For many years automotive wiring harnesses have been gradually increasing in complexity as the number of electrical circuits required in vehicles has been increasing. The main materials used in the cable elements of an auto harness are copper for the conductors and PVC or XLPE (cross-linked polyethylene) for the insulation. In many markets there is an increasing interest in zero halogen insulation materials.
Within an auto copper is also used extensively in the winding wire of electric motors. Modern vehicles with features such as electric windows use many additional small electric motors, in addition to the traditional starter motor, generator, wiper motors, fuel pump, etc. Copper is also widely used in the connectors within the wiring harness, normally in the form of brass alloy, and in other electrical components (e.g. motor commutators). As a result, copper is one of the key materials used by the auto industry, with a typical content of 20 kg or more of copper per vehicle. Copper was at one time also used for other vehicle components, but in some applications it has lost ground to alternative materials. Thus most cars now use aluminium radiators, rather than copper/brass.
As with all other suppliers to the automotive industry, there has been increasing pressure on auto harness producers to achieve cost reductions, year after year. This has resulted in a shift in regional harness production to lower cost labour areas, so that for example, locations like the Philippines have developed a major industry in auto harness assembly for export. The rise in raw material prices, impacting especially on the cost of the copper conductor, but also on the cost of insulation materials, has disrupted the well-established trend of ongoing cost reductions in the auto industry. Of course, over the last two years other major cost elements within a vehicle, for example the steel used in bodywork and many mechanical components, have also risen substantially in price. Auto manufacturers have been very reluctant to accept any price increases from their suppliers to reflect material cost increases.
Though most automotive cables use copper conductors, some companies have introduced battery cables with aluminium conductors. This has been driven mainly by a need to achieve lower weight, rather than cost reduction. The weight distribution of a high performance car is improved by placing the battery at the rear of the vehicle, requiring a battery cable several metres long, which would be very heavy if made of copper. Because of their physical size, battery cables with aluminium conductors may need to be made flat rather than circular and mounted underneath the vehicle. As a result of the more sophisticated connectors that are required to achieve highly reliable connections, aluminium cable systems are not necessarily cheaper than copper equivalents, even though the conductor cost is much lower than with copper.
In principle, aluminium conductors could be used more widely in vehicles within the primary wiring, with potential for a weight saving of several kilograms. Achieving weight reduction is a key design consideration in modern vehicles, as this can lead to lower fuel consumption. One of the main technical problems limiting greater use of aluminium conductors is the need to achieve high reliability in connectors. Furthermore, the greater bulk of aluminium conductors can be a problem where several cables have to occupy a small space.
Lower weight, not so much lower cost, has been the main driver in looking to alternatives to traditional copper conductors for auto cables. Even when copper continues to be used, cable designs can be refined, for example through the use of true concentric strands rather than bunched conductors, allowing thinner insulation and a more compact cable without sacrificing flexibility. Amongst the major wiring harness producers, different companies are looking at a number of different alternatives to copper conductors. As noted, aluminium primary wire is one possibility, but copper clad aluminium is another. For finer sizes of wires it may also be possible to reduce weight while staying with copper by reducing conductor sizes and using hard-drawn copper or copper alloys with greater tensile strength than the usual annealed copper wire. The timescale for any such developments is likely to be slow, as harness designers have to work very closely with the car producers and any successful innovations would be introduced as new models come on stream.