Hi Herrie - I think you are calculating current assuming the voltage drop across the wire is 12V. At 35 kA you would be dissipating 420 kW in a 3cm wire, so it would not last long, not that it matters here as we are talking about much lower currents.
I think in practice there are three considerations for wire size:
1. The maximum power you can dissipate in the wire before heat problems arise, commonly referred to as ampacity for steady state. Given the short duty cycles here, it may not be a concern.
2. The maximum voltage drop you can stand due to the resistance of the wire. If you use, say, a 0.25V drop in each wire as your target, you should use 0.25V instead of 12V in your math above, so the limit is 48x lower.
3. The electro migration limits of the copper itself. I thought that was the 95 A/mm2 I quoted, but on further googling the actual limit seems to be 10^4 to 10^5 A/mm^2, so not a concern.
Please correct me if I'm wrong.
