Understanding Copper Alloy Grades: C101, C102, C110 and Beyond

When a buyer tells us they want "copper fittings," our first question is always: which grade? The answer matters more than most people realise. The difference between C110 and C122 is not subtle — it determines whether your brazed joint holds or fails, whether your fitting survives aggressive water chemistry, and whether your electrical conductivity requirements are met.

The copper alloy grade system is more straightforward than it looks once you understand the underlying logic. This article uses the American shorthand — C101, C102, C110 and C122 are short for UNS C10100, C10200, C11000 and C12200. (The old British designations use similar-looking numbers for different grades; see the warning further down.)

The Purity Hierarchy

Copper grades are primarily distinguished by purity — how much copper versus oxygen, phosphorus, and trace impurities are present. These trace elements dramatically affect key properties despite being present in tiny quantities.

C11000 / Cu-ETP — Electrolytic Tough Pitch Copper

The most widely produced copper grade. "Electrolytic" refers to the refining process — copper is dissolved and re-deposited electrolytically to achieve high purity. "Tough pitch" refers to the slight oxygen content (around 0.04%) which gives the copper a particular grain structure and excellent electrical conductivity (100% IACS).

The catch: that oxygen content causes a problem called hydrogen embrittlement. If ETP copper is heated in a reducing atmosphere (like the flame of a plumber's torch in a confined space with insufficient oxygen), the hydrogen in the atmosphere reacts with the internal copper oxide to form steam — causing internal cracking and porosity. For soldering and brazing applications, this is a real risk.

ETP copper is the right choice for electrical applications. It is not the preferred choice for plumbing fittings that will be soldered or brazed.

C12200 / Cu-DHP — Phosphorus Deoxidised High Residual Phosphorus

This is the plumber's copper. The grade specified in EN 1057 and EN 1254 in Europe, in ASTM B88 tube and ASME B16.22 fittings in the USA, and in virtually every other plumbing tube and fitting standard.

The phosphorus (0.015–0.04%) acts as a deoxidiser — it reacts with and removes oxygen during melting, leaving a copper free of internal oxides. The result: a copper that can be soldered and brazed without hydrogen embrittlement risk, even in less-than-ideal conditions.

The trade-off: phosphorus reduces electrical conductivity slightly (to around 85–90% IACS). For plumbing, this is completely irrelevant. For electrical applications, it matters.

When a plumbing fitting is marked "copper" without further specification, it is almost certainly C12200/Cu-DHP. This is the correct grade for all capillary solder fittings, press-fit fittings, and end-feed fittings in potable water systems.

C10200 / Cu-OF — Oxygen-Free Copper

Produced by melting copper in a protective atmosphere to exclude oxygen entirely. The result is a copper with no internal oxides — excellent for applications requiring the highest electrical or thermal conductivity, and for environments where the fitting may be exposed to reducing atmospheres (certain industrial processes, hydrogen-rich environments).

Oxygen-free copper is significantly more expensive to produce than ETP or DHP. It is specified in electronics, cryogenic systems, and high-frequency RF applications. For standard plumbing, the additional cost buys no meaningful benefit — DHP covers the solderability requirement equally well at lower cost.

C10100 / Cu-OFE — Oxygen-Free Electronic Grade

The highest purity copper produced commercially — 99.99% minimum copper content. Used in semiconductor equipment, high-frequency waveguides, and specialised scientific instruments. The price premium is substantial. For any mechanical or plumbing application, this grade is over-specified. For the specific electronic and scientific applications that need it, nothing else will do.

A Warning About "C101" and "C110"

The same short numbers mean different coppers on the two sides of the Atlantic. In the American UNS shorthand used in this article, C101 is oxygen-free electronic copper and C110 is ETP copper. In the old British Standard designations, which UK stockholders still use every day, it is the other way round:

An order for "C101 copper" therefore means ETP copper to a British buyer and oxygen-free electronic copper to an American one. Put the EN number (CW004A, CW008A, CW009A, CW024A) or the full five-digit UNS number on the drawing and the ambiguity disappears.

How to Read a Material Certificate for Copper

When receiving copper fittings with documentation, the material cert should show:

• Cu + Ag % — total copper and silver content (silver is counted with copper in DHP specs)
• P % — phosphorus content for DHP grade (should be 0.015–0.040%)
• O % — oxygen is limited for ETP copper (0.040% maximum) and is not normally reported for DHP, where the residual phosphorus shows that the metal has been deoxidised
• Any other trace elements within specification limits
• Reference to the relevant standard: EN 1254-1 for solder fittings, EN 1254-2 for compression, etc.

A cert that simply says "copper" without grade or composition data is not a material certificate — it is a label. For any regulated application (potable water, gas, medical gas), a proper cert with composition data is non-negotiable.

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Last reviewed: September 2026. Standards and regulatory references are checked at each review.