looks fine to me.
18W X 7  = 126W
126W + 100W (normally) = 226W.

Normally one point should be a able to support at least 1000W or more so you should be fine.

i emphasis on normally bcs i have seen contractors cut cost and use cheapo wires 

1. Better upload as attachment rather than use the upload images function (too low res to see)

2. Water Heater RCD (one each per WH unit) From the pic, no 10mA RCD for water heater was installed. This is statutory requirement. For old installation nvm but since you gonna redo, follow current standard.

Why 10mA RCD needed for water heater?
Because wet floor has very nice conductivity for fault current to flow through human = https://www.malaymail.com/news/malaysia/202...c-shock/1896447

ELCB is dinosaur technology
ELCB in WH cannot, will not, and certainly DID NOT protect against leakage for current flowing through human. It only protect L-PE leak (ie equipment protection only). L-N or L to other E (wet floor) leakage is not included in ELCB scope.

How much does this RCD (or RCBO) cost?
RCD ABB (Italy) or Hager (France) ~168 (online)
RCBO Schneider (PRC) ~100-105 (online)
other china brand also around 70 bucks but this is one thing not to skimp on.. treat it as a one off life insurance.. without yearly renewal. Maybe change once per 20-30 years.

[attachmentid=10802564]
It only takes 0.05A of 230V to kill a person.

[attachmentid=10802565]
It is very easy for an electrician to hook up a 10mA RCD per water heater circuit. Just need to identify the dedicated N for that circuit and connect to RCD 10mA. RCD 10mA line side L feed from 20A (C20) MCB load side; RCD line side N connect to common neutral. It is not rocket science. But it will definitely protect you so you can buy me a coffee.

3. All the N is common neutral when it return to TNB so basically it is correct. Common neutral and common PE (Earth).
Individual circuit (dedicated neutral) is required for special case like 10mA water heater circuit.

4.ELCB is old dino tech, you mean RCD/RCCB for mains protection right?
Only one mains (whole house) 30mA RCD needed to cover the whole house.

Use 30mA (0.03A) as whole house RCD (aka RCCD/RCCB) will give you best life protection (in general) against any fault current - be it 13A socket or light circuit. And it serves as a useful secondary line of defense even if the 10mA failed to trip on time (for WH RCD).

Note:
Anything else (100mA / 0.1A) or (300mA/0.3A) gives fire protection for building protection only. These do NOT protect human life.
Coz if there is a fault, the human dieded 2x or 6x over.

5. As for the 18W lamps.. you will need 100 pcs of them to be equivalent to a single electric kettle. One ceiling fan only takes about 85W. All in all they are low loads.
I doubt you will exceed a total of 6A (1380W) even if whole house LED and ceiling fans are turned on simultaneously.

The ones to look out for are the big loads such as water heaters (3000W typical storage heater) or (3300W-3800W typical instant heater); kettles ~1800W;; rice cooker slow cooker; oven be it microwave or conventional; electric stove/hob/induction cooker/air fryer, basically in short heavy heating appliances do not do looping shortcut but run a dedicated line to DB box with proper MS2113 cables (mega kabel, caramay, fajar cable).

6. Choice of 3 units of single phase (2P RCDs) per red/yellow/blue phase or 1 single unit of a three phase (4P RCD).
Both are not wrong, the 3x of 2P RCD is more for "business continuity" in case red phase has fault, you can still operate things on the yellow and blue uninterrupted.
Whereas in the case of using 1x of 4P RCD, any one phase has fault detected, entire house goes dark until the fault situation is rectified.
Cost wise, one 4P RCD is still cheaper relatively as compared to three units of 2P RCDs.

Sis actually. 

