How would you connect the cable shielding, metal enclosures and power ground on following system: enter image description here

Since I had problems with noise before I wanted to add filtering on power input for "my PCB" (Common mode choke on the schematic) and block noise both incoming and outgoing.

So my main questions would be:

  1. How to connect cable shield to chassis, both ends or only one end. If one end then which one?
  2. How should one ground the PCB to the chassis, before or after the choke?
  3. Should maybe a capacitor used instead to connect PCB to chassis to avoid ground loop with the load in the same chassis?

The system should be robust against external ESD events and indirect lightning surges also.

  • \$\begingroup\$ Do not b confused with name "ground". Power ground is a Protective Earth. Power supply ground very often just common. \$\endgroup\$
    – user263983
    Dec 29, 2021 at 15:19
  • 1
    \$\begingroup\$ Noise is one thing but, what's the bigger picture in terms of ESD and indirect lightning surges that you have to withstand. In other words define ALL the threats or you might make the wrong decision. \$\endgroup\$
    – Andy aka
    Dec 29, 2021 at 17:31
  • \$\begingroup\$ Indeed indirect lightning and ESD would also be a concern here. Although it is not a permanent fixture and probably wont be deployed with stormy weather. \$\endgroup\$
    – tarmogr
    Dec 29, 2021 at 20:46
  • \$\begingroup\$ What's the purpose of the common mode choke in this application? Wouldn't it be better to put it before the isolated DC-DC converter? \$\endgroup\$
    – SteveSh
    Dec 29, 2021 at 21:05

1 Answer 1

  1. The cable shield should be grounded on both ends, to both chassis with a good low impedance connection (no pigtail).

  2. You can connect the load to chassis as you have shown. Indeed that is the default grounding arrangement for many RF systems.

  3. If you do #1, then it makes little sense to put the CM choke where you have it now. Any CM noise on the power supply & return lines are not going to escape with the shield terminated as I suggested.

  4. Most systems I've worked on has the CM choke between the battery and the DC-DC converter. But those system have other things connected to the battery.

  5. I know you didn't ask about this, but could you move the DC-DC converter to Device 2?

  • \$\begingroup\$ Oh im sorry but i did make a mistake on my original schematic, I have fixed it. The CMC is essentiallt between battery and my load (which also has a non isolated DC converter inside). looking at the schematic now would those points still be valid? \$\endgroup\$
    – tarmogr
    Dec 30, 2021 at 9:16

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