E.C. Grade Copper: Electrolytic Tough Pitch for Conductors

Copper cathode from the refinery is melted and cast into wire bar, cake or continuous-cast rod. In tough pitch copper the oxygen is deliberately left at a few hundredths of a percent. That oxygen combines with impurities such as iron, tin and sulphur and pulls them out of solution as tiny oxide particles. Impurities in solution are what spoil conductivity, so locking them up as oxides is why ETP reaches 100 % IACS without being as costly to make as oxygen-free copper.

The result is a metal with a minimum of 99.90 % copper (silver counted as copper), roughly 0.02–0.04 % oxygen, and very tight limits on bismuth and lead, both of which make copper brittle during hot working.

Different standards cover different stages and shapes, and a purchase order should name the product standard rather than just the grade.

• IS 191: the Indian specification for copper in refinery shapes, which defines the Cu-ETP grade alongside Cu-DHP, Cu-FRHC and others
• IS 613: copper rods and bars for electrical purposes, the usual reference for busbars in Indian panel and switchgear specifications
• IS 1897: copper strip for electrical purposes
• ASTM B187: copper bus bar, rod and shapes, with soft (O60) and hard (H04) tempers
• ASTM B152: copper sheet, strip, plate and rolled bar, which lists C11000 among its coppers
• EN 13601: copper rod, bar and wire for general electrical purposes, where the grade is Cu-ETP, CW004A

IACS is the International Annealed Copper Standard, set in 1913. It fixes the resistivity of a reference annealed copper at 0.15328 Ω·g/m² by mass, equal to 0.017241 Ω·mm²/m by volume at 20 °C. That reference is called 100 % IACS, or 58.0 MS/m. Annealed Cu-ETP has to meet it; good modern material usually tests a point or so above, around 101 %, because refining has improved since 1913.

Cold work costs a few percent. Hard drawn wire to ASTM B1 is allowed down to about 97 % IACS for heavy sizes. If your busbar specification calls for a conductivity figure, check which temper it applies to before comparing certificates. For the trade-off in detail, see our pages on hard drawn copper and soft annealed copper.

The same oxygen that helps conductivity is ETP copper's one real limitation. Heat it above roughly 400 °C in an atmosphere containing hydrogen, such as a reducing furnace or an oxy-acetylene flame, and hydrogen diffuses in, reacts with the copper oxide particles and forms steam. Steam cannot diffuse out, so it builds pressure at the grain boundaries and the copper cracks or blisters. Engineers call this hydrogen embrittlement.

In practice this means ETP is fine for bolted busbar joints, soldered lugs, crimped terminals and exothermic earthing joints made quickly, but tube work and furnace-brazed assemblies are made from deoxidised copper instead. That is why our copper pipes and tubes are DHP grade, not E.C.

Oxygen-free copper (Cu-OF, C10200) is cast under a protective atmosphere so oxygen stays below about 0.001 %. It is immune to hydrogen embrittlement and is used for vacuum devices, high-end electronics and parts that are hydrogen brazed. For busbars, earthing and general conductors, ETP gives the same 100 % IACS at a lower price, which is why it dominates Indian electrical work.

We handle E.C. grade copper as round, square and hexagonal bars, busbar flats, strips, sheets, plates and wire, in hard or soft condition and bare, tinned or nickel-plated. Sizes are confirmed at enquiry. Busbar sizes and weights per metre are on the rods, bars and flats page.

Two things are worth settling before you order. First, the temper: soft for anything bent or formed on site, hard or half hard for straight runs that must stay rigid. Second, the paperwork: if your customer is a utility, a PSU or an EPC contractor, ask for the test certificate to report conductivity as well as chemistry, because that is the figure their inspector will check first.