The DB already have a rccb. Why install another 1 that so near?

The extra rccb for heater is mean to install as near as possible to the heater side.

I guess it is the cheapest way.

As long as it work, it is okay. Safety 1st.

There is few way to make it nice. All is in the back post. But of course price will be expensive a bit.

I prefer the nicer way.

In US, those appliances using high power like heater, hair dryer, aircon etc, the 2pin plug is equip with the rccd. So the appliances that they buy have the rccd built into the plug. This is a good idea to protect you and the device from fire.

This is a aircon plug.

It should be install next to the heater plug or direct point.

You can use sharethebest picture way or nicer way at the back of the post.

https://forum.lowyat.net/topic/3413210?hl=rinnai

That is rccb too.

If change 10mA might too sensitive. 30mA should be alright.

The heater have another set of rccb of 10mA.

You might just need a 30mA less sensitive for a nuisance trip.

It is not getting spoil but the contact inside the MCB dirty. It cover with carbon which cause the static jump between. That cause the buzzer sound.

Do you always ON/OFF the MCB ?

Try ask the electrician check the wire secure to the mcb correctly. Screw tightly the wire on the mcb. Loose wire may cause the same problem.

Change to more good quality mcb.

Makesure the MCB rate at C20 (20A).

It is better for the heater to run the wiring separately. I not sure will this cause by the fridge.

You can try to run the fridge separately by another wall socket. For a yrs and see what happen.

You never heard people have such problem with MCB only for heater.