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#23938 - 03/31/03 09:52 AM Raised Floor
electrician02125 Offline
Member
Registered: 02/01/01
Posts: 89
Hi all

A couple of questions for the data center guys:

How is the raised floor grounded? Do you bond every leg or do you rely on the floor tiles to maintain this bond?

How are your PDU's grounded?
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#23939 - 03/31/03 12:33 PM Re: Raised Floor
HotLine1 Offline


Member
Registered: 04/03/02
Posts: 6778
Loc: Brick, NJ USA
All the jobs that I have been on have had every other leg bonded, in a checkerboard fashion.
Cabinets are bonded to the grid.
John
_________________________
John
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#23940 - 03/31/03 12:47 PM Re: Raised Floor
DBC1 Offline
Member
Registered: 03/15/03
Posts: 16
Loc: Tulsa, OK USA
I design data center's power and grounding and the answers depends if you are just looking for a code compliant method or a code compliant design method.

If it is just a code compliant method you are looking for all you have to do is ground the structure with a piece of 6 AWG to the nearest building steel or sub-panel. That is not much to go on but that is all you will get from the codebook. The PDU's are treated like any other SDS to nearest building steel and water pipes.

If you are looking for a design that gets more complicated. IEEE Emerald book gives very good details on how to construct a signal reference grid (SRG) out of the raised floor, and proper PDU terminations.

Basically I run a 2/0 bare, stranded copper conductor around the perimeter of the raised to form a closed loop. Then I construct a grid of # 4 AWG, bare stranded copper conductors on 2-foot centers inside the perimeter cable. I “H” tap the grid conductors to the perimeter cable, and at each intersection of the grid I use a pipe stand clamp to bond the grid conductor to each other and to the pipe stanchions that support the raised floor grid. Then on the perimeter cable around the room, I “H” tap a # 6 AWG to the perimeter cable and bond it to the stringers of the raised floor at every pedestal using a two-hole compression lug bolted to the stringers. That completes the construction of the grid.

After the grid is constructed I bond it everyplace where is passes by building steel, water pipes, conduits, etc. I then bond the perimeter cable to any and all sub-panels ground buses in the room. In addition I run a 2/0 AWG insulated conductor from the two opposite corners of the perimeter cable back too the service entrance GEC.

For the PDU’s I bond to the nearest building steel under the raised floor. Then as equipment racks are installed they have a #6 AWG bonded from the equipment frame with a 2-hole compression lug back to the SRG with either a “H” or “C” tap. Keep in mind this not to replace any EGC’ required to be ran with phase conductors from the PDU. It is a signal reference ground, not a fault clearing ground. However it will aid in clearing a fault.

There are several methods you can use. As already mentioned you can purchase the IEEE Emerald book or download FIP’s-94 document and/or Grounding Sensitive Equipment by ITIC at http://www.mikeholt.com/freestuff.php?id=freegeneral. But they all follow the same basic guidelines. Good luck. Dereck
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#23941 - 03/31/03 12:50 PM Re: Raised Floor
electrician02125 Offline
Member
Registered: 02/01/01
Posts: 89
Nice job guys

Thanks a million
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