1

Why separately ground the device case?

I had some work to do to install network devices in a rack. And in the course of work, I had a question. I had a Cisco switch in my hands, on the front panel of which there is a separate output for connecting to ground.

enter image description here

Judging by the description, I have to connect it to the rack itself in which it is installed. Why is this being done? Power is connected to the switch itself, which already has a ground line (C13 connector). And all devices in the rack, in theory, should already be grounded, since all are connected to a powerline that already has grounding

P.S. It is also worth noting that not all devices have such a pin, for example, on a router (cisco) I did not find such a separate ground pin

Improve this question
2
  • 1
    I’m voting to close this question because theoretical questions about consumer electronics aren't home improvement.
    – isherwood
    Commented Nov 22, 2022 at 16:14
  • @isherwood I apologize if I got into the wrong SO forum, if it is necessary to improve the site, you can transfer it to another forum
    – RoyalGoose
    Commented Nov 22, 2022 at 20:49

2 Answers 2

Reset to default
3

I can only guess this is for similar reasons to the audio industry. By strapping all your equipment together, linked to a single earth you provide a single ground plane - all equipment shielding & return paths are at the same level.

This is more important for signal grounding than actual mains safety earthing.

From comments: though domestic ethernet is rarely shielded, grounded & earth-strapped, industrial ethernet is predominantly done this way.

From Cisco's instruction/installation page

Note Ethernet cables must be shielded and grounded at both ends when they are used in a central office environment.

Improve this answer
3
  • Ethernet, being isolated at both ends, doesn't care a whole lot about signal grounding, but it can't hurt.
    – Criticizing Israel not allowed
    Commented Nov 22, 2022 at 10:28
  • @user253751 - you're only considering domestic application. Industrial predominantly uses shielded cable. See controldesign.com/connections/connectors/article/11297404/… and electronics.stackexchange.com/questions/522850/… for examples. Even without shielding, having a flat signal ground as well as mains earth is just more stable & safer. Simple twisted pair, the same as balanced audio, still has a base potential. Also advised by Cisco themselves, link to their install page added to answer.
    – Tetsujin
    Commented Nov 22, 2022 at 10:45
  • This particular equipment has dedicated bonding connections for safety reasons.
    – KMJ
    Commented Nov 22, 2022 at 22:14
5

That specific pictured switch is an ME 3400. This is in Cisco's 'Metro Ethernet' series, intended for installation in central offices. When installed in a central office these devices are subject to the specific grounding and bonding requirements laid out in ANSI/NICA/BICSI 607 and other similar and related standards. Going through the full detail of these standards is way too much for here. This particular switch can also use DC power supplies which do not have a provision for grounding. When installed using two of those power supplies, bonding via the chassis is absolutely required.

Improve this answer

Not the answer you're looking for? Browse other questions tagged or ask your own question.