What is copper C110 (ETP copper)?

Copper C110 (UNS C11000) is Electrolytic Tough Pitch (ETP) copper — the most widely used commercial copper grade worldwide. It is produced by melting electrolytic copper cathodes and casting in air, resulting in a copper oxide (Cu₂O) content of approximately 0.02–0.05% (200–500 ppm oxygen). The Cu₂O exists as small inclusions at grain boundaries. ETP copper achieves 100% IACS electrical conductivity and is the standard for electrical wire, bus bar, and terminal applications that will not be exposed to reducing atmospheres at elevated temperature.

What is hydrogen embrittlement in ETP copper?

Hydrogen embrittlement in ETP copper (C110) occurs when the Cu₂O inclusions react with atomic hydrogen diffused into the metal at temperatures above approximately 700°F (370°C): Cu₂O + H₂ → 2Cu + H₂O. The steam (H₂O) produced cannot escape the metal lattice, builds up pressure at grain boundaries, and causes intergranular cracking and severe embrittlement. This happens in silver brazing (braze temperatures 1,150–1,650°F (620–900°C)), torch welding in reducing flame, or use in hydrogen-atmosphere furnaces. The fix is to use OFHC copper (C101) instead, which has no Cu₂O to react.

Can I braze copper C110?

You can silver-braze C110 with a neutral or slightly oxidizing flame in air, but NOT with a reducing flame (excess fuel). Under a reducing flame, atomic hydrogen is produced and causes the hydrogen embrittlement failure mechanism described above. If your brazing process uses a hydrogen-containing atmosphere, reducing furnace, or if the joint will be heated multiple times, specify C101 (OFHC) copper instead. For torch brazing with an oxyacetylene or air-acetylene torch in the field, C110 is generally acceptable if a neutral to oxidizing flame is maintained and the joint is not overheated.

What ASTM standard covers copper C110?

ASTM B187 covers C11000 rod and bar. ASTM B152 covers sheet, strip, plate, and rolled bar. ASTM B1 covers soft-drawn wire. ASTM B2 covers medium-drawn wire. When specifying on an engineering drawing, the correct callout for machined bar stock is: "Copper, UNS C11000, ASTM B187, Temper H02 (Half-Hard)." Note that C11000 is the most stocked copper alloy and typically has the shortest lead time and lowest cost among pure copper grades.

How does C110 compare to C101 in cost?

C110 (ETP copper) is typically 5–15% less expensive than C101 (OFHC copper) due to the simpler casting process — ETP is cast in air rather than in vacuum or inert atmosphere. Both are priced off the COMEX copper spot price, so the premium varies. For the vast majority of electrical applications, C110 is the correct material choice and spending the premium on C101 is unnecessary. Only specify C101 when hydrogen embrittlement is a genuine risk (brazing, vacuum service, hydrogen atmosphere furnaces).

What is the machinability rating of copper C110?

Copper C110 has a machinability rating of approximately 20% relative to the C36000 free-cutting brass reference standard (100%). This is identical to C101 copper. Both grades produce long, continuous chips and are prone to built-up edge on tool rake faces. Sharp, polished uncoated carbide or PCD (polycrystalline diamond) tooling is required. Coated carbide is not recommended — the coating promotes built-up edge on copper. Positive rake angles (+8° to +12°), high surface speed (200–350 sfm / 61–107 m/min), and flood coolant are the standard approach.

Material Guide · 10 min read

Copper C110 Properties and Machining Guide

UNS C11000, 100% IACS, 99.9% Cu minimum. The workhorse commercial copper — correct for 95% of electrical applications and lowest cost among pure copper grades.

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Copper C110 Key Data

UNS DesignationC11000

Common NameETP Copper

Cu Purity≥99.9%

Oxygen Content0.02–0.05% (Cu₂O)

Electrical Conductivity100% IACS

Thermal Conductivity385 W/m·K

H₂ Embrittlement RiskYES above 700°F (370°C)

Machinability20% (vs. C360)

ASTM (rod/bar)B187

Cost vs. C1015–15% lower

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C110: The Default — Not the Compromise

Copper C110 (ETP) is the correct material for the vast majority of copper applications. It carries 100% IACS conductivity, the same thermal conductivity as C101, and costs less because it is produced in air rather than in vacuum. The single case where C110 should NOT be used is when the copper part will be heated above ~700°F (~370°C) in a hydrogen-containing atmosphere. This guide covers the full property set, the hydrogen embrittlement mechanism you need to understand before designing a brazed assembly, and the exact drawing callout to prevent shop-floor substitution.

