Danal based on you responses:
Replace glass fuse to 10A
Personally, I would use an SSR to PWM the Heat Bed itself (i.e. the 'second' SSR) and use a mechanical relay as the safety device (the 'first' one).
I don't understand this point as the heat bed is AC. How will I use PWM with AC current and does this require addition of a 3rd SSR???
3)
Me, personally, I'd ditch most of what you are doing as overly complex (no offense) and just go with a single thermal fuse on the bed, and another in the enclosure, series wired to the first entry point of mains power. Given what you are doing, yes, I'd use a thermal fuse as the ultimate safety net.
No offense taken. This is overly complex and along with safety implications I also want to do this to see what I am capable of designing. I am in software and believe in writing defensive code and that has probably flown into my hardware design. But your point is well taken. Thermal fuses should be in my protection scheme as they are reliable and easily solve many of the problems I am solving using SSR's.
So I should mount the thermal fuse in series with the heatbed and then attach the fuse to the bed using proper epoxy.
As a side question how do you connect the thermal fuse to 12 AWG wire. Butt connectors I have are 10-12 AWG both sides and if the fuse is not 12AWG the butt connector will not work. Also butt connectors will probably melt when heated.
4)
Other changes: I'd consider making the 5V supply subject to the first SSR (which I suggested above be a relay). Meaning, if the ESP32 decides to cut power, it should cut ALL power. The fire could be in the 5V areas… I've seen it happen. This does mean you need a way to power up, perhaps a momentary contact mechanical switch that bypasses the first SSR/Relay to get things going, or similar. Short version: If you are going to the depth of your original design, go all the way.
What is I just replace 5V PSU with a USB jack charger 5V 2A connected to a USB hub. The hub will power the ESP32. Then I can connect the ATX on/off switch for my case to the ESP32 and use it as a switch to turn on/off the 24V PSU.
Will also incorporate the E-Stop switch in the design. And for relay I have an optocoupler isolated electromagnetic relay rated at 250VAC 30A which should fit nicely.
