atcomsystems.ca/forum Forums Wiring - Telecom Carriers - Trunks & Services Cabling Telephones Systems Wiring Grounding racks

I kinda think it will stop working when you start cutting up the computer.

I think this is a joint effort by the IT "professionals" and that Chernoble Dr. guy over on Sandman.

-Hal

Don't you know that a $200 "2 meter" power cord is at least 20 times better than a $10 6-foot one? And it's quoted in metric, which as everybody knows, signifies high quality.
Seriously, I know people whose "home theatre" system is probably worth more than their homes, what with the housing crisis. And I have seen situations where the grounding of a system cost more than what the install of a small KSU system would cost. As far as I could see, the installer just run some jumper cables from the components to a perfectly ordinary rackmount busbar and then some green wire to a rod in the basement. The sales literature was full of terms like "custom isolated ground", "enhanced operation", blah blah blah.

Hal, "Skin Effect". The power in a wire actually flows on the outside surface and power density gets lower the closer to the center you get. Compare the circumference of 10?-18ga? wires to 1-6ga wire. (The 10-18ga wires is a guess, I never really thought about the number of strands in a 6 ga wire, or any other stranded wire, for that matter.) And the higher the frequency, the more important "skin effect" gets. Consider the microwave 'wave guide'. It's nothing more than a wire that has been cored out, in effect. Because microwaves truly run only on the outer 10% or less of a wire.

Skin effect? At 60 Hz? There's a nice comfy room waiting for you over at the asylum...

-Hal

I believe we have just entered....

I am no electrician wait let me repeat I am no electrician.

But I can place a pretty good bet that skinning will be very small if at all. Especially with the ground being larger than a 3/0. But I have to tell you this has now peaked my interest. I really didn't think this conversation would make it this far.



I really have to applaud the brain power here. It impresses me every time I think it could not get any better.

We have a very large customer that is a financial institution. They have set standards for the data racks at their bank branchs. Their standards on grounding/bonding is extensive. They have us bond a TMGB to the main distribution panel. Depending how far away the MDP is away determines the wire size. In some banks this has been 2/0 wire. Then we also have to run a wire from the TMGB to building steel. Also length determining the wire size. It's a least a #6. Then we bond from the TMGB on the backboard (thats usually mounted behind the rack) to the TGB on the data rack. Also the ladder tray is bonded to the TMGB. Then we provide a ground wire from the TGB to their Cisco router in the rack. We have to use 2 hole compression lugs for every termination. We have probably done this at maybe 1000 banks. Seems overkill, but its their standards and they are paying.

the fun thing is building steel may not be a clean ground depending on how the place was built. so now you are attaching the bonded electrical ground to the floating structure.

The reason I learned for bonding the rack separate from the device was more for static dissipation. True the self tapping rack screws should take enough off with the scraping washers to make a solid connection and a clean path. I have also seen computer power supplies fail to the case instead of failing to the ground on the cord. so additionally bonding the rack will safely shunt that current to a real ground 'IF' the bonding was done correctly.

Bonding gone wrong...
I saw one idiot bond to what they thought was a cold water pipe and instead turned out to be a gas line. I've also seen cold water pipes that have new plastic fittings in places where cheap work was done making the pipe an isolated hunk of metal. A high quality mega-ohm meter should let you check continuity of ground.

" A high quality mega-ohm meter should let you check continuity of ground."
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But, make D--- Sure it's NOT a gas pipe before you use that MEGGER!

Actually it is not their standard. As it follows TIA 607-B (grounding and bonding data and telecom equipment) to the letter. And that's a good thing, IMO, as both customer & installer have an objective frame of reference. But the OP mentioned only a single rack. Not the complicated infrastructure (component->rack->telecom closet->equipment room) that would necessitate structured/hierarchical bonding/grounding as described in the standard. Within a single rack, a #6 copper (or maybe #4 aluminum-as per your code) would be more than enough, as it would handle close to 200A (I don't remember the exact figure offhand).
Don't forget this is a performance or to use the proper term technical ground. Its main function is to protect equipment against electrical noise. There has been loads of research on this, as these problems are the hardest to pin down. And yes, paint can act as an insulator. All bonding surfaces should be bare. Another reason is that bonding/grounding effectivesness is related to the geometry of apparatus such as the TelecomMainGroundBar. IE thickness, dimensions, number & size of terminals, material of construction, AND contact-surface area. If you use a certain size ground lug/screw it is understood that its bonding surface (however many square millimeters it is) should be the one expected as per the standard. I agree that maybe this is all too much. On the other hand, if the budget is there, they're pretty easy to implement, and as I've said above the standard does provide with an objective reference.