OFHC vs ETP Copper: Which Grade Should You Specify for Investment Casting?

OFHC and ETP copper are both high-conductivity grades of pure copper — both exceed 99.9% copper content, both deliver electrical conductivity at or above 100% IACS, and both are widely investment cast. Investment casting — also known as lost wax casting — of pure copper grades is a process that serves the electrical, marine, oil and gas, and precision engineering sectors across a substantial range of component geometries and applications. The two grades are not, however, interchangeable. The difference between them — primarily the oxygen content — determines whether a component will perform correctly in service or fail in a specific application that ETP copper cannot serve.

This guide sets out what separates OFHC vs ETP copper in the investment casting context: the technical differences, the process implications at the foundry, the standards and designations used across US, European, and Indian procurement, and a clear decision guide by application type.

For a complete overview of all copper alloy families available in investment casting — including aluminium bronze, nickel aluminium bronze, copper chromium zirconium, tin bronze, and the brass range — refer to detailed guide Copper, Brass, and Bronze Investment Casting: Metallurgy, Process Control, and Industrial Applications

What Is ETP Copper (C11000) — and When Is It the Right Specification?

Electrolytic Tough Pitch copper (ETP, UNS C11000) is the most widely produced and investment cast pure copper grade globally. The grade is produced by electrolytic refining of copper to a minimum purity of 99.9%, with oxygen deliberately retained in the melt in the form of cuprous oxide (Cu2O) at concentrations of approximately 150–400 parts per million. The oxygen serves a practical function in the refining process — it helps eliminate trace impurities — but it becomes a liability in specific high-temperature applications.

Electrical conductivity of ETP copper is exactly 100% IACS (International Annealed Copper Standard) by definition — ETP copper is the reference material from which the IACS scale is defined. This makes ETP the correct and cost-effective specification for the majority of electrical investment casting applications: bus bar junctions, distribution board connectors, terminal blocks, switchgear contact arms, and general electrical hardware where the conductivity requirement is 100% IACS and the operating conditions do not involve high-temperature hydrogen exposure.

When ETP is the correct specification:  Standard electrical conductors, bus bar connectors, switchgear components, terminal blocks, and general electrical hardware operating at standard temperatures (below 200°C continuous). For applications in these categories, ETP copper delivers the required conductivity at lower cost than OFHC and should be the default specification.

Explore our detailed article on Investment Casting of High Conductivity Copper & Brass Parts for Electrical Switchgear to understand the challenges and advantages of producing precision electrical components. You can also read Casting vs Fabrication of High Conductivity Bus Bars for a comparison of manufacturing routes, design flexibility, and production considerations for high-current bus bar systems.

What Is OFHC Copper (C10100 / C10200) — and When Does the Premium Apply?

Oxygen-Free High Conductivity copper is produced without the introduction of oxygen in the melting process — achieved by melting in an inert atmosphere or vacuum, preventing atmospheric oxygen from dissolving into the melt. The result is copper with oxygen content below 10 parts per million (C10200, the standard OFHC grade) or below 5 parts per million (C10100, the electronic-grade OFHC with minimum 99.99% copper purity).

Conductivity of OFHC C10200 is a minimum of 100% IACS and typically measures at 101% IACS — the 1% advantage over ETP is real but rarely the primary justification for the grade upgrade. The correct reason to specify OFHC copper is the absence of cuprous oxide and the consequences of that absence in specific conditions.

In ETP copper, the Cu₂O present in the microstructure is chemically stable under most service conditions. However, when ETP copper is heated above approximately 400°C in an atmosphere containing hydrogen — whether during brazing, annealing in a reducing atmosphere, or in service in a hydrogen-rich environment — the following reaction occurs:

Cu₂O  +  H₂  →  2Cu  +  H₂O (steam)

Cuprous oxide reacts with hydrogen to form steam inside the copper matrix — causing hydrogen embrittlement (steam disease)

The steam produced by this reaction cannot escape from the solid copper matrix. It accumulates at grain boundaries and creates internal voids, causing severe embrittlement and loss of ductility — a failure mode known as hydrogen disease or steam embrittlement. Components that have undergone this degradation may appear visually intact but are structurally compromised, often failing catastrophically at brazed joints or under mechanical load.

