Basic theory question-- "positive ground"

[Buzz]

At my level of knowledge the plumbing analogy works pretty well for me.

You can compare current flow to water flow, wires to pipes, resistors to water valves etc.

I know it's not a faultless analogy, but it works fine when playing on the breadboard.

Helps me understand positive ground in a simplistic manner.

[induction]

"Nor by the fact that electron flow is the opposite direction of current density. "

But think about what you're saying there. It's equivalent to saying "traffic flow is the opposite direction to velocity". The sentence itself makes no sense. Velocity is a measure of traffic flow; velocity itself is not a moving object.

If electrons are negative (and we all agree they are) then so is the current density in the direction of electron flow. That is the construct of conventional current, and there is nothing backwards about it. The only obstacle standing in the way of newbies is accepting that a negative number in one direction is the same thing as a positive number in the opposite direction. That's just maths. They're not opposites but 'duals', two sides of precisely the same coin. The whole 'problem' of conventional current is a myth, and vanishes the moment you make the mental connection between negative charge and negative current.

Show me a negative car, and I'll agree with your analogy. Maybe there's a road where everyone's driving backwards. That could work.

All I was trying to say is that naming conventions in electronics can be arbitrary and counter-intuitive, and can cause people to make mistakes when they try to use them as a basis for logical inference.  Your first post in this thread seems to indicate that you agree.

Beyond that, you appear to be arguing against a position I don't hold, so I don't feel qualified to respond.

[R.G.]

Helps me understand positive ground in a simplistic manner.

You're over thinking the whole thing. The complete understanding of "positive ground" is here.

Ground has nothing to do with electron flow.

Ground is a REFERENCE POINT. It's the place in the circuit we designate with the voltage of 0.00000000000V. A battery can have its negative terminal connected to ground, leaving the + end free to power the circuit. This is negative (battery terminal) ground(ed). It can also have its positive terminal tied to the reference voltage point, leaving its negative terminal free to power the circuit. This is positive (battery terminal) ground(ed).

[GibsonGM]

^  + 1,000,000     

[Ice-9]

One many's ceiling is another man's floor.  

In a nut shell.

[Buzz]

Helps me understand positive ground in a simplistic manner.

You're over thinking the whole thing. The complete understanding of "positive ground" is here.

Ground has nothing to do with electron flow.

Ground is a REFERENCE POINT. It's the place in the circuit we designate with the voltage of 0.00000000000V. A battery can have its negative terminal connected to ground, leaving the + end free to power the circuit. This is negative (battery terminal) ground(ed). It can also have its positive terminal tied to the reference voltage point, leaving its negative terminal free to power the circuit. This is positive (battery terminal) ground(ed).

Thanks RG. Understood. PRR has explained this to me in the past. I withdraw my statement "helps me understand positive ground in a simplistic manner"

My wife says if I don't lick any windows for the whole day I can have ice cream tonight.

edit: ^ Aussie humour that may be misinterpreted. I mean no offence to people with disabilities.

[R.G.]

My wife says if I don't lick any windows for the whole day I can have ice cream tonight.

edit: ^ Aussie humour that may be misinterpreted. I mean no offence to people with disabilities.

I'm actually very fond of Aussie humor. My good friend Tim Taylor and I spent many hours with him recounting the Aussie humor (and slang!) to me while I rolled around on the floor laughing hysterically. Wish I could send you a beer. Texas beer is getting quite good, but it'd be flat by the time it got there. 

[PRR]

> Show me a negative car

I'm not fond of that car analogy.

You have a wallet. Money comes in. Money goes out. If you get paid $100, then buy $100 of Texas beer, 100+100= 200. However you look in your wallet and there sure aint $200 in there.

You do math like this with + and -. When the "money" is invisible particles you may assign + and - arbitrarily. In *your* wallet it makes sense to assign + to income and - to outgo. So +$100 pay, then -$100 for beer, (+100)+(-100)= zero, and now the math agrees with your empty wallet.
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"Positive ground" is very simple. Hold a 9V battery. Now run a wire from its + terminal to your case. You have a positive-ground power supply. What is the problem with that? Millions of cars were wired positive-frame. Many streetcars ran positive on earthed tracks.
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> Ground has nothing to do with electron flow.

Moreover, no current flows *to ground* in any situation we want to be in.

That 9V battery where you connected one terminal to your case. Either terminal. Even say the case is sitting on ground. Does current flow from battery to case? While you might build so circuit current flows *through* the case to the circuit, it has NO reason to flow to dirt. Why would it?

If you fly a kite in a lightning storm, yes current flows to/from ground. A long-term view is that an equal charge was scrubbed-off from/to ground in the unsettled weather before the lightning storm. However idiots who fly kites in lightning will only see part of this circuit (the more dramatic part).

The way electric utility power is distributed, if you connect a Hot wire to dirt there will be a current to/from ground. This is not supposed to happen. "Incidental" ground leaks do happen but are required to be very-small. My house is one of the worst, and at full 40A load about 0.4 Amps returns in the dirt; 98% of the time this is under 0.1 Amp.

[PRR]

Another different way to think + and -.

What is the height of that post? Of that tree? Standing on my land, it is convenient to reference all heights to "ground". The post is 8 feet high (above the dirt), the tree is 77' (up from the muck).

Large-scale, cities and mountains, it makes sense to measure to "Sea Level". Denver is a mile above the sea. Flying west, you have to climb to 2 miles to scrape the lower mountains.

I'm digging a sewer line. It is not above ground, it is below ground. I could say it runs 16 inches below the dirt.

OTOH, I could say it runs 98'8" above sea level. But even though the sea is only a mile away, I don't really know how high I am.

And actually what I did was define a *new reference level*, 36" above the top of the lower end of the pipe. That way I could peep my transit (builder's level) sitting down, instead of sprawled on the dirt or in a hole. The line must slant (poop must flow downhill or it don't flow at all!), so it runs from -0.5" at the lower end to -12.8" at the upper end, *referenced to* that 36" level above the top of the bottom of the pipe. By measuring 8 points along the run I could verify that EVERY segment of pipe slants, all about the same, no dips, no slow-flow runs.

And if you think that analogy stinks, you are right.

[plexi12000]

excellent!!!! great comments, thank you.   PRR and R.G.-- you guys are great. you can keep at MY "level"....."electricity for dummies"!!!  LOL 

It's STILL dang confusing if you've never had any schooling or training!!

[PRR]

> never had any schooling or training!!

I don't think schoolin' helps here.

There are situations, like sewer lines,which are "always negative of ground level". (Actually I know a place where the sewers run above ground!)

But a power line can be run overhead OR underground, positive or negative of ground level. And with rubber-cover wire, it kinda makes no real difference. Difference of support and rubber-type to stand sun or dirt, but the electrons do not care.

So more like using your practical experience in other areas.

I had so much practical experince today that I need to get to bed.