Copper (Cu-ETP)

Copper grades and what they are used for

Cu-ETP contains 0.02-0.04% oxygen, which does not affect conductivity but causes hydrogen embrittlement if the copper is brazed or welded in a reducing atmosphere. Cu-OF (oxygen-free, CW008A, C10200) avoids that and is chosen for vacuum and welded assemblies. Cu-DHP (CW024A) is phosphorus-deoxidised plumbing copper with only 85% IACS and should not be used for busbars. Copper alloys such as CuZn37 brass and CuCrZr are covered on their own pages; CuCrZr is the choice for welding electrodes and high-temperature contacts because it keeps 80% IACS with three times the strength.

Laser cutting copper: limits and edge quality

Copper reflects around 95% of 1 µm fibre laser light at room temperature, which is why CO2 lasers could not cut it and older fibre lasers limited it to 3 mm. Fibre lasers of 4 kW and above with back-reflection protection cut Cu-ETP cleanly to 6 mm and with oxygen assist to 8 mm. Nitrogen assist gives a bright, oxide-free edge suitable for electrical contact; oxygen assist is faster but leaves a thin dark oxide that must be cleaned before plating. Kerf is 0.2-0.3 mm and the minimum hole diameter is 1 × thickness.

For thicker busbar (10-20 mm) waterjet cutting is used; it produces no heat-affected zone and holds ±0.2 mm. Punching is efficient for repetitive busbar hole patterns in 5-10 mm bar and leaves a slight roll-over on one side that is acceptable for bolted joints.

Machining and bending behaviour

Pure copper is gummy: it forms a built-up edge on the tool and produces long stringy chips that wrap around the workpiece. Suppliers use sharp polished carbide inserts with high rake angles, flood coolant and high spindle speeds (300-500 m/min surface speed). Tapping needs a 65-70% thread height rather than the usual 75% or the tap will seize. Milled copper heat sink bases reach Ra 0.8 µm; lapping to Ra 0.2 µm is possible for thermal interface surfaces.

Bending is done in the soft (R220/R240) temper. Half-hard R290 busbar bends to a minimum inside radius of 1 × thickness across the grain and 2 × thickness along the grain; below that the outside surface cracks. Edgewise bends (bending a 10 × 100 mm busbar in the 100 mm direction) require a dedicated busbar bender and are limited to radii of 2 × width.

Surface finishing for MENA conditions

Bare copper tarnishes within weeks in the humid coastal air of Alexandria, Jeddah and the UAE, and the oxide layer raises contact resistance. Busbars for switchgear are therefore tin plated (5-15 µm) or silver plated (3-10 µm) at bolted joints. Tin is standard for indoor panels; silver is used above 90 °C operating temperature or where contact resistance must stay below 10 µΩ. Full-length epoxy or heat-shrink insulation is applied after plating. For decorative copper cladding in Riyadh or Dubai, a clear lacquer slows the change to brown but does not stop it; a chemical patina applied at the factory gives a stable dark finish.

• Tin plating 5-15 µm: standard for busbar joints and earthing
• Silver plating 3-10 µm: high current density or above 90 °C
• Nickel plating 5-10 µm: barrier under gold for electronics
• Clear lacquer 20-30 µm: decorative parts, slows tarnish
• No coating: parts that will be soldered or brazed within days

Sizing a busbar: worked example

A 400 A feeder in a panel at 40 °C ambient, typical for a Riyadh substation room, needs about 1.5-1.8 A/mm² for a single bare copper bar in free air. That gives 400 / 1.6 = 250 mm², so a 5 × 50 mm bar (250 mm²) is the starting point; standard practice in the region is to step up to 6 × 50 or 5 × 60 mm to cover enclosure derating. Bolted joints should overlap by at least the bar width and use M10 bolts with Belleville washers to hold contact pressure as the copper creeps. Send the busbar drawing as DXF with hole positions and bend lines; suppliers cut, punch, bend and tin plate as one order.

Applications

Pricing and lead time

Copper part cost is dominated by material, which is typically 60-75% of the price and moves with the LME copper rate; the second factor is cutting method, since laser cutting copper is 40-60% slower than the same thickness in steel and waterjet slower still; the third is plating, which adds a separate process and a transport leg. Quantity helps less than with steel because material dominates. Laser-cut copper parts ship in 3 to 6 working days, machined copper parts in 6 to 10 working days, and plated busbars in 8 to 14 working days depending on the plating shop schedule.

Frequently asked questions