Special Cables and the Challenge to Meet NFPA 79® Requirements

Special Cables and the Challenge to Meet NFPA 79® RequirementsStefan M. GrunwaldProduct ManagerLutze Inc.Charlotte, NC+1-704-248-5310sgrunwald@lutze.comJörg BörProduct ManagerFriedrich Lütze GmbH & Co KGWeinstadt, Germany+49-7151-6053-274joerg.boer@luetze.deAbstractNFPA 79 Electrical Standard for Industrial Machinery 2007Edition is currently the electrical standard for industrial machineryin the USA. A number of significant updates were implemented inthe 2007 edition. The NFPA 79® is a standard published by theNational Fire Protection Agency (NFPA), the same agency thatpublishes the National Electric Code (a.k.a. NEC® or NFPA 70®).The NFPA 79 has special provisions addressing safe wiringpractices for industrial machinery such as machine tools. Chapter 12of the NFPA 79 addresses cables and cords for use with industrialmachinery. Article 12.2.7.3 enforces a significant change as itspecifically prohibits the use of AWM (Appliance Wiring Material)style cable “unless it is part of a listed assembly”.Permitted under NFPA 79 2007 regulations are UL listed typecables if suitable for the intended use and Machine Tool Wire(MTW). The common practice of freely combining AWMinsulation styles with jacket styles is not permitted for UL listedcables; therefore, the level of customization to meet applicationrequirements may be limited.Keywords: NFPA 79; Special Application; AWM; IndustrialMachinery; Standard; Industry Standard; custom cable; machinetools; oil resistance; abrasion resistance; UV resistance; Industrial;flexing cable; continuous flexing; super flexible; high flexible; NEC1. Introduction1.1 StandardsA standard can be defined as “a set of rules” that allows to measurequality and offers a reference for comparison. These rules describe aproduct, procedure or process. A standard may also provideinstructions on how to do a task safely and consistently. Everycountry that is participating in the global economy has some sort ofstandard describing proper procedures in order to ensure safety forthe operator and protection for the equipment. That makes astandard more than just common practice; a standard is an officialset of written and published rules which are accessible to the public.Standards are not considered mandatory by law directly, until theybecome a code or are adopted into law by authorities, such as a localor state government.Standards are evolving with the engineering advancement that isbeing made every day. In today’s global economy it is veryimportant to have standards that not only protect the safety interestwithin the country to which the standard applies to, but also toensure the equipment can safely be used in other countries as well.Every country or community, however, has its own rules on how astandard is being implemented and how it is being observed. Thishas lead to an important process in the development of standardscalled ‘harmonization”. An example of harmonization would be if astandard’s committee writing a standard in the USA is consideringthe contents of a similar standard written in Europe to ensure thatthe basic message is the same.1.2 Industrial Machinery and its historyIndustrial machines are devices or groups of devices working in acoordinated manner to process material. Industrial machinery hasbeen used to perform work for centuries and while the firstmachines were driven by human or animal power, it wasn’t for longthat machines were powered by other sources, such as hydro orwind power. Since the Industrial Revolution machines have becomemore complex and versatile; and since the electrification ofmachines the term “machine tool” now associates electrical powermeans to drive it. Along with the electrification of machines a newera of devices was born. Motors, gears and transmissions offeredmore versatility and power output. The more complex thesemachines became, the more parties got involved in specializing inthe development of certain components or sub assemblies. In orderto make these components or sub assemblies work together,standards had to be introduced. Some standards aimed to make themachines and subassemblies compatible with each other, whileothers were introduced to improve the safety for operators andequipment. Different countries followed different philosophies, andas a result the standards for industrial machines could differ in theindustrialized countries.Industrial machinery and its equipment can vary greatly in form andfunction. State of the art machinery comes in sizes as small as ahandheld