@outbackhut does not seem to know anything about the Uno
Mmmmm…
Take some time to reread my message. As I said, depending on who made the board, ground is generally shared….
On some poor quality clones, the USB shield is not connected to GND either directly or through ESD protection, but the USB GND is still shared…
Take some time to read into GND sharing. Specifically multi source GND sharing.
Not worth arguing that point, but I can build one from parts without looking at a schematic or datasheets and it works first go…
Spent many many hours disassembling, reassembling, designing, tweaking, and customizing Uno boards, Uno clones and embedded Uno systems. 
It should never be and it done wrong on the Uno.
No it should not.
That schematic is wrong.
You are entitled to your own opinion, but 95% of electrical engineers and other professionals disagree with you on that. The most common consensus being “It probably won’t be needed, but might as well include it, especially if your device is not being plugged in and never touched” and I can tell you most of us have our Uno on our workbench, being used, moved, continuously unplugged and plugged in, moved, used for testing, etc. I have a broken official Uno that had problems due to some poor design choices 
For the cost of a ESD diode, the reward is greater than the risk.
And, respectfully Jim, I see you frequently love saying people are wrong, but I rarely see you do much more.
I see yet another of my many trolls.
Hang around and you may learn something and not just do like the 95% do.
I look forward to learning said things.
I am waiting for your reasons why you know better than the professionals with bated breath!! I welcome this enlightening learning experience.
What professionals?
You mean the ones who say things like this:
“It probably won’t be needed, but might as well include it, especially if your device is not being plugged in and never touched”
"probably" "might as well" ?
Doesn't sound like they are very sure about what they are doing.
If you need professional language to make it easier to grasp:
Most applications of a USB port don’t require ESD protection due to being stationary objects. Quite a few edge cases do exist, especially portable or well used products (ie conatant unplugging and replugging). Which Arduino falls under for many of us who use them on a daily basis.
As general advice, not knowing the exact application of your USB port/device, I recommend including protection as it is cheap: both financially, and taking up little space. The benefits of proper design outweigh the risks.
Please read the links I kindly sourced and provided previously, they show you the industry standard according to TI, and many “real people” explaining in a friendly manner, exactly why your opinion is outdated, unsafe, and wrong. That way you can stop taking umbridge at my wording and maybe you can contact the industry to explain why their standard of ESD protection is incorrect.
Now I do not claim to be all-knowing or infallible, but when it comes to these subjects, I do my OWN research and follow the advice of the 95% who seem to be doing perfectly well in their profession. The 5% (which you claim to fall under) needs to have earth shattering evidence before I blindly follow them into the ditch they staggered out of so to speak.
So if they are moving they do need ESD protection?
Now you are just talking nonsense.
I do my OWN research and follow the advice of the 95%
"If everybody does it it must be good"
Argumentum ad populum (Latin for "appeal to the people") is a fallacious argument which is based on claiming a truth or affirming something is good because the majority thinks so.
You will never win this argument with me.
According to some other Forums, yes. According to industry standard, ALL devices require it. I notice you still haven’t so much as looked at that.
If you see this as purely an argument I feel very sorry for you. You remind me of my grandfather who is very set in his ways, cannot learn anything, and honestly isn’t worth explaining things to. If it is something you or I are trying to “win” then it is unfortunately an egotistical battle of the wills.
To date, you have given no reason why you state ESD is not required, or why my example schematic is incorrect. You have not quoted any sources. You have done nothing useful in this conversation, and honestly brick walls are better to communicate with.
I do not see this as a argument, I see this as a debate. Hence sources and evidence are paramount.
You are 100% correct. Hence sources and evidence are needed. To believe someone blindly is a grave error. Hence I recommend you take a look at my sources (which you haven’t clicked yet!!), or at the very least, link your own research!!! Especially since you seem to be struggling to explain why I am wrong…
Nothing to do with being smart.
I’m mostly concerned that you have told me I am wrong about multiple things and think you are so mighty that I must take your word with no evidence. And not just on this thread. A lot of threads, as soon as I type something, you tell me I’m wrong - with no reason! It begins to feel personal, and my entire point is if I am wrong - prove it! You aren’t a God I must trust implicitly, and no one learns by being told whats wrong and not what’s right!
I’ve already asked this to be split to a new topic - awaiting moderators to action that.
Maybe I misunderstood this:
Totally!
Care to explain? Or too much effort…
I'm sorry it not personal and don't take it that way, I tell many people they are wrong.
Care to explain? Or too much effort…
Go back and carefully read the entire topic from the beginning.
I've split this from the original topic because it has become a separate discussion between you two, perhaps related to the other topic but still worth being in a topic of its own.
Does anyone know how the UGND <> GND jumper pads on the Uno R3 with the through hole '328 were meant to be used by Arduino?