Thank you for giving me credit but I’m afraid that I do not have electronic design expertise to make that comment, @enl_public is the one that made the comment.
You’re right… corrected. You’ve usually got good comments though!
I can definitely move the 5V trace further from the 120V, as designed I have 70 mils spacing between the two. I could probably triple that spacing easily and might as well since it’d a good design practice with no downside. The reason I did not was I don’t understand why I would need too.
70 mils spacing is greater than or equal to what I’ve calculated needing using applicable IPC and UL specs. 5mm spacing is what IPC-2221B wants for like +1000V peak to peak. I would need to do more homework on this, but there’s a good chance there is no potential anyway between the 5Vdc and 120Vac; I’d bet at least $1 the 24V power supply is electrically isolated from the AC side of things.
Have I totally missed the plot here? Wouldn’t be the first time. If the intent is to make sure I’m aware of these things and have checked them, the design is safe to the limit of my ability to check it. If the intent is to say the design is currently unsafe or broken, it might mean I’m a total idiot. I have done sportier trace spacing than this on higher voltage designs and those blew up for completely unrelated reasons!
As an aside, after some thought, sticking with the traditional relay for a few reasons: cost and more importantly, solid state relays tend to fail closed (bad/unsafe) whereas a standard relay tends to fail open (safe, at least in this application). A solid state relay definitely dominates any time you are looking to do anything resembling regular switching but that’s not what m-code controls are good at.
As a second aside, if you guys are worried about this, you definitely don’t want to see what’s coming next…
The 24V supply should be isolated, but introducing this element into the system introduces a place where that isolation could be compromised.
For professional reasons, I tend to think in terms of: if this part faults, how will it affect the rest of the system? Can this change the safety certification status? Can this affect energy source isolation status (think lock out/tag out) elsewhere in the system?
I definitely do want to see what comes next, though I might not want it in my shop.
See PM for more. I think I will learn a bit here.
Moved some stuff around, closest spacing between 120V and the 5V is now 3.5mm; my garage is super comfortable with this level of risk. Boards on order, should have prototype operational in ~2 weeks!
3.5mm would suit most of the places I deal with.
I look forward to seeing the final product in action.