Thanks so much for the quick reply!!

Around RM20k+ for master bedroom toilet and garden renovation. For the water heater single point wiring is RM260.

The house is on 3 phase, this one doesn't matter right?

Yes, the wires they used is Sirim MS 2112-3 certified, not sure what brand though, I can't find the packaging. 2.5mm wire should be good enough for 3kW water heater right?

Yes, after learning from the sifus here, I've installed an EPS 10ma RCCB a few years back.
OK, I will ask them to re-pull the wiring tomorrow or worst case knock down the new wall tiles. Thanks for the advice again!

Understood, thanks lj0000, ceo684 and Selene Yeo for the advice!! Sorry for late reply, was busy juggling work and renovation.
The contractor basically just pushed the blame on his staff. Excuse is 2.5mm finished, so his staff used 1.5mm. Quite BS la.
I warned him to be more careful and professional.
By the way, I've also decided to change completely new wiring for the common bathroom's water heater from DB too.

I bought Mega 4mm wire for the contractor to use this time.
The (instant) water heater I bought is Deka 4.5kW high power version.
For the RCBO, I bought Schneider Easy9 25A, 1P+N, 6kA, C Curve 10mA.
Schneider RCBO somehow doesn't have 20A version.

1) Should I buy EPS 20A 2P 10mA 6kA RCBO Type AC instead?

25a is ok
4500/230=20amps already


2) Why EPS RCBO has 2 poles, while Schneider RCBO only has 1 pole?

Rcbo need to compare live and neutral
Mcb only measure the live.

3) Is RCBO only good enough? Or should I use MCB + RCCB setup?

Rcbo save space. It's only 1din size. so ya it's good idea to use rcbo. Drawback is, if fail then harder to buy and more expensive compare to separate mcb+rcd.
There are debates that voltage based rcbo should be used. When tnb voltage is low then the current sensing won't work, that should not happen for domestic lah



Thank you all again!!