Residential cannot be using 300 mA anymore. Has to be 100 mA for lights, and 30 mA for sockets. Also there has to be 10 mA protection for wet areas. Also why is the incoming 63 A but the protection 40 A?

The electrician said 40A is enough as we split it into 2 - one for lights and one for 13A sockets. He totalled it and said 40 +40 is good enough..
He said he usually use 300mA and no problem and cheaper..but I m buying the stuff now so I want to make sure to use the correct ELCB, MCB
He also said if use 100mA will be easier to trip when there is lightning but I also added Surge Protector (SPD ) to the DB.
So the protection should also be 63A?

The 40A is the rated capacity of the ELCB. It really depends on the connection paths of your house wiring. When your electrician says splitting he probably means parallel connection, under full load the split contains 31.5A+31.5A = 63A, that's why he says 40+40 is enough.
But this is under assumption that on any one of the series part, your max current load is only up to 40A. For residence under normal usage (e.g. one plug connects to one device) this is usually okay. The only danger comes when some people like to abuse their power sockets, like connecting multiple high-load devices using power extension cords and so on.

Just because you split into 2 you think the electrical current will respect your split and only let 40 A go into one branch of the circuit?

Anyway, I wasn't discussing your installation as told to you by your electrician, I was telling you the rules that are stated by Suruhanjaya Tenaga. You can follow or not, up to you.

I think I better ask another qualified electrician...thanks for the guidelines...

You should definitely stop listening to your current "electrician"