Because they are installed in walls and ceilings, Ethernet cables must meet fire safety standards. Ethernet cables are low-voltage, carrying only a small amount of electricity at high frequency to transmit data, so the odds of them catching fire are very low. Nevertheless, fire codes require Ethernet cables to have jackets that minimize the risk of fire traveling along the cables from one part of a building to another.
Article 800 of the National Electric Code (NEC) has established the CM, CMR, and CMP fire ratings for Ethernet cables. These ratings designate the fire resistance of various cable jacket types.
What Is a CM-Rated Cable?
The CM or “Communications Multipurpose” rating is the minimum standard for Ethernet cables installed within the walls of single-story commercial buildings. To be CM-rated, cables must pass a standardized flammability test. CM cable jackets are made from polyvinyl chloride (PVC), which is cost-effective and flexible but can produce thick smoke and release dangerous gases in a fire.
What Is a CMR-Rated Cable?
CMR stands for “Communications Multipurpose Cable, Riser” and is a higher rating than CM. CMR-rated cables are designed for installation in the risers, or vertical shafts, between the floors of a building. CMR-rated cables go through stricter testing to show that they are sufficiently flame retardant to prevent a fire from spreading from one floor to another.
Riser-rated cable jackets may be made from either low-smoke PVC or fluorinated ethylene polymer (FEP). Although CM-rated cables may not be used where CMR-rated cables are required, CMR-rated cables can replace CM-rated cables. Therefore, CMR-rated cables are generally recommended because they can be used to meet multiple cabling needs.
What Is a CMP-Rated Cable?
The CMP rating, which stands for “Communications Multipurpose, Plenum,” is the strictest of the cable jacket ratings. It designates Ethernet cables that may be used in a building’s plenum, such as a dropped ceiling, raised floor, and other air spaces. Non-air-handling dropped ceilings may also be considered plenums if the ducts aren’t sealed properly.
Plenum-rated cables must limit flame propagation to five feet or less and minimize the amount of smoke emitted. Therefore, cables designed for installation in plenum spaces must use a jacket material that burns cleanly and self-extinguishes easily. Because air travels through the plenum, CMP-rated cables must not give off toxic fumes in a fire. CMP cables may be used in any application, but are generally reserved for plenum spaces due to their higher cost.
Supporting Your Cabling Needs
Although Enconnex has discontinued our line of network cables, our sister company, Liberty, offers a robust portfolio of connectivity products. Their team is ready to help. View their offerings at Libertyonline.com and get in touch at orders@libav.com or 800-530-8998.
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