1. What is the "MCB C20 WH"? is it different type of other MCB?
Standard C20 MCB.
WH denotes the one for WH circuit.

2. if I have 4 header, which mean I will need FOUR 10mA RCD?
Yes correct. WH 10mA RCD is per unit of WH. Each WH should be on its own dedicated circuit as one WH enough to use 15-17A nominal (WH is heavy appliance). Your 2.5mm cable only support 21A. And the 10mA RCD, only come (from branded mfg) up to 25A max current. In short, the standard cable sizing, the RCD current capacity (max 25A) all only suited for single unit WH as it is sensitive device (0.01A /10mA).
Whilst there are champions from china making 10mA RCD that can handle 40A I also dare not use.

3. The purpose of 10mA RCD is to trip when the heater leaking to our body? my current installation if leaking it won't trip?
Your current installation only trips at 300mA - by then, the human dieded 6 times over.
As the mains is 300mA, it allow 300mA leakage before it trip.
A human RIP at 50mA.
[attachmentid=10803044]

4. In short, I only need to have 10mA RCD in between the MCB and Header individually? Any other wiring need to be change/improve?
Yes, correct.
RCD is comparing input and output current difference. Input and output must = equal the same +/- RCD tolerance of say 10mA (0.01A).

Meaning, if WH input is 16A on L, at least 15.99A must return on WH output (N) else it has deemed to be lost somewhere.

Lost somewhere mean could be leaking through human.
So when the return not enough (<15.99) say only 11A return. The 4.99A cannot be lost, it mean it leak. As 4.99A far exceed the 0.01A allowed by 10mA RCD it will immediately trip.

MCB only consider single wire (L) amount of current passing through (short circuit prevention).
For a C20, meaning the speed limit is 20A.
Slight overload at 23A will trip the SLOW thermal overload after say 20 min.
Major overload at 100A will immediately trip the magnetic overload.

5. between I'm quite confusing are ELCB & RCCB the same? can you correct me if the naming in the image below wrong?
The difference is how and where they measure.
ELCB only detect earth current rise >0 leak (L to PE) leak on that appliance's earth. If it leak via anywhere else (L-N, or L-other PE eg wet floor, L-human) it will not bother. Hence in short I just say it protect that appliance only.

RCD because it constantly compare L input =N output + allowed tolerance (like 10.00A in on L, >9.99A must return as allowed tolerance is 0.01A for normal operation things like wire resistance that do NOT constitute a fault condition). It does not care where it leak through, RCD always compare in and out current so if it leak through any method (L-N, L-PE, L-other PE, L-human) it always trip.

Note: There is something called RCBO which do both function of MCB+RCD in one.
6. Appreciate if you can share the image of "MCB C20 WH" and 10mA RCD
MCB C20 is any usual C20 (20A MCB). WH is just designation for the WH circuit.

10mA RCD (must be used in conjunction together with C20 MCB) ie. add this along with MCB C20
ABB= https://www.lazada.com.my/products/abb-f202...i2IABn&search=1
Hager= https://www.lazada.com.my/products/hager-cc...l5n2dU&search=1
Schneider = https://www.lazada.com.my/products/schneide...8t5PsK&search=1

10mA RCBO = RCD+MCB in one package pao kah liao 2 function in one
Schneider RCBO https://www.lazada.com.my/products/schneide...PVCaV4&search=1
The drawback is, officially, their MCB is a C25 equivalent so you need to use with 4mm cable. As 2.5mm cable only good up to 21A rating.


First one from left  is MCB 3P (3 pole) C63 (63A)
Second one is 4P RCD but this is 300mA. Only used in commercial/industrial where they use heavy motors. Not safe for residential and its against regulation, as the human has dieded 6x before this trips. (RCD/RCCB/RCCD = same function with diff name like zebra crossing=pedestrian crossing)
Third one is MCB 1P C10 (10A)

You will then ask, why do people still put the 300mA in residential?
Just to save the few bucks for more profit/lower tender cost

Sis actually. 

