATV (Cable TV)
Used for general TV and video installations.

CL3 (Class 3)
For in-wall installations in non-riser, non-plenum spaces with higher voltage.

CL2 (Class 2)
For in-wall installations in non-riser, non-plenum spaces with lower voltage.

CMX (Communications, Limited Use)**
The lowest UL/cETLus fire rating for communication cables, determined by flame and smoke testing. 

OSP (Outside Plant)

Designed for outdoor installation. OSP cables are resistant to UV light and water and are typically not fire rated for interior use (Unlisted).

CATVX (Cable TV, Residential)
Used for TV and video installations in residential environments.

CL3X (Class 3, Residential)
For in-wall installations in non-riser, non-plenum residential spaces with higher voltage.

CL2X (Class 2, Residential)
For in-wall installations in non-riser, non-plenum residential spaces with lower voltage.

Do not confuse CMX fire ratings with outdoor cable--that is two different subjects. Most OSP communications cable is not fire rated at all. Commercial rules treat CMX fire rated communications exactly like OSP cable, making no differentiation between how and where it may be installed.

The Most Common Jacket Ratings, One by One

Unlisted (also OSP or Outside Plant) 

• Definition: 
  • Unlisted Ethernet cable has not been tested by NRTL (Nationally Recognized Testing Laboratory) such as UL or ETL for fire and flame performance and has no fire rating at all — unmarked or explicitly labeled Unlisted or OSP. If there is no ETL or UL Listing number printed on the cable jacket, then the cable is Unlisted. 
• Location/Application: 
  • Unlisted is typically seen with OSP or Outside Plant cabling. OSP cable is designed for outdoor installation, typically using LLDPE jacket material instead of PVC.  
  • LLDPE is resistant to water, UV, snow, ice, and severe temperature swings. Gel filled (icky-pic) burial cable is a great example. 
  • Unlisted cable may enter a structure from outside to inside a maximum distance of 50 feet (or full IMC conduit protection for longer runs) per the NEC/NFPA 70 before requiring termination or transition to a fire rated cable.  
  • Restrictions apply to commercial and residential structures.
• Flame Test Performance: 
  • Unlisted cable has not passed any fire/flame testing and must not be used as general indoor cable.

CM or CM/G

• Definition: 
  • Communications, General-purpose fire rating
  • Untreated PVC jacket
  • No added fire protection
• Location/Application: 
  • Limited commercial use (single-room connections, exposed horizontal trays outside plenum)
  • Broader residential interior use, though trueCABLE still recommends Riser for the added protection
  • Typically associated with pre-terminated patch cords

• Flame Test Performance: 

  • Burns like untreated PVC plastic
  • Emits toxic smoke and fumes and will promote the spread of flame

CMR

• Definition: 
  • Communications, Riser fire rating
  • Designed to not promote the spread of flame vertically (risers)
  • PVC jacket with mild fire resistant treatment
• Location/Application: 
  • Anywhere in a structure except plenum spaces
  • CMR is the most common and cost-effective jacket type on the market
  • Suitable for vertical runs between floors and in walls
  • trueCABLE recommends CMR rated Ethernet for general commercial and residential indoor use due to the reduced ability to promote the spread of fire
• Flame Test Performance:
  • Tested for vertical flame spread performance
  • If burned, will emit toxic smoke and fumes
  • Flame propagation is contained better than CM or CM/G

CMP

• Definition:
  • Communications, Plenum fire rating
  • CMP rated Ethernet is constructed from FR-PVC and FEP components throughout — jacket, conductors, spline, rip cord (aramid/Kevlar), and foil shield backing (if present) all use flame-resistant, low-smoke materials
  • Designed to prevent flame propagation with self-extinguishing characteristics in vertical and horizontal drops
• Location/Application:
  • Required in plenum air-handling spaces (above drop ceilings, below raised floors)
  • May be used anywhere Riser can be used, at a higher cost
  • No required residential application; the CMP fire rating is aimed at sensitive commercial building spaces
• Flame Test Performance:
  • The highest fire performance tier for indoor communications cable
  • Low toxicity smoke emission and designed to self-extinguish flame

Inside a commercial building (this can mean office, school, hotel, motel, and more) the construction contractor likely installed a HVAC system where air handling occurs. This is called the plenum. The plenum area is a likely spot for installing cabling. As convenient as this is, it brings special considerations related to fire and toxic smoke!

