Vendors of marine battery wire are already well-familiar with the necessary certifications, as well as maintenance considerations and installation processes. However, sailors and vendors alike may not be aware why it is so important that such wire be made of specifically copper, and specifically copper treated in a certain way. In truth, few materials could be suitable for marine application other than copper, but copper alone is not enough.
Copper is in many ways the ‘default’ wiring of the modern world, and has been for a great deal of time. Copper’s conductivity and durability make it invaluable for wiring everything from homes to cars to, of course, boats and marine installations. However, there are other alternatives, and copper’s primary advantage is price. However, copper alone is not enough.
The reason copper on its own is insufficient is that copper corrodes. While it does not oxidize so dramatically as iron in damp conditions, especially in salt water, it is still a metal subject to electrolysis and will still corrode. Anyone in possession of an old American penny will have seen this before. Corrosion is why pennies turn green, even though pennies aren’t made of pure copper. Salt water’s affinity for corroding metal is already bad enough, but the addition of electric current means that improperly treated marine battery wire will be made very short work of, potentially causing rapid failure, but at best requiring frequent maintenance.
This is why marine battery wire is almost always made with tinned copper. A tin-copper alloy remains conductive while being significantly more resistant to corrosion. This does not mean that it is corrosion-proof. However, it means that the wire will hold up significantly better with the assistance of proper insulation. If the insulation is maintained and the terminals are not put through inordinate mechanical abuse, maintenance will be infrequent and relatively simple.
Gold, of course, would make a far better choice, as it will conduct electricity without corroding. This is why it is used on space vessels. However, it is used on space vessels rather than sea vessels because it is prohibitively expensive. Most gold never sees practical application because another option will perform acceptably well, and the same holds true here. Tinned copper simply provides the best cost-benefit ratio of most other options because the availability of copper and tin is superior to so many other elements.
It is true that tinned copper is not, strictly speaking, required. A common misconception holds that there is some legal requirement that electrical systems on marine vessels must use tinned copper to prevent system failure. In truth, many vessels use ordinary, unalloyed copper to reasonable effect without repercussion. The reason to use alloyed, tinned copper for marine battery wire is not to avoid legal fallout, but to avoid maintenance costs over time, a worthy concern for sailors, and thus a worthy concern for vendors looking to provide products of the best quality possible to their customers and clientele.
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