The 25mA and 10mA is the trigger point when the MCB tripped to protect people from electrocution. So, the 10mA is recommended to be installed at water heater by TNB.

The water heater circuit breaker is additional to the house MCB.

There's discussions here.
https://forum.lowyat.net/index.php?act=ST&f=231&t=2107287

C16 OK for 3300W WH.
4200W WH pls run a new line (electrician required) with 6mmsq cable else you gonna burn down ur hse. Of coz salesman everything can, burn also not his place

Bathrooms with extremely low water pressure usually have issue turning on the water heaters, as most water heaters use flow switch to turn on (at minimum consistently maybe around 2 litres / minute water flow, and water heater's heating element and built-in pump might not turn on if water flow is lower than that).

But I saw CENTON has a newly launched instant water heater (Atlantis range, shown below) with a Pump Activator function, which when the button is pressed, it will manually jump starts only the built-in pump to increase water flow enough for the flow switch to turn on the water heater. I think this function should be more important for you. Here is the Shopee link if u need it - Shower Rail / Rainshower



I suggest u to only go for rainshower instant water heater if your original water flow is already sufficient, since built-in pump, regardless of whichever brand u buy, won't cater enough water pressure for your rainshower if your original water pressure is already low.

If rainshower is a must and your bathroom's water pressure is low, I suggest u to install those external booster pump like Grundfos instead (Shopee link here).


Table above and below is taken from Suruhanjaya Tenaga's guideline. So basically for instant water heaters (common ones are from 3.6kW to 4.5kW), they will require the MCBs / RCDs to be 25A rated with 10mA sensitivity (for appliances installed in wet areas). 25A is the current rating (In), 10mA is the trip sensitivity.

In conclusion, I think u will need a 25A rated current, 10mA sensitivity, double pole (cut live and neutral) RCD. Experts, please correct me if I am wrong.

Please do not confuse between RCD and MCB.

MCB you have now is a C16 to safely allow up to 16A LOAD.

RCD which you don't have now, and you will need, is a 10mA RCD rated to sense up to 25A, this is the bestest protection -
https://shopee.com.my/ABB-F202-25-0.01-ELCB...1856.9133931062

or this also can, if budget is an issue
https://shopee.com.my/Schneider-Easy9-25A-2...4033.3943044744

Failure to install a proper 10mA RCD will lead to unwanted outcome, usually death.
https://www.straitstimes.com/singapore/cour...oroners-inquiry
https://www.freemalaysiatoday.com/category/...ed-in-bathroom/

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Since we're here,
your existing installation is totally illegal, and is useless for human life protection.

3.5 RCDs and Direct Contact Shock Protection
The use of RCDs with rated residual operating current of 30mA or less are recognised as
additional protection against direct contact shock. Regulation 415.1.1 refers.
Direct contact shock is the result of persons or livestock inadvertently making contact with
normally live parts with one part of the body and, at the same time, making contact with
earth potential with another part of the body. Under these circumstances, the resulting
electric shock will be at full mains potential and the actual current flowing to earth will be
of the order 230mA because of the relatively high body impedance involved. It has already
been shown in Section 2.3 that currents as low as 40/50mA can result in electrocution.
Read more here https://forum.lowyat.net/index.php?showtopi...ost&p=106857006

The quality of components used are questionable if they already installed C16 MCB.

Your scope of work:

change the mains (entire house) RCD to 30mA.
install a new 10mA RCD for EACH WH (water heater) circuit.

You do not need a RCD for every floor.

Correct. Replace like for like since you have 63A three phase supply.
This is a RCD. The spec is 4P 63A 30mA (0.03A).
Estimated barang only- RM2xx for a good one from ABB/Hager.

https://shopee.com.my/ABB-FH204-63A-4P-300m...2787.3248905327