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The busbar's flat-face width, measured across the wide dimension.
Combined with thickness, this sets the busbar's cross-sectional area, which drives its current-carrying capacity.
The busbar's thickness, measured through the narrow dimension.
The bar itself, not its plating or insulation. Thickness is the dimension that buys the least ampacity: current crowds toward the surface, so widening a bar helps more than thickening it, and two bars of identical cross-section but different proportions do not carry the same current. That is why switchgear uses several thin bars in parallel rather than one thick one.
The allowable current per unit cross-sectional area for the busbar material and installation conditions.
Copper busbar in free air is commonly rated around 1.6 A/mm² at a moderate temperature rise; aluminum is lower, commonly around 1.0 A/mm², since it has higher resistivity.
Estimated busbar ampacity
516 A
Current density varies significantly with allowable temperature rise, ambient conditions, enclosure ventilation, and copper-to-aluminum thermal interface effects at joints/connections — this is a preliminary estimate only; final busbar sizing should follow the manufacturer's rated ampacity tables or IEC 61439/UL 891 test data.
- Cross-sectional area
- 0.5 in²
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Busbar Ampacity Calculator (Current Density Method): 516 A — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Simplified current density method: ampacity = busbar cross-sectional area x rated current density (commonly cited as ~1.6 A/mm2 for copper busbar in free air at a moderate temperature rise, lower for aluminum) — a widely-used preliminary sizing approximation; actual ampacity also depends on temperature rise limits, ambient temperature, enclosure ventilation, and proximity effects from adjacent busbars
Inputs used
- Busbar Width
- 2 in
- Busbar Thickness
- 0.25 in
- Rated Current Density (A/mm², ~1.6 for Copper, ~1.0 for Aluminum)
- 1.6
Intermediate steps
- Cross-sectional area
- 0.5 in²
Confidence note: Current density varies significantly with allowable temperature rise, ambient conditions, enclosure ventilation, and copper-to-aluminum thermal interface effects at joints/connections — this is a preliminary estimate only; final busbar sizing should follow the manufacturer's rated ampacity tables or IEC 61439/UL 891 test data.
What this calculation does not cover
- Current density is a continuous-duty rule and knows nothing about fault current. During a short circuit the magnetic force between parallel bars runs to thousands of newtons per meter of run (hundreds of pounds per foot), and that force — not heating — is what sets insulator spacing, bar thickness and how the run is braced. A bar chosen for its normal load can be thermally sound and still be thrown off its supports.
- Ampacity does not scale with thickness the way area does. At mains frequency the current crowds toward the surface of the bar, so doubling the thickness buys appreciably less than double the current, which is why switchgear runs several thinner bars in parallel with air between them rather than one thick one — a straight area times density product flatters the thick section most.
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This result is a specification — 516 A — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-06 · in the site-wide review of 2026-09-06 · v1.0.1
Regulatory standards & verification citations1
- Simplified current density method: ampacity = busbar cross-sectional area x rated current density (commonly cited as ~1.6 A/mm2 for copper busbar in free air at a moderate temperature rise, lower for aluminum) — a widely-used preliminary sizing approximation; actual ampacity also depends on temperature rise limits, ambient temperature, enclosure ventilation, and proximity effects from adjacent busbars
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