Panthip
Dirty Dog is correct in his short wire list. But to be really sure you must look at the name plate of the cookers and water heaters and if in kw convert to amps.
for example a 1 point water heater for just the shower is usually 3.3 kw so 3300 divided by 230v= 14.35 amps so you would be tempted to save money and use 1.5 wire which is rated at 15 amps, but because of voltage loss over long runs due to resistance and solar impact as you are running the wire in the attic it is much wiser to use 2.5 wire w/ a 20 amp breaker . I use the name plate amps and then multiply x 120% which would be 17.22 amps..a common practice in usa.
Most Thai electricians don't know the proper size breaker for the wire. Do not trust them. I encounter these problems every day.