Electronics > Power & Renewable Energy

Field Mounted Switch Enclosure and Grounding/Bonding

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Ground_Loop:
I have a project in a large industrial facility that requires several field installed Ethernet switch enclosures dedicated to my equipment.  The power source begins at a 480 3p distribution panel dedicated to my equipment, through a 480-208 transformer to a 208/120 panel board through to the load.  Proper grounding and bonding is maintained from the source to the load and its enclosure.  The only connections from our switch cabinets to the main server room are non-conductive fiber runs through air gapped conduit to cable tray.  All conduit and cable tray is properly bonded, but there is no conductive path between our switch cabinet and the server room, just single mode fiber without armor or shield.

Our client is insistent that we install a ground conductor from our switch cabinet to the server room central equipotential ground bus.  I am arguing that installing a conductive path where none currently exists has no technical merit.  Further, tying all my cabinets to the server room ground would connect all the power supply commons to the server room common potentially creating ground currents.

The client is quoting ANSI/TIA 607 which clearly implies the scope of equipment is that which is already co-located in the server room or has an existing electrically conductive path.

And finally to my question: Have any of you experienced a situation like this and is there justification to ground the switch enclosures to the server room central common?
This is literally a $1M question.

bdunham7:
How is the server room connected relative to the 480V/3PH panel that you said was the beginning of the distribution chain powering your stuff?  If you trace back the grounding of your cabinets and the server room, do they go back to a common point or are they otherwise bonded now?  Or are they on completely different distribution systems?

If the former, obviously you are creating a....ahem.....Ground_Loop.  If the latter, I do have some experience with this and it's all bad, but I can't provide an expert advice on regulations or anything like that.  What I can suggest is that if you are compelled to install something like that, you look at how it is routed and whether you can use (or parallel) the existing grounds back to some point where they are closer together and just bridge or bond them there.  Just running a random ground wire between two currently unbonded, unrelated points seems just as idiotic to me as it apparently is to you.

Ground_Loop:

--- Quote from: bdunham7 on September 16, 2021, 04:52:37 pm ---How is the server room connected relative to the 480V/3PH panel that you said was the beginning of the distribution chain powering your stuff?  If you trace back the grounding of your cabinets and the server room, do they go back to a common point or are they otherwise bonded now?  Or are they on completely different distribution systems?

If the former, obviously you are creating a....ahem.....Ground_Loop.  If the latter, I do have some experience with this and it's all bad, but I can't provide an expert advice on regulations or anything like that.  What I can suggest is that if you are compelled to install something like that, you look at how it is routed and whether you can use (or parallel) the existing grounds back to some point where they are closer together and just bridge or bond them there.  Just running a random ground wire between two currently unbonded, unrelated points seems just as idiotic to me as it apparently is to you.

--- End quote ---
My 480 source is solely dedicated to my equipment.   The power sources for the server room and my system merge at the substation 4160.

bdunham7:
Is the "server room central equipotential ground bus" itself bonded directly to the grounding system of its  own power service entrance?

It seems that situations like this come down to winning an argument.  And they effectively want to bridge the air-gaps you deliberately put in the conduit for the fiber.  :palm: 

You may have already thought of this, but perhaps argue like this:  If the service panel for the servers and the one that you get your power from are fed from separate transformers that get their 4160V 3PH--but not ground-- from the substation, and the initial grounding point for each is separate and they are not bonded together, then you might propose simply adding whatever grounding is needed to complete the connection between your service panel and wherever the "server room central equipotential ground bus" point is.  If that seems unacceptable, then point out that the ground wire they are proposing will do the exact same thing.

Now in reality, those points may already be connected.  I don't know anything about this facility, but a lot of times connections end up being made whether they are intended or not...so maybe it would be interesting to test that.

Brumby:
Firstly - I have no experience in this type of topography, but I can offer you a suggestion as to how you might argue the point....

What happens when something goes wrong?

The objective is to define fault scenarios and demonstrate the risks involved in what they have asked for against the risks in what you have delivered.

Anything goes here, including lightning strikes, somebody driving a truck through a wall, flooding or any other hazardous event.  Maybe look up an agency that reports on electrical incidents for ideas.  There will be scenarios where such a grounding conductor would become live - something with very obvious risk.


Just my thoughts.


bdunham7 seems to have some experience on the subject.   :D

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