What is Oxygen-Free Copper (OFC) Wire?

For more than a century, copper has been the backbone of our residential, commercial, and industrial electrical systems. 

Known for its vibrant reddish hue, copper is conductive, corrosion-resistant, and flexible, making it an excellent choice for electrical power. However, it also contains tiny amounts of other elements, including oxygen. Although the percentage of oxygen is incredibly small, it’s still enough to potentially cause damage over time. That’s why for projects where reliability, strength, and conductivity are key, oxygen-free copper (OFC) is a game-changer. 

But how do we create oxygen-free copper? How does it make electrical wire more effective, and is the additional cost worth it in the long run? 

Oxygen-Free Copper: Tale of the Tape 

True to its name, oxygen-free copper has virtually no oxygen content; it measures less than 0.001% in the rod or bar used to make the wire. And, before you ask, the name is somewhat of a misnomer. Although there is no such thing as pure copper, OFC comes as close as possible to reaching that point. 

This doesn’t mean the copper we commonly use for electrical projects, cathodic protection, and other jobs is low quality. Standard Electrolytic Tough Pitch (ETP) copper rod is 99.9% pure, which is considered commercially pure for electrical wire and cable manufacturing. 

But even within the category of oxygen-free copper, we have different tiers. C10200 alloy OFC is 99.95% pure copper and has a maximum oxygen content of 0.001%. C10100 copper alloy is even more pure, coming in at an astounding 99.99%. This copper variation only contains 0.0005% oxygen and is considered “ultra-pure.” 

Enhanced Production Process 

The process for making oxygen-free copper is similar to ETP copper, but with some additional steps thrown in. 

To remove as much oxygen as possible, manufacturers have several methods to get the job done, including: 

• Coating molten copper with charcoal or another carbon-containing compound. The carbon in the materials reacts with the oxygen to create carbon dioxide. 

• Melting the copper under a sealing gas like carbon monoxide. 

• Using a vacuum to vaporize and remove oxygen. 

• Combine the copper with gases like hydrogen to create chemical reactions with oxygen atoms. 
   

No matter which option we choose, the result is a higher-quality copper that performs better for the lifespan of the wire or cable. 

Low Oxygen, High Performance 

Oxygen-free copper’s high purity gives it several benefits over its standard ETP counterpart. 

Improved Conductivity 

First, OFC’s lower oxygen content makes it more conductive. ETP copper has a conductivity of 100% International Annealed Copper Standard (IACS), but OFC measures at 101% IACS or more. While it seems like a small difference, the upgrade is crucial for applications like high-fidelity audio and high-speed data. High-conductivity copper means less distortion for audiophiles and faster data transfers. 

More Durable, Stronger Performance 

You’ll also see that OFC has better corrosion and oxidation resistance than ETP. One problem standard copper has is that at high temperatures, the oxygen in ETP can mix with hydrogen. This chemical reaction results in water vapor, which can create voids in the wire. Over time, it can lead to hydrogen embrittlement. 

OFC excels in this regard because with so little oxygen present, there is less risk of water vapor forming. 

Oxygen-free copper is also more flexible, has better impact strength, and dissipates heat more effectively than its ETP counterpart. Products using OFC tend to suffer less from brittleness, have better ductility, and maintain thermal stability at higher temperatures. 

Quality Comes at a Cost 

For as good as high-quality oxygen-free copper is, it comes at a cost. Because the copper must go through a more complex process to reach its final form, it costs more than your standard ETP copper. 

Luckily, ETP is a fine choice for most applications, including general electrical wire and cable installations. However, for high ductility projects and applications where signal loss is unacceptable, OFC is worth the additional cost. Basically, the more precise something needs to be, the more necessary OFC becomes. 

Where is Oxygen-Free Copper Used? 

You can technically use OFC copper for any ETP copper application, but the cost may not justify it. 

With that said, OFC would absolutely be the better option for several applications, including: 

• High-quality audio applications to maintain fidelity and minimize signal loss. 

• High-speed data systems to minimize signal loss. 

• Precision electronics require high electrical conductivity and low signal loss. 

• Transistors and vacuum seals, where durable, high-purity copper improves quality. 

• Vacuum or hydrogen environments, where hydrogen embrittlement could be an issue. 

• Aerospace and military applications to minimize signal loss and improve corrosion resistance. 

• Medical devices, thanks to OFC’s high reliability and durability, consistent conductivity, and low corrosion risk. 

• Semiconductor production, where lower-purity materials could negatively impact performance. 
   

Small Difference, Large Impact 

While the average crew might not be tripping all over themselves to buy OFC wire because of the price, it has its specialized uses. 

For most of us, though, a high-quality ETP copper wire or cable gets the job done safely and economically.