devices or large enough to fill several football fields.Some machines may perform relatively simple tasks while othershave complex operations following a timed program precisely andrepeatedly. The speed of motion and the level of intelligence canvary greatly as well. Machine tools can perform tool exchangesfaster than ever before and linear motor technology has greatlyimproved the traversing speed of modern machines. Theintroduction of field bus and network systems into the world ofindustrial machines applies more and more intelligence to thedevices in the field level.Putting that level of intelligence into the field level of industrialmachines means that digital input and output signals are beingcomputed and transmitted via copper or fiber cable in harshindustrial environments. For example, the introduction of industrialEthernet required cables and connectors to meet the requirements ofthe field level and started the development of industrial Ethernetcable. Cables for industrial machinery must be designed towithstand the harsh environments in which they are used. Theserequirements can vary greatly depending on the environment theInternational Wire & Cable Symposium 163 Proceedings of the 58th IWCS/IICIT

machine will operate in. Some of the requirements in suchenvironments may be:• Abrasion resistance• Oil resistance (especially in metal cutting devices)• UV resistance• Flexibility for easy routing and bending• Flexibility to perform continuous flexing operation• High temperature resistance• High shielding capabilities in EMC applications for noisereduction• Reliability (especially for data cables)• Flame retardancy and burning behaviorAll these requirements and more have to be considered when a cableis designed for industrial applications. In addition to meeting allthese requirements, a cable also needs to be compliant to“Standards” and “Codes” to ensure the required safety.1.3 Special ApplicationNeither the NEC Code nor the NFPA 79 Standard includes “specialapplication” as part of their definition. But if machines becomeevermore complex and customized, the level of what is considered“special application” must exist.The NFPA 79 however does define “special cable” as a cableintended for specific limited purposes. Following that notion, aspecial application would be an application that performs a task thatrequires a cable not available as a standard product and is designedto meet the specific requirements of the application. Such cablecould have design properties to meet mechanical, temperature orsimply termination requirements. Examples for such applicationscould be:• Constant flexing cable for linear motion requirements• High temperature cable• Composite cableIn each case the cable would fall into the definition of special cableperforming a task limited to a specific purpose in the application.2. NFPA 79 2007 edition2.1 IntentionThe NFPA 79 code is named: “Electrical Standard for IndustrialMachinery 2007 Edition”. As such it covers specifications forelectrically safe machinery, protection of people and equipment,machine control design, installation of equipment and wiringmethods and the proper marking and documentation. The NFPA 79standard initially started in 1941 as a subcommittee which wouldinvestigate exceptions and add-ons to the National Electric Code forindustrial machinery. Today the NFPA 79 has developed into thestandard for electrical industrial machinery and has beenharmonized to some extend with international standards such as IEC204-1 (EN60204-1).“Guard against the risks of fire and shock. Work with thebenchmark for industrial machinery safety: NFPA 79! Apply thenew best practices for the full spectrum of equipment—from singlemotoreddrill presses to complex automated manufacturing systems.Revised based on advanced technologies and industry needs, the2007 NFPA 79: Electrical Standard for Industrial Machineryprovides up-to-date design and installation provisions for all typesof electrical/electronic machinery.” [1]2.2 Scope of NFPA 79 2007 editionThe NFPA 79 is intended to apply to the electrical equipmentoperating at 600V or less used with a variety of machines. NFPA 79begins at the point of connection of the supply to the machine.2.3 Applying NFPA 79In most cases the AHJ (Authority Having Jurisdiction) decideswhether or not the NFPA 79 is being applied. The AHJ usually isthe organization or individual who approves or operates theequipment and can be the owner or operator of equipment, theinsurance company or the technical inspector. If the NFPA 79 hasbeen adopted into law, such