Code Specs

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Copper Wire & Cable NEC Fire Resistance Ratings
Article 800 of the National Electrical Code (NEC), also known as NFPA 70, covers requirements for low-voltage
communications cables. The NEC requires that cables used in premises, both commercial and residential, be
“listed for the purpose” by a Nationally Recognized Test Laboratory (NRTL, pronounced “nurtle”). Other coun-
tries have similar requirements. UL (Underwriters Laboratories Inc.) is the most recognized listing agency in the
US. UL 444 is the overall specification used to identify the requirements for listed communications cables.
Many of the fire resistance test procedures called out in UL 444 are written by UL. However, other laboratories,
such as ITS (Intertek Testing Services) and CSA (Canadian Standards Association), can also provide listing com-
pliance to the NEC.
Five levels of fire resistance are specified. These are outlined below, from most stringent to least. The ratings
are hierarchical, i.e., from a fire resistance standpoint, a higher rating can be substituted for any lower rating,
but not vice versa.
NEC Designation Common Term Test Comments
CMP Communications
Plenum
NFPA 262 Cable must have resistance to flame spread and reduced smoke
generating properties. These cables are approved for place-
ment in air handling ducts and chambers (plenums) without the
use of fireproof conduit. The purpose of the rating is to lessen
the transmission of fire and visible smoke to unaffected parts of
the building. Toxic or corrosive elements of the smoke are not
measured.
CMR Communications
Riser
UL 1666 Cable must not transmit flame from one floor to another when
placed vertically in a building shaft (riser).
CMG Communications
General use
CSA C22.2
No. 0.3-M
(Vertical Tray)
Cable may not transmit flame for more than 4 ft, 11 in. It shall not
penetrate floors or ceilings, i.e., may only be used within a single
floor. This designation was added as a part of the harmonization
efforts between US and Canadian standards.
CM Communications
General Purpose
UL 1581
(Vertical Tray)
Cable may not transmit flame for more than 4 ft, 11 in. It shall
not penetrate floors or ceilings, i.e., may only be used within a
single floor.
CMX Communications
Limited Purpose
UL 1581 VW-1
(Vertical Wire)
Cable meets the least stringent flame spread requirements of all
ratings. For residential use, but can only be installed in one and
two-family (duplex) housing units. Often rated with optional UL
requirements for outdoor use
1
.
1 These “outdoor” requirements are limited to some cold temperature properties and UV resistance. They do not qualify a cable to be substituted for an Outside
Plant cable. For example, they have no protection against the intrusion of water, which can destroy a cable’s transmission properties and physically degrade a
cable as well. The purpose of the “outdoor” rating is to ensure the cable can withstand outdoor exposure in the short run between the Network Interface Unit and
the point of entry into the interior of the home.