OFHC copper contains no Cu2O. The reaction above cannot occur. This makes OFHC copper mandatory — not merely preferred — for components that will be brazed in hydrogen atmospheres, operated at elevated temperatures in hydrogen-rich environments, or used in applications such as vacuum interrupters and electron devices where outgassing of Cu2O from ETP copper degrades vacuum quality.

ETP vs OFHC Copper — The Technical Comparison

Oxygen Content and What It Means in Practice

Property	ETP Copper  C11000	OFHC Copper  C10200	OFHC Electronic  C10100
UNS Designation	C11000	C10200	C10100
Minimum Copper Purity	99.90%	99.95%	99.99%
Oxygen Content	150–400 ppm (as Cu₂O)	< 10 ppm	< 5 ppm
Electrical Conductivity	100% IACS (reference)	Min 100%, typically 101% IACS	Min 101% IACS
Hydrogen Embrittlement Risk	Yes — above 400°C in H₂	None	None
Suitable for Brazing > 400°C	No — hydrogen atmosphere brazing only with OFHC	Yes	Yes
Suitable for Vacuum Devices	No — Cu₂O outgassing	Yes	Yes — preferred
Investment Casting Melting	Air melting (standard)	Vacuum or inert gas melting required	Vacuum melting required
Raw Material Cost Premium	Reference (lowest cost)	+30 to 45%	+50 to 75%
ASTM Reference	B152, B187	B170, B187	B170
EN Material Designation	CW004A (Cu-ETP)	CW008A (Cu-OF)	CW009A (Cu-OFE)

Conductivity — When the 1% Difference Actually Matters

The 1% IACS difference between ETP (100%) and OFHC C10200 (101%) is real but context-dependent. In a standard bus bar junction carrying 200A in a distribution board, the difference in resistive heating between a 100% IACS and a 101% IACS component is negligible — well within the safety margins designed into the system. Specifying OFHC for conductivity alone in this application adds 15–25% to material cost without a corresponding improvement in system performance.

The conductivity difference becomes meaningful in two scenarios: ultra-high precision electrical applications where absolute resistivity consistency across batches is a design requirement (scientific instruments, precision measurement equipment, certain telecommunications hardware), and where localised resistive heating under sustained high-density current loads is the specific design constraint being optimised.

In these cases, specifying OFHC C10200 or C10100 is the correct decision, but conductivity is rarely the sole reason — it typically accompanies another OFHC-mandatory requirement.

 

Porosity and Density in Investment Castings

In investment casting, porosity in a copper conductor is non-conductive volume within the conductive cross-section. A porosity-free casting of the same nominal dimensions conducts more efficiently and more consistently than a casting with distributed microporosity — a distinction that is particularly important for OFHC applications where conductivity consistency across batches is a design criterion.

ETP copper investment castings are produced by air melting. Oxygen dissolved in the ETP melt must be managed during casting to prevent gas porosity from dissolved oxygen precipitating during solidification. Proper degassing, controlled pouring temperature, and shell management reduce porosity to acceptable levels in most electrical applications.

OFHC copper investment casting requires vacuum or controlled inert-atmosphere melting to prevent oxygen pick-up from the atmosphere re-oxidising the melt — which would defeat the purpose of the OFHC grade. Vacuum melting also eliminates dissolved gas porosity from atmospheric contamination, producing denser, more homogeneous castings. The combination of OFHC chemistry and vacuum melting delivers the highest-quality conductor cross-section achievable in investment cast copper.

