What is the formula for Copper Busbar Ampacity Calculator (Heat-Balance Method)?

Core formula: I = √(h·P·ΔT·A/ρ(T)), ρ(T) = ρ₂₀·[1+α(T−20)]. The tool returns results instantly using this formula and the selected parameters.

What engineering notes should I keep in mind when using Copper Busbar Ampacity Calculator (Heat-Balance Method)?

Ampacity depends strongly on mounting, ventilation, altitude and surface finish. This tool uses a heat-balance model whose effective heat-transfer coefficient is calibrated against the IEC 61439-1 Table 5 current ratings; typical sizes are within about ±20%. Parallel bars do not add linearly (proximity effect): two bars give roughly 1.8×, three about 2.5×. For final design use the manufacturer’s multi-bar table. Mounting a rectangular bar edgewise (wide faces vertical) cools…

Copper Busbar Ampacity Calculator (Heat-Balance Method)

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Solves copper busbar ampacity from the heat balance between I²R heating and convection/radiation cooling: size the current from bar width and thickness, or back-solve the minimum width for a given current and snap it to standard sizes, with current density, resistance/loss/drop per metre and AC skin-effect correction.

Key points

铜排（Rectangle母排）Current capacity由发热and散热的平衡决定：I = √(h·P·ΔT·A/ρ(T))，其Medium h 为Equivalent换热系数、P 为有效散热周长、A 为Cross-section积、ρ(T) 为工作Temperature下的铜Resistance率。按 IEC 61439-1 的基准（35°C Surroundings、65K 温liter），100×10mm Violet铜排单根自然冷却≈ 1.8kA，25×5mm ≈ 440A。ampere装方式、通风、贴装面数and多根Shunt都会显著改变结果，最终选型仍需查厂家载流Meter并校核短路动、热稳定。

Inputs

I = √(h·P·ΔT·A/ρ(T)), ρ(T) = ρ₂₀·[1+α(T−20)]

Calculation modeBar width WmmBar thickness TmmTypically 3–12mm; thick bars show noticeable skin effectAmbient temperature Ta°CBusbar current tables are usually based on 35°C ambientAllowed temperature rise ΔTKBare copper bars usually run 65K; match the insulation temperature classMounting / cooling facesSurface mounting or clamping reduces the cooling area, so ampacity drops accordinglyCooling methodNatural cooling is calibrated to standard current tables; forced air and enclosures use factorsOperating frequency fHzSkin depth in copper at 50Hz is about 10.7mm; use 0.01 for DCBusbar length LmUsed for voltage drop, losses and copper weight

Calculation model (updates with parameters)

Current capacity I	1.83 kA	ΔT = 65K, bar temperature 100 °C
Cross-section A	1000.0 mm²	100 × 10.0 mm
Current density J	1.83 A/mm²	Rules of thumb use 2–4 A/mm² (narrow thin bars can run higher)
Effective cooling perimeter P	220.0 mm	All four faces exposed (free-standing)
Effective heat-transfer coefficient h	5.31 W/(m²·K)	Natural convection (still indoor air)
Resistance per metre R	22.66 µΩ/m	bar temperature 100 °C
Loss per metre	75.9 W/m	P = I²·R
Full-load voltage drop (L = 1.00 m)	41.47 mV	ΔV = I·R·L
Copper weight	8.96 kg/m	total about 8.96 kg
Skin depth δ	10.71 mm	copper at bar temperature, μr ≈ 1
AC / DC resistance ratio	1.00 ×	bar thinner than the skin depth — DC calculation is fine

Engineering notes

Ampacity depends strongly on mounting, ventilation, altitude and surface finish. This tool uses a heat-balance model whose effective heat-transfer coefficient is calibrated against the IEC 61439-1 Table 5 current ratings; typical sizes are within about ±20%.
Parallel bars do not add linearly (proximity effect): two bars give roughly 1.8×, three about 2.5×. For final design use the manufacturer’s multi-bar table.
Mounting a rectangular bar edgewise (wide faces vertical) cools better than flat; surface mounting or clamping blocks cooling faces and lowers ampacity.
At 50Hz the skin depth in copper is about 10.7mm; for bars thicker than 10mm use stacked thin bars to reduce AC resistance.
Also verify short-circuit mechanical (peak force) and thermal (I²t) withstand, and check insulator spacing against the fault current.
For a quick current-density-based selection, use the “Busbar / copper bar selection” tool.

FAQ

What is Copper Busbar Ampacity Calculator (Heat-Balance Method) for?: Solves copper busbar ampacity from the heat balance between I²R heating and convection/radiation cooling: size the current from bar width and thickness, or back-solve the minimum width for a given current and snap it to standard sizes, with current density, resistance/loss/drop per metre and AC skin-effect correction.
What is the formula for Copper Busbar Ampacity Calculator (Heat-Balance Method)?: Core formula: I = √(h·P·ΔT·A/ρ(T)), ρ(T) = ρ₂₀·[1+α(T−20)]. The tool returns results instantly using this formula and the selected parameters.
What engineering notes should I keep in mind when using Copper Busbar Ampacity Calculator (Heat-Balance Method)?: Ampacity depends strongly on mounting, ventilation, altitude and surface finish. This tool uses a heat-balance model whose effective heat-transfer coefficient is calibrated against the IEC 61439-1 Table 5 current ratings; typical sizes are within about ±20%. Parallel bars do not add linearly (proximity effect): two bars give roughly 1.8×, three about 2.5×. For final design use the manufacturer’s multi-bar table. Mounting a rectangular bar edgewise (wide faces vertical) cools…

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