Maximal current load of wire


Allowable current load of the wire as a function of temperature rise


Example of the calculation :
Required current is 8 Amps with maximal 30°C temperature rise of. How wide wire shall I use on board with 35µm Cu foil?

In graph we find point A, which refers to 8 Amps current and intersect with 30°C temperature rise curve (point B ). Then we connect point B with bottom curve, which refers to Cu foil of 35µm (point C ). From this point C we can read required width of the wire (point D ).

In this case it is 2.5 mm

More information can be found here :

Wire width equation (Rovnice výpočtu šíře vodiče) :

I = 0.0150(DT 0.5453)(A 0.7349) for norm IPC-D-275 (inner layers wires)

I = 0.0647(DT 0.4281)(A 0.6732) for norm IPC-D-275 (outer layers wires)



I = maximal current in Amps

DT = temperature rise in °C

A = Area of cross section of the wire in square mils

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