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

I believe you will have unnecessary tripping faults. You have made a common Neutral busbar for both the top RCCB (Marked "40A 30mA" - Let's call this RCCB1) and the bottom RCCB (Marked "63A 100mA or 40A 30mA" - Let's call this RCCB2)

This may happen : Current flows through RCCB1 live > MCB 16A > socket in room > appliance > Neutral wire back to DB > Neutral busbar > RCCB2 Neutral.
Your RCCBs will trip. You have to split the Neutral busbar for RCCB1 and RCCB2.

The WH Neutrals must be connected to the RCCB2 Neutral busbar, as the current to the WH originated from RCCB2.

Also, physically, when I am making the connections, I would connect the 10 mm² wires together. This is for the WH Live. In the drawing it is connected through the Live busbar at each end. Potentially the Live busbar will heat up.

This post has been edited by stormer.lyn: Oct 3 2023, 09:08 PM

Yes, this diagram looks good. What I meant about the water heater live wire is in the picture below.



This is the physical connection of the wires. This way the Current to the WH doesn't go through the busbar, but goes wire-to-wire. If you look at a busbar, the bar is rated for 120A (example) but the tines are rated for the Current to an MCB only. They way wiremen stuff the incoming wire into the MCB and get it to distribute is dangerous in my opinion.

Sorry, a bit busy to get on LYN. In the marine line, many ships right now. But I'll try to get back to you asap if you have any further questions.

You are right, and that is an extremely valid question. Kudos for noticing that.

An RCCB, although marked 40A 30mA DOES NOT TRIP on 40A overcurrent. Ideally, the 10mm² wire would enter a 2 pole MCB rated 40A, and then only to the RCCB. This means there is overcurrent protection (MCB) and also leakage protection (RCCB) The wires are also protected, because the MCB will trip at 40A before the wires have a chance to heat up and melt.

But this makes the DB become very big. If I were doing the wiring, I would explain all this to the homeowner.

So why did I let this "fault" go without mention? It is because the 10mm² wire is still "safe" from melting no matter what happens. The INDIVIDUAL MCBs in the DB will trip if there is a fault (6A, 16A, 20A as in the poster's drawing) The 10mm² wire will never experience a 40A current unless the fault is within the DB itself, but this is very, very unlikely to happen.

Edit to add: Of course if you change all the 10mm² to 16mm², and the main RCCBs to 63A xxmA, you don't have to worry about any of the above. But you are now dealing with 16mm² wires within the DB, and that is a whole other issue

This post has been edited by stormer.lyn: Oct 12 2023, 09:01 PM

Because the OP is stuffing 2 sets of wires into the 63A MCB, and if they are trouble if they are 16mm². Part of the problem is that all electrical wires have 7 strands. They are small when the wire is 2.5mm², but each strand in 16mm² wire is relatively huge, and thus hard to bend and shape. Not impossible, just troublesome. And then finally you will realise you should have used a larger DB!

Your keyboard must have a separate keypad. Press and hold Alt then 0, 1, 7, 8 on the keypad. Technical person, so below are my most used symbols



For manual usage in this forum you can use the superscript tags

This is purely opinion - Please read with an open mind. No problem if you disagree.
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Well, I have the exact same Traxnele item installed in my own DB, and I do like it even though it is not SIRIM certified, and generally not used in M'sia. My concern is that the Neutral at the substation (or somewhere along the line, anywhere, say your meter room) will be damaged and disconnected. Even though you only use one phase, the distribution is in 3 phases, shared single phase between various housing units. If the Substation Neutral is disconnected, any unit may experience up to 415Vac (the 3 phase voltage) within their own single phase Live and Neutral. This Traxnele thing could prevent that overvoltage when it disconnects, and save your appliances from blowing up.

I know your wiring is single phase, so this fault could only happen in the wiring outside your unit. For people with 3 phase wiring? Never, ever disconnect your Neutral with the phases still active.

I have read about TNB overvoltage before, and TNB does reimburse for your damaged appliances. But for the RM 70(?) this Traxnele cost I feel is cheap prevention insurance. Again my opinion only. YMMV.

