Grounding and bonding

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PowerdT

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San Diego
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Electrical Engineer
Hi,

I have computer cabinets/service racks that needs to be grounded. My question here is can I pull a ground from sub panel and connect the ground wire to the ground bus bar then from the ground bus bar connect #6AWG to the cabinet?
 
Sure, or you can mount some equipment in them that also has a grounding conductor and let that do the work. (There are a fair number of threads on this forum about the subject.)

There's nothing magical about grounding/bonding equipment racks, lots of people require it but for little to no reason.
 
zbang said:
Sure, or you can mount some equipment in them that also has a grounding conductor and let that do the work. (There are a fair number of threads on this forum about the subject.)

There's nothing magical about grounding/bonding equipment racks, lots of people require it but for little to no reason.
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Thank you. When you say mount some equipment, are you referring rack ground busbar? Also, there is 4’’ conduit with fibers, can I use the same conduit for the ground conductor or does the ground conductor needs to be in separate EMT?
 
Dennis has it- If there equipment in the rack is grounded, then the rack is grounded. But also if there's a conduit attached to the rack (is it?) and that's bolted to building steel, then that also grounds the rack.
If you want to run separate ground wire to the rack, Sure, go ahead. In many places it can be a single wire, some locations it'll need to be in some sort of protection (conduit, flex conduit, etc). All of that is driven by Article 250 and the location.

All that aside, some datacom people insist that you need large ground wires to a large ground bus, and that tied to a triad of ground rods (and sometimes those need to be driven during a new moon by a left-handed electrician). None of that is NEC, and in many cases, none of is is necessary.
 
How do these computer racks distribute power to each individual computer? Usually, there is a PDU in the rack that does this. If that PDU has a ground lug, connect that to the rack structure (or rack ground lug if it has one). This will ground the rack via its incoming power circuit. If no ground lug on the PDU, I use special bonding screws to mount the PDU to the rack rails. They are made by Panduit, and have teeth under their head to bite into the mounting rail. They also have a cage nut version with teeth on the nut.

Note that many rack mounted items have painted ears and sometime the rack rails are painted. Bacause of that, you can't rely on mounted items to ground the rack unless you scrape paint. Many rack screw have nylon washers to keep from marring the ear surface which also keeps it from grounding things.

If the rack has a ground bar, these are usually isolated from the rack structure which would then require a separate wire back to a single point or mesh "room ground". The idea is to keep that bar away from the "noisy" equipment ground of the source circuit with all the computers possibly putting noise on the ground. It seems the network, telecom, and crypto (comsec, not bitcoin) guys like to do that.
 
zbang said:
Dennis has it- If there equipment in the rack is grounded, then the rack is grounded. But also if there's a conduit attached to the rack (is it?) and that's bolted to building steel, then that also grounds the rack.
If you want to run separate ground wire to the rack, Sure, go ahead. In many places it can be a single wire, some locations it'll need to be in some sort of protection (conduit, flex conduit, etc). All of that is driven by Article 250 and the location.

All that aside, some datacom people insist that you need large ground wires to a large ground bus, and that tied to a triad of ground rods (and sometimes those need to be driven during a new moon by a left-handed electrician). None of that is NEC, and in many cases, none of is is necessary.
Click to expand...

The racks are some wall mounted and standalone, and I was confused at first because I thought they are grounded with the branch circuit. I tried to explain the customer that. However customer keeps says they r not grounded and still wants to bring earth ground near the server racks, that was why I asked if I can pull that ground wire from the nearest panel Instead of doing ground rod.
 
suemarkp said:
How do these computer racks distribute power to each individual computer? Usually, there is a PDU in the rack that does this. If that PDU has a ground lug, connect that to the rack structure (or rack ground lug if it has one). This will ground the rack via its incoming power circuit. If no ground lug on the PDU, I use special bonding screws to mount the PDU to the rack rails. They are made by Panduit, and have teeth under their head to bite into the mounting rail. They also have a cage nut version with teeth on the nut.

Note that many rack mounted items have painted ears and sometime the rack rails are painted. Bacause of that, you can't rely on mounted items to ground the rack unless you scrape paint. Many rack screw have nylon washers to keep from marring the ear surface which also keeps it from grounding things.

If the rack has a ground bar, these are usually isolated from the rack structure which would then require a separate wire back to a single point or mesh "room ground". The idea is to keep that bar away from the "noisy" equipment ground of the source circuit with all the computers possibly putting noise on the ground. It seems the network, telecom, and crypto (comsec, not bitcoin) guys like to do that.
Click to expand...

The racks are fed from AC power, there is no PDU.

will note on the paint.

The racks will have one of those Panduit ground bar
 
Etanuye said:
The racks are fed from AC power, there is no PDU.

will note on the paint.

The racks will have one of those Panduit ground bar
Click to expand...
If you drive a separate rod for the rack, you would need to tie it into the existing grounding system or you could cause a difference in potential between the separate grounding and existing.
 
Etanuye said:
The racks are fed from AC power, there is no PDU.
Click to expand...
That doesn't say much, is the any kind of power distribution (which includes a quad recepticle) mounted to the rack? If so, scrape some paint to the box metal touches the rack and call it good.

If the customer want to pay for a separate ground lead, get it from the closest branch circuit or panel. Depending on building type & occurrence, you may need to run it in conduit (as mentioned above).

Do not install a separate ground rod (unless paid for) and if you do, follow Bill's advice.
 
Had an O scope once where the ground conductor was open.

There was 60 vac on the housing due to an interference filter for incoming power acting as a capacitive divider.
For sure, you could feel it.
IIRC, 0.1 uF for each of the two caps.

So I guess if you measure between ground and your ground lead, you'll see 60 vac. And this voltage should be able to source some current.
9 mA?
 
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