I know that electricity doesn’t just dissolve in the ground, it must return to the power source. But once the electricity is in the grounding device, how does it find its way back to the substation if it can be relatively far away?
Edit: I know ground isn’t used in normal working mode and where I live there’s no grounding in sockets.
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A lot of these answers seem to be trying to explain what electricity is, but to answer your question simply: if there’s a fault to earth, it will indeed flow back to the source (upstream transformer) through the earth.
Getting slightly technical, and this depends on how the transmission system is set up, some of the fault goes back along the static/shield wire, if it’s continuous along the transmission line. In analysis, this would be the split factor.
When designing grounding systems, you want a low impedance to remote earth and fast clearing times in order to reduce the step/touch potentials in fault conditions. This is done typically with an adequate ground grid and the use of copper rods that are driven into the earth. In a residential setting, this is why you should find a copper rod driven into the ground near your electric meter/where the electricity comes out of the house.
Grounding is used to protect users from stray currents/sparks when using electricity in flammable environments.
For example you use an electric pump to pump a liquid from A to B. Something get’s broken in the electric circuit and a wire touches the metal casing? If you touch the casing the current will start flowing from you to the ground. Not something you want. When a pump is grounded. The casing is connected to the ground. When the same situation happen the current flows through the wire instead of you. Hopefully blowing a breaker making you aware of a fault.
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>how does it find its way back to the substation if it can be relatively far away?
Good news! It doesn’t have to all the way back to the substation. If you live in a properly grounded house, then you have a cable that goes from your panel, outside your house, and connects to a steel plate that lays a couple of feet deep in the ground.
That plate makes sufficient contact with the earth around it that it can drain hazardous voltages safely. Now you might ask why steel? Well steel also conducts electricity, even if not as well as copper, silver or aluminum. The application here also isn’t optimal performance, but making surface contact with the ground.
Remember, the ground is mostly there for safety, so that any fault/hazard currents have a path to get out that is of lower resistance than your body.
Engineer here. I read the top few answers and I don’t think any of them adequately answered your actual question.
You sound like you’re familiar with how electricity flows in closed loops/circuits (i.e. you know it takes two wires to light up a lightbulb) but want to know how “ground” completes the circuit.
The answer is simple and relies on two facts:
1. Although earth isn’t seen as being particularly conductive (in the sense that you can’t really make wires out of rocks and sand), the planet is so massive (the crust alone is many many kilometers thick) that if you connect to it well enough, it’s actually a pretty good conductor. In a building, grounding is done by a massive copper pole buried deep under ground, so it makes really, really good contact with the earth.
2. This depends on the country and the electrical standards in place, but in UK-style systems like in my country, the substation’s neutral wire is connected to ground. So let’s say you stick your finger inside a toaster in your house. Current follows this path: Substation Transformer -> live (hot) power line -> your house -> toaster -> your finger -> your feet -> the ground under your feet -> the ground between you and the substation -> substation earthing rod -> bonding line between earth and neutral at substation -> substation transformer.
As you can see it’s a complete circuit. From the substation/power station’s standpoint since it has a bonded neutral, earth and neutral are both equally usable current return paths. In some other countries with different electrical codes, the bond might not exist, or might be done at a different place (for example at input to the house itself).
And if the toaster was operating normally the path would simply be substation transformer -> live wire -> toaster -> neutral wire -> substation transformer.
Now, you might be thinking why we bother with ground, or how it makes things safer. The answer is because your house is protected by devices called GFCIs (ground fault circuit interrupters). They work in a very simple way. They measure the current going out of the live wire and the current going into the neutral wire. If the difference between the two gets too great (normally over 30 milliamps), it will trip because that means electricity is going somewhere it’s not supposed to go (like through a human).
Let’s say you have a washing machine and a live wire inside it breaks and makes contact with the metal case of the machine. Let’s say there was no earth wire and no GFCI. The entire metal case of the washing machine is now live. The instant you touch it, electricity will flow through you and into earth (because you’re standing on it), killing you in the process.
But with earthing and GFCI, the entire metal case of the washing machine is connected to earth. The instant that live wire makes contact with the metal case, a huge current will flow from live to earth (bypassing neutral) and the GFCI will detect it and trip. And you won’t be able to turn on that outlet before you unplug the faulty washing machine.
So that’s why every human-touchable metal part of any appliance is earthed. It makes sure that it’s at the same electrical potential as you are (you being grounded by virtue of standing on the ground), so current will never flow from anything metal to you, unless there was a fault in the earthing. In that case, the case of the appliance could still become live, and the GFCI wouldn’t trip (because the earth return path is broken). But as soon as you touch it, you’ll be completing the circuit to earth, the GFCI will sense it, and it will trip before your heart stops.
BTW, did you know large, long undersea cables sometimes don’t include the return line – they rely on the earth for a “free” return line (no additional copper required to complete the circuit). It’s not without its problems (galvanic corrosion for example), but it’s an interesting proof of what I said earlier that the earth is large enough to be considered conductive. So let’s say you had a large, DC undersea cable. Instead of running thick cables for both plus and minus, you’d only run a single plus cable between the two countries. Then each country would have a ground connection, and the”minus” wire is the earth itself, so the project just saved 50% of the copper cost.
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