One reference website here
Here is another.
Yes, your single phase supply is actually affected by the other unit's electrical load should the Neutral disconnect

You have to mount it at the end if you are using an MCB busbar as the RCBO needs to be connected with wires, and will not fit this busbar

What do you mean "main ingredient"? All items in the DB are important and should be considered before installation.

As for the input isolation, the use of an electronic isolator or a fused isolator doesn't matter. Make sure it is double poled to isolate both the live and the neutral for safety.

No 2 better, but you could use an RCBO and just replace the current MCB being used
No 1 I think can, because it doesn't say that 1 RCCB for 1 water heater, just that wet area be protected by 10mA RCCB. But better wait for more knowledgeable people to chime in.

I personally would do No 2.

Yes can.
You could also mount it near the water heater switch. There are small casings that fit only an RCCB

The rating of the MCB is to protect the cables that are connected. So for example a 2.5 mm² cable has a rating of 24 A**, then the MCB should be not be 25 A, but 20 A.

1. Yes, must change to RCBO, or add RCCB with the C32. If wire is 4 mm² can maintain C32, but I would strongly suggest C25. (Maximum 5700 W water heater with C25) If the wire is 2.5 mm², then technically you already cannot use C20 as Suruhanjaya Tenaga say cannot use 2.5 mm² wire for water heater. Realistically the water heater won't be at maximum heat, so you can get away with a C20 RCBO. (My own instant water heater with rain shower and warm enough for me draws ~16 A measured)

2. Again mainly depends on the wire size. You should also look at the rating of the appliance. For 3500 W, then you would have about 16 A at full cooking power. So, going down to a C20 would be safer no matter the wire size.

3. It does sound extremely oversized. Most hoods are less than 1000 W, so a C16/C20 would be fine.

My own unit:
Lighting 1.5 mm² MCB C10
13 A socket 2.5 mm² MCB C16
A/cond 2.5 mm² MCB C16
Water heater 4 mm² MCB C20+RCCB 10 mA -or- RCBO C20 10 mA
Specialty appliance 4 mm² C25 (Oven for example) Edit I have a row of 3 x 13 A sockets at my kitchen counter. I can foresee myself using an air fryer and an induction cooker while boiling water at the same time. Individually they are not more than 1500 W each, but collectively to the looped sockets it is more than C20. Hence the wire feeding these looped sockets are 4 mm²
Note that ST says air conds are to use 4 mm² wires, but I think that is absolutely overkill as a 2 HP a/cond is at maximum 2000 W (~9A). So I don't follow ST rules to the letter. I'm okay to match the MCB to the wire to the power draw of the appliance.

** This rating depends mainly on the heat that is produced when the wire is flowing the rated amperes. This 24 A is the rating at best case, when the heat can dissipate from the cable. Make that situation worse, by burying that cable in the wall, run 3 phase together, run lots of wires together, etc, and that rating will reduce.

This post has been edited by stormer.lyn: Nov 10 2024, 10:31 PM

Technically cannot. ST requires a RCCB 30 mA for 13 A sockets. Your DB should have 2 RCCBs, the 30 mA one feeding all the sockets and appliances, and a 100 mA one feeding all the lighting.
-BUT- you could have one RCCB 30 mA feeding everything, as ST specifications say MAXIMUM rating of the RCCB. So using a 30 mA for lighting does not exceed the 100 mA specification.
Actually, ST recommends using 3 x RCCB, one for each phase-neutral pair for residential applications. This is because you may be 3 phase, but you are actually 3 single phase for residential.

Could you cite the ST source for this please? I unfortunately can't remember ever seeing these specifications.

There is generally also a size difference if your DB is limited in additional space, RCBO generally being smaller and a drop in replacement for the MCB.
I'll repeat what Zot said in that RCCB does not trip on over current, meaning you still need to maintain the MCB, making the space required even larger.

Cost wise an RCCB vs RCBO are comparable within the same brand for the same specs.

