I have a question related to shielding and grounding of ethernet cabling in industrial environments, offices and datacentres.
What I assumed as correct so far (please correct me if I’m wrong):
- In Consumer PCs the ethernet shield is connected to the case via the IO-Shield. The case is grounded over the PE-conductor in the PSU.
- On a commercial server it is the same (only had one to check).
- The ethernet standard specifies signal transformers at each interface to achieve a galvanic isolation between endpoints.
- For a cable shield to be effective (at high frequencies) and not act as an antenna, it should be grounded at least at both ends. For very long cables more ground connections may be necessary. To break ground loops this connection may be capacitive at one end.
- The galvanic isolation on the signal line is, I presume, there to protect the sensitive electronics from a potential voltage difference between the two endpoints. But if you use shielded ethernet cables, then you will create a low impedance connection between the two endpoints and a current will flow through the shield.
Now to my question: Industrial interfaces like EtherCat have a capacitive coupling of the shield to the case. And I assume in datacentres and the likes the grounding system is tightly controlled so no potential differences can arise. But how is this handled in office buildings? Is it just assumed that the grounding system is good enough so that there are no, or only very small, balancing currents on the shield between the two endpoints? Or are these currents just no problem in these practical applications?