I need guidance for passing the IEC 61000-4-5, 2 kV Surge test from the AC ground (protective earth, PE) to the neutral and live wires. This grounding techniques may be a bit different that passing FCC or CE emission tests and a bit more complicated.

How does DC board grounding be done in a multiple boards design interconnected (e.g. USB) installed in a metal enclosure feeding off an AC power supply? This is a bit more complex than a single board connection to Chassis ground.

Should the AC ground and DC power supply grounds be tied to the metal enclosure at one point by the power supply module and all the other board DC grounds be isolated from the metal enclosure or the boards DC grounds should also be solidly i.e. low inductance be connected to the metal enclosure?

What about the board interconnect cable shields (e.g. USB)? Should these be connected to each board DC ground or connected to the chassis ground and totaly isolated from each board DC grounds?

It is assumed that digital ground and DC ground are the same on all boards and there are no analog circuitry involved.

  • 1
    \$\begingroup\$ Welcome to EE.SE! Please provide a schematic and/or block diagram and explain what DC board is in your circuit. \$\endgroup\$
    – winny
    Sep 17, 2020 at 16:23
  • \$\begingroup\$ Schematic please (simple if necessary but, the devil is in the detail with indirect lightning). \$\endgroup\$
    – Andy aka
    Sep 17, 2020 at 17:49

1 Answer 1


connect PE with the metal case is OK, if not a must (would need to lookup the standards...)

Connect the DC GND to PE - can be done. Like here https://en.wikipedia.org/wiki/Extra-low_voltage#/media/File:Extra_low_voltages_(third_safety_class).JPG But you should add capacitors in parallel with varistors (or other suited surge protectors) from DC+ and from DC-GND to PE. If you connect directly huge currents can be an problem

Shields are also only connected with PE (via resistor in parallel with a capacitor at both ends, or with a capacitor only at one only) - you do not want DC current flowing in the shield, the resistor is only to provide a path, so it is not floating.

And AC neutral line is no GND and normally uses can plug in the plugs to sockets reversed, so suddenly Net's L1 suddenly is your neutral and you won't that connected with your DC-GND


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