Practical Engineering: Where Does Grounded Electricity Actually Go?

[BrianHG]

Enjoy...

[liteyear]

I've often wondered whether electronics is harder to learn in the US, because of the common use of the term "Ground". I'm used to calling it "Earth", as a concept distinct from "Ground", and find I have to make a conscious effort to interpret US literature correctly because of the ambiguity. The confusion seems pervasive, unfortunately. I think language might have a lot to do with it.

[jwet]

Entertaining- I watched the video and don't know if I now know more of less? 

The latter part of the video delves into single wire power distribution and I found it confusing.  Single Wire Earth Return (SWER) is a rare, archaic system used mostly "down under".  What the video fails to mention is that SWER is done at high voltages (11 to 50 kV) that are relatively compatible with the high impedance return path and other losses.  If these distribution losses are outweighed by the cost of an additional conductor for return, it makes sense, otherwise it doesn't.  The place where it generally makes sense is in very low population density areas (Australian Outback, Rural USA) where one customer needs power on the end of a 10 mile connection.  I don't know why he included this- it just confused me and implied that ground conducts as well as a return wire (it doesn't).

My model of "earth" is the idea of an arbitrary zero potential.  Since voltage is always measured relative to some reference- "ground or zero" is a convenient point to measure from.  The earth has a potential relative to itself of zero to first order, in the real world, ground differentials are common.  A good model for earth is as a near infinite capacitance.  The differentials that exist locally are because the connection to this infinite sink is through a high impedance like a ground stake.   Any current put into to this capacitance will be sinked and infinitesimally increase the voltage of the earth relative to the rest of the solar system.  Though, as you are pushing current into the earth, someone else is pulling it out so it all stays in balance- every now and then, there may be a lightning storm that forces current to flow between earth and the heavens to keep things in balance.  Even lightning strikes don't appreciably effect the overall potential of the earth- except very local to the strike where the high impedance connection to the infinite sink can create high local potentials that will eventually flow and balance out. 

Also, any power produced on earth is independent of ground initially, it can be connected or referenced to ground but begins as a floating potential.  The beginning of the video illustrated this with a 3 phase generator isolated from ground- this was pretty cogent.

These very basic questions test your understanding and your models of how things work.  Its like the Vertasium million miles of wire and light bulb thought experiment and the idea that current doesn't flow in wire (it does).

Thanks

[CatalinaWOW]

He makes a couple of simplifications and very near errors but overall a solid presentation.  Like the other videos of his I have seen.

I do wish he had spent more time on the section where he explained that current doesn't follow the easiest path.  In my mind this is the heart of most peoples confusion about grounding and noise control.  There are many paths in any system to the "ground reference point".  And without understanding all of them, the ones deliberately created, the ones that happen in the physical layout of the system and those created both intentionally and unintentionally in the powering and adding measurement instruments, you can't really say you know what is going on.

[pickle9000]

The wall socket is installed correctly.

[Sredni]

Just to add that the role of capacitance, mentioned above, is almost never cited in these divulgation videos, and yet it is key to understand why the earth is not just a conventional level for the electric potential.

To be clear, it's the humunguos earth *self*-capacitance that allows for its potential to remain on average constant, despite the addition and removal of electrostatic charge. The value (750 uF IIRC) is gigantic as far as self capacitances go, while only moderate from the point of view of mutual capacitances.


PS
Veritasium never said that the current does not flow in wires, it's the power (energy) that seems to flow mostly in the space between and around the wires. Power is current times voltage and if the current is the same in the whole circuit, voltage is significant only at the resistor (ok, and generator) due to the presence of local surface and interface charges.

[Someone]

Veritasium never said that the current does not flow in wires, it's the power (energy) that seems to flow mostly in the space between and around the wires. Power is current times voltage and if the current is the same in the whole circuit, voltage is significant only at the resistor (ok, and generator) due to the presence of local surface and interface charges.

Please dont start that again, a range of shielded conductors/cables readily demonstrate that the power, energy, current, etc are all happily contained inside (where higher frequencies end up as waveguides).

[Sredni]

Inside, between the shield and the conductors?

[SiliconWizard]

It goes to its room, as it's been grounded. Sounds obvious.