Facts About Ethernet Cable Jacket Ratings

Facts About Ethernet Cable Jacket Ratings

Written by Don Schultz, Technical Sales Representative and Fluke Networks Certified Technician

An Ethernet data cable has an outer sheath protecting the interior wires called a jacket.  This jacket can come in many variations designed for different applications.  All jacket types are borne from the National Electric Code (NEC) which was published by the National Fire Protection Agency, and happens to be 600 pages long and potentially confusing. To help you, allow us to share the most important facts about Ethernet cable jacket ratings.

From the NEC, here are some of the more common acronyms.  Many of these you will recognize, although a few you will probably not.  I have underlined the types that apply to this article. 

  • CMP: Communications, Plenum - can be installed in any space
  • CATVP: Cable TV Plenum
  • CL3P: Class 3 Plenum - for in-wall installation in plenum, riser and general spaces
  • CL2P: Class 2 Plenum - for in-wall installation in plenum, riser and general spaces
  • CMR: Communications, Riser
  • CATVR: Cable TV, Riser
  • CL3R: Class 3, Riser - for in-wall installation in riser and non-riser spaces
  • CL2R: Class 2, Riser - for in-wall installation in riser and non-riser spaces
  • CM or CMG: Communications
  • CATV: Cable TV
  • CL3: Class 3 - for in-wall installation in non-riser, non-plenum spaces
  • CL2: Class 2 - for in-wall installation in non-riser, non-plenum spaces
  • CMX: Communications, Outdoor / Residential
  • CATVX: Cable TV, Residential
  • CL3X: Class 3, Residential - for in-wall installation in non-riser, non-plenum spaces
  • CL2X: Class 2, Residential - for in-wall installation in non-riser, non-plenum spaces

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.

Before we delve into what Ethernet cable ratings you are likely to encounter for sale and where to use it, here are some terms you need to know.

  • HVAC stands for heating, ventilation, and air conditioning. This term refers to an industry standard for how air is moved inside a building. 
  • Plenum means the spaces usually occupied by the HVAC system, found above and below floors. This empty air space is commonly used for moving air around with or without a dedicated duct.
  • Riser means vertical, typically inside walls and between floors.
  • PVC (Polyvinyl chloride) is the material used in the majority of cable jackets. PVC is simply your typical vinyl.

A network data cable installer is likely to use CM, CMP, CMR, or CMX type jackets.

Plenum Rated (CMP)

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 FEP (fluorinated ethylene propylene).  FEP is essentially a plasticized Teflon.  FEP emits little smoke when burning and is low toxicity. 

Plenum cable is more expensive than non-Plenum cable.  Ultimately, the decision won’t be the installers 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.  Plenum rated cable can be installed in all spaces but the per-foot cost involved typically prohibits this.

Riser Rated (CMR)

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 or strands of fibers baked into the jacket that limit the ability of the cable to carry a flame.  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.  Riser rated cable may be used in any part of your structure EXCEPT the Plenum.

Ethernet Cable Jacket Variations

General Use (CM/CMG)

CM rated 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 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 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.

Outdoor (CMX)

CMX rated Ethernet cable is designed primarily for outdoor use, such as open-air or even direct burial.  Given that CMX rated jackets are not fire rated, but are UV rated, there are different rules governing where and how it can be installed.

In commercial applications CMX rated Ethernet cable installed outside may run inside up to 50 feet prior to termination per NEC Article 800.113.  CMX may be used outside the commercial structure with no restrictions.

In residential applications the NEC Article 800.113 allows for CMX rated Ethernet cable to be used as indoor/outdoor cable without restriction assuming the following rules are obeyed:

  • The cable OD (overall diameter) does not exceed 0.25”
  • The structure is limited to a single family or duplex dwelling 

Please note that riser rated Ethernet jacket is still preferable if the runs are indoor only.  The reasoning is riser rated jackets are often less expensive, a bit easier to terminate due to thickness, and have some degree of fire protection built in.

CMX rated 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.  CMX cable can be expensive due to how the cable is constructed, but not as expensive as Plenum rated cable.  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. 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 presents the information on our website, including the “Cable Academy” blog and live chat support, as a service to our customers and other visitors to our website subject to our website terms and conditions. While the information on this website is about data networking and electrical issues, it is not professional advice and any reliance on such material is at your own risk.

Albert Kleyn February 14, 2020

Thank you for a series of absolutely excellent articles.
Most informative, Comprehensive and very very well written!
Sadly, being in Ireland precludes me buying from you, but where I in the USA, I would most certainly be customer.
Again, thank you for the time and effort put into these articles.

John Schaffer November 06, 2020

I was wondering if one needs to run a cable from the outdoors to an inside plenum space and desired a continuous run to the IDF/MDF what options could be available? The only ones I would think, would be to run the cable through conduit outside, but that is not always possible. The other choice, less desirable is to put a break / splice in the cable inside the outdoor wall, connecting CMP cable to CMX if a conduit option is not available.

trueCABLE November 13, 2020

If this is a commercial structure, then running CMX rated Ethernet cable into the plenum space at all is strictly forbidden by law (NEC/NPFA). If an inspector should notice, they will order removal of that cable from the plenum space before final approval. As for running indoor rated cable (CMP) in an outdoor environment (even inside conduit), that is further not a good idea. CMP rated cable has a PVC + Teflon bearing jacket which will allow water vapor to get near the conductors. Normally this is not an issue unless the environmental temperature swings do not make the vapor condense into liquid water, such as in relatively stable indoor temperatures. The vapor will egress/ingress unnoticed indoors. Not so outside, where vapor can enter the cable and then condense into water at night. The water will not be able to escape and this will destroy data transmission. The less desirable (from an installation standpoint) option is your only option. This means your overall Ethernet Channel will involve an extra termination or two and multiple jacket types. Using Component rated jacks, plugs, structure Ethernet cable, and patch cords are important to maintaining good overall Channel performance.

- Don, trueCABLE

    1 out of ...