Like the title says what does it exactly mean when something is grounded? What does it serve for with humans and electrical system?
Also presume someone somehow gets zapped by a massive amount of energy from some source: is it safer or worse to be grounded and does it matter what we are grounded to?
In: Physics
The universe at large, or at least the parts we can see, has zero net electric charge. For every bit of positive charge somewhere, there is the same amount of negative charge somewhere.
For the most part, these charges are in the same place. Almost every atom has the same number of electrons and protons – net zero charge.
Given enough time, any charge that forms will sort of disappear into the din – any errant proton will find an errant electron and we once again have no net charge anywhere.
This is the ‘ground’. By connecting an electrical circuit to it, we can fix the voltage of that wire to be zero – the same voltage as most of the rest of the universe. In some situations, this can be a good thing, while in others it can cause electricity to flow in unwanted ways.
It depends on what kind of circuit you’re talking about, but at least for your home AC power, a “ground” connection leads eventually into the literal ground. Electricity goes from where there is more of it to where there is less of it. This can be a positive *or* negative voltage potential. If there are too many electrons they will go to where there are fewer; and, if there are too few electrons (or too many positively charged “holes”) electrons will flow into the holes.
With your home AC power, the voltage alternates between +110 and -110v and the reference – the zero voltage point is, ultimately, the literal ground. The ground is big^[citation ^needed] and can either absorb extra electrons or give up electrons very easily without affecting the overall charge because you have the entire planet’s worth of electrons and holes to mess with. The “hot” side of your socket provides the power by alternating between ±110v. The neutral side connects – eventually – to the ground, which provides a place for those electrons to go or come from as the current alternates. The neutral side first goes through various things along the line back to a transformer or a power station to monitor the flow of electricity.
The *ground* wire – if the plug has one – connects directly to a ground rod or probe (just a long-ass chunk of metal embedded in the ground) probably under your home, or maybe to metal plumbing if it goes into the ground. The ground wire also connects to any metal surfaces on the device you’re plugging in.
So let’s say you’re about to use your microwave, but unbeknownst to you there’s a short in it. The hot wire coming into the microwave has been damaged and a piece of that wire is touching the metal casing of the microwave. Let’s say there’s no grounding wire. Where is that power going? Right now, nowhere. The voltage is *trying* to move electrons around, but there’s no place to take them or give them, so they don’t move. Then, you go to use the microwave and touch the case. You are touching the microwave, and your feet are touching the floor, and the floor is touching the ground, and the hot wire now has a place to move electrons to and from, *through your body*. This is obviously bad for you.
The grounding wire provides a direct connection to the ground through the case. Since it’s a metal wire going all the way to a metal grounding probe or metal plumbing the path has a much lower resistance than trying to go through your body and through the floor. Since electricity takes the path of least resistance, it will flow through the ground wire instead of you and you’re much safer. Note that the grounding wire doesn’t stop the electricity from flowing at all; it just gives it somewhere to go that is the least dangerous path. This also prevents fires because a short somewhere can cause electricity to arc between whatever the hot wire is touching that it shouldn’t be touching and some other part of the device. Again, the grounding wire gives it a more direct and safer route.
Since the ground plug bypasses the neutral wire, it also helps your plug “detect” that there’s a short. That’s what a GFCI socket does: *basically* when electricity is flowing through the hot side and isn’t also flowing through the neutral side, it must be going *somewhere* and odds are good it’s going somewhere that it shouldn’t – like, through your body. The socket has a breaker that trips when this happens so even if there’s no grounding wire on your device and there’s a short and you touch it you’ll only get a very short, probably not lethal but still very painful shock before the breaker trips, cutting power. This is important in the kitchen and bathroom because there’s a lot of water and a lot of metal that might lead to metal plumbing that goes into the ground. If you touch a hot wire while wearing shoes and standing on a typical insulated floor with a wood subfloor, odds are good you won’t get much of a shock because the resistance is too high (**still don’t try it, though, obviously**). When you’re in a bathtub full of soapy water with a metal drain there’s not nearly as much resistance so you will definitely get electricity flowing through your body and it will definitely kill you if something doesn’t stop it.
Unfortunately, in electrical engineering that term has multiple slightly different meanings, depending on the context.
For a layman, it usually refers to being at the same voltage level as “Earth ground” or “safety ground”. Some devices have a metal chassis or casing that is actually connected to the ground. This provides shielding against unwanted electromagnetic radiation, and it can act as a safety feature. If a high voltage fault occurs, it is likely to go to this piece of metal *before* it gets to a human, thus protecting the human.
If you’re going to get hit by high voltage, it’s best to NOT have your body between it and Earth ground. The electricity is going to tend to flow there, and if you are in the way it’s going to flow through you. If the electrical charge carries enough power (like lightning or a high voltage line) this can be a very bad thing.
If you place a ball on a table, the ball might fall off the table on its own (if it were moving to begin with), and fall to hit the *ground*
However when on the ground, the ball will never spontaneously “fall upwards”. And that should make plain old common sense.
In electricity, instead of gravity we have “voltage”. Performs the same function, except we have control over it.
Saying something has a specific voltage doesn’t mean anything by itself. If the ball is on the table, but there are borders on the table preventing the ball from falling, ground is irrelevant. It’s on the ground as far as it’s concerned.
So we have to make up some *reference*, some particular value of the voltage that we are just going to call “zero” or “ground”, and all other voltages will be measured *in relation* to the ground.
Different places can have different levels of electrical charge. When you connect a place with high amounts of electrical charge to one with low amounts of electrical charge, they will attempt to balance out so the charge is even across the entire connection.
Think of filling your sink full of dirty dishes. The water may start on top of that plate precariously perched on a few pots, but it very quickly runs down to the bottom. Sometimes you’ll get pools of water in dishes/pots – until they overflow the edges and continue their journey down. But the basic principle is that the water wants to spread out evenly. Sometimes it just can’t.
‘Ground’ is the place where electrical charge is lowest and the high electrical charge is attempting to drain towards.
When something is ‘grounded’, that just means it is connected to ground.
Now, if I’ve got an electrical appliance, being ‘grounded’ is a good thing. That means the high electrical charges in the device are connected via a very efficient pathway to a place where there isn’t much electrical charge. The benefit of this is that the electrical charge won’t be taking the relatively low efficiency path through me if I touch the wrong thing.
Likewise, if I’m working on something electrically sensitive, I want to be grounded. I don’t want high electrical charges building up on my hands – that are touching the sensitive components – but instead dissipating elsewhere.
On the other hand, if I’m grabbing a power line, I absolutely do not want to be ‘grounded’ because I don’t want all that power flowing through me – I want it flowing down the power line.
If you have a switch, light fixture or some kind of machine that has power running to it, you only want it running to specific parts of that machine. A loose wire or something else can electrify the housing and create a danger to the user. For that reason a wire is attached to the housing and is given a low resistance path back to earth instead of going through you. On plugs and outlets this what the bottom prong is.
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