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I have designed a pcb board (2 layer) that deals with high voltage 220VAC and it also converts it to 5VDC and 3.3VDC. So, because it is my first design and I deal with high voltage I want to be sure that the design its safe and I havent overlook something important. The board is meant to use the esp module to turn on and off two relays. Also, the board shape needs to be circular 50mm radius in order to fit where I want.

Here is the design: enter image description here

Top side:

enter image description here

Bottom side:

enter image description here

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    \$\begingroup\$ Without knowing what an ACS712LC is, and an HLK1, nobody can answer this question. \$\endgroup\$ – The Photon Dec 31 '18 at 18:42
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    \$\begingroup\$ Please add part names and numbers to the schematic. We don't have a crystal ball here... It would also help if you'd tell how the device is going to be installed as it can critically affect safety. \$\endgroup\$ – filo Dec 31 '18 at 18:48
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    \$\begingroup\$ Your incoming 220v traces are very close together... No way they meet CE or UL requirements as is. Also I assume you are heatsinking the TO220 packaged SSRs? \$\endgroup\$ – MadHatter Dec 31 '18 at 18:55
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    \$\begingroup\$ Are you trying to maintain isolation between mains and the low voltage power supply? If so the clearances look insufficient. 8mm is a good number. Think about situations like (re) programming the MCU where that clearance is between your computer (and you) and the mains. Also consider the cross-mains voltage clearances.The Darlingtons have a lot of drop and are not required for 16mA of "coil" current for the SSRs. Use an MMBT4401 or a 2N7002 instead. There may be other issues, those are just what jumps out at me. \$\endgroup\$ – Spehro Pefhany Dec 31 '18 at 18:56
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    \$\begingroup\$ This is using eagle? Did you run a layout check on it? Also I would set the high voltage lines as a separate group and keep at least 100mill between L and N for hobby usage, for commercial usage you need to meet local codes like CE. \$\endgroup\$ – MadHatter Dec 31 '18 at 18:59
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To start with, if this is something you're going to install permanently in your home, it probably needs to meet the local building code requirements. In the USA, this would generally mean the NEC, which in turn would imply UL listing. Your jurisdiction may be different in the details, but the gist will be equivalent — if you don't meet this requirement, your homeowner's insurance might deny a claim, and you could face criminal prosecution in the event of property damage and/or personal injury.

But ignoring that for the moment, the first key requirement is isolation: can you draw a line across your schematic with all of the mains-connected items on one side and all of the low-voltage items on the other, with only components with suitable isolation crossing that line? Can you draw a similar line on your PCB, with at least an 8mm physical gap between the conductors? If not, then the design cannot be considered "safe" by most measures. This is just the first step in making sure that the end user cannot contact lethal voltages.

A second requirement is to mitigate the effects of component failures, such as making sure that short circuits don't allow excessive currents to flow. You have some fuses, etc. in your design, so you largely have this covered. However, you also need to make sure that you are protected against the kinds of surges that can occur on mains-connected equipment, such as those induced by nearby lightning strikes. This is another reason that isolation is important — including among the different conductors on the mains side of the isolation barrier you drew above. Spark gaps, MOVs, and other components can help prevent such surges from propagating into more delicate areas of your circuitry.

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  • \$\begingroup\$ @user134: Dave is right. That 8 mm gap is "no-man's land" separating the high voltage and low voltage circuits. See the image I posted in this question which is for four simple opto-isolators. Your PCB needs to be just as good. \$\endgroup\$ – Transistor Dec 31 '18 at 21:33
  • \$\begingroup\$ I'm going to make a leap of faith and say with 220V NEC and UL does not apply but is similar to IEC and other codes. 3mm air gap might be similar to 8mm surface gap under some dust and RH conditions more or less. but not as good. The air gap is far better than exposed epoxy blank surface (no man's land" as it relies on conformal coating of pads and solder joints \$\endgroup\$ – Tony Stewart Sunnyskyguy EE75 Dec 31 '18 at 21:36
  • \$\begingroup\$ The other alternative is to treat the entire board and all outputs and inputs as live, and encapsulate it accordingly. For instance LED light bulbs does this for power supplies; everything is encapsulated, so separation and isolation is not an important feature. Space is. \$\endgroup\$ – vidarlo Dec 31 '18 at 22:21
  • \$\begingroup\$ @vidarlo: That's rather oversimplified -- you still need internal clearances for surges, etc. Besides which, with a connector labeled "TOUCH", I'm pretty sure that this is a non-starter in this particular situation. \$\endgroup\$ – Dave Tweed Dec 31 '18 at 22:30
  • \$\begingroup\$ Sure, it's not universal, and probably not applicable in this case. But in some cases it may be viable to design for failure, and allow for it. \$\endgroup\$ – vidarlo Dec 31 '18 at 22:31
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If you put a slotted air gap >= 2 mm between any AC line voltage and DC, it may meet some criteria for lightning 3kV dielectric insulation. But as it is , this design fails many DFM criteria and insulation breakdown tests. (Design for Mfg) There must be no sharp points between conductors of AC and DC at the nearest gap.

So back to the drawing board or go research design more before you try this.

The only way this could pass is if the assy were dried in an oven and conformally coated properly around all AC to increase the BDV from 500 V/mm to 5kV/mm after moving pads away.

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