Not all copper is the same. For a busbar in a control cabinet you need a different grade than for a brazed pipeline. The difference lies in the oxygen – and it decides conductivity and brazeability.
Problem
The problem: conductivity or brazeability
In control cabinet construction, copper is used mainly as busbars, earthing strips or contact parts. Here as little voltage as possible should be lost and as little heat as possible generated. For pipelines and refrigeration and air-conditioning technology, on the other hand, what counts is that the copper can be brazed and welded reliably.
If you try to meet both requirements with the same grade, you either give away conductivity or risk brittle brazed joints.
Cause
The cause: oxygen and phosphorus
E-Cu (Cu-ETP, CW004A) is electrolytic copper of conductor quality. It conducts electricity and heat almost as well as silver. However, it contains some oxygen; when brazed or welded in a reducing atmosphere it can become brittle (hydrogen embrittlement).
SF-Cu (Cu-DHP, CW024A) is deoxidised with phosphorus. As a result, it does not become brittle when brazed or welded. The phosphorus, however, lowers the electrical conductivity.
| Property | E-Cu (Cu-ETP) | SF-Cu (Cu-DHP) |
|---|---|---|
| Electrical conductivity | about 58 m/(Ω·mm²), 100 % IACS | about 45 to 50 m/(Ω·mm²) |
| Thermal conductivity | about 390 W/(m·K) | lower than E-Cu |
| Soldering / welding | very easy to solder, easy to weld | very good, without hydrogen embrittlement |
| Typical form at MVG | Flat, round and square bars | Round tubes, sheets |
| Typical use | Busbars, earthing, contact parts | Pipework, soldered joints, sheets |
Standard values to EN 13601 (Cu-ETP) and EN 1057/12449 (Cu-DHP); the certificate of the respective delivery is binding.
Solution
The solution: E-Cu for current, SF-Cu for brazing
For busbars and earthing, choose E-Cu as flat bar. For brazed joints, tubes and sheet metal work, choose SF-Cu. Dimensioning a busbar (cross-section, current-carrying capacity, clearances) is a job for a qualified electrician and follows the relevant standards and the switchgear manufacturer’s specifications.
- Brush the contact surfaces of busbars bright before assembly.
- Copper smears when sawn: use a coarse tooth pitch and plenty of cooling.
- Soft copper bends excellently; cold forming makes it stronger and more brittle.
Remember: Conduct or braze: E-Cu for the busbar, SF-Cu for the brazed joint.
At a glance
- Clarify the task: conducting current or brazing/welding
- Have a qualified electrician define the busbar cross-section
- Note the length and quantity per bar
- Clean the contact surfaces before assembly
Matching products
Frequently asked questions
Which copper do I use for a busbar?
E-Cu (Cu-ETP): it has the highest electrical conductivity, about 58 m/(Ω·mm²). We stock it as flat, round and square bar.
Why not always E-Cu?
E-Cu contains oxygen and can become brittle when brazed or welded in a reducing atmosphere. For brazed joints, SF-Cu is the safer choice.
Do you state the current-carrying capacity of a busbar?
No. Dimensioning depends on standards, the installation situation and the system manufacturer’s specifications and is the task of a qualified electrician. We supply the bar in the required cross-section and cut to length.