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Wrench Realities
The Great Welding Cable Debate Continues
Drake Chamberlin
Welding cable has been used successfully for battery interconnects for decades. Many retailers of renewable energy equipment use welding cable for premade battery interconnects and inverter cables. It has not, however, been permitted in areas where the National Electrical Code (NEC) is enforced.
Many renewable energy (RE) workers consider welding cable the favorite material to use for connecting batteries and inverters. It is readily available and relatively inexpensive. It is extremely durable and flexible. It is also very resistant to being damaged by battery acid.
What the Critics Say About Welding Cable
In Code Corner, HP82, John Wiles stated that many cables do not have “any marks or labeling that ensure that they have been tested and evaluated for safety in any application.” These cables are available from “auto parts stores, hardware stores, building supply stores, and welding shops.” He also said that the Underwriters Laboratory mark needed to be on the cable. Without the UL symbol of approval, Mr. Wiles notes, the suitability of a cable cannot be determined.
John continues the argument by saying that without this marking, it cannot be known if the manufacturer cut costs in the construction of the cable. The cable’s copper might have higher resistance. The sheath of the cable might crack or catch fire more easily. Additionally, a UL mark on a cable guarantees that the product has been thoroughly evaluated by a competent, national testing laboratory. Without a UL marking, the cable may or may not be adequate for any particular application.
UL-Approved Welding Cable
I recently did some research, and found that many brands of welding cable are indeed UL approved. According to the UL Web site, however, there will not be a UL mark on the sheath of the cable. The listing mark of Underwriters Laboratories is only to be found “on the attached tag, coil, reel, or smallest unit container in which the product is packaged.”
Listed welding cable is in compliance with NEC Article 630, Part E, which deals with the secondary circuits of electric welders. It can be rated at 60 to 90°C (140 to 195°F), and 100 or 600 volts.
The listing mark on the tag that comes with these products includes the name or symbol of Underwriters Laboratories, together with the word “listed.” It also contains a control number and the product name, “welding cable.” The temperature and voltage ratings may be marked on the sheath, as well as on the tag. If they are not marked, the temperature rating is assumed to be 60°C, and the voltage rating 100 V.
When the cable has the higher voltage and temperature ratings, markings will appear on the sheaths. The markings of 600 volts and 90°C will be printed on the insulation. The UL listing mark, however, will not appear. UL-listed welding cable comes in sizes from #8 AWG to 250 kcmil (8 to 127 mm2), in flexible stranded copper. The individual strands are #34 to 30 AWG (0.02 to 0.05 mm2).
John Wiles says that cable that does not bear the UL marking cannot be verified to be a tested, safe, and durable cable. Welding cable, however, does not have a UL stamp on its sheath, even when it is listed. Information about UL-listed welding cable can be obtained from the UL Web site. Specific information can be obtained from the manufacturers, whose addresses are provided on the site.
The Acid Test
My article in HP80 (page 84) documented the effects of battery acid on some welding cable insulation, and certain other types of cable insulation. The welding cable we tested was unharmed. The 1996 NEC required battery cables to be acid resistant, and to be chosen from Article 400. This created a contradiction, since there were no cables listed as acid resistant in Article 400. The 1999 NEC no longer requires cables to be acid resistant. Theoretically, this is because plastic and rubber conductors are considered to be inherently acid resistant.
In the RE Lab’s “acid test” of various cables, type THHN/THWN cable showed a tendency to dissolve in battery acid. Section 310-13 of the NEC lists this cable as “heat resistant thermoplastic.” Yet it slowly melts in battery acid. It appears that acid resistance might still be a reasonable requirement for battery cables. UL-listed “Super ExCelene®” welding cable is rated for acid resistance.
Welding Cable for Batteries & Inverters
Welding cable has traditionally been a favorite material to make battery interconnects. In early systems, welding cable was routinely used to connect battery banks to inverters. Welding cable was often run from battery boxes to inverters without conduit. Although not code compliant, this practice is still common today.
This seemed appropriate, since welding cable is exposed to physical contact when used with arc welders. The cable is energized with similar voltages in RE systems as in welding operations. The electrical potential in both applications is usually DC.
Welding cable is very robust. It may be in frequent contact with molten metal. It is exposed to a wide variety of mechanical impacts. It can lie on shop floors with scraps and shavings of metal, where it can be run over by forklifts and automobiles. Welding cable is safe to use. Arc welders are used in the construction of metal frame buildings. A truckmounted welder may be several stories below the location where the arc is struck with the welding rods. Welding cable carries the current from the welding machine to the point of use. Welders and other workers standing on conductive metal framing may be exposed to the cable. Similar situations exist for welding operations on metal towers.
Welding cable is used for applications that are much more abusive and potentially dangerous than renewable energy installations. At least some varieties have been demonstrated to be acid resistant. Welding cable is certainly an adequate product for use with batteries and inverters.
Permitted Cable
Battery interconnections are required to be made with flexible cables as identified in Article 400 of the NEC Welding cable is not listed in Article 400. Interestingly enough, some cables that we are permitted to use, such as finely stranded USE-RHH-RHW Hypalon diesel locomotive cable, are not identified in Article 400 either. Since both types of cable are UL listed, and neither are identified in Article 400, there seems to be little logic in allowing one while forbidding the other.
Many suppliers sell battery interconnects made from welding cable. RE systems are still being rejected by local inspectors because welding cable is used. The acceptance or rejection of a system is ultimately based on the code interpretation of the particular inspector. If a system is rejected because of the use of UL-listed welding cable, certification and specifications of the cable can be obtained from the manufacturer. The inspector may accept the cable based on this information. It would be helpful if wrenches would contact Mr. Wiles with their concerns about the welding cable ban.
This investigation into welding cable has been conducted as an activity of the Renewable Energy Lab, as described in HP80, page 84. Chris Sinton of Alfred University is actively seeking funding under the name “Renewable Power Installers Advocacy Program.”
Access
Drake Chamberlin, Electrical Energy Contracting and Consulting,
3138 Lyle Ct., Denver, CO 80211 • 303-399-1025
solar@eagle-access.net • RE Lab Web site: www.eagle-access.net/solar
See Web site for listing of RE Lab membership.
Chris Sinton, Acting Director, Center for Environmental and Energy Research,
Alfred University, Alfred, NY 14802 • 607-871-2642 • Fax: 607-871-2618
sintoncw@alfred.edu • http://ceer.alfred.edu
ULWeb site: www.ul.com/database
To find listed welding cable, search by the keyword "welding cable.”
For info on UL listing tags click on "ZMAY.GuideInfo."
John C. Wiles, Southwest Technology
Development Institute, New Mexico State University,
Box 30,001/ MSC 3 SOLAR, Las Cruces,
NM 88003 • 505-646-6105
Fax: 505-646-3841 • jwiles@nmsu.edu
www.nmsu.edu/~tdi
National Electrical Code and NEC are registered trademarks of the National Fire Protection Association.
The 1999 NEC and the NEC Handbook are available from the NFPA,
11 Tracy Dr., Avon, MA 02322 • 800-344-3555 or 508-895-8300 • Fax 800-593-6372 or 508-895-8301
custserv@nfpa.org • www.nfpa.org
Chamberlin, Drake. "The Great Welding Cable Debate Continues." Home Power Magazine Aug.-Sept. 2001. #84. |
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