Be safe with the Sonoff

To Start I have Sonoff switches everywhere in my house from the wall switch, fan control and have plenty Sonoff basic around my house.

So I connected the Sonoff TH16 to heat my water boiler and it almost got on fire.

Before I connected it I tested it with a clamp meter (12.9A) I thought it is ok as TH16 has max of 15A and it was working fine for a week.

Can some one tell me what went wrong?

Thank you

Take a look at the spec sheet for your water boiler, what does it says its max possible draw is. Just because the device pulled 12.9 when you measured it, doesn’t mean that is the max it will ever draw.

Was this the first run or has it been running for awhile?

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That is what I thought too. They can draw a lot more power when starting up.

With all due respect, ‘what went wrong’ were the assumptions you made. You assumed a device rated to handle 15A @120VAC is adequate for handling a steady current of ~13A.

Here’s what you overlooked:

  • This device is self-certified and is never tested by an independent testing authority like UL, ETL , CSA, etc.
  • It’s allegedly rated to handle 15A @120VAC but (evident from the photos) has no overcurrent/overvoltage or thermal runway protection. In other words, it has no means of protecting itself from catastrophic failure (i.e its only “protection” is to melt).
  • You were planning to run this device at 87% of its rated current-handling capacity without consideration of the accompanying increase in temperature and how this device would handle it (i.e. poorly). In other words you did not “derate” the device based on the expected load conditions.
  • There’s also the matter of inrush current. That’s the initial brief inrush of current drawn by the load when first turned on.

This device is under-designed and inappropriate for switching a high-current load.

I had same situation with old sonoff with powering electric car.
And after resoldering it works fine.


My personal view to your case is that your contact made between the Sonoff and power cable was not good enough to handle 13Amps, its getting hotter and hotter until the plastic connectors melted.

There is no sign of defects on the Sonoff PCB, meaning its able to handle your 13A resistor.
Weakest points broken first, so next time measure the current, plus the temperature of the connection to be sure.

To be honest, with such high currents I wouldn’t trust any device that is not certified by a well known authority. Spending double or triple the amount of money on a certified device is well worth the investment if the cheap one burns down your house.

To be honest I would always consider a Shelly over a Sonoff, it’s certified, you’re supporting a EU company and it has great customer support.

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Thank you everyone for your replays. Next time I will be more careful what I’m connecting.

I think for every device is better to run it on 50% load max, just to be safe.