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In our last issue we examined what makes up good quality wire for high performance (street and strip) automotive use. If you recall, we pointed out that fine strand copper wire is at the top of the heap, at least when it comes to practicality versus performance. In this issue, we’ll take a close look at the jackets that cover the wire. There’s more here than first meets the eye.
Wire Jacketing
In the early years of the automobile, there was no such thing as plastic. Wires were typically covered with rubber, which was extruded over a series of twisted strands of wire. The rubber-covered wire was then surfaced by a cotton braid, which in turn was coated with a shellac compound. Not only was this type of covering brittle, it also had a tendency to attract fungi. The solution came in the ‘50s: Plastic. Some forms of plastic wire coverings are still in use today (typically PVC plastic). In military aircraft, the PVC coverings were usually fortified with a layer or two of synthetic fiber over-braids (occasionally, the bare wire strands were first covered with the braid, then sealed with a PVC covering).
PVC and other plastics aren’t perfect. They are porous. Chemicals eventually leak out of a plastic container. In the case of wire, contaminants eventually pass through the PVC jacket and attack the wire (particularly un-plated copper wire). Another solution is a wire jacket manufactured from Teflon. Teflon is magical stuff. It stays flexible and soft at both extremes of its operation range. But there's a big caveat attached to the use of a pure Teflon wire jacket: It's not very resistant to abrasion. The solution (at least in the aircraft industry) was to wrap the Teflon coated wire with a PVC jacket. It's an expensive wire, because the wire has to first be plated in silver or nickel before the Teflon can be formed over the bundle. Furthermore, it's said that in the event of a fire, Teflon can give off toxic fumes.
So what's the answer? There really isn't a whole bunch of choice. You can use PVC insulated wire in most areas of a hot rod, with the possible exception of regions close to the engine (engine compartment in a car). There are two common types of PVC insulation available. One is rated to 80° Centigrade while the other is rated at 105° Centigrade (80° C = 176° F; 105° C = 221° F; to give you some perspective, water boils at 100° C). Teflon, on the other hand, won't melt at temperatures in the 400-500° F range (that's why you see it used on things like "nonstick" frying pans). Wire bundles outside of the engine compartment can routinely see temperatures that range as high as 180° F. Unfortunately, engine compartment temperatures might be as high as 300° F (or more in localized areas). Factor in the chemicals commonly seen in automobiles (fuel, oil, brake fluid, solvents used for cleaning, etc.) and you can see that the wire insulator lives a tough life.
Tefzel jackets might be one answer. "Tefzel" is a close cousin to Teflon (and falls under MIL Spec W-22759), but it doesn't quite have the sheer temperature resistance. It has been known to be the cause of some aircraft service problems, particularly in regions of extreme heat, but it is more abrasion resistant than conventional Teflon. For some high-end modified vehicle applications, it might be just right. And by the way, Tefzel can be found at aircraft avionics shops and at some aircraft surplus outlets. Typically, it's available in a good range of gauge sizes. If you do some shopping, you’ll often find better auto parts stores offer high quality wire with insulation that offers good heat protection and is resistant to abrasion.
The Bottom Line
As you’ve probably gathered by now, the best choice for wire is fine stranded copper. The more strands in the core, the better. If you can afford it, use a silver-plated or nickel-plated wire. If not, use a tin plated copper wire. If you use wire with a PVC insulator, keep a close eye on heat. If you use a Teflon coated wire, watch for abrasion. In the end, you get what you pay for. The better quality the wire, the longer the wire service life.
Try to stay with the aftermarket part wire color-coding whenever possible.
For example, if the tach wiring uses a green wire, keep it green. If the ignition system uses a yellow wire, keep it yellow and so on. It’ll save a huge amount of confusion down the road.
Wire size is critical. It’s a good idea to increase the size of the wire when it becomes necessary to lengthen it. You can never go wrong with too large a wire size. In the end, it boils down to routing and managing the wire. Very large wires are a pain to route, difficult to bend and sometimes even more difficult to bundle. Wire that’s too small can’t carry a given load. Here, bigger translates into better.
