The first transcontinental telegraph was a single wire that used the earth as a return conductor

interesting that you mention this. I can't find any photographs of the line. Some depictions show two wires on poles. Others show what appear to depict a pole with a single conductor wire at the top.

Yup. Short range runs could be two wires, it was more cost effective given the poor performance of the earth return system. Much longer runs were a single conductor on the pole. At either end you'd have a gigantic metal plate sunk deep into the ground to act as your return path. It had to be deep enough to stay wet, or the operator would have to dump water (or other fluid) on it.

There were also repeaters in the transcontinental run, the signal was just way too weak. These were initially electromechanical devices that dip a needle into a pool of mercury.

Things were wild before we really invented electronics.

The entire electrical grid relies on the ground as a conductor. If your electrical outlet has two wires, one of them is connected directly to the literal ground via a metal post buried outside your home. If it has three wires, usually two of them are connected directly to the ground.

In most electrical systems one of those ground wires is also connected to a neutral wire that leads back to the generator. But there do exist "Single Wire Earth Return" systems where the neutral return wire is omitted and everything still works. https://en.m.wikipedia.org/wiki/Single-wire_earth_return

Wait.. if you've got two conductors it's neutral and hot. Neutral, as far as I know isn't connected to a literal metal post in the ground. That would be the third wire which would be called ground and is connected to a metal post.

Am I wrong?

In the US, usually neutral is connected to the center tap of the transformer on the street, literally hooked to the middle of the winding. It is brought to ground level by hooking it up to the ground at the house, but the signal/power goes back to the transformer because the resistance is far lower than going through ground. That's why you have two power rails in the breaker box, the two hot wires coming in are 220v apart, the neutral is in the middle making for a pair of 110v rails at 180degree phase angle apart. See https://en.wikipedia.org/wiki/Center_tap

The literal ground doesn't have the same potential everywhere. This is obvious in case of lightning strikes, but also happens in normal circumstances. You as a human standing on the ground are mostly at ground potential. If neutral was connected to ground at the nearest substation or the next power plant but not at your home you would get an electric shock whenever you touch a neutral wire because of the difference in ground potentials.

Neutral can also be connected to a neutral line on the grid. But you pretty much always want to connect it to the local ground through a literal metal post.

In the US, the neutral and ground are generally bonded in your breaker panel.

Maybe depends on where you are? All the systems I have worked on in a few countries have the neutral connected to earth ground at the feed point for the building, at the servíce entrance.

what you're describing would be an "IT system". Most of north america uses something like a "TN system"

https://en.wikipedia.org/wiki/Earthing_system#IT_network

> Wait.. if you've got two conductors it's neutral and hot. Neutral, as far as I know isn't connected to a literal metal post in the ground.

Neutral and ground are bonded together in the service entrance. The neutral is a center tap off the utility transformer and the ground is usually a ground rod.

In older houses the service entrance is typically the main panelboard. In a house built after 2020, the service entrance will be a disconnect switch after the meter socket.