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 Home Electrical MCB, How to size Miniature Circuit Breaker

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SUSslimey
post Jul 1 2018, 09:39 PM


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QUOTE(Cyberbullies @ Jul 1 2018, 08:48 PM)
Hi guys, have some questions due to disagreement with my electrician:

1) I asked to put 10mA 63A RCD for water heater + electric water closet + 2 power socket but he said it's better to do 1-to-1, meaning 1 RCD for 1 water heater instead, which does not make sense to me. Is 10mA too sensitive to be practical for what i am planning to use for? If not, i am planning to use only single 10mA RCD for 2 bathrooms lol.

2) He asked me to only use 1 RCD for all the lighting, fans and power sockets for the whole second floor, which i disagree with because it would mean total blackout when it trips.

3) I have asked for 30mA RCD for the lighting, fans and power sockets but he said to use 100mA RCD, which i again disagree with as anything over 30mA would be meaningless as it would greatly increase the fatality rate.

Having said that, i am concerned with nuisance tripping so would like to ask if there is anyone who changed 30mA for the house and 10mA for the water heater and experienced constant nuisance tripping?

4) Is it wise to use 30mA RCD for aircon? Or should i use 100mA or higher? Heard inverter aircon often causes nuisance tripping. But seems like no point when we go over 30mA.

Thanks!
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1. your electrition is right.
2. that's up to you.
3. if you use 30 you will need more RCD than 2.
don't worry about nuisance tripping for water heater. for house you can get those with high immunity and protected by SPD.
4. same as 3.
SUSslimey
post Jul 1 2018, 09:40 PM


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QUOTE(heloooo @ May 19 2017, 10:04 PM)
1 aircond draw 3.91 Amp, and we know 2.5mm cable can safely carry current up to 15Amp, so can i install 2 aircond using same cable?
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technically yes.
also need to take into effect the distance of wires of course.
SUSslimey
post Oct 17 2018, 09:58 AM


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QUOTE(FrankieSiow @ Oct 17 2018, 09:40 AM)
Hello, I have read through few threads including this thread, I have some questions on RCCB for water heater. My house is using 3-phase power, and currently I have 2x 4-pole RCCB (100mA & 30mA) installed in my DB. Let's say I want to install additional 10mA RCCB for each water heater that I have, what type of RCCB to be used? 2-pole? How will be the wiring diagram looks nice? Appreciate your kind advise, TIA.
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Your water heater runs on single phase right? Then 2 pole it is.

You need to find out which mcb is for the heater currently, and which neutral wire it is using if you plan to install it at the distribution box.

If too much hassle doing that, just install a 4 way distribution box next to the water heater switch with a single rcd, 20amp, 10ma tripping value. Wiring diagram is on the rcd.
SUSslimey
post Oct 17 2018, 01:18 PM


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QUOTE(FrankieSiow @ Oct 17 2018, 10:24 AM)
Thank you for your slimey prompt response. I understand based on what you explained just now. Could you also enlighten me on questions below?

1) If I have extra space in DB and I choose to install the RCD at DB, will it be less effective compared to RCD nearer to water heater?
2) If I have to install at nearer to water heater, the RCD should be installed before the 20A switch as per sequence below?
    (Main RCD (30Amp) - Water Heater MCB- RCD(10Amp)-20A Switch-Water Heater Power Inlet)
3) I found Hager 2 Pole RCD only has 16A and 25A rating with 10mA tripping value, which one should I get for my 20A water heater? (See attached photo)

Cheers!  smile.gif
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1. Negligible difference. But if the neutral to the water heater switch is shared with other stuff then it is rather troublesome or inconvenient. Either need to pull new neutral line or if not the rcd trip will cause other stuff shared on the neutral line to trip together.
2. No real difference before or after.
3. Erm....check the wire size going into the water heater. If less than 4mmsq do not use 25a unless it is already protected by a 20a mcb in the distribution board.
16a i think will trip if use full power of water heater.
SUSslimey
post Oct 17 2018, 01:39 PM


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QUOTE(FrankieSiow @ Oct 17 2018, 01:36 PM)
Really thanks for your explanation. I understand the whole concept already. I will discuss this with my electrician on this matter.  smile.gif
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To add on. If trip the neutral without tripping the live of the appliance that share the neutral is dangerous.

All the neutral that share it will actually become live which is more dangerous than before.

And since you have 3 phase electric supply , kaboom if different phase mix into neutral line which lost the link to the main neutral link.

This post has been edited by slimey: Oct 17 2018, 01:43 PM
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