Busbar / Bus Duct
Distribution
Solid copper or aluminium bars that distribute heavy current inside panels — the motorways of a switchboard. Sized by cross-section, spaced for fault forces, and insulated by air, sleeves or enclosure design.
What it looks like
Busbar / Bus Duct
A typical distribution — exact shape, colour and markings vary between manufacturers.
Types & variants
Key specs
Cross-section
mm²With material, sets current capacity (~1.2–1.6 A/mm² for copper in air, derated in enclosures).
Current rating
AContinuous rating at a stated temperature rise.
Short-circuit withstand
kA/sMechanical bracing must survive fault magnetic forces.
Material
Copper (standard) vs aluminium (cheaper, bigger, joint care needed).
Markings
Phase colour sleeves or paint (R/Y/B or brown/black/grey), earth bars bare or green/yellow marked.
Standard values
25×3, 25×5, 40×5, 50×10 mm copper flats; comb busbars in 1P/2P/3P for MCB rows.
How to choose
Panel-builder territory: size from current + derating, brace for the prospective fault level, and torque joints to spec with belleville washers. For DIY DC projects, marine-style bus bars keep battery wiring sane.
Pinout & package
Drilled flats joined by bolted overlaps; joint quality (clean, flat, torqued) decides everything.
Example circuits
- Comb busbar feeding a row of MCBs
- Battery-bank positive/negative distribution bars
- Rising bus duct up a building
Common failures
Hot joints from loose/corroded bolts (the classic thermal-camera find), inadequate bracing letting bars slam together during faults, aluminium joints creeping loose over thermal cycles.
How to test
Thermal scan under load — every joint should be near bar temperature. Dead: millivolt-drop across each joint at test current, and torque-check bolts to spec.
Substitutes
Copper bar per the design spec only; for hobby DC distribution, commercial fused bus bars beat DIY every time.