Section 1 of 5

Composition and Standards

Element / Property	Specification	Notes
Copper (Cu)	≥99.9% min	Lower purity floor than C101 — still very high purity
Oxygen (O)	0.02–0.05% (200–500 ppm)	Present as Cu₂O inclusions at grain boundaries — the defining characteristic
Impurities (total)	≤0.1%	Small trace amounts of As, Bi, Fe, Pb, Sb, Sn, S
UNS designation	C11000	Unified Numbering System
European equivalent	EN CW004A (Cu-ETP)	DIN / EN designation
ASTM wire	ASTM B1 (soft-drawn), ASTM B2 (medium-drawn)	Most widely used copper wire standard
ASTM rod/bar	ASTM B187	Rod, bar, and shapes
ASTM sheet/strip	ASTM B152	Sheet, strip, plate, and rolled bar
ASTM tube	ASTM B75, ASTM B280	Seamless copper tube (B75) and ACR tube (B280)
Common tempers	O61 (Annealed), H02 (Half-Hard), H04 (Hard)	H02 is standard for CNC bar stock

Section 2 of 5

Electrical, Thermal, and Mechanical Properties

Property	Value	Condition / Notes
Electrical conductivity	100% IACS minimum	At 68°F (20°C); slightly below C101 due to oxygen impurity
Electrical resistivity	1.724 µΩ·cm	At 68°F (20°C) — the reference value for the IACS standard
Thermal conductivity	385 W/m·K	At 68°F (20°C) — 6 W/m·K below C101 (not practically significant)
Density	8.94 g/cm³	—
Specific heat	385 J/kg·K	At 68°F (20°C)
Coefficient of thermal expansion	17.0 µm/m·°C	68–212°F (20–100°C)
Melting point	1,981°F (1,083°C)	—
UTS (Annealed O61)	220 MPa (32 ksi)	Annealed condition
UTS (Half-Hard H02)	290 MPa (42 ksi)	Standard bar stock
Yield strength (H02)	250 MPa (36 ksi)	0.5% extension under load
Elongation (H02)	14%	In 2 in gauge length
Hardness (H02)	HRF 84 / HB 40	—
Machinability	20%	Vs. C36000 free-cutting brass = 100%

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Section 3 of 5

Hydrogen Embrittlement: The One Risk to Manage

Hydrogen embrittlement is the only significant limitation of C110 copper. Understanding the mechanism lets you design around it — or select C101 when you cannot.

Conditions That Cause Embrittlement

✗Silver brazing or torch brazing with a reducing flame (excess fuel) above 700°F (370°C)
✗Processing in hydrogen atmosphere furnaces (annealing, heat treat)
✗Welding with oxyacetylene in reducing mode
✗Repeated brazing cycles that extend exposure time above 700°F (370°C)
✗High-temperature service in mixed atmospheres containing H₂

Safe Conditions for C110

✓Brazing in air with a neutral flame — C110 is fine
✓All ambient-temperature electrical applications (bus bar, terminals, connectors)
✓Thermal management parts operating below 570°F (300°C) in air or inert gas
✓CNC machining, forming, stamping, rolling — no H₂ involvement
✓Plating processes (EN, silver, tin) — all operate in water-based chemistry

The Reaction Mechanism

Cu₂O (present in C110) + H₂ → 2Cu + H₂O (steam). The steam has no escape path, builds pressure at grain boundaries above the copper yield strength, and causes intergranular cracking. This produces a characteristic brittle fracture appearance — no necking, no ductility, catastrophic failure. If you see a copper brazed joint that cracked catastrophically after brazing, hydrogen embrittlement in ETP copper is the first diagnosis to rule out.

Section 4 of 5

Machinability and CNC Parameters

Turning Parameters

Tool material:Uncoated carbide (K-grade) or PCD

Surface speed:200–350 sfm (61–107 m/min), carbide

Feed rate:0.003–0.006 ipr (0.08–0.15 mm/rev)

Rake angle:+8° to +12° positive

Coolant:Flood — 8–10% water-soluble

Insert geometry:Sharp edge, polished flank face

Milling Parameters

Tool material:Uncoated carbide, sharp cutting edges

Surface speed:400–600 sfm (122–183 m/min)

Chip load / tooth:0.001–0.003 in/tooth (0.025–0.076 mm/tooth)

Helix angle:45° preferred for chip evacuation

Entry strategy:Ramp in — avoid full-width plunge

Surface finish:Ra 32–63 µin (0.8–1.6 µm) typical with carbide

Section 5 of 5

Drawing Callout Format

Rod/Bar (Standard CNC Parts)

Copper, UNS C11000, ASTM B187
Temper: Half-Hard (H02)

C11000 is the default for electrical terminals, bus bars, and connectors. No special notes required unless you need to explicitly allow substitution.

Electrical Wire

Copper, UNS C11000, ASTM B1
(Soft-Drawn)
or ASTM B2 (Medium-Drawn)

Most commercial copper wire is C11000 by default. Reference the relevant wire spec directly — ASTM B1 for soft-drawn, ASTM B2 for medium-drawn. Specify gauge (AWG) in the notes.

Sheet/Strip

Copper, UNS C11000, ASTM B152
Temper: O61 (Annealed)
or H02 (Half-Hard)

Annealed for forming operations; H02 for parts that require spring-back or greater stiffness. Specify as-machined or as-rolled requirements.

Tube (ACR / Refrigeration)

Copper, UNS C11000, ASTM B280
(ACR tube, seamless)

ASTM B280 is the air conditioning and refrigeration tube spec. ASTM B75 covers seamless copper tube in general industrial sizes. C110 is the standard alloy for both.

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