The rating of the MCB depends on the size of the wire that is used, not the number of sockets connected to the MCB. For C32, the wires would have to be a minimum of 4 mm², or a ring circuit with 2.5 mm². I've asked Zot for the source of his information so I can restudy it and correct myself if I am wrong. Stay tuned once he cites the source.

Using a single RCCB is fine, all that happens is that all the phases will lose power if there is a fault in any single one. With 3 x RCCB, a fault in one phase will only affect that phase and not the two other. Just thought to mention what ST recommends in their documentation, and to point out 3 phase vs 3 single phase usage.

Just imagine you follow all the recommendations of one 30 mA RCCB for socket outlets and one 100 mA RCCB for lighting, and then you have 3 phase - so now 6 RCCB in the DB - and then maybe 4 bathrooms, each with one 10 mA RCCB..... the DB is going to be hugely unpractical!

This is a hard question to answer definitively because ... it all depends.
Personally, I would do it. But that is just me being an engineer. In my line, people get hurt or worse when things are done without that inherent safety factor incorporated into the implementation.

Practically though.... you probably are never going to be pulling 20 A continuously from the sockets in a loop such that the wires can overheat and cause a fire. Suppose there is a short circuit. Is it going to be pulling 19.9 A and overheat without tripping the MCB, or it is going to be >20 A and trip the MCB making it safe? I'd say >20 A is more likely.

So you make a trade-off for the price you pay vs the safety factor vs the trouble to do vs the inconvenience vs probability of failure vs many other things you think off. And only you can make that decision. I'm perfectly fine running 2.5 mm² wire to the TV area with a C16 MCB feeding 8 socket outlets. Because a 55" TV, an amplifier, some speakers, maybe the router, HTPC, phone charger, a lamp, Amazon Echo, and maybe sometimes a vacuum plugged into the loop will never pull more than 10 A when everything is turned on. But my kitchen counter is 4 mm² C25 MCB to only 3 socket outlets, and I have said why in a previous post.

Exposure determines risk. If you never swim in the wilds, you probably are not going to be mauled by a shark. (Sharknado notwithstanding) So I urge you to understand what you are trying to do, and consider which ones need to be changed based on your needs.

Very sorry, but you have made a mistake, as lj0000 has also pointed out to you. I reproduce the diagram from the ST document you linked to below



The MCB protects the wires from melting, not you put a 32 A MCB you can have 4 socket outlets. The wire sizes are stated in the diagram, and are the determining factor for the MCB rating. You can see the ring circuit is using 2.5 mm². (2 x 2.5 mm² = 5 mm², which is larger than 4 mm²) That is the Cross Sectional Area of the wire, not diameter.

lj0000 also points out that in the ring circuit a wire may be disconnected, and then it becomes unsafe. This really happens from my experience, as different techs will service the wiring without knowing the ring connection. There is also specific requirements if you want to branch off from a ring circuit. I do not like ring circuits for these reasons.

Except it won't. Pull 30 A through a 2.5 mm² ring circuit protected by a 32 A MCB, and if one of the wires is faulty, the wires will overheat well before the MCB trips.
Here's the thing - a ring circuit that has a faulty connection/wire still has power so you don't know it is faulty - until you overload it and things catch fire.

One reason for using a ring circuit is so that you can use under specced wires to perform like larger wires, ie 2 x 2.5 mm² wires can perform like 4 mm². Did your installer tell you they used 4 mm² in a 32 A ring circuit, and did you confirm this for yourself?

Because it makes no sense to use 4 mm² in a ring circuit as 4 mm² is already rated individually for 32 A. Now if you said the ring circuit is 50 A but using 4 mm² then it makes sense.



(Slight aside : The other reason for a ring circuit is to ensure less voltage drop over the wiring for very large areas. Malaysia supply is 230 V +10% -6%, so minimum of 216.2 V must reach the appliance.
2.5 mm² wire has a resistance of about 7 ohm per km.

So according to the online calculator, it would require 49 m of 2.5 mm² wire length to drop that 13.8 V at full 20 A loading. I guess it is possible if your incoming is already low, and you area is very large, but my experience is TNB supply is always on the high side)