I have researched and asked some questions around this before, so let me explain.
I understand by bonding an Earth ground (literally a green wire to a metal rod in the ground) to the neutral bus bar, basically the voltage difference between ground and a neutral wire is almost 0 (yes assuming no improper wiring).
But my brain can't work that way, I need explanations to all the small questions or it doesn't make sense.
So Ohm's law states V=IR. In an imbalanced load, all the current on a hot wire through say a lamp goes back through the neutral. So by that logic, both the hot and neutral have similar resistance AND current. Adding a wire into the ground does not change current and resistance overall. Can someone explain looking at voltage this way and how the neutral is still near 0? I think I am mis-understanding this concept.
P.S. A picture/illustration may help, I kinda think of two big buckets of water with a pipe attached at the bottom and a big heavy turbine (a load) in the pipe, but then add a large water pump at the "hot" bucket. So being near the pump, but before the turbine on the "hot" side is more dangerous. Wondering if there is a better way to explain
Best Answer
Ohm's law still holds, but I think you may be misunderstanding the purpose of a ground wire & its relationship to the neutral.
In an ideal world, when we apply a voltage to a load with our "hot" wire, we assume all the voltage drop occurs across the load, and none appears across the wires to and from that load. This would mean that the voltage on the neutral (also called the return wire) is automatically zero at all times, and automatically equal therefore to our reference: the ground potential.
If this were true we could dispense with the return wire and simply drive a copper rod into the ground right next to the load and connect the return side of the load to it. But a hundred miles of dirt leading all the way back to the power plant is not a good conductor, and the transmission losses would be really big. So we furnish a neutral return wire instead and run it all the way back to the power plant along with the hot wire.
Now that return wire should be at zero potential, but because a hundred miles of return wire has some (small) resistance, there will be a (correspondingly small) voltage drop across it and right next to the load, the voltage of the return wire will be perhaps a volt for example above ground while it is carrying the load current.
If the load current is 1000 amps and the return voltage is one volt, we will have an electrical arc welder on our hands if the return wire ever fails anywhere along its length- and when the wire burns out at that point, the return line voltage at the load jumps up to the source voltage and now both sides of the load are hot.
This means the load now presents a shock hazard and we have started a fire at the break in the return line.
The purpose of the third (ground) wire is to provide an emergency path to ground in case a short circuit occurs in the load or a fault arises in the return line for any reason. Normally, zero current flows through the ground line and all the load current flows through the return at near-zero voltage, and Ohm's law is satisfied- in the approximation that the load resistance is much greater than the return line resistance.