I have been testing a SOnoff MiniR4 with ESP Home.
I have just unplugged it to get ready to install it in the light switch socket in the wall and noticed that it felt quiet warm.
I don’t have a way at present to measure the temperature but when I do I have two questions:
I am not keen to burn my home down 
As per the specificiations:
it’s about the same for most other relay’s as well i.e my Aqara T2 relay is rated to that temperature range.
Is that not the temperature in which conditions the device is guaranteed to operate which doesn’t say anything about how warm they are supposed to get before it becomes dangerous?
For true safe temperatures you would look at the materials they are made of, in the case of PVC casing that most would be made of as listed in the sonoff one:
That melting point is where you want to really stay under. via Polyvinyl chloride - Wikipedia
It’s why you don’t want to overload things with too many devices on a single plug for example and why so many fires start when people stack multiple power splitter plugs that are low quality. i.e because the plastic melts and causes the cables to short leading to the fire (an example of this is with improper made molex to sata adapters).
For reference this is my T2 I am using in a shared laundry room behind the socket that is linked to my unit:
Said socket is also in a brick wall so thermals should be stable even in summer (will be monitoring as well just to make sure since its starting to get hotter here)
edit: added more info in gen.
I think
Pheat=I2⋅R
suggests that 50c is the hottest this device should get under any normal circumstance.
over 70c is posing a risk to combustible or plastic materials.
Thanks all. I reckon my Sonoff is possibly getting up to the upper 20s so all good. Going to do some testing though to see if it is only getting warm when relay activates or if also when just sitting idle.
