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Our server room has four cabinets (not fully utilized) and is supplied by several electric circuits from two different electrical services. Some of the equipment is 208V from a 3-phase service and some is 120V from a "regular" 2-phase service. (I don't know how or why the building ended up with multiple services.)

Right now none of the equipment is grounded other than whatever grounding is done by the wiring. E.g we don't have a ground bus bar, the racks aren't grounded (except maybe through the servers, if their chassis are tied to ground internally).

I assume since the cabinets are supplied by different services that there is the possibility of a ground difference, but I don't know whether that's an issue or how I would determine it. Getting all of the equipment onto a single electrical service is probably not reasonable considering the distance from the service panels.

  • Should we try to tie all of the equipment together with grounding wires connected to a bus bar in the server room? If so, which service ground (or both?) should we tie it to?
  • Should we try to isolate the different electrical services in separate racks and then only connect them via non-conducting fiber (this is probably not feasible given the amount of connectivity and our budget, but we could look into it).
  • Should we just leave well enough alone, since we're not noticing any issues?
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5 Answers 5

In theory, there should be a ground to earth that all electrical stuff is tied to, but get an electrician to help. I am nothing near an expert, but that is my understanding, poke around enough, and someplace they should be earthed (often to a water pipe in a house, for instance), and that would give you a common one. You would hope it was done right. ;-)

Again, if you are worried, get a good electrician to go over it.

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creating a common ground by bridging to the water pipe sounds ... interesting. At least where I live the water pipes (as well as telco cabling screens) need to be connected to a common ground for security reasons, but the ground itself is provided through an earth electrode. –  the-wabbit Nov 22 '13 at 9:58

As you are surely aware, any electrical potential difference in a conductor will induce a current. This is also valid for potential differences on the ground line. The "ground currents" are rumored to bring all kinds of havoc - corrosion of grounded pipes and even the steel armor of the building's concrete, signal interference and bad Feng Shui.

Yet, any of these only would really be a problem if the currents reach significant levels. There are exceptions to this - for example in cases where you are using analogue imbalanced transmissions (analogue audio or CCTV over coax lines) so even small currents might cause signal interference through ground loops. Or the Feng Shui, which of course is disturbed by any level of current but likely would not be of any relevance to switches and servers.

Note that even if you have a significant potential difference between the ground wires provided by the different services (which is not all that likely as a utility ground should be connected to a building's earth electrode in most cases), the only place where the ground current may be flowing in a proper installation would be the shield of your data cabling - the Ethernet PHYs isolate the transmission wire pairs from the ground. If you do not use shielded cable runs, you should not have current flows through your cable plant at all. If you have a shielded plant, the balanced nature of Ethernet transmissions and the low frequency of the current will make sure that the resulting interference would not impact your transmissions.

Should we try to tie all of the equipment together with grounding wires connected to a bus bar in the server room?

Yes, for electrical safety you should.

If so, which service ground (or both?) should we tie it to?

The one you are drawing power from (as I noted, it should not make much of a difference anyway)

Should we try to isolate the different electrical services in separate racks and then only connect them via non-conducting fiber

No, unless you are having specific interference issues due to EM radiation along your cable runs

Should we just leave well enough alone, since we're not noticing any issues?

If you are worried about the quality of the electrical installation, have an electrician check it - he also will be able to tell you if the different utility grounds are connected to a common building ground and have the equipment to measure ground currents.

Disclaimer: I am not living in the U.S., so your mileage concerning the electrical installation and standards might vary. Common sense should not.

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  1. Your building has multiple services to provide redundancy. It's likely that that "service" goes back and splits into two or more feeds at the PDU/UPS/Generator (this is especially true if it's a colocation facility).

  2. You won't need a ground wire for each service. Again, if this is a colocation facility the racks should already be grounded, you don't need to ground every device in your all of your racks separately. That being said, if this is not a colocation facility, consult an electrician if you're not sure (as Ronald said) - they're licensed for a reason.

Now to answer the questions you asked more directly:

  1. If it's a colocation facility, it's already grounded (or should be) - you can create a support ticket with the facility to verify. If it's not a colocation facility, you'll only need a single ground wire large enough to handle the worst case scenario, again, consult (hire) an electrician.

  2. Not necessary.

  3. This is completely up to you, if it's within your budget to ground the racks (assuming they're not already), then you might as well. However for what it's worth, it's probably safe to leave it - however I'm not an electrician, nor would I go around recommending it.

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The building is a small commercial office building, not a datacenter. By "service" I mean a metered electric utility connection. We have 2 sets of wires coming into the building from the grid –  Henry Jackson Nov 21 '13 at 0:44

If your servers (or, preferably, UPSes) have multiple redundant power inputs, you should bring power from both circuits to each of them; this would provide redundancy if one of the utility services goes down.

That said, yes, everything should be grounded, but grounding should be common. The ground is usually tied to the building, not to the services themselves; so your two grounds are probably already one, even if they don't look to be.

Anyway, have a professional electrician check your setup; it's the right thing to do. Everyone has his/her job... an electrician would (hopefully) call a professional sysadmin to check a server problem ;)

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Please note that ground must be local to your building, or you are in risk that if you lose a wire conenction to "somewhere" you get ungrounded and, thus, unsafe. Think on a storm that first cuts the wire you use for grounding and then strikes the building with a ray. Bad news...

Always ground locally.

So:

Should we try to tie all of the equipment together with grounding wires connected to a bus bar in the server room?

Definitely yes

If so, which service ground (or both?) should we tie it to?

None. Ground locally, to a well connected pike to the earth under the building.

Should we try to isolate the different electrical services in separate racks and then only connect them via non-conducting fiber (this is probably not feasible given the amount of connectivity and our budget, but we could look into it).

No. If you want to properly service a rack with multi-power-supply servers, you must feed it from both services, to avoid that if one service fails the server falls. No isolation among services possible. What you need is a good set of current filters on the input point to the building from each provider.

Should we just leave well enough alone, since we're not noticing any issues?

No. It is a human safety issue (as well as a machines safety one).

Regards

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I've found about the US regulations in the Wikipedia that you are using TN-C-S and that apparently an obligation to connect neutral/ground to local earth at the entry point of the building exists as well. So if the electrical wiring has been performed according to the NEC's regulations, there would typically be no need for a separate ground (except where you have especially picky requirements regarding EM radiation so you would need nearly potential-free earth and a low-resistance connection to it). –  the-wabbit Nov 22 '13 at 18:03

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