The best metal for conducting electricity isn't gold, as many believe. The absolute best conductor is pure silver. The second best is copper, with a very good conductivity at 97.6 percent that of silver. This is the main reason that copper has been the most popular material for an electrical conductor-it's a fraction of the cost of silver, with almost equalperformance. Gold comes in third, with 76.6 percent the performance rating of silver (the real benefit to gold is its ability to resist corrosion and oxidization). Aluminum, however, comes in a distant fourth at the 63 percent mark, or about two-thirds the conductivity of copper. Stated another way, and when we include the tiny bit of copper applied, CCA cable has about 34 percent greater resistance than a pure copper cable of the same gauge and construction. Let's take a look at what that additional resistance can mean in the real world of car audio.
If you're reading CA&E, you probably already know that resistance in a conductor causes a loss of power in that conductor, in terms of voltage and/or current. It also can become a source of heat if the resistance and amount of power delivered arehigh enough. A quick Ohm's law refresher reminds us that E*I = P or, for those not familiar with the symbols, voltage multiplied by current equals power. So if we want to maximize the ability of our amplifier to make power, we need to maximize the voltage and current that supplies it. Any amount of resistance in the conductor delivering that voltage and current becomes a limiting factor to maximumpower delivery
It's not essential to go into the mathematics here. The point is that for optimum performance with a given supply voltage and a known current delivery requirement, we can calculate how much resistance in the conducting cable is acceptable. Since most of us have been taught the general rule of thumb for selecting wire gauge in systems of various power levels using pure copper cables, it's very important to rethink those requirements when using a less effective conductor, like the CCA cable. While some of you already have your mental light bulb coming on, for those of you new to CCA cable, I provided some additional data to explain what goes on from a technical perspective.
Lab Measurements
As we discussed earlier, additional resistance will increase the heating in the conductor and decrease the amount of power delivered. Let's look at safety first and examine the heat developed in the cables.
Why is the heating important? In most vehicles a portion of this conductor must "live" in the vehicle's engine compartment. Vehicle underhood temperatures here in Arizona often exceed 180F. The insulating jacket on most cables is only rated at 105C, or about 221F. That doesn't leave much of a safety margin for internally developed heat and, in extreme cases, can lead to softened or even melted insulation on the conductor.
They say a picture is worth a thousand words. Here at Cogent Audio Labs, we're fortunate enough to have a special camera that allows us to photograph heat. In the accompanying photos (see below) you'll see radiometric images of three different cables, all sold as 4-gauge and measured under identical test conditions.