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Data, Network & Bus Technology
UL Listed or UL Recognized,
Which Cable is the Right One?
helukabel-group.com
J
ust because it has a UL mark does not necessarily guarantee acceptance; after all, approval can be a tricky
business. So before choosing a cable for a device or machine design, it makes sense to obtain comprehensive
information about the different approval types.
The North American market is an important one for
selling internationally produced machinery and plant
engineering. Underwriters Laboratories (UL) approval is
just as important for manufacturers because it facilitates
entry into the US and Canadian markets. UL approval can
apply either to an entire machine or to all the individual
components used, although it’s generally the latter
that facilitates acceptance. However, there are major
differences between the individual approval types and
the way in which they are handled by inspectors, which
might cause potential problems to occur during the
acceptance process.
There are two types of UL approvals – UL Listed ( ) and
UL Recognized ( ) – and each has their own unique
differences. Inspectors are generally more familiar with UL
Listed requirements, which means that they more readily
accept this marking. Inspectors tend to have the standard
memorized since they encounter it repeatedly, and can
therefore make faster decisions during the acceptance
process. For machinery and plant engineers, this saves
a great deal of time and reduces costs because test and
acceptance costs are much lower.
The UL Recognized mark, on the other hand, conceals
hundreds of Appliance Wiring Material (AWM) Styles
which can be found on the UL identity card, which
identifies a manufacturer’s existing AWM Styles.
Machinery and plant equipment manufacturers who produce for the
North American market should be aware of the various UL approvals
required for industry compliance.
Approval is granted after a product for a machine or
wired device is submitted to UL with information about
the application (e.g. voltage level, flame retardant
properties, temperature range, etc.). UL personnel then
test the product’s mechanical properties and issue an
existing AWM Style if the required parameters are met. If
this is not the case, a new AWM Style is issued.
However, acceptance can be a daunting task. Due to the
vast number of AWM Styles, the inspector cannot say off
hand which category the product belongs. Additional
research is required to determine the correct category and
with 50 to 80 different cables for each machine, this can
take a long time to verify. Furthermore, during the research
process, the inspector might come across a criterion that
prevents acceptance. In this case, the customer would
have to adjust its equipment before applying for approval
again. Obviously this costs valuable time and money.
Generally, if any problems occur it’s not because the
product is not approved, but rather because it has the
wrong type of approval. The following example explains
the complexity of the issue.
A machine engineer sets up several machines in a factory.
The machines are wired together with a polyurethane
(PUR)-jacketed track cable that has a UL Recognized
AWM Style or UL Listed CMX approval.
While PUR is an excellent material for permanently
moving cables that require a long service life, however,
PUR does not have a high level of flame retardancy due
to its chemical composition. So while this cable may be
suitable for wiring inside the machine, it is not suitable
for connecting individual machines. Then there’s the
following problem: the cables are laid along the floor
in open or closed cable trays. Cables installed in this
way fall under the generic cabling classification (CM/
CMG), which requires a bundled fire test. When cables
are installed in trays, UL requires them to have high
flame retardant properties. Therefore, the fire marshal
conducting the tests will accept the wiring inside the
machine, but not the wiring between the machines. As
a result, the already installed cables must be completely
or partially removed and replaced with versions that have
a PVC jacket and UL Listed CMG approval, for example.
Customers often have no idea which requirements their
applications must fulfill or what the different installation
Listing Typical Application
Type
Flammability Test
Industrial Automation Relevance
CMP
Highest flame resistance safety requirement;
installation without additional protection
FT6
None
CMR
Cabling in multi-level buildings, minimum
two stories (vertical duct)
UL 1666
None
CM,
CMG
Cabling for buildings, with general use;
optional PLTC approval (vertical duct)
CSA FT4
Cabling for manufacturing facilities,
cable trays, in the field and machinery
CMX
Limited use within buildings
UL 2556, VW-1, CSA FT1
Field and machine cabling
options offered by North American suppliers actually look attention is paid primarily to the materials used, such as
like. Since the issue is so complex, it is recommended to the number of high-risk plasticizers or lead-free products.
Cables installed in buildings must be halogen-free and/
use UL Listed cables as much as possible.
or have low smoke density or low toxicity characteristics.
When in doubt, choose UL Listed
However, flame retardant properties are the priority for
UL certification. Unfortunately, flame retardance is not
Purchasers or technicians should always opt for UL Listed
Europe’s first priority in when smoke, combustible or toxic
first because it’s easier to check the standard of the cable,
gases are produced in a fire. While regulating agencies may
and acceptance takes place quicker. When a product
disagree on the right way of going about it, the fact is that in
complies with a UL Listed standard, the inspector will be on
North America fires also break out when extremely flame
the customer’s side as they are spared the need to do any
retardant cables are used due to all the hazardous materials
AWM research. Only when you cannot find the appropriate
they contain, and fires are no less avoided when European
standard should you look into AWM Styles.
solutions are used.
AWM Styles are perfectly legitimate since they are tailored
to the application, but not all applications can be squeezed
to fit the requirements of a UL Listed standard. Case in
point: a woodworking machine will have different wiring
The highly flexible HELUKAT PROFINET Type C data cable has CMG PLTC
requirements compared to a metalworking machine or an FT4 approval and is suited for cable tracks in automated machinery.
automated machine.
UL Listed data cables
The following example illustrates the best approach to take
when choosing the right cable. A track cable needs to be Data cables are described in UL Standard 444. Depending
UL approved. For this, two standard jacket compounds on the application and flame retardant requirements, the
are available to choose from — PUR and PVC. PVC jackets individual chapters list the CMP, CMR, CM, CMG and CMX
can be CM or CMG listed. PUR jackets can be AWM Style standard allocations according to the respective data cable
or CMX Listed. However, the latter version only satisfies criteria.
the individual cable fire test and therefore does not bring
CM or CMG UL Listed (bundled fire test) as well as AWM
any advantages with regard to fire resistance. While the
Style UL Recognized (individual vertical or horizontal fire
inspector will immediately be aware of the relatively weak
test) versions apply to PVC-jacketed cables. The same
fire test of the CMX standard, he will have to look this up
applies to Flame Retardant Non-Corrosive (FRNC) versions.
for the AWM Style. If the CMG track cable with PVC jacket
CMX UL Listed or UL Recognized versions are applicable to
is used, this cable will not last as long in the track as the PUR
PUR jackets; however, both types only exist with individual
cable. However, the cable can also be installed in a cable tray
vertical or horizontal fire tests.
and so the inspector will accept this.
Cables with polyethylene (PE) jackets for outdoor or
Europe focuses on the materials used in the cable, underground installation have no flame retardant
while the USA concentrates on flame retardant properties and are therefore not UL certified. In terms
properties
of flame retardant properties, PUR can never satisfy a
Unfortunately, North American and European approvals bundled fire test, however this material has good chemical
do not always align, since many elements have become and mechanical resistance. In cable track applications, this
involved over time and there are many different ways of cable has a significantly longer service life than PVC-based
looking at the situation. With European approvals, great materials.
HELUKABEL® USA · 1490 Crispin Dr. · Elgin, IL 60123 · Tel. 847-930-5118 · Fax 847-622-8766 · sales@helukabel.com
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