as is case in the sate of Ohio, thestandard becomes mandatory and has to be applied.2.4 Meaning for CableThe NFPA 79 standard has provisions for cable and flexible cord inChapter 12. The standard describes in detail how cables should beconstructed to meet application requirements. The NFPA 79differentiates between “cables” and “flexible cord” as cord is notconsidered cable for fixed install and only permitted as described inNEC 400.7 and 400.8.One of the changes in the 2007 edition of the standard is describedin paragraph 12.2.7.3, which states that the use of cable, typeAppliance Wiring Material (AWM), is no longer permitted. As anexception AWM can only be used when it is part of a listedassembly suitable for the intended application. Permitted are onlylisted conductors and cables such as Machine Tool Wire.This change was adopted by the committee because AWM isgenerally not evaluated for direct field installation. AWM cables areconsidered a UL recognized component for factory installedappliances wired within the overall enclosure of appliances orexternal interconnection of appliances.UL AVLV2. Guide Info Appliance Wiring Material - Componentstates: “The devices covered under this category are incomplete incertain constructional features or restricted in performancecapabilities and are intended for use as components of completeequipment submitted for investigation rather than for directseparate installation in the field. THE FINAL ACCEPTANCE OFTHE COMPONENT IS DEPENDENT UPON ITSINSTALLATION AND USE IN EQUIPMENT SUBMITTEDTO UNDERWRITERS LABORATORIES INC.” [2]2.5 AWM UL recognized vs. listed cables2.5.1 UL recognizedAppliance Wiring Material is regulated by UL 758 and is generallya UL recognized type of cable showing a recognized logo:UL offers a variety of AWM styles which specify how a cable mustbe built e.g.:• Wall thickness of insulation and cable jacket,International Wire & Cable Symposium 164 Proceedings of the 58th IWCS/IICIT

• Temperature range,• Insulation materials,• Voltage, etcWhat makes AWM unique is the combination of styles whichallows designing a cable that meets the application requirements.Figure 1. Combination of insulation and jacket stylesThe combination of AWM styles function almost like “recipes” tomeet an application requirement. If the application calls for acable with TPE 600V insulation and an oil-resistant Polyurethanejacket, it is permissible to combine styles provided they meet thecommon requirements for the overall assembly. For example, inorder to satisfy the requirement of 600V, both the insulation styleas well as the jacket style must be rated for 600V. If the insulationstyle is only permitted for use as 300V, the whole cable can onlybe marked 300V even though the jacket style would permit 600V.2.5.2 UL listed cablesCommon examples of UL listed cables for the use with industrialmachinery are MTW, TC, TC-ER, PLTC, ITC, and CM. Thesetypes are evaluated in more detail then AWM cables and a freecombination of styles is not allowed. The UL “recipes” tomanufacture these products are much more detailed and theevaluation requires testing of the actual product. UL listed cablesmay carry the following UL mark:insulation only allow UL marking per UL AWM and do notqualify for any listed cable types.2.6.2 Composite cableA control application may require composite cable that consists ofcomponents of different gage sizes and is to be terminated in onelarge custom connector. AWM offers an easy way to build acomposite cable per the equipment manufacturer’s specificationsand apply this cable into the machine control design. In thisprocess each component would have been built per proper AWMprocedure and the composite cable would be jacketed inaccordance with a matching jacket style. Manufacturing onecustom composite cable and have it evaluated for UL listing willin most cases be cost and time prohibitive.2.6.3 Flexing cables for continuous motionAs traversing speeds get faster with the use of linear motors, themechanical requirements on flexing cables have increaseddramatically. Speeds of 10m/s and travel distances of 100m arereality in state of the art devices. Advances in material technologyand long term performance tests by equipment manufacturersoffer measurable results in cable performance. Competitiveproduct warranties force machine tool manufacturers to deploybetter and longer lasting cables. Many high performance flexingcables use thermoplastic elastomer based on polyolefin, such aspolypropylene for the insulation and polyurethane for the jacket.The popularity of