1. What is the "MCB C20 WH"? is it different type of other MCB?
Standard C20 MCB.
WH denotes the one for WH circuit.

2. if I have 4 header, which mean I will need FOUR 10mA RCD?
Yes correct. WH 10mA RCD is per unit of WH. Each WH should be on its own dedicated circuit as one WH enough to use 15-17A nominal (WH is heavy appliance). Your 2.5mm cable only support 21A. And the 10mA RCD, only come (from branded mfg) up to 25A max current. In short, the standard cable sizing, the RCD current capacity (max 25A) all only suited for single unit WH as it is sensitive device (0.01A /10mA).
Whilst there are champions from china making 10mA RCD that can handle 40A I also dare not use.

3. The purpose of 10mA RCD is to trip when the heater leaking to our body? my current installation if leaking it won't trip?
Your current installation only trips at 300mA - by then, the human dieded 6 times over.
As the mains is 300mA, it allow 300mA leakage before it trip.
A human RIP at 50mA.
[attachmentid=10803044]

4. In short, I only need to have 10mA RCD in between the MCB and Header individually? Any other wiring need to be change/improve?
Yes, correct.
RCD is comparing input and output current difference. Input and output must = equal the same +/- RCD tolerance of say 10mA (0.01A).

Meaning, if WH input is 16A on L, at least 15.99A must return on WH output (N) else it has deemed to be lost somewhere.

Lost somewhere mean could be leaking through human.
So when the return not enough (<15.99) say only 11A return. The 4.99A cannot be lost, it mean it leak. As 4.99A far exceed the 0.01A allowed by 10mA RCD it will immediately trip.

MCB only consider single wire (L) amount of current passing through (short circuit prevention).
For a C20, meaning the speed limit is 20A.
Slight overload at 23A will trip the SLOW thermal overload after say 20 min.
Major overload at 100A will immediately trip the magnetic overload.

5. between I'm quite confusing are ELCB & RCCB the same? can you correct me if the naming in the image below wrong?
The difference is how and where they measure.
ELCB only detect earth current rise >0 leak (L to PE) leak on that appliance's earth. If it leak via anywhere else (L-N, or L-other PE eg wet floor, L-human) it will not bother. Hence in short I just say it protect that appliance only.

RCD because it constantly compare L input =N output + allowed tolerance (like 10.00A in on L, >9.99A must return as allowed tolerance is 0.01A for normal operation things like wire resistance that do NOT constitute a fault condition). It does not care where it leak through, RCD always compare in and out current so if it leak through any method (L-N, L-PE, L-other PE, L-human) it always trip.

Note: There is something called RCBO which do both function of MCB+RCD in one.
6. Appreciate if you can share the image of "MCB C20 WH" and 10mA RCD
MCB C20 is any usual C20 (20A MCB). WH is just designation for the WH circuit.

10mA RCD (must be used in conjunction together with C20 MCB) ie. add this along with MCB C20
ABB= https://www.lazada.com.my/products/abb-f202...i2IABn&search=1
Hager= https://www.lazada.com.my/products/hager-cc...l5n2dU&search=1
Schneider = https://www.lazada.com.my/products/schneide...8t5PsK&search=1

10mA RCBO = RCD+MCB in one package pao kah liao 2 function in one
Schneider RCBO https://www.lazada.com.my/products/schneide...PVCaV4&search=1
The drawback is, officially, their MCB is a C25 equivalent so you need to use with 4mm cable. As 2.5mm cable only good up to 21A rating.


First one from left  is MCB 3P (3 pole) C63 (63A)
Second one is 4P RCD but this is 300mA. Only used in commercial/industrial where they use heavy motors. Not safe for residential and its against regulation, as the human has dieded 6x before this trips. (RCD/RCCB/RCCD = same function with diff name like zebra crossing=pedestrian crossing)
Third one is MCB 1P C10 (10A)

You will then ask, why do people still put the 300mA in residential?
Just to save the few bucks for more profit/lower tender cost

Ideally, per ST WH Guidelines page 14, the RCBO (25A 10mA) is connected after the mains RCD 30mA as well. So you will have the 30mA (whole house) as second level RCD protection.

