Wow...nice.

Can't understand the table. mine showing me which are for 10A, 20A and 32A from the table?

My original DB also look like this.

It show the cable thickness and its properties. A more layman site http://www.epanorama.net/index.php?index=calc_cable It give you very general guideline if room temperature are 20c, if you have bad quality cable or long run cable the guideline won't apply.

This post has been edited by weikee: Oct 10 2013, 09:35 PM

Look at the Column called "NEC copper wire ampacity with 60/75/90 °C insulation (A)[7]"

NEC in USA means National Electrical Code which is the rules for wiring etc.

This Column has 3 numbers which correspond respectively to whether the wire has 60 or 75 or 90 Deg C insulation.

In that column find the maximum Amps you need to carry, and then look across to the the Wire Diameter in mm2.

BTW unless you are sure best to always assume your wire is the lowest rated insulation ie 60degC

eg Lets say you want to caryy 32A, there is no 32 A for 60degC, only 30 or 40 A, so select 40A then look across and you will see you need 8.37mm2 wire.

Now 8.37mm2 wire sounds a little bit big to me for 32 A, which I seem to recall (assuming my memory is working correctly) 32A usually needs about 4mm2. Now from the table you can see that 4.17mm2 wire can carry something between 30 and 40 A if it is 90deg C insulated (but like i said always better to oversize wires and be safe than sorry).

BTW I'm an Aerospace, Mechanical and Industrial Engineer, NOT an Electrical Engineer so take the about as friendly advice only. Best to consult an Electrical Engineer or licensed Electrician.

Cheers

Weikee, Sydneguy,

Tq very much. Now I am somewhere to it already.

I am not trying to master. Just want to know if the existing wire is safe and use the right CB for the circuit when I get my electrician to replace and add the CBs. Not just blindly follow what he says. I should have that many CBs as what Weikee has with 2 DBs.

The idea of having 2 DBs is great. I just need to locate where the original developer wires supply to 1st floor. I think it should be somewhere at the ceiling where there is a bunch of wire out from one of a side wall. There will be some hacking but it is ok.

1 Lowyat forumer problem solved, 23,494,985 to go

Just to confirm one more question.

Diagram below refers:


In the radial circuit as circled in red. The circuit is protected by a 20a CB.

Question:

Am I right to say the amperage of the wire(denoted in red) it carries in the radial circuit is the sum of all the 10 power points? If each point consuming 1a, the total amperage of the "red" wire is 10a?

Similarly, The "green colour" wire is the sum of 7,8,9 and 10?

Yes, but 10 is way too much. If the circuit break for whatever reason you lost 10 points. And if got flyback say from lighting strik to one equipment you may loose all the connected equipment.

One more question comes to mind. Look like never ending...

If I get to locate the bunch of wires run up to the first floor and cut them and fix a new DB at the 1st floor, I then need to run a thick cable from the new DB to the main DB at the ground floor right?

Question:

Instead of pulling a new thick cable (live, neutral and earth), can I twist a few or all of the existing "cut" cables (become a big thick cable) that I cut (for making the new DB) which connect down to the ground floor DB, same twist them together? See drawing below:



This post has been edited by stevie8: Oct 11 2013, 12:37 PM

Ewwww ... really bad design .. your power sockets are no better than a RM30 extension bar since they all share the same fuse. One blow all blow ... and you have a high chance of overloading unless you are consciously remembering how many devices you are putting on that circuit.

This is not my house wiring la. This is from wikipedia just use it to illustrating and asking a question.

You could but its not really the right way to do it for a few reasons.

1) after cutting the old wires probably be to short by a few inches to go from Main DB to sub-Db. remember you want to cut the upstairs wires from sockets a bit longer so its easy to connect into Sub-DB and you are not trying to stretch wires.

2) joined parallel wires don't really have the same capacity in practice as they do in theory. Also its easy for 1 or 2 wires of a twisted set to come loose from the crew point, then youve got loose wires and reduced capacity and remaining wires are now free to come loose also.

3) It will be very hard to join those several wires into the DB and sub Db.

4) its just plain messy.

5) AFAIK its probably against the wiring rules/codes.

6) the 2-3 mtrs of big wire from sub to main will only cost less than RM50, so its not a bifg cost

the only real reason to do what you suggested is to save $ and time inconvenience on hacking and plaster back, but this is easly out voted by reasons 1-5 above.


Cheers

Add on to that; How sure the existing cables not tap to other place? If it was tapped you risk sending live current to unknown place.

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

You old house wiring come with 4mm wiring too?

hmmm.... thanks, have to be super careful. I think the way to find out is to switch off the MCB how it is linked and double check.

Not sure, I did not take notice of the old DB before the reno if there was any 32A MCB. But during reno the electrician could have use 4 mm since he put so many 32A MCBs.

This post has been edited by stevie8: Oct 11 2013, 03:06 PM

OK, found it. Of the 32A MCBs, the no. 4,5 and 6 are used only for 1st floor. These could be 4mm wires not shared else where with down stair.

Don't assume, need to confirm. Put 32amp some can put 2.5mm because then amps for starting load only.