CMX 

• Definition: 
  • Communications, Limited Use fire rating
  • Usually constructed from HDPE or more rarely LLDPE
  • Limited Use means minimal vertical flame testing
• Location/Application: 
  • CMX is often associated with indoor/outdoor coaxial and Ethernet cable that may be used throughout a residential structure with restrictions (0.25" or thinner diameter, single/duplex dwelling only)
  • CMX fire rating is treated as Unlisted for commercial structures and the 50ft ingress rules apply
  • Any CMX Listed cable above 0.25” in diameter must obey the 50ft ingress rule regardless if the installation is residential or commercial
• Flame Test Performance:
  • Passes only minimal vertical flame testing, but not enough to meet a commercial riser fire rating
  • Emits toxic smoke and fumes when burning
  • Must be backed by proper regulatory certification or risks being counterfeit - always check for a UL or cETLus Listing number and ask for the Certificate of Compliance that applies to the particular cable you are purchasing

Critical Additional Information Regarding OSP vs CMX

OSP and CMX Are Not the Same

Although it is possible for a cable to be both CMX and OSP, the terms "CMX" and "outdoor Ethernet" cable address completely different things. The terms are often misapplied and confused with each other. The CMX term is now widely misunderstood as a result. CMX is a fire rating, but OSP is not. A marking of OSP is only an indicator of the cable’s intended installation environment.

OSP vs CMX: What’s The Law?

Commercial Structures

Commercial structures are treated the same regardless of circumstances. Any Outside Plant cable, including CMX fire rated, is considered not fire rated at all and may not be installed inside a commercial structure EXCEPT the cable may come into the structure up to 50 feet before termination or transition to an approved indoor fire rated cable like CM, CMR, or CMP. An exception is made where the cable may go further into the structure but the entire run coming in must be sealed in intermediate weight (IMC) threaded metallic conduit. The threads of the conduit sections must also be sealed.

Residential Structures

Residential structures have the same restrictions as commercial structures except CMX fire rated outdoor cable may be used with restrictions as follows:

1. The CMX fire rated outdoor cable must be 0.25" or thinner in overall diameter
2. The structure may only be a single or duplex residential dwelling

Apartments

What about apartments? Multi-unit dwellings like apartments are treated the same as commercial structures and all commercial rules apply.

Local Code dictates the Law in your jurisdiction, but the NEC/NFPA 70 National Guidelines are often accurate for your locale. It is always best to check first, especially in a commercial installation. Since CMX cable may only be installed in residential structures in a limited number of scenarios, riser fire rated cable is the preferred choice for most indoor residential installations.

How to Choose the Right Ethernet Cable Jacket

It’s important to make good choices and to put the right cable in the right place. If you install either CMR or CMP cable outdoors, the jacket will begin to degrade immediately and will fail in a matter of months. Given the critical nature of selecting the right fire rating and environmental application for the cable to be installed, here are some quick reference guides to help!

* Be careful. Only CMX that is less than or equal to 0.25” diameter and installed into a single or duplex dwelling qualifies for this exemption.

Conclusion

There you have it! Now you know that “CMX vs. CMR vs. CMP” is describing differences in fire safety standards. Generally, unless you are heading up into the plenum space or installing cabling outdoors, Riser Rated cable will provide a degree of safety and good value, not to mention being easy to install.

trueCABLE has a wealth of resources to ensure a proper installation. Poorly manufactured cable jackets can leave your network exposed to moisture, heat, and other weather conditions. Visit our extensive Cable Academy to understand essential aspects of installation, including cable jacket ratings, terminations, Ethernet cable Category types, and practical advice on how much cable you need to purchase for your installation. Our comprehensive library of over 200 blogs and articles on Ethernet and fiber optic technologies empowers you with the knowledge to select quality Ethernet equipment you can depend on.

HAPPY NETWORKING!

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