August 2008
AWM Wire Not Permitted in Industrial Machinery
The 2007 revision of NFPA 79, the electrical standard for industrial machinery, clarified that AWM
wire is not permitted in industrial machinery unless installed as a component of a listed assembly.
The applicable section of NFPA 79-20071 reads as follows:
"12.2.7.3 Appliance Wiring Material. Single conductor or multi-conductor Type
AWM shall not be permitted.
Exception: When part of a listed assembly suitable for the intended application,
Type AWM shall be permissible."
A "listed assembly" is code speak for an electronic enclosure or subassembly that has been
previously tested and approved by a nationally recognized testing laboratory such as UL2 or
Intertek (ETL)3. As a result of the revision, questions have been raised regarding why the standard
was changed and what types of wire can be used to meet NFPA 79 requirements.
Why Was NFPA 79 Revised?
It has long been the industry's intent that type AWM wire should not be used in industrial
machinery. Type AWM wire (Appliance Wiring Material) is defined in industry standards4 as a
"Recognized Component" rather than a "Listed" product. Recognized Components are parts
intended for use in OEM equipment where the finished product will eventually be tested for
compliance with safety requirements as a completely finished (and Listed) product. The UL marks
that are used to distinguish between the two types of approvals are shown above. All UL Styles
such as 1007, 1015, 1213, etc. are AWM wire types and, as such, are also considered Recognized
Components.
Listed Mark
1
Recognized
Component
Mark
NFPA 79 "Electrical Standard for Industrial Machinery", National Fire Protection Association, www.nfpa.org
Underwriters Laboratories Inc, www.ul.com
3
Intertek, www.intertek-etlsemko.com
4
UL 758 "Appliance Wiring Material", Underwriters Laboratories Inc., www.ul.com
2
Below are some of the specific reasons NFPA 79 was revised to clarify the proper use of type
AWM wire:
• The NEC® (NFPA 70)5 does not recognize type AWM wire as an acceptable method
of field installed wiring because electrical and mechanical test requirements for
Recognized Components are less stringent than they are for Listed products.
•
Type AWM wire was being incorrectly used as part of the building infrastructure
during installation of industrial machinery, such as incorrectly running type AWM
wire from the main source of power (circuit breaker or fuse box) to the control panel
of the machine.
•
The insulation thickness of certain AWM wire types can be as thin as 0.002 inches
and may not provide adequate mechanical protection in some installations.
•
The NEC® does not permit the use of type AWM wire for installation within a
building, even if installed in conduit.
OK…So What Wire Types Can be Used?
Chapter 12 of NFPA 79 spells out in detail the types of wire and cable permitted in industrial
machinery. In general, Listed wire types are permitted, but Recognized types are not. These are a
few examples of the many Listed wire and cable types that are permitted:
MTW
SJOW
THWN
SEOW
RHW-2
SJEOW
THHN
STOW
RHH
MI
TC
XHHW
PLTC
THW
ITC
RHW
CM
XHHW-2
CL2
SOOW
It should be noted that electrical wire can have multiple ratings. For example, AWM wire made by
some manufacturers also has an MTW rating. Such dual-rated wire can be used either as AWM
wire or as MTW wire in a given installation. In this example, the wire is permitted in industrial
machinery by NFPA 79 because it is MTW rated—the AWM rating can just be ignored (wire
manufactured with multiple ratings must comply with all the requirements of all ratings).
Many wire and cable types can be used in industrial equipment instead of AWM wires to comply
with NFPA 79. Just remember, they must be selected and installed in such a manner that they
comply with all other Code requirements—including those for conductor stranding, conductor size
(ampacity), voltage rating, temperature rating, moisture resistance and flame-retardant properties.
WDW
5
NFPA 70, "National Electrical Code", National Fire Protection Association, www.nfpa.org