Warning : burned sonoff basic (modified / hacked)

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I was monitoring a fairly new model dryer, I guess it would have been max 10amps (but for longer periods, say 2 to 3 hours). Sonoff replaced my units but I don’t use them for this purpose anymore.

So you don’t understand the difference between switching inductive and resistive loads and you blame the device?

Good grief.

Your logic is not sound. If you drink too much water you will die. There is no label on water telling you how much you can drink before you die. Should we ban water?

The sonoff basic is rated for 10 amps. If you hook it to a 15 amp breaker and then run 13 amps through it your going to have a problem. There is no legislating stupidity away, and you shouldn’t take the capability away from people who do know what they are doing.


Im not quite sure what your picture is, but the newer versions of the sonoff basic use wires instead of thick traces. I think I read somewhere that keeps people from shocking themselves with mains as often. Although people should never have mains connected with the case off.

Then why use proper power plugs and jacks?
Just connect Line and Neutral of the appliance to Live and Neutral coming from Main, with bare hands.

If you are careful nothing happens.

That’s your logic

Why put safe rail in balcony, if you are careful you never trip and fall from 10th floor to the ground floor

Safety measure are there not for the very clever and attentive people that studied Electricity in school/University, but for the average user that has no clue of what may happen: and there are tons of those type of users as you can clearly notice even here in this forum.
Besides even the most intelligent/prepared/attentive user can get distracted, tired, and so on,… and get electrocuted .

I have a Sonoff POW and I’m wondering a) if this is one of the ones produced AFTER the issue with the fuse grips was identified and b) what I can do to use it to SAFELY monitor my washing machine. Any tips?!! I figure if I mount it in a metal box, it won’t be able to communicate with my AP anymore due to the Faraday effect?!

buy a different product: a zwave neo coolcam plg+socket (20 euro), or the new shelly 1 power , a shelly 1 with power meter (15 euro),

There is one thing you can do with a Sonoff basic and it requires the use of a heavy craft knife,
That’s to cut the tracks both L&N so the relay contacts are tottally isolated, and leave at least a 4mm gap between the mains input and the tracks to the relay. Use what was the neutral track to the output for the other relay contact
Then just use it as a wifi controlled relay, and use a bit of common sense what you use it to switch.
its very useful for switching 50V at 1A .
If you want to switch kW , use the relay contacts to activate either a large relay or contactor.
BTW CE means China equipment, thats what they say when pressed why so much crap carries a CE mark and could never pass any type approval testing.
Just my opinion

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I have several sonoff basics at home controlling lighting.

In the UK, since 1947 we use a magical device in all our plugs called a ‘fuse’. A fuse was necessary because of the way we choose to wire our homes in the UK in a ‘ring’ which means that the circuit breakers are typically a much higher capacity (eg. 32A) that could be drawn by a single appliance plugged into a single socket.

So, a UK plug has a fuse in line with the live wire to limit the current that can be drawn by the attached appliance. These range from a max of 13A down to to 3A. So a heater would have a 13A fuse, whilst a table lamp would be fitted with a 3A fuse.

The average current I switch with my sonoff basics is 0.025A ([email protected]), they are also fused…, I’m not worried… That said, there is no way I would use them to switch anything close to 10A…

Are you sure you have the correct decade, I can remember as a child in the 1950’s the round pin 15A and 5A plugs in use and on sale, and you could still buy bayonet to two pin 5A adaptors… Lighting circuits in the UK are fused at 5A, 13A square pin plugs came in to use in the late 1950’s, still being replaced in the next decade.
But dont put too much reliance on a fuse breaking just above its rated current, which the max
before breaking.
The last job I had before retirement I designed and built a pice of test equipment for surge testing. Basically to test the effects of mains surges and induced current from lightning to equipment plugged in to the domestic mains outlet socket.
The supply board mains fuse 100A was only blown once, yet I was taking up to 1000A for a few microseconds, enough to brown out one phase of the supply.
In fact testing had to be conducted after working hours as computers were crashing in nearby companies.
A fuse can be easily fitted to the Basic, there is enough room to cut the Live out track , both sides of the board and drill two 1mm holes spaced 21mm apart , and then with a 1mm piece of wire soldered top and bottom side of the pcb , solder a 20mm fuse in between the wires.
The contacts on the relay are NOT suitable for switching more than 5A at mains voltage.
And thats for a resistive load , for an inductive load reduce by at least 50%.
If you need to switch more, use the sonof as a relay to energise a solid state relay
Devices that are designed for switching AC loads at they switch at the zero crossing point
Not expensive, abour 50mm , 25mm deep and with 4 terminals.
Even at the expensive suppliers like RS they are $30, AND thats for a 50A relay.

The legislation changed in 1947, and ring mains became standard after that mainly due to copper shortages after the war. That said, my aunt was still using bakerlite round 3 pin plugs in the late 1980’s, and my wife’s uncle was still using gas lights in 1991 !

That’s to cut the tracks both L&N so the relay contacts are tottally isolated, and leave at least a 4mm gap between the mains input and the tracks to the relay. Use what was the neutral track to the output for the other relay contact

To take this further, you can power the sonoff with 5v DC directly (bypassing its own AC>DC conversion) from a USB supply. Then conerns of isolation are gone.

