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Current density in a track

The current density is given by the current divided by area, and expressed in A·m^–2:

Now this seems an enormous number until you convert it into something nearer reality! This current density is equivalent to 0.57 A per square mm, or 1.14 A in a 0.8 mm diameter wire (similar to 20 AWG or 21 SWG). As such wire fuses at around 9 A in free air, we have a safe margin, but not as big a margin as one might intuitively think!

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