IT&electronics room grounding

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electrics

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What about the grounding in these rooms?
Need to make a separate electrode system?
or just a separate earthing bus apart from the remaining earthing system?
 
You are bound by Article 250. Inevitably, all grounding systems within the building need to interconnect, just like any type of building.
This is primarily a design issue.
The NEC will require you to bond metal parts that may become energized as a minimum.
 
electrics said:
What about the grounding in these rooms?
Need to make a separate electrode system?
or just a separate earthing bus apart from the remaining earthing system?
Click to expand...

What's wrong with Article 645, which pushes back to 250, if there's other equipment other than "IT" in this room, try the Index and carefully look over grounding.

Article 645.15 Grounding. should also be of interest here.

Or take s look at NFPA 75-2003 as listed in Article 645

I've (it's been awhile) used a copper bus that was either sent to the main panel in IT room, and / or bonded the raised floor which was sent to that same panel or to the panel that serves that room.

In layman's terms of all places this is the one where you don't want any stray potential energy floating around. Or even potentially create a potential difference. So in answer to your last question is, No.
 
what I am asking is whether do we need to have any separate earthing terminal installed in main panel (and it is bonded with main earthing terminal )and all the protective grounding conductor coming from all the devices will avoid the rest of earthing system and directly will be connected to this "separate " earthing terminal??
can u give me a typical scheme representing this type of earth...
 
Why would you want to have the equipment connected to a seperate earthing system? There may be need of additional rods somewhere if the ground resistance test is not satisfactory but I doubt that will be the case. In this type of application we normally have copper bussing on the wall connected to the ground on the panel at some point (in larger facilities the bus runs in several rooms may be interconnected and go back to the bus runs in a room that does have a panel for interconnection). If there is electrostatic discharge tiles, they usually have a copper strap laying in the floor and then running up the wall for about 6-12" then connected to panel or copper grounding bus, but obviously follow the mfg. recommendations. Google ground bus details they're all over the place.
 
İn short I wanna learn the criteria when we speak for IT rooms, What do we need to take into consideration ? As far as I guess the point is that it is not allowed to bond all the equipment grounding conductors to the same potential earth conductor but it is forced to make them all connected to a IT room grounding busbar so that there will be no ground loop...is it true? please tell me the gist not so much detail ...
 
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electrics:

First, I assume you do what the code requires.

Then the question is --- what problem do you want to solve?

If you need to keep radio frequency interference out, then you need a screen room as a minimum.

Are you worried about interconnecting different pieces of equipment that reference a signal to the chassis and that chassis in turn is required to be connected to the EGC? Solution here is to use an isolated type of interface if possible. In general Ethernet is isolated by transformers in the data path. Straingage elements should be isolated from ground. The measuring elements in LVDTs are usually isolated from ground. Sometimes thermocouples are grounded at the measurement point. This might mean the need for an isolation amplifier. Current loop stuff is usually isolated at one end of the path.

Computer stuff, if no isolation is used, needs to have all the associated equipment plugged into the same outlet strip. We make optical isolation devices for use in RS232 communication over long distances between computers and CNC machines. This isolation of the conductive path between the two ends of the communication path solves the ground noise problem that in some cases is not solvable by direct connection.

Do these comments stimulate any specific questions?

.
 
Well in my experience the clients have usually tried to ground to the same system and use input filters for both power and communications to certain rooms for noise, but i guess I see what you're getting at - You could also use 647 for sensitive electronic equipment which is a pretty broad definition. Also note that article 647 only covers systems operating at 120V line-to-line and 60V to ground. Per 647.6 you need a seperately derived system and yes this could mean additional rods depending on how you achieve this based on art. 250. Based on 647.6(b) you need a 'Technical Equipment Ground' bus marked so in the source panelboard - this bus needs to be connected to the ground conductor on the line side of disconnect means of the SEPERATE ground system. I recommend you definitly review article 250 to get a good grip on seperately derived systems.
 
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