Copper Grades Explained: ETP, EC, OFC & DHP
Ask three people in the copper trade what "pure copper" means and you may get three different answers. A cable maker is thinking about conductivity. A plumber is thinking about brazing. A PCB plating engineer is thinking about how the metal dissolves in a bath. They are all talking about copper, but not the same grade of copper.
Picking the wrong grade is an easy mistake and an expensive one. Copper that works well as a busbar can crack when brazed, and copper that is perfect for tubing can waste energy as a conductor. This guide explains the main grades, what the letters and numbers mean, and how to match each grade to its job.
Why Copper Comes in Different Grades
Copper straight from the refinery is already very pure. What separates one grade from another is mostly two things: how much oxygen it contains, and whether small amounts of other elements such as phosphorus have been added.
Oxygen is the key. Even a few hundred parts per million of oxygen changes how copper behaves when heated, welded or exposed to hydrogen. Phosphorus is added on purpose to remove oxygen, which makes the copper easier to join but slightly lowers its conductivity. Every grade is a trade-off between purity, conductivity, workability and cost.
The Starting Point: Cathode Grade Copper
Almost every Copper Product begins as cathode grade copper. These are sheets of refined copper, typically 99.99 percent pure, produced by electrolytic refining. They are melted and cast into billets, rods or slabs and then rolled, drawn or extruded into finished products.
Cathode itself is a raw material rather than a finished grade. What happens at the melting and casting stage, especially how oxygen is controlled, decides which grade you end up with.
What Is ETP Copper?
ETP copper stands for Electrolytic Tough Pitch copper. It is the most widely used copper grade in the world.
- Purity: minimum 99.90 percent copper (silver counted as copper)
- Oxygen content: roughly 0.02 to 0.04 percent, which is deliberate
- Conductivity: at least 100 percent IACS in the annealed condition
- Designations: C11000 in the UNS system, and often called Cu-ETP in European standards
The word "tough pitch" refers to the small amount of oxygen left in the metal during casting. It is controlled so that the copper sets with a flat, sound surface. That oxygen exists as tiny copper oxide particles, and it does not noticeably hurt electrical performance.
Common uses: busbars, wires and cables, Electrical Strips, transformer windings, switchgear parts, terminals and general electrical components. If you have seen a flat Copper Busbar in a panel, it was very likely ETP.
Limitation: ETP copper can suffer from hydrogen embrittlement. If it is heated above around 400°C in a hydrogen-containing atmosphere, hydrogen reacts with the oxide particles to form steam, which creates internal cracks. That makes it a poor choice for brazing or welding.
ETP vs EC Grade Copper
This is one of the most common questions in the Indian market, and the confusion is understandable because the two are close relatives.
EC grade copper means Electrical Conductor grade. In India it is commonly associated with IS 191 and related standards for copper used in electrical conductors. In practice, EC grade is ETP copper with tighter controls on conductivity and impurities so that it reliably meets electrical requirements.
Here is the practical difference:
| Feature | ETP Copper | EC Grade Copper |
|---|---|---|
| Basic nature | General high-conductivity copper | ETP copper meeting conductor specification |
| Main focus | Purity and workability | Guaranteed electrical performance |
| Typical use | Wide range of products | Wires, busbars, conductors |
| Conductivity | At least 100% IACS | Controlled to meet conductor standards |
| Oxygen content | Controlled, tough pitch | Same range |
So when you compare ETP vs EC grade copper, you are not comparing two different metals. EC is best understood as ETP produced and tested specifically for electrical conduction. If your product carries current, ask for EC grade or confirm the conductivity value in writing.
Oxygen Free Copper (OFC)
Oxygen Free Copper is made by casting in a protective atmosphere or under vacuum, so almost no oxygen gets in. There are two common levels.
- C10200 (OF): oxygen-free copper with a maximum of about 0.001 percent oxygen and at least 99.95 percent copper
- C10100 (OFE): oxygen-free electronic copper, with a minimum of 99.99 percent copper and extremely low oxygen and impurity levels
Because there are no oxide particles, OFC resists hydrogen embrittlement, can be welded and brazed safely and keeps its properties at high temperature. It also has excellent conductivity, typically 100 percent IACS or slightly higher.
Common uses: vacuum devices, semiconductor and electronic components, high-end audio cables, superconductor stabilisation, waveguides, and the ribbon used in solar cell interconnects, where softness and purity matter.
The price is higher than ETP because of the extra process control, so it makes sense only where those properties are needed.
DHP Copper
DHP copper stands for Deoxidised High Phosphorus copper, designated C12200 in the UNS system.
