Why Copper Grade Selection Matters
Oxygen-free copper and electrolytic tough pitch copper are both high-conductivity refined coppers, yet they suit very different service conditions. ETP copper, UNS C11000, dominates general electrical work because it balances conductivity, formability and cost. Oxygen-free copper, UNS C10100 and C10200, is chosen where residual oxygen would cause embrittlement, outgassing or surface defects. The choice comes down to three questions: what purity is required, how the part will be processed, and which standard governs the product form being purchased.
What Is ETP Copper (UNS C11000)?
ETP copper is electrolytically refined and then melted under a controlled atmosphere that leaves a small, deliberate amount of oxygen in the metal. That oxygen is not a defect: it combines with residual impurities during melting and helps remove them, which protects conductivity.
Copper content: approximately 99.9% minimum
Oxygen content: typically 150 to 400 ppm, or 0.015 to 0.04%
Electrical conductivity: about 100% IACS, with equally high thermal conductivity
Formability: excellent for drawing, bending and rolling
Limitation: susceptible to hydrogen embrittlement in high-temperature hydrogen-bearing service
Typical uses are power cable conductors, busbars, transformer and motor windings, building wiring, switchgear and general industrial fabrication.
What Is Oxygen-Free Copper (UNS C10100 and C10200)?
Oxygen-free copper is melted and cast under oxygen-free or reducing conditions, so oxygen is essentially eliminated. Residual levels are typically below 10 ppm, and premium C10100 heats can reach 1 to 5 ppm.
C10100: 99.99% minimum copper with very low residual deoxidants, giving the highest conductivity of the wrought coppers
C10200: 99.95% minimum copper, the standard oxygen-free grade for most fabrication work
Conductivity: about 101% IACS for C10100 and about 100% IACS for C10200, with better stability at elevated temperature
Behaviour: highly resistant to hydrogen embrittlement, low outgassing in vacuum, and no flaking during severe forming
Cost: higher than ETP because of the special melting practice and tighter process control
Applications include vacuum and accelerator components, high-voltage electrodes, semiconductor process equipment, medical imaging hardware, high-end audio and RF conductors, and brazed assemblies that must stay leak-tight after thermal cycling.
Head-to-Head Comparison and Hydrogen Embrittlement
| Property | ETP Copper (C11000) | Oxygen-Free Copper (C10100 / C10200) |
|---|---|---|
| Oxygen content | 150 to 400 ppm | Below 10 ppm, often 1 to 5 ppm |
| Copper purity | About 99.9% minimum | 99.95% minimum for C10200; 99.99% minimum for C10100 |
| Electrical conductivity | About 100% IACS | Up to about 101% IACS, more stable at temperature |
| Hydrogen embrittlement | Risk in wet reducing atmospheres at elevated temperature | Effectively immune in normal brazing, annealing and vacuum cycles |
| Vacuum behaviour | Not recommended for critical vacuum seals | Low outgassing, suitable for vacuum service |
| Relative cost | Lower | Higher |
| Typical application | Wiring, cables, busbars, motors, transformers | Aerospace, medical, semiconductor, vacuum, audio |
When ETP copper is heated in a hydrogen-bearing atmosphere, dissolved oxygen reacts with hydrogen to form steam at the grain boundaries. The resulting internal pressure cracks the metal, and the damage is invisible before service. Brazing, annealing and sintering are exactly the processes where this happens, so the fabricated assembly rather than the material datasheet usually decides whether ETP copper is acceptable. Oxygen-free copper contains too little oxygen to support that reaction, which is why high-reliability assemblies specify C10100 or C10200 whenever the part will meet hydrogen, wet reducing gas or sustained vacuum at elevated temperature.
Standards, Supply Forms and Selection
| Grade | UNS designation | Applicable product standards | Common supply forms |
|---|---|---|---|
| ETP copper | C11000 | ASTM B187 for rod, bar and shapes; ASTM B152 for plate, sheet and strip; ASTM B49 for rod for electrical purposes | Busbar, rod, wire, strip, sheet, tube |
| Oxygen-free copper | C10100 and C10200 | ASTM B170 for oxygen-free electrolytic copper refinery shapes; ASTM B187 for rod, bar and shapes; ASTM B152 for plate, sheet and strip | Rod, tube, wire, strip, plate, custom shapes |
Choose ETP copper C11000 for conductors and busbars, indoor wiring, motor and transformer windings, and parts that are not brazed or annealed in hydrogen.
Choose oxygen-free copper C10100 where maximum conductivity, vacuum integrity and complete resistance to hydrogen embrittlement are required.
Choose oxygen-free copper C10200 for the same oxygen-free behaviour at a more moderate purity and price point.
Specify the standard, the temper such as annealed O60 or hard H04, and the tolerance class together, because one grade is covered by different standards depending on the product form.
Frequently Asked Questions
Q: Is oxygen-free copper much more conductive than ETP copper?
Only marginally. C10100 reaches about 101% IACS against about 100% IACS for C11000. The real advantage is conductivity stability and freedom from embrittlement at high temperature.
Q: Can ETP copper be used in brazed assemblies?
Yes, provided the brazing atmosphere is dry and free of hydrogen or moisture and the part sees no sustained reducing service at temperature. For vacuum brazing or wet reducing atmospheres, oxygen-free C10100 or C10200 should be specified instead.
Q: What is the difference between C10100 and C10200?
Both are oxygen-free. C10100 requires 99.99% minimum copper with very low residual deoxidants, while C10200 requires 99.95% minimum copper. C10100 is chosen for the most demanding conductivity and vacuum applications.
Q: Which standards apply to copper rod, bar, plate and strip?
ASTM B187 covers copper bus bar, rod and shapes for general purposes, and ASTM B49 covers copper rod for electrical purposes. ASTM B152 applies to plate, sheet and strip, and ASTM B170 covers oxygen-free electrolytic copper refinery shapes.
Q: Does oxygen-free copper cost more than ETP copper?
Yes. Oxygen-free grades carry a premium because of the special melting and casting practice and tighter quality control, and that premium is justified only where hydrogen embrittlement, outgassing or maximum conductivity genuinely matter.
Q: How can the delivered grade be verified?
Request the mill test report showing chemical composition and conductivity, and confirm the oxygen content by the method agreed in the purchase order. Independent check by spark emission spectrometry or inert gas fusion is common for critical orders.
