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What to Test We first needed to determine what the differences are between welding cable and the cables approved by the NEC. Most of the popular, acceptable battery cables have conductors composed of finely stranded copper wire. Welding cable conductors are also made from finely stranded copper wire. The difference between the cable types is in the insulation. The concern is the presence of battery acid in the cable’s environment. The issue to be determined was whether or not welding cable insulation is sufficiently resistant to battery acid to justify its use in battery boxes. Would there be any catastrophic reaction if welding cable was subjected to contact with battery acid? Would the insulation dissolve or lose its resistance to electrical potential? The Acid Test Several samples of cable sheath were removed from their copper cores. The cables ranged from welding cable to various cable types currently deemed acceptable for use in battery enclosures. The cable samples were all roughly 2 inches (5 cm) in length.
All of the specimens were removed from the acid on August 6, 2000. They were then dipped in a solution of water and baking soda. All samples, including the spilled specimen, fizzed dramatically when doused in the soda solution. All specimens were then thoroughly rinsed in cold water, dried, and stored in labeled envelopes. Later, they were examined and tested for electrical resistance. The Results The only specimen to show any visible deterioration was the THHN-THWN. Within a day or so of being immersed in the acid, it began to darken the solution. Within a week, the solution was black. The insulation was apparently losing mass.
After more than five months of soaking in acid, all the other specimens came out of the solution with no signs of degradation. The two samples of welding cable mained flexible. They maintained mechanical integrity, as evidenced by the inability to damage the sheath by twisting and pulling. The electrical resistance of the samples was tested with an Ideal-Sperry 61-780 insulation tester. This device applies 1,000 VDC to the material being tested. It will test for resistance values up to 2,000 megaohms, or 2 billion ohms. The accuracy of the meter was investigated by testing 10 megaohm resistors, individually and wired in series groups. One test involved one hundred 10 megaohm resistors wired in series. That adds up to 1 billion ohms, or a gigaohm! The tests demonstrated that the accuracy of the meter was adequate. The meter readings showed less resistance than the theoretical value of the resistors. The resistors were rated for a 5 percent variation. If the insulation tester was off, it appears that its readings were conservative, showing less resistance than the material being tested. The total variation is insignificant to the hypothesis under investigation. The samples were tested by inserting a bare #4 (21 mm2) copper wire through each empty tube of insulation. The sample wall was squeezed between the bare copper wire and a metal plate. One electrode of the tester was attached to the wire, and the other to the plate. Each piece of insulation was tested repeatedly. A short circuit connection was made between the plate and the #4 copper wire after each test to verify the connections. The bottom line is that none of the insulation specimens registered any conductance whatsoever. Even the sample of THHN, which partially melted in the acid, showed resistance beyond the range of the meter. Conclusions The insulation specimens had hundreds of times more exposure to battery acid than cables would in real systems. The welding cable, which we are forbidden to use, showed no signs of being damaged by prolonged submersion in battery acid. The welding cables tested are excellent products for use in battery enclosures, and their use should certainly be permitted. A Note on the RE Lab There are many other issues about regulations that affect RE installations. Many of these issues have a far greater impact on system cost than the banning of welding cable from battery boxes. The welding cable experiment was chosen as the first because it was relatively inexpensive. The RE Lab would like to address other issues that are important to RE system installers. At present, the RE Lab is operating with no formal budget. We are looking for sources of funding, and for volunteers with grant writing skills. With adequate financial backing, we would perform a series of experiments dealing with other controversial areas of RE installation. RE Lab volunteers would like to become involved in the code writing process. Our goal is to evolve clear guidelines—based on testing—that allow for safe, economical, and effective renewable energy installations. Access Drake Chamberlin, Electrical Energy Contracting and Consulting, 3138 Lyle Ct., Denver, CO 80211 303-477-4739 • solar@eagle-access.net www.eagle-access.net/solar 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. "Welding Cable Acid Test." Home Power Magazine Dec. 2000 - Jan. 2001. #80. Back to Wire Main |
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