- Phosphorus content: about 0.015 to 0.040 percent
- Copper content: minimum 99.90 percent
- Conductivity: lower than ETP, typically around 80 to 90 percent IACS, because phosphorus reduces it
Phosphorus is added to the melt to grab the oxygen, leaving practically no free oxide. The result is copper that can be brazed and welded without embrittlement and that bends and forms very well.
Common uses: plumbing and refrigeration tubes, air-conditioning coils, gas lines, heat exchangers and many water pipe applications. These are products that must be joined by brazing, and that rarely depend on peak electrical conductivity.
A related and important point: Phosphorised Copper with a lower, tightly controlled phosphorus level, roughly 0.03 to 0.07 percent in a different product form, is also used as anode material for acid copper plating, where the phosphorus helps control how the anode dissolves. Same family, different job.
C101 vs C110 Copper
You will often see these UNS numbers on drawings and mill certificates. The comparison of C101 vs C110 copper comes down to oxygen.
| Feature | C10100 (OFE) | C11000 (ETP) |
|---|---|---|
| Name | Oxygen-free electronic | Electrolytic Tough Pitch |
| Minimum copper | 99.99% | 99.90% |
| Oxygen | Extremely low | About 0.02 to 0.04% |
| Hydrogen embrittlement | Immune | Susceptible |
| Brazing and welding | Excellent | Not recommended |
| Cost | Higher | Lower |
| Typical use | Electronics, vacuum equipment | Power conductors, busbars |
If the part simply carries current in a panel or cable, C11000 is almost always the sensible choice. If it will be brazed, used in hydrogen, in high vacuum or in sensitive electronics, step up to C10100 or C10200.
Understanding IACS Conductivity
IACS stands for International Annealed Copper Standard. It is a benchmark set in 1913, where the conductivity of pure annealed copper is defined as 100 percent. Other materials are expressed relative to that.
This is why you will see ETP copper listed at "100 percent IACS or more" and DHP at a lower figure. Silver sits slightly above copper at around 105 percent, while aluminium is around 61 percent. Higher IACS means less power lost as heat, so it matters most in long cable runs and heavily loaded conductors.
What Does 99.9% Purity Really Mean?
The figure of 99.9% purity is the standard minimum for most commercial grades, but it does not tell the whole story. The remaining 0.1 percent includes oxygen, silver, and trace elements. Two grades with the same headline purity can behave very differently because of what that remaining fraction contains. Oxygen versus phosphorus is the best example. So when comparing copper purity grades, always look beyond the percentage and ask about oxygen, phosphorus and the conductivity test result.
Quick Guide: Which Grade for Which Job?
- Busbars, cables, windings, electrical strips: ETP or EC grade
- Plumbing, refrigeration, AC tubes: DHP
- Brazed or welded parts in reducing atmospheres: OFC or DHP
- Electronics, vacuum and high-end audio: OFE or OF grade
- PV ribbon: high-purity OFC or ETP, annealed to be very soft
- Acid copper plating anodes: phosphorised copper with controlled phosphorus
How to Verify the Grade You Receive
Copper is expensive, and substitution does happen. A few habits protect you:
- Ask for a test certificate showing chemical composition and conductivity
- Check the standard named on the document, such as IS, ASTM or EN
- Verify dimensions and weight, since undersized material often hides lower quality
- Request a trial lot for critical applications
- Buy from suppliers who control their casting process and can trace batches
Frequently Asked Questions
What is ETP copper?
- It is Electrolytic Tough Pitch copper with at least 99.90 percent purity and at least 100 percent IACS conductivity, widely used in electrical products.
Is EC grade the same as ETP?
- Essentially yes, but EC grade is produced and tested to meet electrical conductor requirements, with conductivity guaranteed.
Can ETP copper be brazed?
- It is not recommended, because hydrogen embrittlement can crack the metal. Use OFC or DHP instead.
Why is DHP less conductive?
- The added phosphorus lowers conductivity, but gives better joining properties.
Which copper grade is best?
- There is no single best grade. The right one depends on whether conductivity, joining, purity or cost matters most for your use.
Final Thoughts
Copper Grades look confusing at first, but the logic is simple. Oxygen helps casting but limits joining. Phosphorus helps joining but lowers conductivity. Extra purity helps in sensitive applications but costs more. Once you decide what your product must do, the right grade usually becomes obvious.
If you are sourcing copper for electrical, industrial or manufacturing use, the team at Koprex can help you choose the correct grade and specification for your application. Share your requirement, dimensions and standards, and Koprex will guide you to a suitable option.
Need the right copper grade for your project? Contact Koprex today for specifications, samples and pricing.