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I've read a lot of things about shielding in twisted pairs cables and I feel like it's a controversial topic. I want to know the correct method to connect two devices using a F/UTP cable.

Assume a PC and a Switch, both with shielded RJ45 housing and both connected to AC power grid with 3 wires (line, neutral and ground). Keep assuming, for semplicity, that a long F/UTP cable is the only thing between these two devices (no patch panel, wall jacks, patch cords). This cable has foil and drain wire making contact with the metal shield on the RJ45 plug:

  • are PC and Switch properly connected with a shielded link betweend each other, effectively reducing EMI interference?
  • is a connection like this secure?
  • should had I connect the drain wire not to the metallic shield of the RJ45 plug but to the ground wire of my power grid (the yellow/green wire) even if the two devices are themself grounded?

Hope someone can iron out my doubts about shielding TPs cables. Thank you

Cristian La Spina
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2 Answers2

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I want to know the correct method to connect two devices using a F/UTP cable.

You simply plug the connectors on either end of the patch cable into the corresponding sockets of the switch and NIC on the PC.

It is as simple as that.

Grounding the drain wire is something that is done when you set up structured cabling, with patch panels, keystone jacks and such. Not when you make an indoors point-to-point connection with a patch cable.

Bob
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Those are very good questions - especially the use of screened cables is often dubious.

are PC and Switch properly connected with a shielded link betweend each other, effectively reducing EMI interference?

Yes and no.

Yes if the grounding on both sides is properly (=professionally) done and there is very little to no compensating current. No if there's a problem with grounding - in that case it's better to use unshielded cabling as badly grounded shielding increases noise. Note that Ethernet over twisted pair is generally free of potential and there no real need for electrical grounding. (Your local regulations might say otherwise, so do check them.)

is a connection like this secure?

Safe to handle? Yes, unless there's something really wrong with the electrical installation.

should had I connect the drain wire not to the metallic shield of the RJ45 plug but to the ground wire of my power grid (the yellow/green wire) even if the two devices are themself grounded?

The yellow/green wire is the protective conductor, not general ground. Of course, it's all wired together at the equalization point, but due to cable resistance and capacitance there may be residue voltage and noise. If you use it for grounding and introduce larger equalization currents you may quickly trip your RCD/GFCI.

The rule of thumb: only use shielded cables if you know your electrical installation provides good grounding. In any other case use unshielded cables.

Zac67
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