There is a DrZZZ video which shows how to fuse a sonoff.

I am surprised that I didn’t catch this thread sooner.
First, my qualification to discuss this topic.
Years ago, I was an industrial/residential electrician while taking Electrical Engineering at the University of Houston. I have a pretty good understanding of the National Electric Code which is pretty much used as the world-wide reference.

There is nothing wrong with the Sonoff Basic. I have several in my home including some inside wall boxes. I even use a couple as designed. I warrant that most of the users are clearly not.

The burning problem is not a design problem as much as a user problem. Itead uses Phoenix-style connectors (which I do consider a design error) which are rated to use 26 to 16 AWG Stranded wire. In the burned photo above, I see solid wire that appears to be 14 gauge- larger than the spec for the connector. What happens with solid wire in a connector designed for stranded wire (like the extension cord zip wire) is that they will not stay secure. They will loosen over time and that makes for a high-resistance which in turn generates heat. That’s when things start to melt.

A fuse would be redundant in this kind of device. Fuses are inserted to protect upstream circuits - not the device they are in. They are mainly for fire prevention. (From the NEC: “At the most basic level, these devices are inserted into the distribution system to “break,” isolate, or disconnect the circuit if there is an overload or short-circuit condition.”)

In my installations inside a fixture box, including two with 10 Amp space-heaters plugged in, I remove the Phoenix connectors and solder 8-inch long pigtail wires of 14 gauge stranded wire. I then just connect to the pigtails with standard wire-nuts and shove the Sonoff into the box. This eliminates the heat hazard of the Phoenix connectors and it makes wiring the Sonoff easier.

If you go to any of the Sonoff Basics you have in service for a few months, I guarantee that you will find that the screw terminals are slightly loose. (Remove the power first). If you tell me that the connector area is warm, I would not be the least surprised.

As I said above, I have a couple of Sonoff Basics that I am using as designed. These are on table lamps and a Christmas Tree extension cord. They are 16 gauge zip wires and I use the Phoenix connectors on the Sonoff. As soon as you use solid-core wire or put the Sonoff inside a fixture box, you are outside of the designed use.

Hope this helps.



This Sonoff basic had burned because all the current is passing trough the sonoff cause of the neutral wiring.
You should have to wire the two power wires outside the sonoff ! And only wiring the pilot line inside the sonoff.
If all your heaters are wired in this way, I think you must modify all wiring and take out the neutral power line.

@Axh3ll I’m not an expert but if you have a look below to the burned sonoff with my wiring I’m not sure I can do better without other alimentation and no pilot wire from wall. As you can see the line is plugged directly to the heater, it “should have been safe”.

Imo the faulty component was the 1n4007.

I’m sorry but what goes in goes out ! If you drain for example 10amps trough the line wire they comes back trough the neutral wire + the sonoff and the pilote consommation

As I understand it, you are splitting the line/live on input to the SOnOff, one runs past the SOnOff and provides the heater with it’s main power line/live. The SOnOff is not involved in this line/live current.

You use the SOnOff to send a control signal to the live return of the electrical heater which tells it to be on or off.

However, @Axh3ll is correctly pointing out that you do not split the neutral in the same way. So all the current the electric fire is consuming via the separate live/line is coming back on the neutral wire, through the SOnOff which is not rated for this task.

It is a common miss conception that neutral wires are somehow safe. They are no different to live wires once in an active circuit. Kirchhoff current law states that the current will be equal at all points in a circuit. In fact when we label a wire “line” or “neutral” is only relative and pretty much arbitrary as to what point a line becomes a neutral. If you were measuring current in a circuit you could not tell from measurements alone which was the live and which was the neutral.

If you have more of these or other things wired this way I would revise them. Split BOTH the live and neutral through Wago’s, not just the live. Create two completely different parallel circuits. One high current, one switch/signal current. Put a very small fuse, like 250mA on the switch line to be sure you don’t get surprises due to failures or shorts.

In fact, I suspect there is a very high probability, if it’s anything like boilers etc., that the wall heater has a switch live out and live return for the pilot control. Just power the wall heater from an outlet and put the SOnOff on that pilot line supplied by the heater, you may then borrow a neutral from anywhere you want. Your SOnOff will have only 1 wire leaving it. Some devices might not like powering the SOnOff from it’s live switch wire, they can have very small value fuses as the switching wire is designed to carry virtually no current, often called (rather incorrectly) “Volt less”. In this case you go back to how I suggested above, two parallel circuits with the SOnOff ONLY switching the pilot wire and the main 16A flow coming nowhere near it.

To be more sure, don’t use a SOnOff Basic. Use a smart switch that is NOT pass through, but simply closes the circuit on the pilot wire and is powered independently. SOnOff variants like this exist as well, I believe the Shelby’s.

I could propose a safety feature that the SOnOff should switch both the live and neutral to prevent this kind of mistake, but as it would incur costs and other issues doing so, it’s unlikely. So a non-passthrough, isolated relay controller would preferential.