It is the distribution box - usually in the store room, can you snap a clear photo and share it here?

That's an example of an electrical schematic, not the rules for what wires can be used. But if you are going 4 mm², then why not over spec even more to 6 mm²? Must be better with even less "straining", right?

The fact is over speccing is not always a good thing to do. Just this thread is evidence of budget being a consideration for wiring works because not everyone has an unlimited budget or unlimited time. And since ST allows 2.5 mm² wiring for air conds 2 HP (or less), that would be what I recommend. Empirical decision (after taking into account the maximum current draw, the voltage drop across the wire, and the temperature rise of the wire), not what I feel is right.

You had this very same question earlier this year, and so good to know that you now have developed your own opinion on the matter. As for me, I am perfectly fine pulling 16 A through a quality 2.5 mm² cable (Mega, Southern or Fajar, as I spec for all my jobs) and don't consider it "straining" the cable according to the relevant ST/IEC standards. YMMV

6mm² would be an overkill in my opinion and the pricing are usually far different. For 4mm² if you are getting a proper price from a proper electrician the price different is not far to consider - taking account into some users who frequently use an aircon in a way that does not allow the compressor to cut off, in fact a 4mm² would present a lower-cost setup in the long run. It depends on how you calculate as some people might decide to sell a house after 5 years so investing slightttttly further does not make sense.
4mm is not really "overspeccing" if you are considering that ST rules for all the developers are now to go for 4mm².
To be exact in finding the best you would have to look into the entire setup - some older air conditioning systems for 1hp would consumes about almost a 2hp similar power, and some 2hp would consumes about 3hp like today's aircon system.

ST rule on the wire size is always "minimum" or the word "minima" so I would beg to differ that 4mm² is overspeccing, but 6mm² would be an overkill in my opinion.

Glad you took the effort to look for my old comment - yes throughout these few months I had decided to do a lot of learnings because I need to govern how my house wiring is setup and even doing inspection in my existing and other older houses which I stayed. These knowledge also helped me to argue with many different wiremen (when I decided to approach them to do re-setup some areas which I felt can potentially be hazardous) - 9 out of 10 wiremen insisted 10mA water heater RCCB is bullshit, suggested nothing lower than 100ma sensitivity. 7 of them had no idea what is RCBO. Was glad I learned a lot from CEO and revisited some of her sharing time after time to calibrate my understanding of what I read which were all true.

As I mentioned, the key word by "ST" is minima and you need to factoring into the economical and supply chain issue when ST are spec-cing all these so it is up to you to find the "optimum" setup which suits your usage - Minimum vs Optimum vs Overkill. A good example is a 100mA RCCB is still allowed in Malaysia where as in Singapore standard is a maximum 30mA only - is 30mA sensitivity an overspeccing?

Anyway, I would say most people visiting the forums would benefit from knowing the "must do" and "good to do" and helped them to be able to explore more, and then making an informed decision. This makes the forum an interesting place to share and learn from each other. I benefitted from it and we all should together.


This post has been edited by davidlow7: Aug 18 2022, 09:52 AM

The 2.5mm² in theory can go up to 22A but in real world many other factors affects the rating. Most significant would be the ambient temperature. Rating on chart m=normally for 25ºC free air. When wire in conduit the rating will drop quite significant because there are other wires that contribute to heat. During operation also the wire heats. The longer the run the more drop in rating. I would agree with you that for 3-pin sockets the 4mm² would be better option no matter what. You don;t know in future what you would use the socket for.

As for the RCCB, it is not about the mA alone. If you look at the ST recommendation, there are two RCCB. The 30mA are monitoring the 3 pin sockets while the 100mA side are general for lighting, fan air-cond and water heater.

As I can see from here the inductive load as put under 100mA. The reason would be to prevent unnecessary tripping during current surge the instant the inductive load is switched on. The 100mA will still give certain degree of protection when it is not possible to use 30mA. Another alternative is to use RCCB with different tripping curve. Type K will trip extremely fast and suitable for sensitive electronics devices. Normally you will see Type C which will trip instantly at 5~10 rated current.

One thing to note that the RCCB will not protect you from Live-Neutral shock.

Because the device thought you were the electrical appliance itself

This post has been edited by davidlow7: Aug 18 2022, 10:03 PM