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Flammability Ratings for Copper Cables Cable jacket ratings for copper cabling combine a wide range of terms, some of which may be more common than others depending upon location: CMX, CM, CMG, CMR and CMP.

Jacket Types

Per NFPA-70, the National Electric Code (NEC article 500), identifies the location where each cable type is to be used.

 CMP (PLENUM): Suitable for use in ducts, plenums, and other spaces used for environmental air and shall also be listed as having adequate fire-resistant and low smoke-producing characteristics. These cables are also referenced in Canadian Standards as CSA FT6.

•  CMR (RISER): Suitable for use in a vertical run in a shaft or from floor to floor and shall also be listed as having fire-resistant characteristics capable of preventing the carrying of fire from floor to floor.

•  CMG (GENERAL PURPOSE): Suitable for general-purpose communications use, with the exception of risers and plenums, and shall also be listed as being resistant to the spread of fire. These cables are also referenced in Canadian Standards as CSA FT4.

•  CM (GENERAL PURPOSE): Suitable for general-purpose communications use, with the exception of risers and plenums, and shall also be listed as being resistant to the spread of fire. These cables are also referenced in Canadian Standards as CSA FT4.

•  CMX (LIMITED USE): Suitable for use in dwellings and for use in raceway and shall also be listed as being resistant to flame spread.

As the flammability and smoke requirements for cables become more rigorous from CMX to CMP, the NEC also offers a cable substitution hierarchy (see Figure 1) to allow the use of more stringent requirement cables in place of a less rigid cable. For instance, a CMR or CMP cable could be replaced for a CM or CMG cable.

See NEC Cable Substitution Hierarchy for additional information.

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