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I'm having trouble understanding why the earth is a viable fault path for electricity brought into my home. Isn't there really high resistance? I mean, it's dirt?
Also, let's say I connect the hot wire coming into my house directly to the ground wire. What is the path that the electricity takes to get back and "complete the circuit?"
I think of the ground as many parallel high resistances paths, which add up to a low resistance. Good earth connections (<50ohm) usually involve a decent bit of copper rod in the ground, for an average pole top tranny you would probably have 4+ metres buried depending on soil resistivity and local regulations. Really good earth connections such as in a district substation are usually less than 5ohm and as such are excellent return paths. From your house, the return path is back to the star (earthed) point on your service transformer, either via the earth or neutral wire depending on the earthing arrangement in your area.
It's not, really. What it is, is reliable in the sense that it doesn't go away. So the earth path is not as good as the wires it's connected to, but it forms a reliable backup path.
If you connect the hot to ground, you short out the circuit, since neutral is connected to ground as well. So current flows from hot through the ground wire to earth, and thence through a short earth path to neutral.
In my country (Australia) we use an earthing system that looks like this:
In case of an earth fault, the fault current path looks like:
Note the connection between the earth bar and the neutral bar at the "MEN link". The "earth fault path" doesn't actually go through the literal earth, i.e. the dirt - it goes through copper wires the entire way.
The above diagram shows what happens if your active wire faults to earth, but the same thing happens if you connect your active wire to earth directly.
NOTE: The above pictures show a "multiple earthed neutral" or TN-CS earthing system to AS/NZS 3000. The earthing arrangements in your country may differ significantly.
