Busbar Size Calculator
Enter the current, choose copper or aluminium, the bar thickness and the run length. The calculator picks a standard bar width, adds parallel bars for high currents and shows the voltage drop and heat loss.
- Copper or aluminium
- Parallel bars
- Voltage drop and loss
A rule-of-thumb sizing. Final design should follow IEC 61439 or the panel maker's rated tables.
Busbars are sized by how much current each square millimetre can carry without overheating. A common rule for bare copper in open air is about 1.6 amps per square millimetre, and about 1 amp for aluminium. That keeps the temperature rise to around 30°C. Enclosed panels run hotter and need more area.
Busbar current chart
Single bar, 1.6 A/mm² copper, 1.0 A/mm² aluminium. Search for a size.
| Size (mm) | Area (mm²) | Copper (A) | Aluminium (A) |
|---|---|---|---|
| 20 × 5 | 100 | 160 | 100 |
| 30 × 5 | 150 | 240 | 150 |
| 40 × 5 | 200 | 320 | 200 |
| 40 × 10 | 400 | 640 | 400 |
| 50 × 10 | 500 | 800 | 500 |
| 60 × 10 | 600 | 960 | 600 |
| 80 × 10 | 800 | 1280 | 800 |
| 100 × 10 | 1000 | 1600 | 1000 |
| 120 × 10 | 1200 | 1920 | 1200 |
Bars on edge cool better than bars laid flat. Painted bars run a little cooler than bare bright copper.
Current and busbar size
10 mm thick bars. Slide the current.
Past about 2,000 A a single copper bar runs out of width, so two or more bars run side by side.
How to size a busbar
Current density. Step through it.
Find the current
Full load amps.
Short-circuit strength matters too. Supports must hold the bars against the huge forces of a fault.
Copper or aluminium
Two busbar metals. Compare them.
Smaller bars for the same current. Easy to join.
Lighter and cheaper, but needs about 60% more area.
Copper with a tin coat for damp or corrosive sites.
Joints between copper and aluminium need bimetal washers or plated bars to stop corrosion.
Busbar design checks
Beyond current. Tick each item.
Tick each item as you go.
Always isolate and prove dead before working on busbars. Their fault energy is high.
What you get
Size and losses. Each tile explains one result.
Width × thickness.
When one is not enough.
Actual A/mm².
Over the run.
Heat in watts.
Power loss turns into heat in the panel. It adds up quickly in long bus runs at high current.
Frequently Asked Questions
No question matches that search.
How do I calculate busbar size?
Area = current ÷ current density. For copper use about 1.6 A/mm², aluminium about 1.0 A/mm².
What size busbar for 1,000 A?
About 63 × 10 mm copper, so a 80 × 10 mm standard bar, or 100 × 10 aluminium.
How many amps can a 50 × 10 copper busbar carry?
About 800 A in open air by this rule.
Why use parallel busbars?
Wide single bars heat unevenly. Two thinner bars spaced apart cool better.
Is aluminium busbar safe?
Yes, when joints are made properly with the right washers and torque.
What temperature can busbars reach?
Usually designed for a rise of 30 to 65°C above ambient.
Do painted busbars carry more current?
Slightly. Dark paint helps radiate heat.
Busbars that stay cool
Divide the current by a safe density, pick a standard bar and check the drop and losses. Confirm against the maker's rated tables, and the panel will run cool and safe.
More size calculators
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