I'm not an electrical engineer, I work with automation, but I'll give an explanation a go. All of this is based on Norwegian regulations, which are very thorough and safe.
What you want to achieve:
- Charge your car as fast as possible
- Avoid damage to your car due to external factors
- Avoid electric shock to people
- Avoid fire hazards
Charge your car as fast as possible
For one-phase connections (standard AC home-system) the maximum current is 32A, giving 7.4kW. There is one phase that connects to the neutral.
For three-phase connections (what is normally in the network itself, and is sometimes led to your power meter), the maximum current is still 32A and you get 400V between the phases. This is a TN network, Terra Neutral for the frenchies.
You may want to have a fuse in your fusebox that is 40A in order for it not to trip on the sustained 32A load. If you electronically limit your charger to 32A (which is the maximum anyway), this should be fine, and you don't need to dimension wiring for 40A.
Avoid damage to your car due to external factors
You need a surge protector. Check that this is installed already in your fuse box. It must be a type that is designed to withstand lightning strikes.
You need an residual-current device that measures the current leak to ground. If you have a type B RCD in the charger itself, it will trip on very small currents, if there is any problem with your car or charging cable.
Avoid electric shock to people
You may want an additional RCD in your fuse box. This can be omitted if you use a double-insulated cable, and the cable is not run in any closed walls.
If say a load is applied between ground and the phase (like a human), it's nice to know that the circuit will break after a very short time.
Avoid fire hazards
If your cable is only installed in open-air cableways, you may get away with only using 6mm^2 wire, providing it's double insulated. If it's in confined walls, the lack of heat dissipation means you must go bigger. Also, the energy dissipated to heat due to the conservative cable size is energy you are paying for, so it's worth considering going up a notch.
Installation instructions and installation norms must be followed to the letter for this kind of installation. Loose connections are one of the most common causes of fires, and here you are sending high currents unattended! Do not do this yourself unless you are authorized to do so.
Additional considerations are load balancing and smart charge timing. Nord Pool pricing is always available, so a smart charger can plan your charging for when it's the most inexpensive. Very relevant with recent pricing. It should also be able to integrate into a load balancer. Then you can use a higher current for your electric car, even if your home network intake fuse might only be 63A. It can limit the amount of power sent to the charger if the total load nears the maximum.
The best charger on the market is Easee, it offers all of the above, RFID charging lock, smallest footprint and more. It has a whole host of security functions, such as temperature sensors on all connectors and lifetime 4G connection for free.
Oh yes and there are some simple "power management system" commands between the charger and car that must take place. Like, ready to transmit, ready to receive, maximum current. It's actually quite clever, the phases and null will connect first, but the pilot and connection pins are deeply recessed, so it will be physically impossible to get a GO to the car unless the power connectors are deeply seated.
