why is there need to install additional RCCB for water heater when i see
some WH already have this protection.
example Joven WH specs states below.

Double Poles EELS System with 10mA sensitivity

Any technical view ?


This post has been edited by Momo33: Jul 24 2024, 03:18 PM

what if the water heater protection fail to work?

remember, avoid any single point of failure for life critical device.

Yes some WH build in ELCB/RCCB but Suruhanjaya Tenaga Does not approve it or Trust it . Must add one more RCCB / RCBO before the WH Switch .

In the event if caught fire or electric shock . Insurance / bomba will fail owner and saman the owner if without addtional RCCB/RCBO .

Hello all,
Thanks for this very informative thread. This thread wakes me up to check my existing DB box and I found a following list of concerns, could the pros here help to comment ?

1. There are TWO water heaters (no pump) connecting to two individual MCB C32. So both got to be changed to a RCBO C20 0.01A ?

2. An electronic induction cooker that comes with Highlight burner connecting to a MCB C32, is this Ok ? Or oversized ? Unfortunately i don't have the spec anymore.. Assuming it is 3000W-3500W, does it really need a C32 MCB or can it be lower down to MCB C20 ?

3. A Pacific kitchen hood is also connecting to a C32 MCB. Again, should i downgrade to a C20 MCB or even C16 would suffice ?

Btw.. this DB Box config was reconfig'ed when i reno my house 10+ years back, wirings were all new (reroute all from DB to all the points). I have recently changed it to a 3Phase electric and stumbled upon this informative thread, hence the question.

Thanks all.

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

--- 13 A socket 2.5 mm² MCB C16 ---

This is another question of mine, all the 13A wall 3 pin are connected with MCB C20 in my DB box now. The 3-Phase RCCB is a single RCCB 0.1A coupled with a MCB C64. Your thoughts please ?

Thanks.

This post has been edited by numbertwo: Nov 11 2024, 09:35 AM

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.

-- all the 13A wall 3 pin are connected with MCB C20 in my DB box now.

Is it critical to have them all change to C16?

yeah, i read the ST diagrams from others thread, 3x RCCB is recommended but it is too late as the 3P upgrade is done. So my priority now is to change the WH MCB to switch to RCBO , then downsize the few C32 to C20 for the time being.

How about water heater RCCB 10 mA, install in DB? Actually how to decide between choosing RCCB or RCBO for WH?

RCCB - Residual Current Circuit Breaker
RCBO - Residual Current Breaker with Overcurrent

RCCB trips when the outgoing current vs return current difference over its rated trip current. However, if there malfunction in appliance is over normal operating current but the outgoing and return current still tally, it will not trip the RCCB. With RCBO, it will trip because overcurrent protection will trip the RCBO. Additional protection.

As for ST guideline:
MCB 16A for 1x 13A socket
MCB 20A for 2x 13A socket
MCB 32A for 4x 13A socket
MCB 32A for 6x 13A socket in ring configuration.

Thank you. In this case got to keep the current ones as most of them connect to 2x 13A. Thank u.

So if developer/contractor uses mostly 32 A, it is fine as long not more than 6 13A socket and not for high load/kitchen use? Anything else that need to take into consideration for right sizing MCB?

Gentlemen, is this the correct spec of the RCBO : Schneider Electric (Easy9 RCBO, 1P+N, 6kA, C Curve 10mA) ?

And for MCB, (Schneider Electric Miniature Circuit Breaker 1P 20A C 6000A 230V) looks right ?


TIA

This post has been edited by numbertwo: Nov 11 2024, 09:26 PM

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.