I have heard that all 10G switches must be grounded. We have two Cisco Nexus 5000 running for years without any grounding, but I am worried about possible outages caused by ESD. Nexus 5000 has system ground connector (http://www.cisco.com/en/US/docs/switches/datacenter/nexus5000/hw/installation/guide/install5500.html#wp1257696).
What is your experience with it? Is it really something I should worry about or is it something which is good to have, but can live without it?
If you ask any responsible electrician all devices must be grounded so that if there is short-circuit they don't become dangerous.
In practice I very very rarely see devices grounded, only incumbents with long history of spending lot of money and manpower have the professionalism to do this.
For legal reasons, I cannot recommend not grounding them, but I would expect exactly 0 problems, and you certainly wouldn't be alone running your boxes without ground.
If you are running AC PSU and you have Schuko plugs the system probably is already grounded.
I pretty much agree with ytti about this, but in some more detail.
First, none of this makes an iota of difference if the kit is operating on voice, a single DS0 or terabits, you ground for other reasons. If you have such a high EMI that grounding might help with errors the actual problem is with whatever is spewing the crap, and likely as not wiring the device to a giant antenna of a ground wire (never loop) will only make things worse.
If you have a DC powered device you REALLY SHOULD ground separately. There are valid safety reasons for this and the cost of doing to handle the safety level is trivial (wire to the rack, rack to a building ground wire which should already exist). DC systems are almost never "grounded" on one or other of the supply lines, and most DC hardware does not connect the case to ground so this is critical. The screws and friction holding the device to a rack is not acceptable, you need a separate wire.
Next, for AC devices.
Those that are optionally DC, or dual supply may or may not have the case grounded to AC ground, so should be grounded for the same safety reason.
Now that (personnel) safety is out of the picture the answer shifts.
If the device directly takes a copper / coax from outside the room I'd strongly suggest grounding to help prevent any surge / lightning damage continuing down a path (also an argument for demark racks containing isolation & protection devices).
So if none of those apply you certainly don't need to ground and will be unlikely to get a benefit from doing so; although you may reduce occurrences of some oddball problems, I usually see a few cases a year where bad grounding may well have contributed to a problem, usually these are cases that take weeks to diagnose and repair, and even if the hardware is replaced under support the time lost may make it worthwhile to do.
All of the above, plus having a safer "standard practice" is largely why most telco's will have pretty stringent grounding policies (at least at their own facilities).
I have to disagree with much of the above. I've dealt with literally hundreds of flaky line cards and bad power supplies at a time whose basic issue came back to incorrect installation where it was (incorrectly) assumed that a correctly grounded power cable was all that was required.
The lug on the chassis exists for a reason and its non-use can- and sometimes will- result in problems with Smartnet entitlement. Do folks get away without it? Sure. If there's a problem it's likely to manifest as a flaky stability issue at an indeterminate point in the future. The lugs are cheap. There's no reason to skip this.
If you're in a colo/DC environment then the equipment cabinets/racks should have been tied together already to provide shared grounding (..in addition to being bolted together metal-to-metal). Consider why this would be if basically all modern equipment has three- or four- wire power?
