A practical guide to laminated busbar design — how they are built, how to choose dielectrics, how current capacity works, and what to check before you release a drawing.
What a Laminated Busbar Is
A laminated busbar is a multi-layer conductor assembly. Flat copper conductors are separated by thin dielectric films and bonded together under heat and pressure into a single insulated part. Terminals — threaded studs, blade tabs or welded lugs — are mounted before lamination or welded on afterwards. The finished assembly installs as one piece.
The idea is simple: instead of routing individual cables or assembling flat buswork on the line, you buy one insulated part with every connection pre-positioned.
Construction, Layer by Layer
- Conductors — C11000 copper sheet, laser-cut or punched to profile, tin plated for corrosion resistance and joint solderability
- Dielectric films — PET, Nomex or epoxy-based (DLF) films, sized to cover the conductor with proper creepage margins
- Stack-up — conductors and films layered in the designed order; adjacent layers are usually offset so terminals stay accessible
- Lamination — heat and pressure bond the stack; the recipe holds dielectric thickness within tolerance
- Edge sealing — cut edges are sealed so dielectric layers cannot creep or track under voltage
- Terminals — studs and tabs welded or fastened in position
- Trim and inspect — final CNC trimming and dimensional verification
Choosing the Dielectric
The dielectric does three jobs at once: it insulates between layers, it bonds the stack, and it sets the thermal class of the assembly. The common choices:
| Material | Strengths | Watch-outs |
|---|---|---|
| PET (Mylar) | Low cost, good dielectric strength, thin for compact stacks | Lower continuous temperature limit than alternatives |
| Nomex | High temperature rating, excellent thermal stability | Higher cost, thicker per layer |
| Epoxy (DLF) | Rigid, self-extinguishing options, good mechanical strength | Less flexible stack-up, material handling during layup |
Our default selection starts from your voltage class and operating temperature, then balances layer count against dielectric thickness to hit your creepage and clearance requirements.
Current Capacity: The Short Version
Two limits govern a busbar: temperature rise (resistive heating) and insulation class (the dielectric sets the maximum continuous temperature). For copper at a 30 °C rise, the common industry reference points are:
| Copper cross-section | Approx. DC current (30 °C rise) |
|---|---|
| 10 × 3 mm | ~150 A |
| 20 × 3 mm | ~250 A |
| 30 × 5 mm | ~450 A |
| 40 × 5 mm | ~550 A |
| 50 × 5 mm | ~650 A |
| 60 × 6 mm | ~800 A |
| 80 × 6 mm | ~1000 A |
These are reference values for a single bar in free air — real designs derate for bundling, enclosure temperature, altitude and AC skin effect at higher frequencies. See our full ampacity chart and derating notes.
Inductance: Why Laminated Construction Wins
Loop inductance is set by loop area. In a cable harness, the forward and return conductors are separated by centimeters — a large loop. In a laminated busbar, the layers are separated by fractions of a millimetre of dielectric, and opposing current directions in adjacent layers cancel magnetically. The result is a commutation loop inductance that can be an order of magnitude lower than the same circuit wired with cable.
For switching circuits this matters directly: overshoot voltage across the device is V = L × di/dt. Halving the loop inductance halves the overshoot — which can mean the difference between needing a snubber and not.
Design Checklist
- Current profile — continuous vs. peak; size conductors against the worst case, not the nameplate
- Voltage class — sets dielectric material and creepage/clearance distances
- Terminal inventory — studs, blades or welded tabs; match mating parts exactly
- Layer count — more layers shrink footprint but add dielectric thickness and cost
- Thermal path — how heat leaves the assembly; mounted bars cool differently than free-air bars
- Mounting — brackets, standoffs and edge seals designed in from the start
- Environment — vibration, thermal cycling and humidity expectations
Common Mistakes We See
- Terminals placed too close to a sealed edge — the weld zone intersects the seal
- Sense conductors sharing a layer with high-current conductors — measurement noise and heating
- Dielectric selected for voltage but not for continuous operating temperature
- Assuming catalog ampacity values without derating for the actual mounting and enclosure
Every SHANYUAN design goes through a DFM review before tooling. If you have a drawing in progress, send it over — we will flag the issues before they become expensive.