these materials lies within the long lifetime,good flexing properties and the cost effective manufacturing ofhigh performance cables. Besides that, polyurethane jackets arevery popular with most industrial equipment manufacturers due tothe improved oil resistance and the fact that cables can be halogenfree which is an important industry requirement in Europe.2.6 Challenges for special cable applicationsSince the main purpose of special cable is to customize a cable tomeet specific application requirements, AWM offered a perfectcategory to accommodate all the specific requirements. Byapplying the proper UL styles manufacturers from all over theworld were able to produce cables which would be customary intheir own countries for an application in the USA. In this processAWM became more and more popular to be used in industrialmachinery applications. While the substantiation to no longerpermit AWM material in industrial machinery makes sense, it isin reality hard to find cables that are UL listed and can perform inthe actual application.2.6.1 Polyurethane drive and encoder cablesOne example is polyurethane power and encoder cable for highfrequency drive systems specifically designed to meet allapplication requirements. These cables are available in bulklength on reels directly from the drive manufacturer and are usedto make custom length assemblies for factory or field installation.These cables represent state of the art technology asrecommended by the drive manufacturer. Not using cable thatcomplies with the original equipment manufacturer’s specificationmay result in noise distortion and or functional errors in thecontrol and drive systems. The materials used for the jacket andFigure 2. C-track applicationUnfortunately, these cable constructions are only available as ULAWM types and not available as any listed cable types.2.7 Comparison MTW standard per NFPA 79 to ULAWM cableNFPA 79 refers to UL 1063 for cable constructions. UL 1063offers two constructions suitable for industrial wiring andinterconnection. Both procedures are being examined forcomparison of MTW versus AWM.2.7.1 Scope of UL 1063“These requirements cover all-thermoplastic Type MTW, 600-V,machine-tool wires and cables for use as specified in the NationalElectrical Code (ANSI/NFPA 70), and in the National FireProtection Association Electrical Standard for IndustrialInternational Wire & Cable Symposium 165 Proceedings of the 58th IWCS/IICIT

Machinery (ANSI/NFPA 79). These wires and cables complywith a flame test and are for use at 90°C (194°F) and lowertemperatures in dry locations and at 60°C (140°F) and lowertemperatures where exposed to moisture, oil, or coolants such ascutting oils and the like. Table 1 Single-conductor constructions”Table 1. UL 1063 insulation wall thickness (simplified)Construction A Construction BConductor sizeAvg. / Min /Avg. / Min (PVC)(Nylon Covering)22/7 - 12 AWG 30 / 27 15 / 13 (4)11-10 AWG 30 / 27 20 / 18 (4)9, 8 AWG 45 / 40 30 / 27 (5)7, 6 AWG 60 / 54 30 / 27 (5)5, 4-2 AWG 60 / 54 40 / 36 (6)1-4/0 80 / 72 50 / 45 (7)213-500 95 / 86 60 / 54 (8)501-1000 110 / 99 70 / 63 (9)The two single-conductor constructions covered are described inTable 1. Both are PVC-insulated and one includes a nylon jacketover the insulation. The multiple-conductor constructions coveredconsist of assemblies of these single-conductor constructions(sizes and styles may be mixed) enclosed by a PVC jacket.Machine Tool Wire and Cables are subject to testing of• Flexibility• Deformation• Flame• Relative Permittivity and Changes in Capacitance• Dielectric Voltage-Withstand and Breakdown Tests• Spark Testing of Single Conductors and Individuals• Dielectric Testing of Multiple-Conductor Cable• Insulation-Resistance TestsSource: UL 1063 [3]2.7.2 Conclusion MTW (UL 1063)Machine Tool Wire offers valid construction for industrialapplications as long as the application is within the temperaturelimits of 90°C and the properties of PVC are acceptable for themechanical requirements. The resistance to oil can be improvedwith agents supplied to the PVC compound and may pass “Oil resI and/or II” tests if formulated appropriately.By using the Nylon skin option, the wall thicknesses can bereduced substantially which will lead to a smaller total outerdiameter of the cable and, therefore, to cost reductions. But longterm flexing tests have shown that PVC is not a good insulator forsevere flexing duty. Especially in warmer ambient temperaturesPVC will break down earlier than materials such as TPE orPolypropylene (PP).But not only the PVC insulation can