high rise or landed?

ELCB test button ok?

You are fortunate that you are still alive. Go get licensed wiremen to check the wiring & compliance to ST guide for the water heater installation.

There is a leak in your wiring.

Hopefully you have had a 10mA dedicated RCCB with its dedicated wiring installed for the water heater only, as it is crucial in saving lives.

ELCB from your heater will not detect leakage OUTSIDE the WH so the RCCB is important.

https://www.todayonline.com/singapore/elder...-heater-1841166

You are lucky didn't get electrocuted to death. This news article of a case in Singapore has some technical explanations of how it can happen.

If going for RCBO get the Schneider one - around RM130. Better still if your DB box has sufficient space, get RCCB 10mA from ABB or Hager, its around RM150 for ABB and RM190 for Hager. If using RCCB, you still need a MCB.
Don't cheap out on breakers and RCDs.

Only the middle one, Maxguard, is the correct specifications for a water heater at a sensitivity of 10 mA or 0.01 A

Sorry, never used before. There's something you must realise which unfortunately is this: Contractors don't recommend something based on your best interest. They recommend something because it is easy to purchase, or that is what they have in stock, or it has a large profit margin, etc.

You also cannot trust something simply because it has a SIRIM sticker. You must get something that has a SIRIM sticker that has passed electrical specifications. A company could very well get a SIRIM sticker on the claimed weight of the item.

That being said, if funds are limited, then go for Maxguard, EPS or Himel branded RCBO with these specs : 20 A overcurrent, 10 mA trip. All have SIRIM and are JKR approved*, meaning they have at least been electrically tested by someone independently. If you go for an RCCB instead of RCBO, then get 25 A, 10 mA trip. The 25A is because there will be an additional MCB for the water heater. NOTE: these specs are if your WH is below, say, 4500 W, which it probably is. Please review if the WH happens to be above this wattage.

I can tell you that the store "Combi Electric" online delivers very fast, and price is fair. Now, saying that "Contractors don't recommend something based on your best interest" why should you trust me? I have absolutely no connection to the store just stated, I am not making money off you, and I am only recommending this based on your safety, because I can't get anything else from you!

Disclaimer: * last time I checked

Just to clarify, you are using a storage water heater correct? Not an instant water heater.

If it is a storage water heater, then FYI storage water heaters do not have a built-in circuit breaker like instant water heaters. So they have to rely on the DB box circuit breaker. BUT if your storage water heater is not grounded / no earth connection, no matter how good quality your circuit breaker is, the circuit breaker will not trip when there is a current leakage, and u will be electrocuted.

Hence why SIRIM / Suruhanjaya Tenaga now set a new guideline for storage water heaters to come with Isolation Barriers placed at both the storage water heaters' inlet and outlet water connection. Most SIRIM certified storage water heater brands already complied to this guideline, and some brands even took the extra safety effort to pre-install the isolation barriers on the heater, such as CENTON, which is extra good, considering some inexperienced installers will missed out installing the Isolation Barriers if they are not pre-installed on the heater out-of-the-box.

Isolation Barriers are simple devices that elongate any current flow from the storage water heater to users, so any current flow (if there is) will barely reach the users. So in your case where there is an unfortunate current leakage because of the lack of earthing, if your storage water heater is pre-installed with Isolation Barriers, the Isolation Barriers will protect u from electrocution to a certain extend. But every device has a lifespan as well, so u will probably be protected until the lifespan of the Isolation Barriers ended. So don't just rely on the Isolation Barriers to protect u. Installation and earthing connection has to be correct in the first place.

Basically just a safety tip for u, if your storage water heater do not have Isolation Barriers pre-installed, u are advised to install them.

JOVEx again haha. BTW, I dont believe any build in electronics ELCB.
Only 2 brands I found is using Electro-Magnetic. ELCB.

YET to me is not enough and by the rules regardless whether the unit comes with built in, they must have an exter RCCB, RCB, RCBO 10mA.

