I'm trying to understand why the recommended wire gauge for a domestic supply depends on whether you're getting three phase or single phase power. Specifically I'm talking about when the power rating per phase is the same.
For example, if I look up what wire gauge I need for a 100 meter run of 12kVA single phase power, I get heavier gauge wire than for 100 meter run of 36kVA three phase power. In my head, I'd figured 36kVA three phase was almost the same as having 3 supplies of 12kVA single phase, except that the three phases can share the same neutral wire. So I would have expected the required wire gauge to be the same between 12kVA single phase and 36kVA three phase (with all other things being equal, eg same phase-to-neutral voltage etc).
Is there some reason that you get less voltage drop in the three phase scenario? Or is it some more mundane reason, eg that you consider phase-to-phase voltage instead of phase-to-neutral in the 3-phase case so the drop is the same in absolute terms but smaller in percentage terms?
EDIT: For those who are asking about the specific recommendations I'm referring to, it's those in France (though I believe the rules in other European countries are similar). Eg, have look at this page https://schema-electrique.net/tableau-choix-section-cable-alimentation-electrique.html and scroll down to the section marked "Le disjoncteur de branchement est éloigné du tableau électrique" -- which just means you've got a significant cable run between your meter (by the side of the road) and your distribution board (in your house). Here, it shows, eg, that, for 60A single-phase ("monophasé"), to ensure a voltage drop of no more than 2%, you need 35mm2 copper for a run of up to 58 meters and 70mm2 copper cable for a run of up to 117 meters. Scroll down slightly further and it shows that, for 60A 3-phase ("triphasé"), for the same 2% voltage drop, you only need 35mm2 copper cable for a run of up to 116 meters. Essentially, for 3-phase, at the same ampage, the allowed distances for any given gauge wire are double what they would be for single-phase.