It is my understanding that if I need to draw, for instance, 30 Amps from a 240 V circuit (Live-Live) then there will be 30 Amps running from both wires, not half and half. So, the AWG sizes for the wires should be something accord to that.
The question arose from the installation manual of an electrical oven I am buying for a my home. It is a 240 V oven, with 4 wires (L, L, N and ground), and it says it needs a 40 Amp breaker. The specs says it draws at most ~31 Amps. So far so good. But then we get to the wiring size recommended and it says "12 AWG". I would expect at least 8 AWG for that load. But as I'm not quite sure if my understanding of currents/loads in a L-L circuit are correct, I rather ask.
In any case, I'm going to use 8 AWG wire, but this got me curious about this subject.
The manual with the recommendations is this, the oven model is WOS92EC0AS. https://www.whirlpool.mx/content/dam/global/documents/201506/installation-instructions-W10351242-RevC.pdf