I spoke to a friend and it appears that there is more to just the amperage on the MCB vs the amount of current you need to size an MCB. If the amount of current is below the MCB's rating multiplied by the value of its type, there'll no trip. In an overcurrent situation, most likely your electrical/electronic device will get fried (it's gotta be already faulty to draw excessive current) before your wire if you're lucky.

To size it, you'll need to know all the resistance involved (wire, devices, earth loop, inrush current). Not sure how many have the equipment to perform these tests?

Anyway, just to share.

http://www.studyelectrical.com/2014/07/min...tic-curves.html



http://www.theiet.org/forums/forum/message...&threadid=32143



The reason I'm researching this is because I have a neighbor who had his concealed wire shorted permanently, something I'd rather avoid.

This post has been edited by beLIEve: May 6 2017, 12:40 AM

Very detailed explanation : http://www.kevinboone.net/cableselection_web.html

wise words, bro weikee. I think that's why the developer gave 4mm2 wires for room aircond despite room airconds are likely 1HP.

My neighbor's house was rented out. No one really knew how that socket was used as he only got back his house recently. It was looped alright. From MCB to 3 sockets. The last point was the one that fried.

I'm installing some new points for my own house. Will be using 4mm2 to minimize the melting problem, regardless of how long I use the current. Price does not differ a lot vs 2.5mm2 when I buy in rolls. The last time I paid for wiring, I was "convinced" that their 1.0mm2 (yes, I read it on the wire several times because I thought I misread it) 3cores is good enough for 2HP aircond. 1 month warranty woh.

BTW, I've read a lot of your useful responses here when I was searching for RCCB. Pleased to meet you, finally. Speaking of RCCB, another neighbor insisted that MCB will trip when there is a current leak when I tipped him about the 10mA RCCB for heater. I guess it would, if the leakage goes beyond the MCB rating x Type.

This post has been edited by beLIEve: May 8 2017, 05:10 AM

That's why he confidently gave 1 month warranty. I always consult my friend before agreeing to all the deals offered by contractors. When problem occurs, can make money pulling new wires again.

Referring to RCCB, yes, after so much research, that's what I learned. Also read that some will trip at 50% of the value. Didn't drill too much into that.

Let me ask you this, since you're a 高人. Which is better? 10mA RCCB between MCB and water heater, or MCB between RCCB and water heater? My friend recommended the latter, but I went for the former after some research. It's sort of whether I want the MCB to protect RCCB from potential overcurrent damages, or RCCB to protect MCB from leakages. I'm protecting the RCCB because it's much more expensive. He said RCCB will not break, though I wonder what will happen when 100A flows through a 25A RCCB.

I'm very short only. That's why have to look up on you

Actually, I thought as long as I add an RCCB, I need to identify the neutral wire no?

My original setup based on my friend's advice :
Live busbar --- wire --- RCCB Live Top --- RCCB Live Bottom --- MCB Bottom --- MCB Top --- Water Heater Live
Water Heater Neutral --- RCCB Neutral Bottom --- RCCB Neutral Top --- Neutral bar

New setup :
Live busbar --- wire --- MCB bottom --- MCB Top --- RCCB Live Top --- RCCB Live Bottom --- Water Heater Live
Water Heater Neutral --- RCCB Neutral Bottom --- RCCB Neutral Top --- Neutral bar

Yes I managed to identify the neutral wire. Small apartment, and developer was generous enough to use a 4mm. Only 2 of these.


Bro, did you misunderstand my posts? Or you see something wrong with my setup having MCB before RCCB?

Thanks for your responses.

thanks bro Richard

Back to the original topic.

Anyone here use MCB Type B at home? Seems like everyone is using Type C, but of course, most were probably installed by developers. Forgotten to find out if Pasar Road is selling Type B. The last time I bought, I didn't know the existence of Types B C D, they just gave me a Type C.

hmmmm that's where my concern is. Or probably it's unwarranted.

Type C will only trip at 5x its rated current. If my understanding is correct, there'll be no trips below 5x. On a 20A Type C MCB, it means that 99.9999A can flow through the cable without it tripping. If it heats up the cables long enough, fire or short circuit.

Of course, knowledgeable people know not to overload any particular circuit, but we can't stop anyone from doing so.

This was the reason why my friend said there's no point protecting the RCCB with an MCB. I guess there's no harm trying though

I don't think I've much choice. Seems like it's our norm in this country to compromise safety for convenience. When I goto shops for 10mA-30mA RCCB, they'll always tell me "don't buy this, always trip". I guess the same applies to MCB, so no Type B for the wicked.

Thanks bro weikee.

Yes, I found it there and my friend is using element14 exactly as you - for rare items. These are made in Europe too Costs 8x more though.

http://my.rs-online.com/web/c/automation-c...archTerm=S201b2 seems cheaper than element14. I don't know who will do the customs clearance and not sure if SIRIM approval is needed.

Edit : Ok, my friend say all the clearance will be handled by element14.

This post has been edited by beLIEve: May 11 2017, 12:13 PM

Thanks bro Richard. You just answered my question! I did some further research based on your answer and found out that it's available on Wikipedia. All other sites just explain the magnetic trigger, which is 5x-10x the rating for our Type C. That explains the line curve to the left of the 5x-10x "rectangle".

This also explained what I observed with my neighbor's MCB. When I first reset the MCB that goes to the faulty line, it took a few seconds to trip. Subsequent resets are almost instant. So it's the thermal effect - it hadn't cool down. I disconnected the faulty link which is last in the loop and no more trips. There was already a partially (say, 10%) melted plug when he got back the house, so I think it's beyond dirt. Not within my skill to fix that

For the RCD, yes, I've searched and read before, just for reading pleasure. I tumpang my friend to buy the 10mA and 30mA RCCBs when he bought his before all the readings. So my house is fully secured, at least, to what is within my knowledge. I'm still using a stack of Type 2 MCBs from the developers though, need to research how much they differ with Type C. I briefly read the other day, Type 2 is old standard.

My friend got everything right minus the thermal tripping part. He was the one who told me about the 10mA and 30mA RCCB. So yes, it's not enforced yet. By the time it gets enforced, there'll be a shortage in supplies

And yes, ventricular fibrillation.


Thanks for the tips. Long story short, my old 100mA used to trip on lightnings while neighbors' houses aren't. Now the new Hager 30mA (I use as main RCCB) survived many lightnings. It tripped once without lightning. At that time, only the fridge and fan is running (2 different circuits). So I think I'll have to clean some wires. I noticed many of my wires have paints on them. Contractors must've painted before they install the sockets. We're the second owner, apartment is 20 years old now.

bro weikee :
Ahhhh ok, thanks for the info. I just briefly browsed that site. Friend told me there are wires better than Mega. So I just searched for the wires, for the sake of knowing, and the MCBs. Both are much more expensive than Pasar Road. I'll check out element14 next time.

This post has been edited by beLIEve: May 12 2017, 02:41 AM

My Hager 30mA never trip on lightning, without arrestors. Perhaps a good brand makes a difference? Besides, shouldn't an RCCB trip on Amp leak rather than Voltage surge?

Sometimes don't get to choose. Most people rely on contractors.