On 11/25/2013 2:18 AM, Danny D'Amico wrote:
On Sat, 23 Nov 2013 10:17:08 +1100, John G wrote:

No current flows in around or thru the ground if all the conductors are
installed to code. :-Z

That's not how I understand it.

Even though the ground is so big that even all the nuclear power plants
in the world pumping electrons into the ground couldn't change its
potential, that doesn't mean that the ground doesn't complete the
circuit.

The earth does not complete the circuit. Wires complete the circuit.

The electrons that flow are in the wire.

If you had DC, an electron flowing out one end of a wire would be
matched by an electron flowing in the other end. A single electron may
not move very far, it can be replaced by another electron. A property of
a metal is that there are electrons that are not tightly bound that can
migrate.

With AC, electrons move in one direction, then the other.


If the power company chose any other conductor other than "the" ground,
then they would have to have a wire for each phase distributed.

The do have a wire for any intentional electrical path.


Since the power company chose to use "the" ground as "their" ground,
the way I understand it, "my" ground is connected to "their" ground,
so, the electron that flows into the primary of my transformer came
from the ground at the power plant, and it goes back into the ground
at my house, to (theoretically) make it back to the power plant.

Since early power distribution days there is a metal connection for the
entire path. Earth is not an intentional path.


Of course, the ground is so big that it's like pouring a glass of
water into the ocean, where that molecule eventually will make it
around the earth - but the immensity of the ground should not be
construed as implying there isn't a loop from the earth at the
power company to the wires to my transformer primary to the earth
at my transformer.

The earth is not used as an intentional path.

The connection to earth is used to limit the voltage between the wires
and the earth. The earth is also a sink for lightning and similar
events, and is used to trip overcurrent protection with crossed wires.

The earth is not allowed to be a path to trip a circuit breaker in your
house if there is a short between a hot wire and ground at, for
instance, a drill. The short circuit current goes through the N-G bond
at the service and returns to the utility transformer through the
service neutral. The earth is not allowed to be the path because it is
not an effective path.


At least that's how *I* understand the typical mains power in the US.

Rather flawed.

Bud, until recently I would have agreed with you. But, whomever wrote this web page obviously knows something about electric power generation and distribution and seems to disagree:

http://www.science.smith.edu/~jcarde...ecPwr_HSW.html

Look at the bottom paragraph in the section entitled "The Power Plant: Three Phase Power" where it says:


And what about this "ground," as mentioned above? The power company essentially uses the earth as one of the wires in the power system. The earth is a pretty good conductor and it is huge, so it makes a good return path for electrons. (Car manufacturers do something similar; they use the metal body of the car as one of the wires in the car's electrical system and attach the negative pole of the battery to the car's body.) "Ground" in the power distribution grid is literally "the ground" that's all around you when you are walking outside. It is the dirt, rocks, groundwater, etc., of the earth.


I don't think he could have said it any clearer.