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Oxygen Free Copper

First, the myth about "OFC" wires: many companies have grown quite proud of their superior Oxygen Free Copper wires. But does that really hold value? And what does it really mean?

 

There are three primary compositions of copper wire that are used for electrical transfer. They are:

 

1. C10100 - This is 99.99% pure copper with less than 0.001% oxygen and is the most expensive of the three. It's sometimes referred to as OFE (Oxygen Free Electronic).

 

2. C10200 - Made of 99.95% pure copper and has at least 0.001% oxygen. This is sometimes called OF (Oxygen Free).

 

3. C11000 - This is called ETP. If I remember correctly, that stands for Electrolytic Tough Pitch and is by far the most common form of copper. This is at least 99.90% pure copper with somewhere between 0.01% to 0.05% oxygen.

 

Now, as far as how they compare to each other, you can clearly see by their ratings that there is almost no difference from copper that is considered oxygen free, and copper that isn't. Based on conductivity requirements for each grade of copper, ETP and OF are identical! They both require at least 100% IACS (International Annealed Copper Standard) conductivity. The practical difference from ETP to OFE is less than 1% IACS conductivity.

 

The primary reason that OFC was developed in the first place was for industrial use where copper under high-duress had a tendency to get brittle over longer periods of time. There is virtually no value in OFC for your vehicle or home.

 

Strand Count/Skin Effect

The second big myth is about the value of strand count. I can’t tell you how many people I have heard say "get the wire with the highest strand count you can find" when the user is just going to be making a straight run of wire from one piece of equipment to another. Why? The real value of a high strand count is in the flexibility of the wire itself and even then, this is often dominated by the thickness and flexibility of the jacket that covers the wire. If you need to 1/0 gauge wire in a 3" diameter circle, then high strand count would hold some value IF the jacket isn’t limiting your flexibility.

 

Of course, someone is sure to shout out "But what about the skin effect?!?" For those not familiar with this phenomenon, it has been observed that alternating current tends to distribute itself within a conductor with the highest current density found on the outer surface of the conductor than at the core. This current "flowing on the skin" of the conductor causes the effective resistance of the conductor to increase with the frequency of the current. This effect is real, no doubt about it. But does it matter for audio usage? Absolutely not!

 

The skin effect is a factor worth considering for radio frequencies and, to a lesser extent, very high current electrical power transmission and distribution systems. To give you some real world numbers, the skin depth at 60 Hz is 8.57mm. At 10kHz, it is just under 0.70mm. Simply put, if passing alternating current through a wire at a frequency of 60 Hz, the skin effect would only be applicable if each strand was 9mm or greater in diameter. I have never seen a cable even remotely approaching this.

 

When it comes to wires, don’t get caught in the marketing hype. Look for an affordable wire with a durable jacket and if buying one with one of the various forms of connectors, be sure that the connectors are strong enough to handle multiple re-attachments to your equipment. If the cable is so much better than what competitor’s offer that it warrants a $10,000 price tag, I’d expect some measurements up front that support this rather than a bunch of buzz-words and a huge price tag