Copper is one of the most widely used industrial metals, and its consumption exceeds that of pure iron in many electrical and thermal duties. More than half of all refined copper is converted into high-purity copper for the electrical industry each year. The grade used for conductors is deliberately kept very pure, with copper contents of 99.95% and above, because even very small amounts of impurities - phosphorus, arsenic and aluminium in particular - sharply reduce electrical conductivity.
Why Purity Governs Conductivity
Conductivity in copper is controlled by how little the crystal lattice is disturbed. Phosphorus is the most damaging common impurity and is deliberately excluded from conductor grades; arsenic and sulphur have a similar, if weaker, effect. Oxygen also matters: a small amount of oxygen is easily picked up during refining, and because it reacts with hydrogen during annealing or brazing it can cause porosity and embrittlement. For this reason, copper intended for the electrical industry is generally supplied as oxygen-free copper.
Conductor grades: 99.95% copper or higher, low in phosphorus and arsenic
Oxygen-free grades: oxygen content controlled to a few parts per million
Deoxidised high-phosphorus copper: used for plumbing and roofing, not for conductors
Typical reference standards: ASTM B49, ASTM B187/B187M, EN 13601, GB/T 3952
Electrical Equipment
The largest single outlet for pure copper is electrical machinery. Copper is used in the production of generators, busbars, power and communication cables, switchgear and transformers, as well as motor windings, commutators and connector hardware. The reason is straightforward: at 100% IACS, copper carries more current per unit of cross-section than any other commercially practical conductor, which reduces resistive losses, temperature rise and the physical size of equipment.
Thermal Equipment
Copper's thermal conductivity - about 398 W/(m·K) at 20 °C - makes it the standard material for heat transfer. It is used for heat exchangers, condensers and evaporators, solar heating devices such as flat-plate collectors, radiator cores, and pipework in refrigeration and air-conditioning systems. In each case the metal moves heat away from a source quickly enough to keep operating temperatures inside design limits.
Forms and Typical Specifications
Copper is supplied in a family of mill forms, each with its own dimensional and mechanical requirements. Matching the form to the right specification at the ordering stage avoids problems during fabrication and service.
| Form | Typical use | Common specification |
|---|---|---|
| Rod and bar | Busbars, wire drawing, machined parts | ASTM B187/B187M, EN 13601 |
| Plate, sheet and strip | Roofing, cladding, stampings, gaskets | ASTM B152/B152M |
| Water tube | Plumbing and domestic services | ASTM B88, EN 1057 |
| ACR tube | Refrigeration and air conditioning | ASTM B280 |
| Wire rod | Cable and winding wire | ASTM B49, GB/T 3952 |
Architecture, Construction and Industry
Beyond electrical and thermal duties, copper serves architecture and general engineering because of its corrosion resistance, appearance and ease of joining. It appears in roofing and wall cladding, rainwater goods, plumbing and gas distribution, marine hardware, and as an alloying base for brass and bronze. Copper compounds are also used in agriculture and in some chemical processes.
Two practical points govern most of these applications. First, copper develops a protective patina over time, so exposed architectural copper is expected to change colour rather than degrade. Second, copper and steel in direct contact can promote galvanic corrosion of the steel in wet service, so joints between the two metals are normally insulated.
Sourcing Considerations
Because copper is fully recyclable without loss of properties, secondary metal is a significant part of supply. Buyers should confirm the grade, temper, conductivity and oxygen content required by the end use, and check that the mill certificate states the applicable standard and the measured conductivity. For conductor work, an oxygen-free grade with a certified conductivity value is the safest choice; for thermal and architectural duties, standard ETP material is normally sufficient.
Frequently Asked Questions
Q: What purity is needed for electrical copper?
Generally 99.95% copper or higher with tightly controlled phosphorus, arsenic and oxygen, so that conductivity stays close to 100% IACS.
Q: Why must electrical copper be oxygen-free?
Oxygen combines with hydrogen during annealing or brazing to form steam, which causes porosity and embrittlement in conductors and sealed assemblies.
Q: Which impurities reduce conductivity most?
Phosphorus has the strongest effect, followed by arsenic, sulphur and aluminium; all are therefore limited in conductor grades.
Q: What is copper used for apart from wiring?
Heat exchangers, solar collectors, pipework, roofing and cladding, marine hardware, industrial machinery components and as the base for brass and bronze.
Q: Is recycled copper as good as primary copper?
Yes, when it is properly sorted and refined; copper can be recycled repeatedly without losing electrical or thermal conductivity.
Q: How should copper components be ordered?
Specify form, dimensions, temper, grade and the reference standard, and require a mill certificate that reports measured conductivity.
