What Does Ground Mean Exactly?

In summary: A reference point used to compare potential across different areas-A system used to minimize the difference in electrical potential over different areas-A part of the electrical system that is used as a common reference point for voltage throughout an electronic system
  • #36
hmm got logged out again on that one. But the draft didn't disappear.

NFuller: a measly one amp will charge Earth's 710 uf at the rate of 1408 volts per second , assuming you can distribute the charge equally over its whole surface. That's 11.7 volts every half a line cycle.
Since you can't distribute charge that fast it'll raise local Earth voltage more at the point of current injection reducing potential difference across your body.

That's why it's current flow around a closed loop that electrocutes people .

Another thread you might like
https://www.physicsforums.com/threads/trying-to-understand-electric-shocks.883550/
 
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  • #37
jim hardy said:
well just lost an hour of typing a response. Something logged me out, draft disappeared when i clicked 'login' . @berkeman - anything fishy looking ? do my PF tracks show signs of a virus? old jim.
I don't see anything obvious. Nice featured thread about PV, btw. :smile:
 
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  • #38
jim hardy said:
The current may be large or it may be small depending on conductivity of the soil, your skin and your shoe soles.

NFuller said:
The resistance of all of that is probably in the mega-ohms, yet people still get electrocuted.

I remember being surprised how much I didn't know about grounding when it came time to learn how to use a "ground Megger" and interpret the results. R=pl/A is but a starting point, but as @jim hardy and @Baluncore point out, coming close to an understanding what's actually going on is a wilder and woolier ride. Biddle has a good write-up of the basics, and is worth reading by anyone interested in what constitutes Earth ground.

www.weschler.com/_upload/sitepdfs/techref/gettingdowntoearth.pdf

Resistance varies in the manner of concentric shells around a grounding point, and is the reason behind step potential, and using a "bunny hop" or "shuffle step" technique to escape the vicinity of a downed power line (images were copped from a BC Hydro slide show and the document above).

ground_sphere of influence.jpg


ground_BC-Hydro_step potential.jpg
 

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  • #39
Wow. I first looked at this thread 36 hours ago. It was simple. But now I see it has become a mess. Ground is indeed a term with many definitions and many nuances.

The OP said his questions have been answered. Most of the following posts seem to go in directions other than the OP's question, so I think it's time to close this thread. If you want to discuss specific grounding practices, feel free to start a new thread.
 

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