ok..

3 phase supply properly balanced across each phase means no current flows through the Neutral.. The neutral only returns the unbalance current across the phases..

11KV transmission lines is only 3 wires.. It is distributed in Delta with all phase current balanced.. Only when step down by transformer from Delta 11kV/433V Star is where the neutral is introduced where the Neutral is earthed..

From Transformer it goes to a Feeder pillar where there will be an Earth fault protection device before it gets distributed to residential properties where is must also be earthed at the DB.. This is known as a T-T (Terra-Terra) system..

The usual tail into a residential landed property is only 2x25mm(60A) or 2x16mm2(40A) Aluminium cable which only provides you the fuse rated max demand load which is a slow blow high rupture capacity fuse..

This maximum demand can easily be exceeded by the high inrush starting current of inductive motors (your aircon motor)..

3 Phase is the name of an electrical supply.. It can be 3 wire (2 phase lines plus Neutral) or 4 wire (3 Phase lines Plus Neutral) supply..

Single Phase is the name of a electricity supply of a 2 wire (one phase plus Neutral) supply..

If in doubt please get a competent electrical contractor to verify the existing maximum demand to check that your wiring can handle the electrical load..

You can easily overload (think electrical fire) your existing wiring if you change your protection fuse to a higher rating without knowing your maximum demand..

What I am saying is basic electrical common knowledge to all electricians..

If you don't understand what I'm saying please talk to an electrical person who knows something about maximum demand and how to use a clamp on ammeter..

Electricity is not your friend .. It is a known killer held in a copper prison just waiting to kill you..

You understand .. but no one knows if he has an inverter unit or a conventional DOL start and that pictures shows a DB with 24 SP mcb's single phase..

I have never seen a single phase DB with so many mcb's..

Add to the fact they're all non branded components easily means if that RCD is defective any surge inrush current from a DOL motor will fuse any of those mcbs short circuit and start an electrical fire..

And it's not all soft start.. There's definitely more conventional DOL AC motors out there than inverters..

We're not talking about a single unit compressor.. The issue is maximum demand..

The maximum current load as in he already running 3 of his existing aircons couple that to the existing running load (refrigerator, lights, sockets, etc) and now his compressor kicks in..

This transient inrush will cause arching to the mcb's contact points..

It doesn't have to happen immediately when the contacts are still new or the spring tension is still good.. This will continue until a weak link in that electrical system fails..

You are an intelligent person.. What would your advice be to this situation?

I suppose so but difficult to isolate if there's a problem ..

The standard practice is to split the load into 2 DB's zones both with a DP RCD protection..

Example :
1.

Say you have a double storey house.. Bottom is one primary DB and 1st floor the Secondary DB

KWH meter to 40A DP (double pole) Isolator split to two 40A DP RCD's (two DB's) with 14 Way outgoing mcb's each..

That way if there's a fault its easier to identify problem mcb circuit..

It's also easier to ammeter clamp on to check the maximum demand current at a time everyone is home kitchen cooking, hot water shower and living room ac on at the same time ..

The peak maximum demand bell curve is usually at around 7am and 7pm for residential..

2.

Another way if it's a single storey is to zone the house into front and back areas and rearrange the wiring accordingly..

Seeing that you already have so many circuits its actually very simple to identify lighting and power ....

Then divide into separate zones and DB .. Both DB's can be next to each other but independently isolated in case of a fault..

I have no arguments with your comments except to clarify my initial statement on 3 phase supply wrt 3ph kWH meters..

The 3Phase kWH meter is always 3Ph4wire

However u don't need to pull in all 4 wires (3 phase voltages and the Neutral) into the residence if you can satisfy your maximum demand with 3 wires (2 phase Voltages and the Neutral) (as residential use almost exclusively single phase load)..

Saves your money..

here in malaysia

3 Phase is 415V (phase voltage) as opposed to Single phase is 240V(line voltage)..

It's only the name of the supply voltage (415V phase-phase)..

I hope thats clear and you're welcome to comment further..

Just to be clear ..

For single phase residential loads..

Your maximum load is limited to the size of the electrical conductor supplied into your home..

The general max size is usually 2x25mm2 Aluminium Overhead cable which gives you a maximum 60A single phase..

This is also why you must not replace the 60A HRC fuse to 100A because that fuse will not blow before the cable starts to burn..

If you need more load then pull in another wire which will give you an additional 60A..

No a 3 Phase kWH meter will cost you more than double the price of a single phase kWH meter and it uses additional cable..

You only pull in another wire if you exceed the existing ..