User manual

January/February 2001 ExtroNews 12.1 7
So, What’s All This Cable Safety
Rating Stuff Anyhow?
So, what does all the safety alphabet
soup mean?
Table 2 (on following page)
is a handy applications table that will help
you organize the cable marking
designations mentally.
Plenum-rated cables (suffix “P”) are at
the top of the cable safety food chain
because they are constructed of materials
having very low “fire load.” Fire load is the
term used to describe how much fuel a
given material provides a fire. A lower fire
load rating means that the material is
more fire resistant and produces less
smoke, which accounts for most
fire-related deaths. Cables obtain the
plenum rating upon successfully passing
UL 910, Test for Flame-Propagation and
Smoke-Density Values for Electrical and
Optical-Fiber Cables Used in Spaces
Transporting Environmental Air. Plenum
is a commonly used term today in the
construction and system installation
industries because, in most cases, plenum-
rated cables may be installed in air
handling systems (air plenums) without
expensive metallic conduit. Plenum cable
can cut installation costs dramatically.
Riser (suffix “R”) describes cables having
a lesser degree of flame retardancy than
plenum, but may be used to convey signals
vertically in shafts without requirement for
metallic conduit. The compliant cable has
a flame propagation of less than 12 feet
and has a temperature of 850 degrees
Fahrenheit or less at a height of 12 feet per
UL 1666.
General-purpose (no suffix) cables may
be used in conduit, behind walls, or other
enclosed locations where the cable is
protected and not in an air plenum.
Commercial installations, at a minimum,
must use general-purpose cables (the
typical CL2 designation for coaxial video
TECHNICALLY SPEAKING...
cables, for example). This type of cable
must comply with UL 1581, the Vertical-
Tray Flame Test. For CSA (Canadian
Standards Association), the vertical flame
test differs in loading (more cable in
bundles), burner angle, and failure
criterion.
CL2X and CL3X are the lowest rated
cable and must comply with UL VW-1
Vertical-Specimen Flame Test. The cable is
not marked VW-1. This rating may be used
in residential dwellings.
PLTC (power-limited tray cable) complies
with a 70,000 BTU/hr vertical-tray flame
test. Cables of this type are marked PLTC
with ink or marker tape.
Getting ‘P’ On Your Cable
What makes a cable into a plenum rated
cable? The materials making up the
MPP
CMP
CL3P
CL2P
FPLP
MPR
CMR
CL3R
CL2R
FPLR
MPG
MP
CMG
CM
PLTC
CL3
CL2
FPL
CMX
CL3X
CL2X
National Electrical Code (NEC) Cable Substitution Hierarchy
MPP CMP CL3P CL2P FPLP MPR CMR CL3R CL2R FPLR MPG MP CMG CM PLTC CL3 CL2 FPL CMX CL3X CL2X
Cable
Type
Permitted Substitution
Plenum Types
Riser Types
General Purpose Types
Dwelling Types
Table 1. National Electrical Code (NEC) Cable Substitution Hierarchy for Fire Safety
continued on next page