Thanks for the input. You got me, "the only real reason to do what you suggested is to save $ and time inconvenience on hacking and plaster back"

Anyway, hacking is unavoidable for the installation of sub DB where I need to hack out the cable long enough to get all of them one by one into the MCBs in the sub DB. The problem is to hack thru the slab and beam. I do not want another hole thru the beam which is at the middle of the house, it only weaken the beam.

I just need to find two 4mm wires each and twist them together which will support 60A, right? Below is the potential load up-stair:

1 x 2 1/2 hp aircond
2 x 1 hp aircond
1 x iron
5 x fans (not on when use aircond)
30 x downlight, wall light and table lamp.
1 x vacuum cleaner (not use when ironing), my wife cannot be doing 2 things at a time
Many power sockets but seldom use other than mentioned above for ironing, vacuuming, also for charging handphone, hair dryer, no water heater (I use solar heater), TV, Audio, PS2 games.

Therefore, one 4mm for 32A could be enough, but 2 x 4mm definitely more than enough. Then need to connect 2 x 4mm wire to one 8mm wire to the sub-DB.

What do you think if I use lead soldering to join the 2 4mm wire together instead of twisting them together for terminating at the sub-DB and the down stair DB? How good is the lead joint conducting electricity compare to bear copper wire?

Cheers

Once you pull all the old wires that went upstairs out there will be a big hole in the floor/beam for you to put the new thick wire through , Problem Solved. 

Anyone knows how to size MCB of our home?

Got B,C,D type and different Amperage. How and what to choose?

[attachmentid=3667236] [attachmentid=3667238]

Hello. I have a situation where a fuse keep kicking back. The pic of the db is attached.  The one that always kicking back is the 20A one.  So the question is, can I change the fuse directly or i should change the wire first to 4mm?
Current wire size is 1.5mm. I think.

Here you go.

By the way your RCCB is 0.3A (300mA). Mine is 0.1A more sensitive.

Is this a new installation and is it a new mcb?
If yes then its probably this circuit is overloaded causing a thermal trip.. Get a clamp ammeter and cheack the load and compare it to the mcb's rating.. If overloaded then remove part of the load to another circuit (If it's more that one load on the circuit)

If no (meaning it was working well previously) then listen carefully to this particular mcb.. If you hear small crackling sounds before tripping then replace the mcb. The mcb has pitted contacts, that means the contact area has reduced to the point where it itself causes the thermal overload.. The device is faulty..

You only replace wiring if the insulation is damaged and you test with an insulation tester (Meggar).. Hire an electrician  for this.. He has the equipment and competency to use it.. You cannot use a multimeter..

Hello. I have a situation where a fuse keep kicking back. The pic of the db is attached.  The one that always kicking back is the 20A one.  So the question is, can I change the fuse directly or i should change the wire first to 4mm?
Current wire size is 1.5mm. I think.

Hi. It was an old thing.  It happened whether i switch on my computer or nothing while I'm not switch anything at all. It kicked back like ikut suka dia. So my plan maybe upgrading the 20A fuse by changing it to 32A fuse. Is it possible the problem will still occur after changing the fuse directly?  Also that fuse goes to one 3-pin point and then loop for two more 3 pin point outside the room for washing machine use.

Hi. It was an old thing.  It happened whether i switch on my computer or nothing while I'm not switch anything at all. It kicked back like ikut suka dia.

So my plan maybe upgrading the 20A fuse by changing it to 32A fuse. Is it possible the problem will still occur after changing the fuse directly?

Current wire size is 1.5mm. I think.

Also that fuse goes to one 3-pin point and then loop for two more 3 pin point outside the room for washing machine use.

Another question. Is there any way for me to determine which wire go to that particular point etc.? I mean if i want to change the whole box with the fuse everything.

So that i can reconnect the wire to the box correctly. 1 seperate fuse for a/c etc.

MCBs are classified according to tripping over range of fault current as follows:

    Type B MCB
    Type C MCB
    Type D MCB


Type B MCB:

This type of MCB trips between 3 and 5 times full load current. Type B devices are mainly used in residential applications or light commercial applications where connected loads are primarily lighting fixtures, domestic appliances with mainly resistive elements. The surge current levels in such cases are relatively low.

Type C MCB:

This type of MCB trips between 5 and 10 times full load current. This is used in commercial or industrial type of applications where there could be chances of higher values of short circuit currents in the circuit. The connected loads are mainly inductive in nature (e.g. induction motors) or fluorescent lighting.

Type D MCB:

This type of MCB trips between 10 and 20 times full load current. These MCBs are use in specialty industrial / commercial uses where current inrush can be very high. Examples include transformers or X-ray machines, large winding motors etc.

All the above three types of MCBs provide tripping protection within one tenth of a second.

*Standard ranges of instantaneous tripping:

Type B - Above 3 In up to and including 5 In
Type C - Above 5 In up to and including 10 In
Type D - Above 10 In up to and including 20 In*

To be classed as a BS EN 60898-1 circuit breaker the following tests must be satisfied (you must remember these are tests carried out in a controlled environment):

*Type B

A current equal to 3 In is passed through all poles starting from cold. The opening time shall be not less than 0.1 s and not more than:

- 45 s for rated currents up to and including 32 A,

- 90 s for rated currents above 32 A.

A current equal to 5 In is then passed through all poles, again starting from cold. The circuit-breaker shall trip in a time less than 0.1 s.


Type C

A current equal to 5 In is passed through all poles starting from cold. The opening time shall be not less than 0.1 s and not more than:

- 15 s for rated currents up to and including 32 A,

- 30 s for rated currents above 32 A.

A current equal to 10 In is then passed through all poles, again starting from cold. The circuit-breaker shall trip in a time less than 0.1 s.

Type D

A current equal to 10 In is passed through all poles starting from cold. The opening time shall be not less than 0.1 s and not more than:

- 4 s for rated currents above 10A up to and including 32 A,

- 8 s for rated currents up to an including 10 A and above 32 A.

A current equal to 20 In is then passed through all poles, again starting from cold. The circuit-breaker shall trip in a time less than 0.1 s.*

*Source: BS EN 60898-1:2003+A1:2004 - Circuit Breakers for overcurrent protection for household and similar installations - Part 1: Circuit-breakers for a.c. operation

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.

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.

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.

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.