[throwaway542134]

When you talk about "electricity" you need to distinguish between "current" and "charge carrier." Current is the amount of charge that flows through a point per second. The charge carriers are the electrically charged particles that actually move. Where current goes is a matter of what we're trying to do with a circuit, where charge carriers go is why we need ground.

What a voltage does is pull or push the charge carriers. When lots of them flow, you have a current. Conductors, like a wire or ground rod, are full of free electrons to act like charge carriers (kind of like a pipe filled with water, the voltage is a pump that moves it).

The duality of pulling/pushing charge carriers is why we need a circuit. In order to push charge carriers, we need something to pull them from (a source) and somewhere to dump them (a sink). When we have no source and no sink, charge carriers have nowhere to come from and nowhere to go.

Ground is a convenient source/sink for charge carriers because it's roughly uniform in charge and huge, so pulling tons of charge carriers from it doesn't impact it greatly.

And it's not that charge carriers are always flowing back to earth, but back to their source. That's why ground is sometimes called a "return path." To move a charge carrier, you need to give it potential. It will lose that potential and return to the point of lowest potential difference from its origin - which is its origin.

But that said, for things like AC power, the charge carriers aren't actually moving very far at all and have a net displacement of 0. They vibrate adjacent charge carriers, and we convert that vibration into unidirectional (DC) voltages that can push/pull from local sources/sinks, be it the literal earth (mostly for safety ground) or a small plane of copper on a PCB.

[shreddish]

Hmm okay starting to make more sense now. Do you know a good visual explanation that shows the "path" electricity takes from the transformer to your home and back out to the ground rod. Note: I fully understand in AC the electrons aren't actually moving along this path. But I guess I don't see how the circuit is ever "complete" or a circle.

[ishigoemon]

This video has a great visual explanation of grounding, imho.

https://www.youtube.com/watch?v=P-W42tk-fWc

[NobodyNada]

It doesn't go "back out to the ground rod," it goes back to the transformer. Note this paragraph in the parent comment:

> And it's not that charge carriers are always flowing back to earth, but back to their source. That's why ground is sometimes called a "return path." To move a charge carrier, you need to give it potential. It will lose that potential and return to the point of lowest potential difference from its origin - which is its origin.