be a limiting factor for someapplications. UL 1063 only allows PVC based jacket compoundsand that can be another limiting factor. While the jacketformulation and available blends for PVC offer many options toadjust the jacket properties according to the applicationrequirements, the adjustments by adding agents or using blendsare limited. The oil and abrasion resistance of all PVC basedcompounds is limited and will not stack up to Polyurethane.Table 2. Flexing life test results for 5 meter traverse pathInsulation /JacketBend radius Speed Cycle countPVC / PVC 10x OD 5 m/s ~ 3 millionPVC / PUR 10x OD 5 m/s ~ 5 millionTPE / PUR 7x OD 5 m/s ~ 10 millionPP / PUR 7 x OD 5 m/s ~ 15 million2.7.3 Scope AWM style 21223/10492The AWM procedure allows the combination of a large variety ofUL listed compounds for insulation and jackets. For comparisonpurposes, AWM insulation style 10492 is combined with jacketstyle 21233 to illustrate the results compared to flexing cablesbuilt per UL 1063.Table 3. Style 10492 insulated wiredRating 80°C 1000 VacConductorInsulationConductor size32 AWG – 2000kcmilPPMils min averagewallSolid or strandedround, tinned orbareMils min wall atany point36-20 AWG 12 1019-16 AWG 14 1215-10 AWG 16 149-6 AWG 22 195-2 AWG 28 251 4/0 AWG 33 30250-500 kcmil 45 40501-1000 kcmil 60 541001-2000 kcmil 80 72International Wire & Cable Symposium 166 Proceedings of the 58th IWCS/IICIT

Table 4. Style 21233 Jacketed cableRating 80°C 600, 1000 VacConductorInsulationJacket36 AWG Solid or strandedminimum round, tinned or bareLabeled or complying withmanufacturers AWM procedurePURTable 5. Insulation wall thicknesses comparisonConductor sizeUL 1063construction Aavg. total wallthicknessUL 1063construction Bavg. total wallthicknessAWM avg.total wallthickness16 AWG 30 19 (15+4) 148 AWG 45 35 (30+5) 22Diameter round under jacketin inchesUL styles [4]Mils min averagewallMils min wall atany point0.400 30 240.401-0.700 30 240.701-1.000 45 361.001-1.500 60 481.5001-2.500 80 64Since the AWM style governs the minimum wall thickness for theconductor insulation, the result is a smaller wall thickness than aPVC insulated conductor and a higher breakdown voltage at thesame time.Not only the electrical characteristics are important factors toconsider for a flexing cable design, but there are also mechanicalrequirements to be met. The insulation also has to satisfy thegliding requirements for the continuous flexing application inlinear direction.2.7.4 Conclusion AWM style 21223/10492The result of combining these two styles will lead to cable that israted for 80°C 600 or 1000 Vac. The cable will be UL recognizedper UL 758 and can be used for external interconnection ofelectronic equipment. The cable insulation as well as the jacketwould have very good properties for use in an industrialenvironment.The oil and abrasion resistance of the insulation and jacket wouldbe superior compared to PVC as used for MTW type cables.Figure 4. Gliding ability of TPE-E, PUR, TPM (PP)A cable using PP insulation per UL AWM style 10492 and aPolyurethane jacket per 21233 would fulfill the requirements ofindustrial applications but can only be marked per UL AWM.Since the cable is only marked “AWM” and not one of any listedtypes, this cable is not compliant with NFPA 79.Figure 3. Volume resistances of insulatorsThe insulation thickness allows smaller wall thicknesses asPolypropylene (PP) has improved insulation properties over PVC.The PP insulation has a higher breakdown voltage Factor by 10 2compared to PVC, therefore PP allows technically even thinnertotal wall thicknesses than the UL 1063 construction “B” withPVC/Nylon.3. ConclusionsOne way to achieve compliance is by careful selection of listedcables that comply with the requirements of NFPA 79 and aresuitable for the application. Typical control cable for transmittingdata or power in non moving applications is readily available withexisting listings such as PLTC, TC-ER, and MTW or CM. TheseUL listed types offer ample options to install cable for static wiringof control systems and for analog or digital data transmission.However, due to the limited choice in listed cable types, someapplication requirements may not be able to be fully satisfied withthe available listed cables. High performance flexing cables, forexample, may require material technology that goes beyond PVC orPVC/Nylon as used in Machine Tool Wire constructions.International Wire & Cable Symposium 167 Proceedings of the 58th IWCS/IICIT