As RCBO = MCB and RCD in one.
The RCBO unit can be installed like an MCB (replace the existing MCB with the RCBO in-situ).
The chain is only as strong as weakest link. All the way should be 4mm as the min cable size per ST guideline is 4mm for 3300-3800W WH.
Because typical load is around 15-17A.
Still can get away with 2.5mm if the 2.5mm cable is good quality (full copper and SIRIM and MS2113 certified) as the 2.5mm cable can take a 21A max load, but it is recommended to use 4mm if possible.

If use 2.5 mmsq cable, then 20a 10ma trip rcbo.

What’s the water heater rated wattage?

I won’t recommend anything higher than 3600 watt although in ideal scenario, a perfect 2.5 mmsq can handle 24 amp

Yes, correct, RCBO 20A 10ma.

Hello, cannot use 4800W.

4800/230=20.8695652173913 A (21A for easy calculation)
by 80% derating factor (same as you don't redline your car every time) you should use cable that can support 26.25A ie minimum 4mm cable.

the minimum (as per ST spec) recommended is 4mm cable to use a 4800W heater (highlands model, usually from Pana or Hitachi).

In the market usually 3kw class is 3000W for storage, and 3300-3800W for instant WH. These are the recommended type (max power) for the 2.5mm cables typically installed.
Next step is 4800W.
Normally rare to find anything in between 3800 and 4800W.
If quality cable used.
If unknown/substandard cable.. insulation very thick, copper all substandard or adulterated so only 3kW class is safe option.

Hi,
4200W / 230V = 18.26A
https://www.electrical-installation.org/enw...a_of_conductors
Per reference method B1 (single circuit, solid stranded cable enclosed in conduit) able to handle up to 21A with 2.5mm² cable.

This 21A is assuming that quality cable (eg Mega Kabel, Caramay, or any of the MCMA cartel members) is being used.. 
If elcheapo or fake cables - you might be running a risk that it is undersized for the load

Also the length should be kept to reasonable length.. if the cables are too long then voltage drop will be a problem as well
Because if effective voltage drops, the amps go up
e.g. 4200W / 200V = 21A.
So there is about a 10% reserve capacity of the cable current capacity with 2.5mm² cables.. insofar as ST regulations go, officially they recommend minimum of 4mm² so that no need to worry or calculate so deeply.

Should be OK, they print their name and spec on the cable, there's an older SIRIM cert issued for MPC cable and it is not in the news for fake SIRIM certs  
There are cases before - https://www.sirim-qas.com.my/forgery-on-license-no-pc000218/

How to identify a sub-standard cable (per https://www.st.gov.my/en/contents/files/dow...ble_testing.pdf )
1) Check and verify MARKINGS on Cable – shall be as per standard requirement
2) Check and verify APPROVAL / CERTIFICATION Mark/Label
3) Measure conductor resistance ( need to have a proper meter)
4)  Measure size(s) • conductor • each strand ( and no of strands)
5) Check and verify copper content • normally by conductor resistance • weight the sample • Sometimes –by weighing the sample, with some experience, we can identify if the samples / weight of sample due to copper content or sheath of insulation

On the other hand w.r.t point no. 4 - there are also complaints on shopee that the cables are not as thick as they claim to be 
https://shopee.com.my/MPC-2.5MM²-PVC-CABLE...2276.3417950523

To answer the question..in diff POV
For upto spec cable, yes when fitted w appropriate MCB yes MCB will trip if the cable overloaded. Slow blow or instant trip depending on overload size. But anyhow this will work regardless slow blow or instant trip

For substandard cable..in the reverse scenario..if MCB sized accordingly to actual true max safe capacity of cable lousy spec then will protect as per above case.
If MCB was sized to untrue claimed spec per the fake labelling (which is normal procedure)..there is such a risk the cable melted before MCB slow blow happens (if the cable is really substandard aka fake shit).

wires run together in the same trunking.

it can induce a potential in nearby wires.

so there is voltage in them even without the switch is on. but if you test the current by putting the voltage to some or any work the voltage would immediately drop to zero.

pretty much normal and not a concern. nothing to do with earth or neutral