OFE vs OFHC vs ETP: Choosing the Right High-Purity Copper Grade for Your Investment Casting Application

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The Bottom Line

• OFE vs OFHC vs ETP copper isn't a purity ranking to memorize - it's a decision that should follow directly from what your switchgear or high-conductivity part actually has to survive in service, not from picking the "best" grade by default.

• ETP copper (C11000) is the cost-effective default wherever conductivity matters but the part won't see a hydrogen-bearing atmosphere at elevated temperature - correctly melted, it reaches 100 to 101 percent IACS at a fraction of OFHC or OFE's cost.

  
  

• OFHC (C10200) and OFE (C10100) contain essentially no cuprous oxide, because they're vacuum melted rather than air melted - that makes them immune to the hydrogen embrittlement risk ETP has to be melted carefully to avoid, and mandatory wherever brazing, welding, or a hydrogen-rich environment is unavoidable.

  
  

• The bigger value than picking the right grade is getting it as a near-net-shape investment casting instead of machined bar stock - complex switchgear geometry cast directly in the certified alloy, without the material waste and machining risk of cutting it from rod or sheet.

The Real Question Isn't Which Grade Is "Best" - It's What Your Application Actually Needs

It's tempting to treat OFE, OFHC, and ETP as a strict hierarchy - OFE at the top, ETP at the bottom - and default to the highest grade available. That instinct gets high purity copper grade selection backwards. All three deliver conductivity in the same 100 to 101-plus percent IACS range; the real differences are in oxygen content, melting process, and what that means once the part is exposed to a specific service condition.

A busbar connector that never sees a reducing atmosphere doesn't need OFE's extra purity margin. A vacuum interrupter component that will be brazed into an assembly can't safely use anything but an oxygen-free grade. The right question isn't which grade is best - it's what this specific part has to survive, and that's the real OFE vs OFHC vs ETP copper decision, not a purity ranking.

When ETP Copper Is the Right Call

ETP copper (UNS C11000, EN Cu-ETP / CW004A) is air melted and carries roughly 0.02 to 0.05 percent oxygen as cuprous oxide - the same composition covered in why a copper casting failed conductivity test and hydrogen embrittlement in ETP copper casting. Correctly melted under controlled atmosphere, it reaches 100 to 101 percent IACS, matching OFHC's conductivity at meaningfully lower cost - and that's really the core of the OFHC vs ETP copper difference: not conductivity, but oxygen content and what it means for hydrogen exposure.

ETP is the right default for the large majority of switchgear hardware - busbar connectors, structural-electrical brackets, terminal hardware - where the part won't be exposed to a hydrogen-bearing atmosphere at elevated temperature after casting. The trade-off is that melt atmosphere control matters, and so does controlling any downstream brazing or welding - both entirely manageable, neither a reason to default to a more expensive grade.

When OFHC or OFE Matters: Hydrogen Immunity and the Purity Ceiling

OFHC (UNS C10200, EN Cu-OF / CW008A) and OFE (UNS C10100, EN Cu-OFE / CW009A) are both vacuum melted, and both contain essentially no cuprous oxide - OFHC is held to a maximum 10 ppm oxygen, OFE to a tighter 5 ppm, against ETP's 200 to 500 ppm. That near-total absence of oxygen means there's no Cu2O for hydrogen to react with, so the steam-embrittlement mechanism covered in hydrogen embrittlement in ETP copper casting simply can't occur - not because the melt atmosphere was controlled well, but because the reaction has nothing to react with. That's the deciding factor for vacuum interrupter contacts, components that will be brazed or welded in a hydrogen-bearing process, and any part operating inside a hydrogen-rich environment, such as hydrogen-cooled generator hardware.

Between OFHC and OFE, the difference is a purity ceiling most switchgear applications never need. OFHC's 100 percent IACS minimum and 99.95 percent copper purity cover the overwhelming majority of high-conductivity structural-electrical parts. OFE's tighter 5 ppm oxygen limit, 101-plus percent IACS, and 99.99 percent purity exist for a narrower band of applications - vacuum capacitors, high-precision electronic components, and instrumentation where every fraction of a percent of conductivity or the certified oxygen-free status itself is a specification requirement, not just a nice-to-have. Specifying OFE by default when OFHC would do adds cost without adding usable performance.

In switchgear hardware specifically, ETP copper covers busbar connectors, structural-electrical brackets, and terminal hardware where the part carries current and mechanical load but stays clear of any hydrogen-bearing process afterward - the majority of current-carrying components fall here. OFHC is the right call the moment that same kind of part will be brazed or welded into a larger assembly, or operates somewhere a reducing atmosphere is plausible - contact carriers and connector bodies joined downstream are the clearest example.

