I have one question. I'm designing a PCB which is a sort of smart switch (so, basically, you have one 230V input and one 230V output, where the output and the input share two wires, N and PE, and the circuit acts on the L. So basically something like this:


simulate this circuit – Schematic created using CircuitLab

Now, the PE connection is not "functional" (the case is plastic, so no earth-connected-case is needed); it's just a connection between the input and output.

Now, my question. In my mind the connector layout should be L-PE-N. On a lot of appliances (for instance the SMPS in metal cage have L-N-PE-low voltage outputs).

Metal cage SMPS

I think the metal cage SMPS have PE between the two to act as a protection, and so I came to think that every layout is fine (provided that the required clearances are respected - BTW I'm using at least 4mm of clearance in the 230V area).

Am I right (so I can use the most functional layout) or you recommend some layouts?


I would use L-N-PE to keep PE out of the way of the power connections for the smart switch's electronics

A "smart" switch will have not only a switching mechanism, but various electronic doodads that control that switching system (otherwise, all you have is a dumb lightswitch, which you can buy at any hardware/home-improvement type store). Of course, these electronics need a supply of power, and this means that they need to be connected not only to the incoming mains live, but to neutral as well to provide a proper and safe return path for the current they draw. As a result, keeping PE out of the way (it may not even need to touch the board!) of the rest of the electronics will make the layout of your board simpler and easier.

  • \$\begingroup\$ Exactly what I was planning to do; that's what I mean with "most functional". Thank you for your answer :) \$\endgroup\$ – frarugi87 Jan 19 at 16:03

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