hi, for concealed, 32A uses 6mm2, 45A uses 6mm2 or 10mm2?
1. Hi, what are you trying to connect with 6mm or 10mm? new db? 10mm more appropriate for 45A

for washer+dryer, aircon, 4mm2 is enough (dedicated wire)?
2. 4mm is enough for washer/dryer or a/c 2.5hp size also no issue.

for kettle, if i want to use same wiring for sockets for Kettle & Vent fan is 4mm2 enough? i know kettle should be running on it's own line but don't have extra spare slot in db.
3. 4mm is enough for kettle, vent fan is less than 50w depend on size.

if i want to tap existing socket to add more, i use 2.5mm2 wires? connection use Terminal Block or something else?
4. just loop in the socket connection and screw them together

if i want to connect 2 wires inside bathroom above ceiling, what is the safest way to do it since normal blocks don't have any sort of cover (in case water leak).
5. can get aluminum tube for wire joint connection and black tape to seal nicely.

the 32A & 45A switch is for Oven & Hob using existing DB (need to mod DB for higher power?), i know it's overspec but i see some folks here did 45A for both oven & hob.
1. if you are renovating i would recommend you put 1 small db set at the kc and just pull 16mm wires from main db. then split the power at the kc. add double pole mcb and additional rccd. do direct connection from mcb to your hob. if 7kw hob imnm max is around 30A+ for full load and i highly doubt you will fully utilizing max power from hob. then you can transmit 10mm cable to your hob and another 10mm to your oven from new db.

i know those standalone Ceramic Hob + Oven combo requires 32A so i though put 45A for future coz i don't know whether power requirements will get smaller or bigger for future designs. Normal Ceramic Hob & Oven usually use what, 20A switch? i think the electrician will laff when they see 45A & 10mm2 wires.
2. i dont think 20A switch can fit 10mm wires. most likely you need do direct connection.

the kettle socket will loop with the fan socket coz i don't have extra MCB to have dedicated wire just for the kettle socket. i rather have dedicated wire for the washer/dryer since it not just run on longer time but uses more power?
3. i would change to a bigger db, or add additional db, why not do it proper once and for all.

regarding the looping, if the socket infront damage, will it affect the sockets behind it?
change new since you are doing it already, risk of short circuit for damage sockets.

do you mean a new db for everything in the kitchen (hob/oven/sockets?). is it normal practice? can you tell me the pros of having a 16mm to a new db compared to pulling individual wires from the existing db? i can't think of a good place for the new db without more hackings compared to running the wires from the db as i don't see any good space for the db around the socket & switch locations. the closest location would be somewhere in between the db & kitchen, which means i don't really save much on the wires but it will be inside a small room so is that safe?
1.some household actually does have a db at kc, my old house have one since my parent did an extension for kc last time. having a db makes the wires easier as its better than pulling many sets of wires. imagine 1set for hob, 1set for oven, 1set for refrigerator, 1set for kettle and two sets aux i.e toaster, microwave etc that's around 18 (6*3) cables. you can place the db inside the built in cabinets not necessarily hack much. wires will be concealed up at plaster ceiling from main db.

the 20A switch i was just asking if standard hob accept that, if not, still got 32A & 45A switch available in market. if direct wire to db it would mean i can't totally turn off the switches without turning off from the db.
2. yes for direct connection you might not be able to fully turn off unless the hob has its own kill switch. 20A or 32A or 45A switch you need to refer to the requirement of hob they serve the same purpose to cut off current.

btw it's just an apartment not big house. i know double storey houses usually have a db on each level.
3. honestly to add db or not all boils down to budget, many house owner not willing to spend additional money.

on the looping, i'm just asking if in future the socket infront breaks, will it affect the whole loop behind it?
4. to what extend hard to say, because damage socket might have short circuit and causes mcb to trips and render the entire loop no current.