Here it's a general consensus that any appliance over 3.5 kW has to be fed with 3ph. In germany there are on-demand water heaters that take 35A/400V, would be pretty hard to connect such a beast to a 1ph supply. Eastern Germany excempts cookers from this rule, they can be wired to a 1ph supply. here in Austria water heaters are either gas or electric storage heaters (rather rare) which run on a dedicated 230V/16A circuit. Cookers are wired up to a 230/400V/3x16A supply. Some ElCheapo cookers come with a Schuko plug, but then the use of rings and oven is limited. In most cases you can remove the jumpers and wire the cooker to 230/400V, then you can use it w/o restrictions.
On board main is used here in single family buildings, 3x Neozed. Appartment buildings typically have the main (= pre-meter) located in the stairway. This has the advantage that you can completely isolate the panel to work on it. However, working inside such an old Diazed main panel isn't too nice. You could cut power at the house main fuses, but that means that all other tenants are without power.
Guess I've to be pretty careful when hooking up our new meter. (We're relocating the meter out to the stairway so the meter reader doesn't have to come into our appartment and the electrician told me just to cut the lead seal, hook up the meter, then he comes and checks the wiring and gets the PoCo to reseal the meter).
