Copper busbar current ratings by cross-section, plus the derating factors that decide whether those numbers survive in your enclosure.
Copper Busbar Ampacity — DC and 50/60 Hz AC
Values below are the standard industry reference for copper bars (C11000) at a 30 °C rise above a 40 °C ambient, mounted flat in free air:
| Cross-section (mm) | Area (mm²) | DC current (A) | AC 60 Hz (A) |
|---|---|---|---|
| 10 × 3 | 30 | ~150 | ~150 |
| 15 × 3 | 45 | ~200 | ~200 |
| 20 × 3 | 60 | ~250 | ~250 |
| 25 × 3 | 75 | ~300 | ~295 |
| 30 × 5 | 150 | ~450 | ~440 |
| 40 × 5 | 200 | ~550 | ~535 |
| 50 × 5 | 250 | ~650 | ~630 |
| 60 × 6 | 360 | ~800 | ~770 |
| 80 × 6 | 480 | ~1000 A | ~960 |
| 100 × 6 | 600 | ~1150 | ~1100 |
Derating: Where the Real Number Comes From
The table above is a starting point. In a real assembly, apply these factors:
| Factor | Effect | Typical derate |
|---|---|---|
| Ambient temperature | Higher ambient raises conductor temperature | −1% per °C above 40 °C |
| Bundled bars | Adjacent conductors heat each other | −10 to −20% depending on spacing |
| Enclosed / still air | Reduced convection | −10 to −25% |
| Altitude | Thinner air cools less effectively | −1% per 200 m above 1000 m |
| AC frequency | Skin and proximity effect push current to surfaces | Material above ~1 kHz; consult us |
| Pulsed current | Thermal mass absorbs short pulses | Can allow higher peaks than continuous |
Laminated Stacks vs. Single Bars
A laminated busbar is not a single thick bar — it is several thinner conductors in parallel. Total cross-section sets the resistive heating, but current sharing between layers depends on terminal placement and connection symmetry. Uneven sharing overloads one layer while another runs cool. This is why terminal layout is reviewed during our DFM stage rather than left to chance.
How We Use This Chart
- Start with your continuous current and voltage class
- Apply the derating factors for your actual mounting and ambient
- Select conductor cross-section and layer count with margin
- Confirm the thermal class of the dielectric against the resulting temperature
Send us your current profile and installation conditions — we will size the busbar and document the calculation with your quotation.