I'm really concerned about the safety of the Sonoff devices.
These photos show a TH-16 unit that was fed from a 13amp fused spur (240V) and feeding a 3kW fan heater. Total load was less than 13A, yet this is the second Sonoff that has self-destructed in 4 months. Although there has been a recall for the PCB track tinning, I believe the fault is with the fuse clips. That is where the charring of the board is the worst - the board has literally melted and the fuse bent over to touch the terminal block (by gravity).
What is the rating of the clips? Schurter of Germany make some of the best, and they are only rated at 10amp (http://uk.farnell.com/…/fus…/dp/1453528…)
Until this is sorted I am only running heaters on half power, and am tempted to short out the fuses, as they are protected by a 13A fuse at the spur.
Guys, this is a mass produced device that is to put it politely not designed as I would do it. Is it a great product - yes, would I trust the ratings of the device - no. I always run the device at very low loads for the reasons above and as demonstrated in this thread, if I need to switch 3000 W - use a relay. The most I would trust on this device would be 100 W.
I refer you to my earlier post on this, these relays are commercially inexpensive and not made as I would make them. I accept that any none Engineers wold take the advised ratings at face value and there may be issues - that's wrong. However, as will all equipment, some will just have and issue and this looks like just one of those.
To get the heat generated as the photographs, there was likely a loose wire or the load was quite heavy and no they should not fail in that manner, of the images posted it always seems to be the same relay type.
I have about 25 of the basic devices in my home and never had an overheating issue, I have had a device fail, but that was the WiFi side.
Its not obvious here, but this is a media set up - TV, Sound System, Sky Q Box and Fire Stick arrangement power rotated by a Sonnoff basic device - no issues. I just think you were were unlucky - as I said above - 300 W max is my view of this devices capability.
It does seem as you say, but this relay type seems to the worst effected, see earlier posts.
You must have had one of the earlier ones with the fuse and not the link, unfortunate, try using the Sonoff Basic range, I have had no issues with them.