You absolutely cannot use a shared neutral through a RCCB/RCBO.

Tankless water heater has to continuously heat the water, unlike tank type. The only reason the socket still survive is just because the heater setting was not not full power, perhaps.

Continuous heat on the 3-[in 13A plug will soften the clamping brass in the socket, thus making contact poorer leading to mere heat generated. This is how most fire get started in houses.

I believe if the N is shared before the RCCB, it is still okay. Not between RCCB and device being protected.

Yup, as this 10mA is for WH circuit only.

Whole house one still return to neutral common link so no issue for the whole house RCD.

Prev owner contractors did funny things for connecting the WH. I pulled new dedicated cables for the WH and all good

Thanks ceo684, finally got someone to fix back everything and change the mcb.

I plan to pull new wires from dbbox since i have shared heater and ac on all three bedrooms upstairs.

always have to off ac before use heater. so far no issue, just troublesome.

Any electrician whom u can recommend or u able to do?

Your new electrician should be able to handle?
Since new wiring (new set of LNE cables) being pulled it may make sense to procure the material yourself and ask him to come to install as labour only if agreeable and also it will save some cost lah.

Ideally, following ST guidelines, core scope of work will be
Pull a new set of 2.5mm² LNE cables for each AC unit
Pull a new set of 4.0mm² LNE for each WH unit
Add in C20 MCB for all the above circuits
Add in 10mA RCD to the DB box, one RCD for each WH circuit
Add in 20A double pole WH switch for each WH circuit outside bathroom
Add in 20A double pole switch for each aircon

Additional nice to haves:
Whether to conceal (need extensive hacking) or just run surface mounted PVC conduit (no need extensive hacking, minor hacking required) will be a price+aesthetic consideration.

Replace whole hse main incomer from switch fuse and old 100mA RCD - to new whole hse RCD 30mA + new whole house MCB (40/63A depending on existing cable size)

This post has been edited by ceo684: Apr 20 2021, 06:36 PM

Cos he doesnt do hack/conceal, only do casing

But i manage to find another electrician already, also prefer not to do hacking so i said will have to find some contractor to do hacking first

So i got quoted 3550RM without hacking for:-

a) install second DB at second floor
b) pull 3 wires for AC & switch
c) pull 3 wires for WH & switch
d) pull 1 wire for water pump & switch
e) pull 3 wires for socket

reasonable?

roughly circa 2100 for the electricals; and the rest will be the hacking work.
Sounds about right.

3550 is just for electrical, without hacking

btw can we change the neutral and live for rccb?

The electrician already changed the whole DB Box and mcb but didnt change the RCCB cos he said still can use but still charged me full sum .

I just ok that time, but now i bought another hager RCCD and think just install myself.

The new RCCB stated that top left no. 1 is live but my old RCCB the top right is live instead and the wire not long enough if wanna switch.

cannot.

with a distribution board so messy............i would change and redo everything

This post has been edited by slimey: Jun 9 2021, 06:14 PM

You need to plan out how to reposition it. When there is limitation of wire length, this becomes tricky.
I've done replacement of DB for such hangmen tight wires that it may require some creative placement (to ensure everything can be connected).
For the wiring that came with the house.. that one no comment la can't do much; but for new wiring enough slack inside the DB box is important so you can configure accordingly.

Not sure how the NEW DB (current condition) look like but from the OLD BOX you can isolate the whole house off by disabling the fuse marked with Danger High Voltage (pull out the fuse and put it safely away on a table).
The incomer will be a problem to shut off but if you can shut off the whole house using the fuse (pull out) then you can work on the downstream components AFTER it.

Your new RCCB (30mA) can replace the existing one (i.e. second module) of the OLD BOX pic AFTER you have isolated the power.

Ref OLDBOX2 pic:
Busbar and 16mm² mega kabel pigtailsin the correct RED/BLACK colours can be purchased as loose cut (by meter).. LINK (Loose cut 16mm)

This post has been edited by ceo684: Jun 9 2021, 08:43 PM


Attached thumbnail(s)

Oh looks like my old setup the live is on RCCB top left, in my new setup (see attached pic), its on top right, so it means no issue to switch from left to right?


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Whoever did this should be banned from working with electricity.
The original (OLD FUSE) is 40A (sized for 10mmsq cable). Cannot suka suka replace with 63A breaker without changing ALL the wire to 16mmsq.
Should be fitted with C40 (NOT C63). 🔥🔥🔥🔥🔥 risk - cable all burn but the master MCB will not trip.."haven't overload >63A mah!"



You can park the new RCD at the far right and just extend with new pigtails.


I see the new one also 100mA Should return it and request to change it to a 30mA RCD instead as 100mA whole house is NOT up to code.
A single phase 40A 30mA RCD is not expensive. It make a world of difference between a 30mA or 100mA if there is a fault situation passing thru a human.


For further reading can see BEAMA (UK/BS standards) on RCDs.  BEAMA_RCD_Handbook__Dec_2010_.pdf ( 4.78mb ) Number of downloads: 51


Only in Msia lives are cheap- we still sell 100mA and 300mA openly






Unmodified file rotated for easier viewing


This post has been edited by ceo684: Jun 10 2021, 12:14 AM

Hmm already buried all the wires into wall can the electrician uncle just pull the cable out without hacking?

