CMR, CMP, and Direct-Burial Cable— What’s the Difference?

So you've already read up on the difference between CAT5 and CAT6 cables, and have chosen the right one for your job. But when you begin shopping you notice a variety of options in cable jackets. 

What’s more, their names have acronyms and words you haven’t seen before, like CMR and Plenum. Don’t worry though, we here at TXM are here to break these various terms down so you know exactly what cable you’ll be getting.

To get started, we need to understand from where each of these cable jacket types come. The National Electrical Code (NEC) was published by the National Fire Protection Association (NFPA) to delineate the proper standards for cable manufacture and installation. The first version of the NEC was published in 1897 and it has been updated every three years since its inception. While the NFPA is not a government agency, their NEC has become the defacto standard for cable installation and manufacturing. As part of the NEC’s set of guidelines, the type of jacket used for certain installations needed to be chosen. That’s what we’ll cover today.

The first type of cable jacket we’ll be covering is “Riser” or CMR cable. This cable, as its name implies, is used primarily for risers and other vertical shafts during cable installation. The jacket on these cables is designed to prevent the spread of fire from floor to floor- definitely not something you want to have skimped out on in the unfortunate event of a fire in your home or business.

The second type of cable defined by the NFPA is CMP or Plenum cables. Plenum cable is rated for the “plenum spaces” in buildings, which are simply the parts of the building that facilitate air circulation in heating and air conditioning systems. Plenum cable is covered in fire-retardant and low-smoke plastics, in the hopes of slowing the spread of fire and smoke to the living spaces in the building. CMP cable meets all the requirements for CMR cable and can therefore be used in risers, but CMR cable can’t be installed in the plenum spaces.

CM or CMG (General) cable is simply an general-purpose cable that can be used in installations not limited to the use of CMR and CMP cable. They are still fire resistant, but don’t meet the strict requirements of either of the previous cables. Typically, CMG cables are used in most home cable installations.

In addition to these safety designations, there is Direct-Burial or Direct Buried Cable which is not regulated by the NEC or the NFPA at all. This designation simply means that the cable has been engineered to be buried without any kind of outside protection. It is built to be more resistant to temperature changes, moisture, crushing as well as other environmental factors. Additionally, it is stiffened by a metal core, which further reinforces the cable’s durability.

And there you have it, everything you need to know about cable jacketing. 

TXM sells a full range of CAT5e and CAT6 bulk ethernet cable in CMR, CMP, Plenum and Direct Burial Options

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