In the Netherlands, most houses have 3 phases coming into the house.
You can have 1 connected, for a 1x40A connection, or have 3 connected for a 3x25 or 3x40 connection.
Switching from 1x40 to 3x25 costs about 400 euro, one time fee. The yearly rate is the same.
With 3x25A coming in, you can divide your existing groups over the 3 phases and add a 3-phase group, with its own GFCI and main switch.
Note that the new smart meters use one of the 3 groups for solar panels if you have them to deliver energy back to ge grid. I am not sure whether it is possible to have 3x25A and solar panels.
The energy required to heat water is 4200 kilojoule per degree Celsius per liter.
So to heat 40 liters takes:
- 40*4200 / 3200W = 52 seconds per degree
- 40*4200 / 5500W = 31 seconds per degree
- 40*4200 / 8500W = 20 seconds per degree
You can use the 5500W element on a 25A single phase connection (5500W/230V = 24A), but you’ll have to ensure everything is dimensionsed at 25A (thicker wiring, bigger fuses and GFCI).
You are required to have a separate mains switch for 3-phase in your ‘meterkast’, but can use an overload + GFCI in one behind it, called an ‘aardlekautomaat’ in Dutch.
P.S. to be allowed to make a new post, you just need to have read a few other posts. It is an anti-spam measure.