dear sifus..
If your cables are 2.5 mm², then you must use the 20 A RCBO. Only if your cables are 4 mm² (or larger) can you install the 25 A RCBO. You can see the size of the wires from the slack that is in the DB.
Alternately, if your water heater is below 4500 W, then you can go ahead and install the 20 A RCBO, no matter the size of the wires (as long as it is 2.5 mm² or larger) This will ensure the RCBO trips on an overcurrent, before the wires overheat.

Either brand is acceptable, as long as they are at 30 mA sensitivity (The ABB FH202 RCCB you have listed in the sh*pee link has a 100 mA option)
It is not necessary to replace the incoming fused isolator EPS SFU-63 at position 24, 25, 26 in your DB

Edit : add information

This post has been edited by stormer.lyn: May 22 2022, 10:26 AM

Thanks for replying. Just checked , all is 2.5mm2 for those with 20A mcb.
Lazada/shopee only have eps or maxguard with 20A 10ma rcbo available , will get the eps brand then ..
Want to use a better quality part also cannot d

LESSON LEARNT :Equip with right adequate knowledge and get a qualified certified technician is important during renovation to avoid all the hassle in future

Hi all sifus,
I just bought a built in oven with 3300W rating but find the cable 2 meters too short. The cable doesn't come with a plug.

As for my socket, the contractor built a 15A socket outlet to the MCB.

My questions is, is it safe to use a 20A connector block (white with screw) to connect to wire and then to a 15A socket?

While it is technically safe to use a 20 A terminal block, I prefer to use the NASA way for joining or also called the Western Union lineman's splice. Do once and I am sure that it will last forever.

If I need a water proof joint, I would add on the marine method for insulation, which is Self-amalgamating tape and and a layer of PVC insulating tape as the final external layer.