UL Standard for Fire Retardancy

If a cable can pass a specified UL fire standard, an UL performance verification mark can be applied onto the cable jacket illustrating both the UL class and the number. There are five primary fire testing standards as follows.

CMP (Plenum Flame Test/ Steiner Tunnel Test)


Plenum rated cables meet the NFPA -262 standard (formerly known as UL910)
which provides the most stringent requirement of all the tests. Cable samples on a
horizontal tray in a tunnel type of chamber are burned at 87.9KW (300,000 BTU/Hr) for
20 minutes. To qualify for a plenum rating the cable specimen musthave the flame spread
of less than 5 feet or 1.5 meters with a smoke density during the test of (a) 0.5 peak and
0.15 maximum average. The CMP cables are usually installed in air ventilation ducts and
air returns widely used in Canada and USA. The fire retardant properties of CMP cables
are much better than that of normal LSZH cables complying with IEC 60332-1 and IEC
60332-3.

CMR (Riser Flame Test)



Riser rated cables meets UL1666. Cable samples on a vertical shaft are burned at
154.5KW (527,500 BTU/Hr) for 30 minutes. To qualify for a riser rating, cable specimen
must have the flame spread of less than 12 feet beyond the ignition point. This test does
not look at the smoke density or toxicity. Riser rated cables are suitable for vertical
shafts not defined as an environmental air plenum.

CM (Vertical Tray Flame Test)



General purpose cables meet UL 1581. Cable samples on a 8 feet vertical tray are
burned at 20KW (70,000 BTU/Hr) for 20 minutes. The cable specimen is deemed to
pass the test if the flame spread will not extend to the upper portion and extinguish by
itself. UL 1581 is similar to IEC 60332-3C except for that the number of testing samples
is different. This test does not look at the smoke density or toxicity. The CMG cables are
usually used in runs penetrating single floor. These cables cannot be installed in vertical
pathways.

CMG (Vertical Tray Flame Test)


These general purpose cable also meet UL1581. CM and CMG are similar and
both are recognized in Canada and USA. This test does not look at the smoke density or
toxicity. The CMX cables are usually used in runs penetrating single floor. The cables
cannot be installed in vertical pathways.

CMX (Vertical Wire Flame Test)



The restricted cables meet UL1581 Limited-use. The test consists of 25 feet long
ventilated tunnel. The cable specimen is placed on a ladder inside the tunnel and the
flame of 30,000 BTU/Hr is applied to the cable 15 seconds on and 15 seconds off five
times for a total exposure to the flame of 1 minute and 15 seconds. To qualify for this
test, after the test flame is removed the cable specimen can flame for not more than 60
seconds and the charred portion will not exceed by 25%. UL 1581 VW-1 is similar to
IEC 60332-1 except for the difference in the time for flame applied. This test does not
look at the smoke density or toxicity. The CMG cables are suitable for use in dwellings
and for use in raceway. These cables cannot be installed in bundles and must be
protected in metal conduit. This type of cable is chosen as the minimum requirement for
commercial installations.