Wire reviews

Audio manufacturers around the globe are waging an unseen battle. Most people have no idea that the war is going on, much less who is winning. You see, a significant percentage of the cost of the electronics and loudspeakers we enjoy and, in particular the wiring that interconnects them, is linked to the price of copper.

Since 2004, the price of raw copper has more than doubled and manufacturers have been fighting to keep the cost of products low, as one must do in a highly competitive marketplace. Although the price of raw copper has a direct affect on amplifiers (PCBs have copper traces and copper windings in transformers) and loudspeakers (most voice coils are copper), no category of car audio has been as directly affected as cable and wire. You may have noticed that a quality "amp kit" that used to sell for $49.95 a few years ago is now $99.95 or more. This increase is directly attributable to the amount of copper in those products and the rising cost of the raw material.



In an effort to reduce "sticker shock" for those shopping for amp kits, several companies began producing a different kind of wire as a more cost-conscious alternative. The new wire isn't really new; it was used occasionally in past automotive applications. But high prices make for innovation and now we have "Copper-Clad Aluminum" (CCA) wire that costs about half the price of pure copper cables. While this can be a great alternative to expensive copper, it can also lead to problems if misapplied and its limitations aren't fully understood. Here is how to find out if it's right for your system.

Description
CCA wire is an aluminum wire or many strands of aluminum wire coated with a very thin layer of copper. In practice, the "copper-clad" part of the nomenclature is mainly there to assuage potential buyers' doubts, as the amount of copper used is inconsequential to the actual performance.

The construction and gauge sizes of CCA wire are the same as copper wire. The strand size and count can differ just like various qualities of copper wire, as will the flexibility of the conductor. The insulating material is the same PVC or silicone-based material found on copper wire.

The big difference between pure copper wire and CCA wire is resistance. If you look up the conductivity of common metals used as electrical conductors, some facts might surprise you.

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 equal performance. Gold ranks 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, is 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 or 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 are high 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 maximum power 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.



A pure copper cable and a CCA cable were measured and proved to be "full-spec" 4-gauge as determined by the American Wire Gauge chart. The second pure copper cable is sold as 4-gauge but is about 10 percent under spec in strand count and diameter. It's also less expensive than the full-spec copper, so that may be an indication for the buyer to pay attention.

Each cable was exactly 20' in length and the heating test involved passing 100A of current through it for a 30-minute duration. This is a severe condition but not impossible to duplicate in large systems. The ambient temperature and the start temp of each cable was 76F (see measurements below).



Conclusion
At this point you might be thinking that CCA wire is bad and shouldn't be used, but that's not the case. We've done extensive testing on CCA wire for several manufacturers and our results show that it can work very well for all but the highest current applications. Because of the additional resistance you simply can't substitute the same gauge CCA wire for the traditional gauge copper wire. Our strong recommendation would be to simply use one gauge larger size of the CCA cable than the copper cable.

That being said, if you compensate for the increased resistance in the CCA cable by going to the next larger gauge size, you'll probably end up with equal or maybe even less resistance than the smaller gauge pure copper. But along with an increase in cable size comes an increase in price. This could mean little difference in bottom line prices between comparable copper and a +1-gauge in CCA, so be aware of what you're buying. —Garry Springgay

Garry Springgay is the owner of Cogent Audio Labs, and a former contributing tech editor for Car Audio and Electronics magazine.

RRR37 wrote:That basically says the same thing. OFC is better, but a size up of CCA will handle as much or more as the copper at equal or lesser resistance. Aluminum is a good conductor and while copper is more common, and a little better, I see Aluminum used every day for commercial and industrial electrical installations. Even on 3000 amp services.
I would say if you are going to use one or the other, just make sure you know what the wire can handle. Go big on wire to avoid any issues and ensure proper current flow while reducing your resistance.
Copper can handle more current than aluminum of the same size, but it is generally cheaper to use more aluminum to make up that difference and then some.