^
I would increase the wire size by one size, i.e. where ABB says 2.5mm2, use 4mm2.
I haven't got my derating tables to hand, but we always use 4mm2 from a 20A breaker - the ambient temperature has a big effect on the current rating of a cable or wire. Simply, the problem is that once the copper in the cable gets to about 90C the insulation starts to melt. The 'thicker' the copper conductor is the less hot it gets when its carrying the same load. The ABB tables appear to be based on European temperatures (ABB is a European company, after all)
On ground rods above, the copper cladding is used to provide a good earth connection and also to prevent the steel rod corroding in the ground (the proper way to do it is with a pure copper rod, but these are expensive, hence the steel rod with a copper sheath to reduce the price. There is also a wide variation in quality. Buy the best you can find.) . Corrosion products are a remarkably good insulator. Galvanised pipe will work at a pinch, but this is a life saving system. Please don't shortcut.
If you can link the heater earth rod to your new rod, do it. This will reduce the resitance to ground for the whole system. If you've got enough 10mm2 cable use that.
The second picture you posted looks like it follows the diagram, my only comment is that the unused end of the bar linking all of the cicuit breakers at the bottom of the board either need to be cut off, or wrapped with insulating tape.
I seem to recall that saf-t-cut (SP) have their own approved installation people. It's well worth finding out who they are and visiting them and paying to have your installation checked over just to make sure you've got it right.
