Grounding of equipment in computer room

[cppoly]

For the grounding of metal enclosures of equipment in a computer room, does this fall under effective ground fault path?

The metal casings of computer equipment, racks, and cabinets are going to a grounding bar on a plywood wall in the room. This grounding bar has a grounding conductor going directly to building steel. What is the purpose of this grounding?

What section of grounding does this fall under? Is this supplemental or auxiliary grounding.

 

[GoldDigger]

There still needs to be a wire or raceway EGC going back to the point where the ground to neutral bond is made. I do not think that building steel is allowed to serve as that conductor.
But it could be added as a supplemental path to satisfy the superstition that it will reduce noise on data interconnections among racks.

Tapatalk!

 

[__dan]

645.15 requires grounding, which as I read it is the effective fault current clearing path *and* the connection to earth by a grounding electrode.

The steel frame, imo, is a bonding conductor but not a grounding conductor. You would want to be bonded to the local steel, but also grounded to the power source equipment ground and connected to the grounding electrode. So you could have three or four conductors from a separate remote grounding busbar, jumper to the steel, jumper to the floor grid, jumper to the power panel EGC busbar, and jumper tap to the GEC.

A single grounding jumper would have to extend and connect to the common grounding busbar of the source SDS where the system bonding jumper, GEC, and EGC are all present at the same point (imo).

 

[cppoly]

Is the purpose of connecting computer equipment metal frames to building steel only to limit surges from lightning or other over voltage?

 

[__dan]

Is the purpose of connecting computer equipment metal frames to building steel only to limit surges from lightning or other over voltage?

Lightning is a factor for the building steel exposed to the outside or for incoming utilities. If there is a nearby strike, what paths are available.

Inside the building, the factors would be fault current over the grounding paths, stray current, and voltage potential differences. That's generally why I see a need for two dedicated grounding type paths and also why I see the code requiring it. Fault clearing events will impose noise on the grounding paths, which can be mitigated by also referencing to earth with another dedicated conductor.

If you are at the origin of the SDS on the busbar at the same point as the GEC and SBJ, that is the zero or earth reference point, including times when the EGC is clearing a fault.

 

[ron]

For the grounding of metal enclosures of equipment in a computer room, does this fall under effective ground fault path?

The metal casings of computer equipment, racks, and cabinets are going to a grounding bar on a plywood wall in the room. This grounding bar has a grounding conductor going directly to building steel. What is the purpose of this grounding?

What section of grounding does this fall under? Is this supplemental or auxiliary grounding.

The grounding you describe is not code required, since you are taking care of any metallic surface that is likely to become energized with the regular EGC in the raceway with the associated feeder / branch circuit. This is over and above and supplementary to the code required grounding / bonding.

This document will help describe some of the reasons (some outdated as the document is) for the additional bonding in a data center or automatic data processing environment.
http://www.mikeholt.com/documents/powerquality/fips94.pdf

This is more recent
http://www.ecmag.com/section/miscellaneous/grounding-bonding-data-center