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RE Lab Experiment #1
Welding Cable Acid Test

By: Drake Chamberlin


The Renewable Energy Test Lab has conducted its first experiment. The lab is dedicated to defining and promoting safe and cost effective methods for the construction of renewable energy electrical systems. We believe that system costs can be significantly reduced by using only what is truly necessary for system safety and efficiency.

In recent years, inspection agencies have become interested in photovoltaic and other renewable energy (RE) installations. An effort has been made by the National Electrical Code to define requirements for these systems. Manufacturers and Underwriters Laboratories also specify conditions for certain system components.

Safety & Common Sense
Solar and other RE systems were being installed for at least a decade before code compliance became an issue. (Wind systems go back many decades.) During this period, many pioneers in the field developed safe and effective methods of constructing systems. There were remarkably few safety problems with these early systems.

When code enforcement began, it was welcomed by many. Some early systems did not use fuses or follow other basics of good electrical design. But as code enforcement developed, it quickly became apparent that the experience of RE pioneers had not been taken into account when drafting the new regulations. Requirements were added that drove up system costs, without benefit to safety or performance. Bob-O Schultze’s early Wrench Realities columns in Home Power documented many of the concerns.

Welding Cable
One area where new requirements ignored the experience of RE pioneers was in the banning of welding cable from use in battery boxes. Welding cable has proven to be an effective material to use for connecting batteries to each other, as well as to disconnects and inverters. Welding cable is readily available, very durable, and relatively inexpensive. Many national suppliers of RE equipment still use welding cable for battery interconnects.

The banning of welding cables from battery enclosures is a perfect example of an institutional barrier. Although welding cable has been used successfully for years in battery boxes, it is not listed for this purpose. Its use has been actively suppressed by regulatory agencies.

Several years ago, inspectors in many areas began to reject systems where welding cable was used. They required cable types that were more expensive, and often hard to get. System rejection has caused many RE electricians to be humiliated in front of their customers. It is often necessary to have exotic cables shipped in, sometimes causing stressful delays in system approval.

RE electricians are happy to do whatever is necessary to construct safe systems. But few electricians believe that the zealous suppression of welding cable is in any way justified to obtain that safety.

Ideal Sperry 61-780 Insulation Tester Results for Cable Insulation Test

Tested Cable Insulation Date InDate Out Visible Change Meter Reading
#2/0 AWG THW or Oil Resistant l4 Mar7 AugnoneOL**
#2/0 Essex Excelene welding cable5 Mar7 AugnoneOL
#4/0 Cobra Wire & Cable X-Flex (Trace cable)4 Mar7 AugnoneOL
#4/0 Carol Prene welding cable, 600 V4 Mar7 AugnoneOL
#4/0 Carol Super Vu-Tron type W RHH or RHW4 Mar7 AugnoneOL
#2/0 Hypalon diesel locomotive cable25 Feb27 AugnoneOL
#2/0 Essex THHN or THWN* 4 Mar21 Aprloss of massOL
* This specimen spilled on 21-Apr, but remained in a puddle of acid until 06-Aug.
** The "OL" reading means resistance is beyond the range of the meter.


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.

Ideal-Sperry 61-780 Insulation Tester on the 1,000 Megaohm Test
Megaohms Deviation
High reading 940 6.0%
Low reading 928 7.2%


All of the samples were submerged in standard strength battery acid by March 5, 2000. Each specimen went into an individual glass jar. One sample jar was tipped over and mostly emptied of its acid by a squirrel on April 21st. This was a specimen of cable that is not approved for use in battery boxes, and not commonly used—type THHN-THWN.

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.

Measured Resistance of Individual Resistors
Test Instrument
Resistor NumberIdeal-Sperry 61-780 Insulation Tester (Megaohms)UEI DM Digital Multimeter(Megaohms)Soar 320 Digital Multimeter(Megaohms)
R-19.9910.0310.04
R-29.709.729.78
R-39.829.889.93
R-49.829.809.90
R-59.579.639.70
Average9.789.819.87
Deviation2.2%1.9%1.3%

To determine accuracy of the insulation test meter, resistors rated at 10 megaohms were tested.

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.
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