OFE concentrates in a narrower band: vacuum interrupter contacts and support electrodes, vacuum capacitor components, and instrumentation where the application specifically calls for certified oxygen-free status rather than just high conductivity. None of these are hard boundaries - a buyer with a genuinely demanding hydrogen exposure risk might specify OFE for a part that OFHC would technically satisfy, simply because the certified purity margin is worth the cost for that specific program. The point isn't a rigid lookup table; it's that the grade decision should trace back to a real condition the part will face, not to which name sounds the most premium.

Beyond the Right Alloy: Why Near-Net-Shape Casting Adds Real Value

Getting the alloy right, as covered above, is essential - a part in the wrong grade fails on hydrogen exposure or purity requirements no matter how well it's made. But the alloy decision is only half the value. OFE and OFHC copper rod and sheet are commodity products - any number of metal distributors stock them - and a switchgear contact, connector body, or vacuum interrupter component machined from round or flat bar stock loses a significant fraction of that material as chips, with every additional machining pass on an oxygen-sensitive high-purity grade a chance to introduce surface contamination or work-hardening that a finished part shouldn't carry. Investment casting - also known as lost wax casting - produces that same complex geometry directly in the certified grade, near net shape, without the waste or the machining risk.

For a switchgear contact body or a multi-feature connector, that difference compounds: complex internal passages, undercuts, or stepped geometry that would need multiple machining setups from bar stock can be cast as one piece, in OFE, OFHC, or ETP copper, with the conductivity and purity already verified before the part ever reaches final finishing. The grade decision and the process decision aren't separate questions - choosing the right high-purity copper grade only pays off fully when it's paired with a process that delivers the finished geometry without undoing the reason that grade was specified in the first place.

The raw material cost tiers upward from ETP to OFHC to OFE, and that premium is real - but it's usually the smaller number in the total cost comparison. A complex switchgear part machined from OFHC or OFE bar stock carries the full material cost of the stock removed as chips, plus the machining time and tooling wear of cutting a relatively soft, gummy high-purity copper into a precise geometry. Casting the same part near net shape means the grade premium applies to a smaller starting mass, and the geometry - internal passages, contact fingers, stepped sections - arrives largely finished rather than being cut in. For a high-complexity part, the process decision can matter more to total delivered cost than which of the three grades was specified.

OFE vs OFHC vs ETP Copper: The Grades Compared

The measurable OFE OFHC ETP comparison, side by side:

Grade	UNS	EN	Melting Process	Oxygen Content	Typical IACS
ETP Copper	C11000	Cu-ETP, CW004A	Air melted	~0.02-0.05% (200-500 ppm)	100-101% (properly melted)
OFHC Copper	C10200	Cu-OF, CW008A	Vacuum melted	10 ppm maximum	100%+ minimum
OFE Copper	C10100	Cu-OFE, CW009A	Vacuum melted	5 ppm maximum	101%+ minimum

What to Specify to Get the Right Grade, Not Just a Grade

A drawing that just says "high conductivity copper" or even names a family without a UNS or EN code leaves the actual grade open to interpretation. A complete specification names the exact designation, states the application's real constraint - hydrogen exposure, an absolute conductivity ceiling, or cost-effective standard duty - and asks for the certification that proves the foundry delivered it.

Specification Item	What to State	Why It Matters
Alloy designation	UNS and EN code (e.g. C10200 / Cu-OF, CW008A) - not just "oxygen-free copper"	Removes ambiguity between OFE, OFHC, and ETP, which share overlapping descriptions
Minimum conductivity	An explicit %IACS minimum matched to the grade	Turns the grade choice into a measurable, testable requirement
Hydrogen exposure requirement	State whether the part will be brazed, welded, or hydrogen-exposed downstream	Determines whether ETP is viable or an oxygen-free grade is mandatory
Material certificate	EN 10204 Type 3.1 with measured composition and conductivity from the production heat	Confirms the grade delivered matches the grade specified

3 Signs Your Copper Grade Was Misspecified

• The drawing names a family, such as "oxygen-free copper," without a UNS or EN code, leaving the actual grade up to the foundry's interpretation.

  
  

• A part that will be brazed or welded downstream was specified in ETP copper without anyone checking whether that joining step introduces hydrogen exposure.

  
  

• OFE was specified by default for a structural-electrical part that never approaches OFE's purity ceiling, adding cost without a corresponding requirement.

  
  

Source OFE, OFHC, and ETP Copper Castings Near Net Shape

Pahwa MetalTech casts OFE, OFHC, and ETP copper investment castings - part of a wider copper alloy investment casting range - as near-net-shape switchgear components in whichever grade your application actually requires, verified to the conductivity and purity level that grade calls for.

Share your drawing and application details through our contact page, and we'll confirm the right grade for your OFE vs OFHC vs ETP copper requirement, along with the verification protocol we'll test against before the first casting ships.