Equipment manufacturers should carefully research each cableapplication and create a list of applications for which UL listedcable is readily available. This only leaves the applications forwhich UL listed cable is not readily available.Some of the remaining applications may be able to be satisfied afterweighing the options of compliance and what is really needed forthe device. A machine that has a moving part that travels at lowspeeds and short distances may not need a high performance flexingcable and a flexing cable per UL 1063 may work satisfactorily.If the now remaining applications require custom cable or cable thatis only available as AWM types, filing for an exception with theAHJ may be a possibility. In this case good technical documentationis recommended; to document the primary application requirements,as well as proof that the AWM cable is the best solution and suitablefor the use as the manufacturer intended. Another way is to havecustom cable built and evaluated for UL listing. This process maybe cost prohibitive and requires careful planning as some tests maytake a long time to be completed.4. Future outlookThe change in the 2007 edition in the NFPA 79 Standard and thefocus on MTW type cable has created a renaissance of PVC andPVC blend compounds. The availability of so called “alloys” or“flex alloys” can greatly improve the performance of PVC basedcables in many applications, especially in those for flexing cables.The first products have already been introduced by variousmanufacturers and some cables with UL 1063 have beensuccessfully tested even in high performance flexing duty with over10 million cycles.The oil and abrasion resistance can also be greatly improved byusing alloys as jacket material.Another direction for relief may be provided by the NFPA 79committee itself. The NFPA 79 committee has appointed an “AWMtask group” and is currently investigating nine different proposalsthat have been filed to reinstate the use of AWM for the nextStandard release in 2011.5. AcknowledgmentsSpecial thanks to Sari Gregson and Juergen Seybold for proofreading the text and help with suggestions for improvements.Special thanks also to Ilona Hirtz, Helmut Schubnell and Joerg Boerwith assistance on the technical part. I also want to thank the IWCSstaff for coordinating this event and allowing us to contribute to thisyear’s publication.6. References[1] www.nfpa.org. Description of the NFPA 79 Standard.[2] www.ul.com AVLV2.GuideInfo Appliance Wiring Material -Component.[3] UL 1063 Machine tool wires and cables.[4] UL style search on UL.com7. The AuthorsStefan GrunwaldStefan GrunwaldProduct ManagerLutze Inc.13330 South Ridge Dr.Charlotte, NC 28273Tel.: +1-704-248-5310Fax: +1-704-504-0223sgrunwald@lutze.comwww.lutze.comStefan Grunwald was born in Hannover, Germany and he started hiscareer as a technician in machine building and automation for alarge Norwegian manufacturer of wood processing and laminationequipment. After Graduation from Fachhochschule Hannover hestarted a new professional career in technical documentation for aGerman Manufacturer of railroad safety systems.He resides in the United States of America since 8 years and is nowthe Product Manager for cable and cable accessories for Lutze Inc.with almost 7 years of experience with Lutze in the field ofindustrial automation and industrial cables. He has attended themanagement development program from Harvard Business SchoolAlumni Club of Charlotte designed for working professionals.Stefan Grunwald is a member of the Electrical Section of the NFPA.Jörg Bör (Co-Author)Jörg BörProduct Manager CableFriedrich Lütze GmbH & Co. KGBruckwiesenstraße 17-19D - 71384 WeinstadtTel.: +49 7151 6053-274Fax: +49 7151 6053-6274joerg.boer@luetze.dewww.luetze.deJörg Bör was born in Hamburg, Germany and following hisgraduation as Diplom-Ingenieur of electrical engineering at RWTHAachen in 1991, he started his professional career as a designengineer with a German cable manufacturer. He focused on thedevelopment of symmetric copper data cables with transmissioncharacteristics specified up to the gigahertz range. Furthermore hewas involved in the development of optical data cables. Later heworked in a cable factory as cable development manager. Currently,Jörg Bör is Product Manager for cables at Friedrich Lütze GmbH &Co. KG.Joerg Boer teaches at the institute of further education of theGerman engineers’ society (VDI). Furthermore, he worked in twosubcommittees of the German electro technical standardizationbody, for fiber optic cables and for flexible power cables.International Wire & Cable Symposium 168 Proceedings of the 58th IWCS/IICIT