Facts About Ethernet Cable Jacket Ratings

Written by Don Schultz, trueCABLE Senior Technical Advisor, Fluke Networks Copper/Fiber CCTT, BICSI INST1, 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. The jacket must also be carefully chosen to meet strict fire safety regulations. All jacket types are borne from the National Electric Code (NEC) which was published by the National Fire Protection Act (NEC/NFPA 70). This document is 600 pages long and potentially confusing. To help you, allow us to share the most important facts about Ethernet cable jacket ratings.

Key Terms and Acronyms You Should Know

When working with Ethernet cables, understanding the terminology is essential. Cable jacket 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.

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. 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.

OSP (Outside Plant)

Designed for outdoor installation. OSP cables are resistant to UV light and water and may or may not be fire rated for very limited application residential indoor use.

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.

Most Common Types of Ethernet Cable Jacket Ratings

A network data cable installer is likely to use CM, CMP, CMR, or CMX type jackets. The outer jacket material has no bearing on whether the cable is Cat5e or Cat6 or anything INSIDE the cable. In fact, the outer jacket material has no bearing on whether we are talking about Ethernet data cable or cable TV cable jacket types. If you’re interested in jackets for fiber optic cables, check out Fiber Optic Cable: Jacket & Fire Rating - What Are The Differences?

Plenum Rated (CMP Cable)

Inside a commercial building (this can mean office, school, hotel, motel, and more) the construction contractor installed a HVAC system inside 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.

• The Plenum area is a great way to channel a fire and resultant smoke from one spot to the next in a building, and quickly.
• PVC cable, without a Plenum rating, will aid in spreading a fire and the resultant highly toxic smoke will end up invading the common living/working spaces which will cause anything from immediate fatality to long term health issues.

Given the critical nature of fire protection, a Plenum cable performance rating was established. Commonly, Plenum cable is constructed from flame resistant PVC (FR-PVC) and FEP (fluorinated ethylene propylene) components. FR-PVC is essentially a plasticized Teflon. FR-PVC emits less smoke when burning, is more resistant to spreading flame, while being low toxicity.

Plenum rated cable is much more than simply a FR-PVC outer jacket to meet the CMP fire rating.  The conductors are typically FEP, the interior spline cross skeleton (if present) is FEP, the rip cord is aramid yarn (aka Kevlar), and any non-conductive plastic raps will be FEP as well.  This makes plenum cable very different from most other cable constructions, in just about every way.  If a foil shield is present, even the foil shield will use flame resistant mylar as opposed to normal mylar backing.

Plenum cable is more expensive than non-Plenum cable. Ultimately, the decision won’t be the installer’s to make. Local fire codes, insurance requirements, or even customer requirements will dictate if Plenum must be used. Regardless, NEVER use plain PVC cable in a Plenum space. CMP cable can be installed in all indoor spaces but the per-foot cost involved typically prohibits this.

Riser Rated (CMR Cable)

Riser rated cable is PVC. Riser rated cable is suitable for use inside walls and runs vertically between floors. Typically, the fire resistance is due to a Teflon coating on the cable jacket. If the cable should actually burn, the resultant smoke and fumes are toxic. Riser rated cable is the most common jacket type found on the market and is much lower in cost. CMR cable may be used in any part of your structure EXCEPT the Plenum.

General Use (CM/CMG Cable)

CM/CMG cable is again PVC, but this time without any added fire protection. This cable will burn just like any untreated plastic and will emit toxic smoke and fumes.

For commercial applications, CM/CMG rated cable is suitable for making connections inside a single room such as ready-made patch cables from the wall to a computer. Secondarily, it may be used in exposed horizontal metallic cable trays that do not invade the plenum space. Given its relatively restricted use in commercial structures, this cable jacket type is seldom seen in this application. Riser and plenum rated jackets are typically used due to legal, insurance, or contractual obligations.

For residential applications, CM/CMG rated cable may be used anywhere in the interior of the structure, but may not be any more cost effective than riser rated. trueCABLE recommends that riser rated Ethernet cable be used for interior-only installations, due to the extra degree of fire protection.

Limited Use (CMX Cable)

CMX stands for "Communications, Limited Use" and is a cETLus or UL fire rating. This means the cable passed (very minimal) vertical flame testing in a laboratory. A CMX fire rating is often seen stamped on certain outdoor and direct burial cables but must be tested per regulation otherwise it is counterfeit. Any CMX rated Ethernet cable needs to be backed up by the appropriate regulatory agency certificate if installed in certain ways as outlined below.

Outdoor Plant (OSP Cable)

OSP stands for "Outside Plant" and means cable that is designed for installation outdoors and is resistant to water, ice, sunlight, and snow to varying degrees depending on the specific cable. This term is applied to above ground outdoor and direct burial Ethernet cable. OSP communications cable need not be marked at all, and may or may not have a low level CMX fire rating.

OSP cable does not use PVC for the outer jacket, but instead typically uses LLDPE (Linear Low Density Polyethylene). LLDPE is UV Resistant and weather proof in nature. Additional cable construction (inside) may make this cable type suitable for direct burial as well. OSP cable can be expensive due to how the cable is constructed, but not as expensive as Plenum rated cable.

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 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 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

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. Because CMX cable may only be installed in residential structures in a limited number of scenarios, riser 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. Patch cables made with CM jackets are not suitable for permanent installation within structures due to the lack of a fire rating. OSP cable can withstand moisture, sunlight, and mild abrasion, but normally should not be installed indoors. Doing so risks the safety of occupants in the case of a fire, and is a violation of the NEC. Plenum cable may be installed everywhere that riser cable can be, but riser cable is less expensive. Riser cable must never be installed in plenum spaces.

Conclusion

Hopefully this article about Ethernet cable jacket ratings clarifies the different Ethernet data cable jacket types you are likely to see for sale and what is the right jacket for the job at hand. 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.

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 types, and whether to use a riser vs. plenum cable. 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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