I plan to buy a 3000watt built in oven for kitchen cabinet.

I need to know,

1. Cable size to use
2. MCB rating (C16, C20, C32)
3. Socket type to use

Any tips? Thanks.

1. 4 mm² for each of the 3 wires
2. C25 or C20
3. Direct wiring with disconnect switch, commando plug or round pin 15A socket + plug

want to ask also is it possible if for a 2500W built in oven, i will use a high amp power extension to share the only one socket slot between induction hob and oven?

i will only use one at one time for obvious reasons.

If TS's thread picks up steam, you are going to have a lot of differing opinions on what you are asking.
But my personal opinion is that if you understand the safety issues, limitations, and the repercussions, then your extension is possible. It is entirely your responsibility at the end of the day anyway.

yeah thats why i want to weigh the pros and cons on both options

i have no intention of frying my electric board/sockets nor destroying the kitchen appliance

only thing is i have experience with playing around lower wattage appliance only which requires 13~A, but higher than that im sketchy

You could make sure only one appliance is used at a time by using 2 plugs and 1 socket, so that only one appliance can be used concurrently. Use quality 15A plugs and sockets only, so that an appliance cannot be inadvertently plugged into another socket. Or use a permanently attached change over switch (but it's a bit ugly)

yeah the idea is since the built in oven is gonna cover the only 20A socket point, the extension tucked behind oven will be supporting just the hob and oven thats all

unless theyre gonna take the effort to pull the oven out of the cabinet to plug in more devices lol

Thanks for the recommendation. Will make sure electrician will follow it.

Is it a problem if neutral and live are 4mm but earth is 2.5mm?

This is not allowed by code in Malaysia. Only wiring larger than 16 mm² may use a Earth wire that is smaller than the power conductors.
(Disclaimer : this is off the top of my head, getting ready for something so reluctant to look for the actual size of wire but it is something like that. Maybe it's larger than 10 mm²?)

You want to save money by using 2.5 mm² Earth wire then that's on you.

Oven itself looks like using 2.5mm cable (from oven manufacturer). I was told even 2.5mm is ok but for good measure use 4 mm (by electrician). Currently no 4 mm earth available so had to use 2.5 mm earth.

Actually can use 2.5 mm² wires, as 3000 W will use under 14 Amp. 2.5 mm² wires are rated at 20 A so should be quite safe. Just ensure the wire is a branded that follows the proper specifications and the size is actually 2.5 mm². Make sure the MCB is C20 if using this size wire. I would use a maximum oven if using 2.5 mm² wires up to 4000 W.

Already check my MCB and its C20. Thanks for the advice.