I have design a power distribution PCB with high AC(230V) and low DC(<10V) voltage power rails. Both are going to be connected to my board by separate cables. Each of those cables have shielding wire, i.e. a high voltage cable have four wires, three for phases wires (connected in delta configuration so there is no neutral wire) and shield (I am sure I'm not confusing shielding with PE if someone could ask). Similar situation with low voltages, few hot and ground and single shield wire.

Should I keep shielding for high and low voltage on separate layers or can it be connected to the same PCB layer?

  • \$\begingroup\$ Is this a power supply? What is the purpose of the board? \$\endgroup\$ – crocboy Jun 8 '15 at 16:09
  • \$\begingroup\$ Yes, it is a power supply. Basically, board will serve as a power rail. It will have one input and few outputs. It will be possible to connect several boards in a chain to extend number of connected outputs. \$\endgroup\$ – user2320394 Jun 8 '15 at 16:46
  • \$\begingroup\$ See my answer below. \$\endgroup\$ – crocboy Jun 8 '15 at 16:56

Typically you want to completely isolate the AC voltage from the rest of the circuit. This is a safety issue, and it's done to make sure no harmful AC voltage leaks into the DC circuits. Most people would even recommend isolating the neutral line because there could be harmful current on that wire as well. This is usually done with a transformer. The delta-connected AC will go into a transformer. The output of the transformer goes into the rest of the supply circuit or whatever it is. You said this was a power supply, so this will most likely be a step-down transformer.

The DC lines should be isolated as well, depending on the use-case. If you are running DC power to many different devices, or chaining supplies together (which you mentioned), you will want to isolate the DC outputs to avoid ground current loops. Chaining boards together introduces the possibility of different ground references. When two ground levels have different voltages, a current will flow. This can cause noise in your DC circuits. Over short distances, this effect is minimized. You need to decide if you need to isolate DC outputs. Usually this is done using a transformer with multiple taps, which gives you multiple isolated AC outputs, which are fed into separate power supply circuits. If you don't care about noise or ground currents, you don't need to isolate the DC outputs.

To answer your original question, I would not connect the shields together. Typically with power supply circuits you want to completely isolate AC power sources for safety reasons, and isolate DC power sources for noise reasons.

  • \$\begingroup\$ No problem, hope it helps :) \$\endgroup\$ – crocboy Jun 8 '15 at 17:16

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