Wire size in the chargers is determined by current (amps), not kW. But batteries and charge time are determined in terms of power-time, so kWh. When we talk about the maximum power that can be delivered by a charger to batteries, it's usually done in the form of current (amps) that can be delivered given the size of wiring, PCB traces, transformer coils, etc. Whether 100A at 5V (500 W) or 100A at 500V (50 kW), you need the same size wire to carry it.
The time it takes to charge the 90 kWh battery, though, depends upon the power (voltage AND current). Higher power means faster charging, but you don't get to control the voltage. Your voltage is determined by your power supplier, grid standards, length of conductors (voltage loss), etc. In the US, it's either 120V (standard half-phase) or 240V (single phase), or 208V (3 phase L-L). In Europe, it's nominally 230V. And voltage (V) x current (A) = power (W/kW).
The current revision Model S charger is capable of charging at 16A per phase across 3-phase power. If used in a single-phase configuration (like we use in the US), the single phase is load balanced across all three inputs. Technically, I believe the Model S charger could do up to 48A single phase, but software restricts it (likely based on wire size somewhere).
When you talk of 3-phase power at 380V, you're using what's called "line-to-line" voltage between phases; Tesla doesn't use this voltage. Instead, it uses the voltage between the "neutral" point of all three power phases and the line conductor, or what's called "line-to-neutral" voltage. You can derive this by dividing the L-L voltage by 1.732 (the square root of 3). A 380V L-L 3-phase voltage will give you 220V L-N. So, 220 * 16 * 3 = 10.56 kW for single charger. If you have a dual charger, it will give you 21.12 kW (great nod to Rush, too) at the voltage.
Model X's European specifications haven't been released. I'm going to assume and speculate that the 48A charger from the Model X is the same one as used in the Model S, so again you'd be looking at 10.56 kW for 3-phase charging; US & Canada will see an upgrade to 48A, likely because whatever constraint found in Model S is relieved in Model X. The high-current charger from Model X may be a 24 x 3 phase charger, which would get you a possible 220 * 24 * 3 = 15.84 kW. Most likely, you will not be able to charge at 22 kW in Europe with Model X. Everything in this paragraph is speculation, though, as European charging specs haven't been mentioned or released yet.