I was thinking about 30mA RCD too but when he tried to install a 10mA RCD at the water heater plug downstairs, it keeps tripping. The plug point has looping (to another 4 sockets which i am not using except for a socket for a hood) which causes the tripping according to him. So to be safe i thought just used back the original 100mA since no tripping issue.

The electrician also install new DB upstairs (as attached). Anything i should ask him to change besides to change the 10mm to 16mm? The water heater cable he is using 2.5mm instead and he said trust him no issue one even after i show him the ST guidelines, i suppose should be ok right since my water heater is only 15amp. Not an easy uncle to deal with, even after i bought 10mA RCD and asked him to install, he refuses saying ppl will laugh at me. Only agreed after i showed him the Electricity Regulations.


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Personally 30mA whole house will be fine since total amps IN = total amps OUT regardless how it is looped after that.

I run 30mA whole house myself no issue.
My parent's place also had this same problem where the WH circuit was shared with other things and its NOT dedicated. 10mA always trip. Resolved by running dedicated LNE circuit to the WH.
The difference is that the SINGLE circuit 10mA RCD had "unexplainable and unaccounted for amps from other devices" that the 10mA cannot account for = trip first talk later, save life more important.
Whereas for WHOLE HOUSE 30mA.. as long as total amps IN = total amps OUT (since there's only one IN and one OUT cable back to TNB meter) it will be fine, even high sensitivity 30mA also OK.

Anyway, congrats for putting in the 10mA RCDs for better electrical safety.

The difference is in 10mA WH circuit:
Even in cases where the WH circuit is actually shared neutral and trips the 10mA (because the neutral also contain other appliances' return so its imbalance with the incoming amp), this will not affect the whole house RCD.


This one can be solved by (a) correct way i.e. running a dedicated LNE circuit to that WH itself, as per code, without looping or
(b) use dirty trick (not so code compliant but likely to work without extensive hacking all over) is to install RCD as a spur i.e. AFTER the 20A switch (load side) and BEFORE the WH, so only that particular line going to the WH is balanced amps between incoming and outgoing.

Regarding the 63A MCB used on 10mm wire..
Changing the 10mm to 16mm will be expensive. In this situation, since your 63A will never trip before the 10mm cable is overloaded, the TNB cutout fuse will be your Plan Z overcurrent protection (between TNB meter to DB box) since that should still be on original 40A fuse.
The difference with MCB vs fuse, one can be reset in case of overload (just flip the MCB back on) whereas a fuse once blow already it need someone to buy a replacement, and that replacement fuse will not be available fast if the electrical supply store is closed.

Regarding 2.5mm cable used for WH circuits;
Should be OK-lah with 2.5mm for WH if its just 15-16A load, within spec of the cable, as long as its all 3kW class heater (3xxx W). You cannot install those highlands model with 4800W using 2.5mm cable.
2.5mm can withstand 21A safely.

That uncle cannot explain why these happened leh.. nobody is laughing



This post has been edited by ceo684: Jun 11 2021, 01:33 AM

The cutout fuse already blown once when I tried to plug in a old computer, so TNB came and changed to new one at 63A

So i should just use back 40A should be enough ? Change everything to 40A since my wiring all is 10mm to the second DB also

Normally, a fuse is sacrificial i.e. rated lower than the cable to protect the cable from burning up.
The other way, cable will burn up first to protect a higher rated fuse from blowing.

The TNB to main DB (incomer) is 10mm also?

Having four water heaters on at the same time is 16Ax4, without adding on anything else. Upsizing fuse need the cable to be upsized accordingly as well.

Tnb to main is 16mm at least I think.

Anyway I asked my electrician to change to 40a main switch and 40a rccb 0.03A. But even with full load of 51a tested using clamp meter, the thing doesnt trip? Something wrong ah? But the cable very hot though, almost 45 degree celcius compared to ambient of just 28 degree

The main switch need to be C40 MCB for it to trip on OVERCURRENT FAULT exceeding 40A.
Note: Just plain switch (isolator) without OVERCURRENT protection (ie No MCB function) does nothing to protect for OVERCURRENT.

When will MCB Slow Trip
In this case 51A > 40A its a sustained overload (MINOR OVERCURRENT FAULT) and it should "slow trip" using thermal trip within few mins.



I'm assuming you got a hager C40 P/N MU240A installed.
According to datasheet, https://www.hager-me.com/products/energy-di...u240a/30368.htm
min/maxi threshold value of the AC thermal operation 1,13/1,45 In (meaning between 1.13x40A and 1.45x40A)
for the 51A (divided by 40A rating) is around 1.27 In
this means a time to trip about 500 seconds based on Hager MU datasheet

‐-----
When will MCB Fast/instant Trip
(It will do a "fast trip" on the magnetic trip only if there is a SHORT CIRCUIT/MAJOR OVERCURRENT FAULT).

-----
RCD working principle is DIFF from MCB

For the 0.03A RCD yes this will be instant trip for CURRENT IMBALANCE (LEAKAGE PROTECTION).
The 40A on this unit is an indicator on how much total current can be safely monitored..but this RCD does NOT & will NOT trip in case of OVERCURRENT (which is MCB job).

RCD only measure "I-in = I-out + (tolerance of loss x up to 0.03A)". If the loss x higher than 0.03 (eg 0.032A) it will trip because "something is missing somewhere".

This post has been edited by ceo684: Jun 19 2021, 03:11 PM