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Wire runs your car. Plain and simple. When it comes to automotive electrical systems, wire is often regarded as a dirt simple commodity, but what type of wire do you really need inside your project? That's a good question. If you take a look at the wiring harness(es) buried inside a modern passenger car, you'll find all sorts of different wire shapes, sizes, colors and configurations. Most of these wires will have one thing in common: They're manufactured with a pure copper core
Why use copper? Copper has been the electrical wire material of choice since the dawn of time. Copper is relatively cheap when compared to other materials that have similar or better conductivity. Silver is likely the only pure metal that is equally suited to the job, and the truth is, it actually does a better job of conducting than copper. Unfortunately, pure silver is expensive (check the price sometime; you'll be a wee bit surprised, although copper ain’t exactly cheap either). That leaves copper, and copper derivatives (silver coated copper wire, copper coated aluminum wire, etc.), as the mainstay of the automotive electrical business.
Speaking of aluminum, there have been some (often big) experiments with the use of aluminum conductors. Both the aviation and the household industries have experimented with its use. Aluminum is both cheaper and (obviously) lighter than copper, but the trouble is it simply doesn’t conduct electron flow as well as copper. What if you increase the size of the wire? It still doesn’t work - it's still a loser from the flow perspective. In the aircraft biz, a couple of manufacturers have tried using pure aluminum battery cable. They've also been used with mixed success in the racing world. Why doesn’t it work? Aluminum material suited to the manufacture of wire is, by nature, soft. Soft aluminum has a tendency to work harden when stressed beyond its elastic limit. When that happens, it becomes brittle and will eventually crack. How does this happen? Look at how a terminal is crimped to the end of the aluminum wire or cable: The crimping process causes the aluminum core to be disturbed. This in turn initiates the work hardening process. If aluminum core wire isn't supported carefully, it can be subject to vibration. This vibration begins the work hardening process the minute the car is started. As a result, the trouble associated with maintaining good wire termination coupled with the vibration issues means it usually isn't worth the trouble, particularly if the weight savings is marginal (ounces).
Fair enough – that leaves us with copper, but there's certainly more than one variety of copper wire. For example, your house is most likely wired with copper – it will use thick, solid wire. On the other hand, something like a cord for an electric drill or a toaster will have a core that is made up with finely stranded wire. It's tough to bend the copper wire used to electrify your house. It's not difficult to bend the wire used for your toaster. Typically, copper is a very ductile material. This means that you can wrap a piece of solid 10 gauge wire around a very tight bend and it will lose very little of its structural integrity. But if you straighten that same wire and then re-bend it a few times, it will work harden too. In this bending and straightening circumstance, the ductility eventually diminishes and cracks will begin to appear on the wire surface. If the bending and straightening continues, the cracks will eventually increase in size. Then the wire will fail.
Is there a solution? You bet. Replace the solid wire with stranded wire. Pretend you place 19 strands of 22-gauge wire into a bundle. This wire bundle will have roughly the same cross sectional area as a piece of solid 10-gauge wire. Now, if you bend this stranded piece of wire over a tight radius (as pointed out above), it won't have a tendency to fracture. That's because the reduction in size of the individual wire in the strand produces (approximately) a proportional reduction of stress. That means stranded wire is good news. When it comes to stranded wire, you usually have a choice between something like 7 strand or 19 strand (using a small 22 gauge wire as the example). In the case of small size wire such as 22-gauge, a total of 7 strands of 30-gauge wire are used to make up the core. If 10 strands are used, then the strands are 43-gauge. Which is better? This is a spot where more equals better.
We’re not done yet either. Copper isn’t perfect. It’s considered an "active" metal. What that means is it readily reacts with oxygen in air, along with moisture and, of course, airborne pollutants. Think about it for a minute: Leave a nicely polished copper teakettle on an open shelf in your kitchen for a month. Grab your polish and polishing rag. You'll need it. The same applies to stranded wire. There is no practical way to completely seal the circulation of air (and moisture) between the respective strands. Most plastic wire insulators are not barriers for the protection of the wire from the environment, particularly when exposed to hydrocarbons (i.e.: gasoline, oil, etc.). Here's the problem: Most automotive wire is not protected from the environment or from hydrocarbon contamination. Because of this, it usually has a service life of something in the order of a decade (maximum). From that point on, it begins to deteriorate. What's the answer? Simple. Plate the wire before it's stranded. Some wire is actually silver-plated. More common, however, is tin plated wire. It's easily applied and much more resistant to chemical "activity" than bare copper. You'll find that wire sold for aviation purposes is tin-plated.
That’s a wrap for this issue. Next time around we’ll look at wire jackets. You’ll find it’s more important than you first thought!
When it comes to wire, never assume you can walk through the aisles of your local auto parts store and buy any color and size you need – you’ll have to do some shopping. Many different types of wire are available.
Auto Meter (yes, the gauge people) once offered a complete line of "Racer Wire” that proved perfect for many high performance applications. It was designed with a special high temperature, abrasion resistant insulator. Inside, the high strand count of high purity copper allowed for low resistance to current flow, excellent flexibility and durability. It’s no longer available, but when searching for wire, copy those attributes.
If you open up a piece of high quality wire you can see just how many strands are included in the bundle. A wire with more strands is much more desirable than one with few strands (or a solid core).
