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I am currently trying to derive the relevance of ethernet connections shielding and grounding. This is regarding the robustness of the design (in terms of communication) and eventual ESD considerations as well. I can find the following scenarios possible (assuming 2 devices connected with an ethernet cable).

  1. Both devices have unshielded ethernet jacks, the cable is unshielded,
  2. Both devices have unshielded ethernet jacks, the cable is shielded,
  3. Only 1 device has shielded jack, the cable is unshielded,
  4. Only 1 device has shielded jack, the cable shielded,
  5. Both devices have shielded jacks, the cable is unshielded,
  6. Both devices have shielded jacks, the cable is shielded.

My assumption is that for the cases where the cable is unshielded (1, 3, 5), the shielding of the connectors is irrelevant. My questions are then regarding the points (2, 4 and 6):

  • If none of the connectors are shielded, does the shielding on the cable provide any difference in terms of noise insulation or ESD?
  • If only one of the devices is shielded, I assume this is the best case, since we do not have any ground loops and insulation is good. But how does it correlates with ESD? Also, in case the shielded connector device is not connected to the PE pin of the AC connector (i.e. only L and N connection available)- is this insulation effective? We can see many networked devices with a 2 pin AC adapter and shielded connectors.
  • If both devices have shielded connectors (both connected to their local GND), what exact effects can it have for the whole system (incl. ground loops)? How should we look at it in terms of ESD?

I would appreciate all feedback to my questions.

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2 Answers 2

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  • Unshielded installation: US style (your case 5, most professional equipment will have shielded jacks) - office Network
  • Shielded installation: EU style (your case 6)

unshielded or not/one sided connected shield... you can disturb the Ethernet easyly with near pulses, e.g. a power line with bad installed machinery next to a unshielded Ethernet is a problem. Just 1-2cm without shield or pigtailed connected shield (not an 360° connected shield) is enough to disturb the bus.

not connected shield or only one side connected shield are minimal better than unshielded in some cases.

shield connected at both ends does not cause any problem if done right (capacitive coupled with at least one resistor in parallel to get rid of static charge)! Industrial Ethernet - at least the European ones always use shielded equipment. Profinet for example defines additional meshed Points: connect shield every ~50cm or so to a Earth connected metal surface.

for industrial use, we select 360° shielded connectors, you can disturb the bus if you do not shield 360°. Standard is Variants of the M12 Connectors, which are good at vibrations also (RJ45 is not!)

The Profinet Guide on shielding and grounding...

https://profibus.com/index.php?eID=dumpFile&t=f&f=63888&token=0f7b589224a95648a661b05a5ae08b71ff4652ea

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  • \$\begingroup\$ Thank you for answer. You point out that double ended shielding with RC filter is helpful, but in practice we can have a situation where the both ends are grounding the shield directly. In that case the both devices grounds potentials are connected together. How does this affect the whole system? \$\endgroup\$ Sep 23, 2020 at 11:34
  • \$\begingroup\$ Well grounding both shields directly I would call "doing it wrong", huge currents through the shield might be an result causing all kinds of problems. In such a case, unshielded might be even a better option. This is only OK if you do it like the Profinet documents states: if you connect very often, so you have a tight mesh of grounding points, so the impedance is so low, that no huge electromagnetic fields can build up. \$\endgroup\$
    – schnedan
    Sep 23, 2020 at 11:55
  • \$\begingroup\$ On a PCB, how should the ethernet jack shield be terminated in your opinion? \$\endgroup\$ Sep 23, 2020 at 12:29
  • \$\begingroup\$ terminated? you mean grounded? depends on the device... plastic home routers with just a DC power in and no connection to earthing? No, its almost useless. A professional 19" Rack switch with a metal case - Yes of course, Industrial equipment - Always, no discussion necessary \$\endgroup\$
    – schnedan
    Sep 23, 2020 at 12:35
  • \$\begingroup\$ Also if you ground a shield on your PCB, you should have a short, low impedance path away from your PCB also. Provide one and only one path! \$\endgroup\$
    – schnedan
    Sep 23, 2020 at 12:37
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IF your housing is plastic,shield connector is useless because ot is not 360 shield. And for the ESD it is better not connect the connector to system ground because it will into it IC ground directly, better to isolate with all circuit.

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  • \$\begingroup\$ You are answering a question that is over a year and a half old. This does not really answer the questions raised. Please be careful with spelling, grammar, and capitalization, this is very hard to read. \$\endgroup\$ May 3 at 21:16

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