For the detailed technical process guide to refer to our article on vacuum investment casting of OFHC copper

Investment Casting Process Differences — ETP vs OFHC

Process Stage	ETP Copper (C11000)	OFHC Copper (C10200 / C10100)
Melting atmosphere	Air melting — standard induction furnace	Vacuum melting or controlled inert-gas atmosphere (argon)
Oxygen management	Degassing treatment to reduce porosity risk from Cu₂O	No oxygen to manage — atmosphere prevents pick-up
Melt temperature control	Standard copper casting temperatures	Tighter controls — no oxidation buffer from Cu₂O
Shell preheating	Standard investment casting protocol	Similar, with atmosphere considerations
Solidification	Standard — shrinkage management via risers	Same — vacuum melting reduces gas porosity risk
Post-cast inspection	Standard dimensional and conductivity testing	Full density verification; chemical analysis to confirm O₂ < 10 ppm
Material certificate	Standard chemical analysis + mechanical test	O₂ content analysis required; EN 10204 3.1 typical for EU
Relative processing cost	Reference	+20 to 40% over equivalent ETP casting

Application Decision Guide — ETP or OFHC?

The following table provides the specification recommendation by application type. The decision is not simply about conductivity — it is about what the component will experience in service and whether Cu₂O in ETP copper creates a performance or safety risk in that specific condition.

Application	Recommended Grade	Reason
Bus bar junctions and connectors (standard)	ETP  C11000	100% IACS sufficient. No high-temperature brazing in service. Cost-effective.
Distribution board connectors and terminal blocks	ETP  C11000	Standard electrical application. No OFHC requirement.
Switchgear contact arms and moving contacts	ETP  C11000	Standard service conditions. Air melting adequate for most specifications.
Components brazed above 400°C in hydrogen atmosphere	OFHC  C10200	Hydrogen embrittlement of ETP is a real failure mode. OFHC mandatory.
Vacuum interrupter contacts and vacuum tube electrodes	OFHC  C10200	Cu₂O outgassing from ETP degrades vacuum quality. OFHC mandatory.
RF waveguides and microwave components	OFHC  C10200	Surface conductivity and outgassing requirements. OFHC standard specification.
Precision conductors — batch conductivity consistency	OFHC  C10200	Absence of Cu₂O provides denser, more consistent conductor cross-section.
Components for operation in H₂-rich environments above 400°C	OFHC  C10200	Hydrogen disease risk with ETP in sustained high-temperature H₂ service.
Ultra-high vacuum (UHV) system components	OFHC  C10100	Highest purity — minimum outgassing. 99.99% copper specification required.
High-temperature bus bar (continuous >200°C service)	OFHC  C10200	Thermal stability; ETP softening and potential H₂ exposure in some environments.

Standards, Designations and How to Specify on a Drawing

Specifying the correct grade on a procurement drawing requires using the ASTM or EN designation, not just 'copper' or 'OFHC copper'. Foundry-level interpretation of an unqualified copper specification defaults to the most commonly available and processed grade — which will be ETP. If OFHC is the required grade, it must be stated explicitly with the UNS designation or ASTM/EN standard reference.

Grade	UNS	ASTM Standard	EN Designation	IS Reference	Specify As
ETP Copper	C11000	ASTM B152 / B187	CW004A (Cu-ETP)	IS 191 Part 1	C11000 (ASTM B152 Cu-ETP)
OFHC Copper	C10200	ASTM B170 / B187	CW008A (Cu-OF)	IS 191 Part 2	C10200 (ASTM B170 Cu-OF)
OFHC Electronic	C10100	ASTM B170	CW009A (Cu-OFE)	IS 191 Part 2	C10100 (ASTM B170 Cu-OFE)

For EU procurement: specify the EN designation (CW004A for ETP, CW008A for OFHC) and request EN 10204 Type 3.1 material certificate confirming oxygen content. For OFHC C10200, the certificate should include chemical analysis confirming O2 below 10 ppm. For OFHC C10100, confirm O2 below 5 ppm and minimum 99.99% Cu purity.

Discuss an OFHC or ETP Copper Investment Casting Requirement

Pahwa MetalTech produces investment castings — also known as lost wax castings — in both ETP copper (C11000) and OFHC copper (C10200 / C10100), with air melting for ETP and vacuum melting for OFHC grades. Components from 5 grams to 70 kilograms. Full chemical analysis and EN 10204 Type 3.1 material certificates available. ISO 9001:2015 certified. Chakan, Pune.

To discuss alloy selection, process capability, or a first article programme — contact us