How to Design a Copper Busbar That Is Cheap to Make
Updated September 26, 2026
A busbar is a simple part with an unusually large number of ways to make it expensive. Most of them are decided in CAD, long before anyone quotes it.
Cross section comes first
The cross section sets the current rating, and ampacity depends on far more than the area of metal: temperature rise allowed, ambient temperature, whether the bar is bare or plated, orientation, how many bars are stacked and how much air moves around them.
A frequently quoted starting point for bare copper in still air is in the region of 1.2 to 1.6 amps per square millimetre at a moderate temperature rise, but that is orientation only. Design against the standard your assembly is certified to and against the manufacturer’s tables, not against a rule of thumb from a blog.
Two practical points that do follow from the physics:
Wide and thin beats narrow and thick for cooling. More surface area per unit of cross section means a lower temperature rise.
On alternating current, thickness has diminishing returns. Current concentrates near the surface, so past a certain thickness the middle of the bar is carrying less than its share. Several thinner bars in a stack often outperform one thick bar of the same total area.
Where the machining cost actually is
Almost none of it is in the outline. Cutting a rectangle from plate is fast. The cost sits in:
- The hole pattern and its tolerances
- Bends
- Edge condition
- Plating area and masking
- Flatness after all of the above
Holes
Separate your holes into two groups on the drawing.
Clearance holes that a bolt passes through. These can be generous, in the region of ±0.2 mm or looser, and they should be. Every one of them tightened unnecessarily adds inspection time.
Locating holes that position the bar against something. These need real tolerance, and there are usually only two of them.
For stacked assemblies, remember that per bar tolerance adds up through the stack. Keep individual bar tolerances loose where a washer or a flexible link can absorb the difference, and control the few dimensions that set the alignment.
Chamfer both ends of every hole. It is a machine operation instead of hand deburring, and on a bar with twenty holes that is a meaningful difference.
Bends
A bend needs a tool, a setup and a trial piece. On a small order, one bend can cost more than the entire hole pattern.
Rules that keep bends cheap:
- Use the same bend radius everywhere on the bar so one tool covers it
- Keep the inside radius at roughly one to two times thickness, more for hard temper material
- Leave enough flat length at each end for the tool to grip
- Avoid bends close to holes, because the hole distorts
- Ask whether two straight bars and a bolted joint would be cheaper than one bent bar
Temper matters here. Annealed copper bends easily and is softer to handle. Half hard material is stiffer and more likely to crack at a tight radius. Say which you need, or say what the bar has to do and let the shop advise.
Edges
Busbar edges get handled by people during installation and they carry current at the surface. Specify the edge condition as a dimension: break all edges 0.3 to 0.5 mm, for example. Do not write “deburred” and leave it there.
Flatness
The contact faces of a bolted joint have to meet. Flatness matters more on wide bars, long bars and anything that has been bent, because bending introduces stress that releases afterwards.
If the joint face flatness is critical, say so, and expect the shop to plan an operation sequence that machines it after bending rather than before.
Plating area
Plate the contact pads, mask the rest. Mark both on the drawing. Full length plating on a long bar is a cost you pay on every piece for a benefit you only need at the ends. Tin, nickel or silver plating on a copper busbar covers which finish to pick.
State clearly whether the dimensions on the drawing are before or after plating.
Grade and temper
C110 electrolytic tough pitch copper is the normal choice for busbars. C101 oxygen free costs more and buys about one point of conductivity, which almost never changes a design. Specify C101 only when you have a vacuum or hydrogen brazing reason.
Free-machining grades are not usually the right answer for busbars, because the part is mostly metal rather than features, and the conductivity loss buys you little.
A busbar drawing checklist
- Cross section justified against the standard, not a rule of thumb
- Grade and temper stated
- Clearance and locating holes separated by tolerance
- All holes chamfered
- One bend radius used throughout, with enough flat at the ends
- Edge break given as a dimension
- Flatness called out only on joint faces
- Plating type, thickness, plated area and masked area marked
- Dimensions stated before or after plating
- Real order quantity and whether it repeats
Get those ten right and you will receive quotes you can actually compare. What drives the cost of copper busbars and heat sinks explains what each line is doing to the price.
Frequently asked questions
Should a busbar be thicker or wider for the same cross section?
Wider is usually better for cooling because it has more surface area for the same area of metal, and on alternating current it also suffers less from current crowding in the centre. Thicker is better when space is tight or the bar needs stiffness.
What bend radius can copper take?
Inside radii of roughly one to two times the bar thickness are common, with softer tempers taking the tighter end. Hard temper material cracks on the outer fibre if you push it. Confirm with the shop and the material temper before you fix the geometry.
Does the busbar need to be a single piece?
Often not. A long complex bar with several bends can cost more than two simpler bars and a bolted joint. Ask for both prices before assuming one piece is better.
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