I'm planning to add some home automation to my home, using a 5V relay and most likely an ESP8266.
This will be used, for instance, to control the lights or the heaters, certainly through Home Assistant. I have experimented a lot with 5V DIYs, but this will be the first time that I will touch to 220V (domestic voltage in France.)
However, most DIY tutorials do not dare to address all the possible security issues. Some are just mentioning "be cautious for fire hazard due to high voltage", but nothing more specific.
In such a relatively small project, what is the worst that can happen and what should be done to prevent it?
Any source of noob-friendly documentation would be very welcome.
Reading the comments, I could refine my search keywords and find some resources.
For instance, you could consider this circuitbasics tutorial (and especially the comments). It certainly doesn't seem to require an electrician but it would be very interesting to be proved wrong here. If they actually teach something wrong I think it is essential to notify it.
Electrical experts should really be aware that DIY is a thing and that telling people to seek qualified persons instead of teaching themselves is useless: they will do it anyway.
However, teaching what should be done in the right context might make some aware that they cannot do all the required things. In this case, they will stop by themselves and ask a qualified person.
I live in a concrete building, as there are almost no more homes made of wood in France, especially in big cities like the one I live in (unlike in the USA I think). This might be important to consider regarding the fire hazard.