The reason is simple, all Water Heater comes with ELCB built in. So electrician just provide one 20A isolator switch. Adding a RCCB will be too bulky and customer complains about it.

Anyway to learn more about the electrical safety circuit breakers. Refer here :

http://electrical-engineering-portal.com/w...b-elcb-and-rccb

Talking about branded ones is from "HAGER". One of the most reliable and branded. Cheaper albeit goes to "MEM" recognized by Britian since the British colony time.

A proper water heater plug is round pin which is rated 15A not our ordinary 13A BS13 plug. Usually the MCB that connects to it rating within 16A to 20A.

Usually available RCCB is valued at 0.3A nobody is too crazy to get 0.1A as is too sensitive and you get pissed off.

There is even RCCB electronically controlled sensitivity range from 0.1/0.3/0.5/0.7/1.0 but is very pricey.

Firstly, changing your ELCB rating from 40A to 63A is not as simple as plug n play. You need to check whether your incoming cable diameter able to coup with it or not. If it can't coup it, might just burden the cable.

Don't take the wire for granted. Is advisable to check the cable core thickness and make sure the Main fuse is really rated for 60A or 32A (the fuse box beside the electrical meter). There is also a big chances there is no HRC Fuse inside the fuse box. Just one strip of copper wire to act as an fuse. It happens in a lot of housing area. I wonder where was the supposed HRC Fuse goes...

Cable core thickness is the one from meter entering to your Main Fuse Box (inside your house)

The fuse box on the left I'm referring to. Inspect the fuse rating or is there really a fuse inside. Please seek a qualified electrician to do so. I strongly do not recommend house owner to check on these stuff as it can be lethal when you get electrocuted. The electrocution from this wires are more harmful and lead to death than the ones found inside your house premises.

Yes is indeed thick but somehow those cable pass-through seems is not as thick as the one supplied

It can be seen the moment you remove the cover of your Main Distribution Board aka your fuse box internal.

That's the benefit of having 3 Phase electrical. 3 phase reduce the burden load of a single phase electrical. There is chances the electrical bill won't be expensive than relying on single phase meter. But don't be surprised when 3 phase electrical having one or two phase malfunction due to TNB electrical fault. You'll notice when one of your room has no electrical supplies