What’s your DRC spacing rule? What overvoltage category does your product fall in?

Your optocouplers doesn’t provide anything since you have shared ground between them.

K1 Com2 is way too close to the ground fill. As well, use slots (cutouts) to extend the creepage distance. You can use normal diodes like 1N4004 across the relay coils. The optos are doing nothing really. As both sides share a common gnd. No protection is gained. You really don’t need a ground fill and your angled tracks aren’t something you’d normally see on a commercial pcb. You can make the tracks fatter if required and run a parallel track on the other side if you want more current capacity.

K1 appears to have the wrong footprint (if SLA-12VDC-SL-C). Clearance and creepage between LV and HV parts are probably not enough. Link data sheets for the relays please.

Note that any diode from 1N914 up will suffice. It doesn't have to be a rectifier: BC337 isn't that strong, nor is the coil. For EMC purposes, you may want a X1 type film capacitor across the mains input; this will help the snubbers do their job.

It is likely that the transistors are always on due to opto leakage current. I also think the optos are useless and this design is just copied from some chinese relay module which boasts optos for isolation which they don't so it is just marketing magic to say that opto-isolators are used.

@winny for 230V track, i've used 2mm tracks with 1mm clearance (a calculator gave me 0.8mm clearance min for coated tracks with 380V max, I've rounded up). I do not know how to estimate possible overvoltages :(

@Kartman Could you explain why the ground fill is not needed? I thought it was always nice to have. By "angle tracks" you mean the 45° angled tracks? I should use 90° angles only?

Indeed it looks obvious the optocouplers are useless! Should I then simply connect the 3V3 signals to the transistors bases? Is there a severe drawback to having the same ground for relays and the microcontroller logic?

You don’t estimate them, the government does :-D To comply with at least CE, depending on where the product will be installed and especially fused, it falls in different so called over voltage categories. I’d suspect you’ll fall in the 2 kV L-N one, but don’t trust strangers on the internet. Does EN 60335-1 apply to your product?

@winny You're asking questions I don't know the answer to :) From what I read from the EN 60335-A summary, yes, it seems to apply to this project (in case it was not obvious, this is just a private project for my pool, no intention whatsoever to share or sell it).

Pool? Depending on where in/by the pool, you may be in Class 4, requiring much higher than normal isolation and immune to multiple faults. Zapping yourself by the workbench is hopefully just a valuable lesson as your body retracts your hand from whatever you weren’t supposed to touch whereas people die in pools from electrocution.

@winny The PCB will be placed in a waterproof case in the shelter that houses the electrical board and the pump/pipes. From what I understand from the (French) norm I could get information on, the main constraint is protecting the 230V electrical devices with 30mA differential circuit breaker. But again, I am not a professional, I do not have access to norm full documents :(

@Silverspur, Your project clearly falls into overvoltage category II. Standard EN 61010-1 stipulates in this case that the insulation distance and creepage distance between L and N must be at least 1.5 mm (on a PCB with pollution degree 2). Depending on the altitude of your project, a multiplication factor of up to x1.5 is applied. And if your product has reinforced insulation, you need to double the distances.

@Silverspur, In france, the protection by 30mA earth leakage circuit breaker is covered by the standard for electrical installations inside buildings (NF C 15-100), and has nothing to do with the design of the electronic device that connects to the building's electrical installation.

@TimWilliams I will add the capacity you suggested! However, I have a hard time finding information about how to choose the capacity value. Do you have any pointers?

Comparable to the snubbers' value would be fine. Probably 0.1 to 1uF.

@Silverspur. As such, 45degree tracks are ok, but if we look at the neutral track on the right hand side of the pcb, you’d usually make the tracks between the connector pin and main track at 90 degrees. Nothing to say you ‘must’ do this, but is more conventional. The ground fill is normally used when you have digital logic to form a ground plane. This isn’t the case with your circuit. Again, nothing to say you shouldn’t do it, but in your case it is not necessarily advantageous, especially with clearance issues. Optos are really only useful if you have separate, isolated supplies.

ESP32 connected to external low voltage things or fully isolated? K1's footprint isn't giving you much isolation and the choice of routing for 230VL, DDFR1 V0+, and the ground place are making it worse

@silverspur, is not the 45 degree angles so much as the 45 degree branches like on 230VN, such acute angles can be problematic to manufacture.

@Jasen In addition, for some reason, K1's COM1 is connected to COM2 within the relay. I feel like distances between COM1 and C1/C2 are really small to guaranty correct insulation. I'll think of choosing another relay.