And probably 99.99% user ignore

All those C20, C32, etc are MCBs.
Your DB box is using Hager components, better for you to buy Hager RCCBs as they will fit perfectly when you cover the enclosure. The enclosure tolerance is tight, if use other brands may not be able to close back, may need to trim the window on the enclosure cover if want to use cheaper brands. Take note that I am not talking about the outer cover, I'm talking about the cover where the stickers (main switch, danger, etc) are on.
On another note, your DB box should not be having those C32 MCBs unless there are ring circuits in your house (which is very unlikely). Check what those MCBs are for and replace them with more appropriately sized MCBs.
You must also change your main RCCB which is using 300mA sensitivity to 30mA (0.03A). 300mA house burn down also RCD will not trip.

Yours is the water heater tank types, not the regular one.

You have current on the tap head - possible causes is you have some wiring work done and neutral and earth wiring got connected wrongly or wiring have issues. Better get a technician to check it ASAP.

Edit : Saw TS found the root cause at post #15. I replied immediately because of the severity of the issue. Glad that you found it.

Is not whether can or cannot. Its mandatory under the Electricity Regulations 1994 to have 10mA RCD fitted for wet floor appliances.

1. You trust your life insurance to cheapo china brand? 
2. Want to do, do properly. ABB or Hager 10mA RCD.

Also like mentioned above, the 3 phase 0.3A = 300mA RCD is useless and against the law, cos of it all your 13A sockets are illegal and unprotected.
You need to change to 30mA (0.03A) RCD. This will cost the good part of RM300-ish for the barang alone.

looking at how TS's electrician installed the water heater and the errors with the DB box.... I'm wondering how many other houses out there are done the same way by the same guy with the same mistake as well? basically all ticking time bomb.....

An overwhelming majority - sad to say.

Just to clarify, you are using a storage water heater correct? Not an instant water heater.

If it is a storage water heater, then FYI storage water heaters do not have a built-in circuit breaker like instant water heaters. So they have to rely on the DB box circuit breaker. BUT if your storage water heater is not grounded / no earth connection, no matter how good quality your circuit breaker is, the circuit breaker will not trip when there is a current leakage, and u will be electrocuted.

Hence why SIRIM / Suruhanjaya Tenaga now set a new guideline for storage water heaters to come with Isolation Barriers placed at both the storage water heaters' inlet and outlet water connection. Most SIRIM certified storage water heater brands already complied to this guideline, and some brands even took the extra safety effort to pre-install the isolation barriers on the heater, such as CENTON, which is extra good, considering some inexperienced installers will missed out installing the Isolation Barriers if they are not pre-installed on the heater out-of-the-box.

Isolation Barriers are simple devices that elongate any current flow from the storage water heater to users, so any current flow (if there is) will barely reach the users. So in your case where there is an unfortunate current leakage because of the lack of earthing, if your storage water heater is pre-installed with Isolation Barriers, the Isolation Barriers will protect u from electrocution to a certain extend. But every device has a lifespan as well, so u will probably be protected until the lifespan of the Isolation Barriers ended. So don't just rely on the Isolation Barriers to protect u. Installation and earthing connection has to be correct in the first place.

Basically just a safety tip for u, if your storage water heater do not have Isolation Barriers pre-installed, u are advised to install them.

All those C20, C32, etc are MCBs.
Your DB box is using Hager components, better for you to buy Hager RCCBs as they will fit perfectly when you cover the enclosure. The enclosure tolerance is tight, if use other brands may not be able to close back, may need to trim the window on the enclosure cover if want to use cheaper brands. Take note that I am not talking about the outer cover, I'm talking about the cover where the stickers (main switch, danger, etc) are on.
On another note, your DB box should not be having those C32 MCBs unless there are ring circuits in your house (which is very unlikely). Check what those MCBs are for and replace them with more appropriately sized MCBs.
You must also change your main RCCB which is using 300mA sensitivity to 30mA (0.03A). 300mA house burn down also RCD will not trip.

Better get plumbers who know how to install storage water heaters to do it for u. At the inlet, u will need to connect it to the pressure relief valve too (water source piping > pressure relief valve > isolation barrier > storage water heater's inlet).

Yes it looks like the one in your picture, but better purchase from the storage water heater's brand distributor so that u get more assurance that it is a confirm fit.