Looks like this power point is just an add-on installation by someone probably self educated technician. He is using the switch with pilot light, which I believe a 20A switch but tap to share power from another line. Normally, house developer will spare a dedicated line for the heater and isolate both L and N wires. This person tap L and N from other lines.

Do you know where the neutral comes from? Was that a 3-pin socket next tot he switch?

If your heater spec is 3kW (normally for instant water heater), then a 10A switch will not be adequate.

Very Risky. I don't see the sonoff can be run on high amp continues.

Why you want a sonoff on the water heater ?

Yes, even a 16A rated sonoff cannot run high amp continuously and many reported burned PCB.

You see the connector, space and the pcb copper strip is already quite risky to run on high amp.

Sonoff need to reinforce more on the design to convince the people it can run on high amp.

Water heater no need automation mehhh, only use 1 or 2 time a day. Maybe can use solar water heater, no need switch, it auto when you open your shower

Probably they use general 1oz copper

Trace can be as thin as 5mm if they use 2oz copper to handle 20A

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Update 1:

Still got one space left for the bulk. Fast fast take.
The parts already ordered and on the way. Target date if finished installed this week will shipped out to you all by next week.

Can provide link to this. For research purpose.

Sifu, you already checked the Sonoff POW and TH16 on this? Please teach why.

I came across feedback in other forums (not Malaysia). It was quite some times, I forgot where already

Well, the rating of current on wire, switch, etc. are measured at 25C normally. At higher ambient temperature like us, the rating is not really valid. Many article suggest rating at about 75% of the rating on switch. So, for 16A, it would be 0.75 x 16 = 12A.

Note that some newer switch has two rating on switch like 20A/16AX. the 16AX means the switch only rated 16A of reactive load such as device with motor like air-cond, fan, etc.

You mean because of heat factor (ambient temperature), the switch can take in only 75% of its rating? Plausible because more colder, running more smoother mah.
Fan also same as air con? In what way?

Found some links about Sonoff POW connecting to water heater.
Someone mention connecting the POW to a high powered contractor to handle the high amps.
Well, the POW that failed is MK1 and not the latest MK2. Use with care.

https://community.home-assistant.io/t/any-s...7a-240vac/17507

http://support.iteadstudio.com/support/dis...ics/11000012976

im running on solar heater, this switch is to turn on and off the heating for solar i think.

normally we only use the heater between 6pm-12pm, so just thought of automating this instead of having to turn on and off everyday.

i am currently on solar heater, this switch is to turn on and off the heating. during hot days dont have to turn on this switch, but rainy days need to turn it on for hot shower. solar system auto on when shower?

Wire (which is copper) resistance change with temperature. The higher the temperature, the higher the resistance. Well, this is basic that you probably well aware. If two wires, one at 25C and the other at 30C, have same current 16A flowing through it, which wire will get hotter? Of course the one at 30C. For switch also the same. The contact has certain temperature rating. Why 3-pin plug get burn mark even though serving only 7A continuous current where it can stand 13A? The idea is the same.

The 75% is a general guide given by many articles. If you want to stretch the limit, it is okay but just aware that you are running appliance at higher risk of fire. Well, it does not mean at 75% your are totally safe either Just be caution.

Since this switch is running for short period and the load is also on/off, I guess not much risk even if you use Sonoff POW.

Ya mine solar heater no switch, guess alway on either hot or cold day

Mean to connect it near to heater?

What else i should buy prior ro receive this item?

Ya, safety factor. Don't run at near max rating.

A 5V micro usb charger rated minimum 2.5A and ethernet LAN cable. Later u can change to using WIFI on the Pi.

I guess anywhere you like.

If the heater is on ceiling like tank heater, I would not want to put the switch on the ceiling either

Well, hard to access and it is hot up there and degrade the performance of electronics and reduce power rating. Maybe fix it on the wall just under ceiling near the heater location. Easier to access if any troubleshooting needed. Maybe encase it in small plastic box if you like. I dunno.

yup. I really don't trust what they claim to be able run on 16A.

The relay is able to run on 16A. But what about the copper strip and connector? Can you push a 4mm wire into the connector ?

You can use the sonoff by additional SSR to control the heater. This is the safest way.