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Let's say I have some electrical appliance plugged into the wall outlet and turned on. If one of the wires coming from the plug is stripped bare and I touch it, what would happen?

I ask this because I saw on a youtube video about electrical engineering, the ground wire can be connected to the conductive metal casing of an electrical appliance so in the event that the hot wire was somehow making contact with the casing then it would take the low resistance path through the ground wire and save a person from an electrical shock. But if you are touching that metal casing which is connected to both hot and ground, how are you protected? Would you still not be in contact with a closed circuit and potentially get electrocuted?

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You've got good answers as far as some of the safety aspects, so I'm just going to clarify something about the ground. There is an additional benefit to the low impedance path it provides. The point is not simply for more current to flow through the ground and less through you, the point is to have so much current flow through the low impedance path provided that the circuit breaker or fuse trips nearly instantly. This greatly decreases the danger of faults since for you to be shocked as an additional path to ground, you have to be in contact with the device in question at the moment of the fault. The scaffold incident mentioned in another answer shows where metal is providing a path to ground but people are shocked anyways, but I would note the scaffold has rubber wheels, which even when wet, would isolate the upper metal part of the scaffold. The wheels also have low surface area in contact with pavement, which is itself a poor conductor, even when wet. If they had had a ground conductor terminated to the scaffold and the metal parts of the scaffold bonded together, it is possible the current would have mostly bypassed the workers, leaving them alive.

An electrical danger chart from wikipedia:

enter image description here

It's for AC current and on the vertical is the time you're exposed and the horizontal is amount of current so we can look and see that 50mA for a second or more may stop the heart, and any current above that exceeds what is necessary to kill. 120 volts is enough voltage with the average person in average clothing. What exactly constitutes a "Low impedance ground path" is affected by the source voltage, impedance and current limit. In the case of 120v or 240v residential lines, a line protected by a 50A circuit breaker requires a larger grounding/bonding wire than one protected by a 15A circuit breaker because for the breaker to trip, a fault at the same voltage must cause more than 3 times as much current to flow. The faster the surge, and the faster the breaker trips, the shorter the surge is. You may have noted that "low impedance path to ground" is quoted, not "low resistance". The ground network must not just be low enough resistance to allow a high current flow and trip the breaker, it must also be low inductance to prevent delay in tripping due to inductive effects.

Now let's look at how much resistance a human has:

enter image description here

You can see from the chart on the right that if you're wet you have much lower resistance, so lets say you're in the rain and you're leaning with one hand on the casing of a piece of equipment. Wet palm touch says your resistance is as low as 1000 ohms. If that piece of equipment is ungrounded and becomes energised to 120VAC, current flow will be equal to

I=E/R

I=120V/1000Ω

I=120mA

So that has a good chance of being lethal. Let's say the device is grounded at the time of the short such that 100 amps flow for a moment on a 15A line, tripping the circuit breaker almost instantly(100A is conservative), in the instant the short occurs and that current flows, the resistance of the 15A supply line and source impedance will cause a voltage drop, end effect being that you are exposed to much less than 120V for less than a hundredth of a second.

Or to look at a piece of equipment fed by a 75f run of 14AWG copper wire, the electricity has to go both ways, so we can calculate the resistance of 150f of 14 gauge wire as 0.379 ohms. So if we apply a perfect 120V to it when the equipment is drawing the maximum 15A, the wires have a volt drop of

E=IR=15A*0.379Ω=5.685V

So even with the full 15A rated current flowing and a reasonable length wire run you can get significant voltage drop. You only have 114.315V at the device. Now lets assume a 14 gauge ground wire and look at how much current we would expect in this example with a short.

I=E/R=120V/0.379Ω=316 amps

Needless to say this will cause a significant voltage drop that will protect you while the current briefly flows, and much more than the roughly ~5x rated current required to trip the circuit breaker near instantly.

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Welcome to the board! Let's start with a caution: random YouTube videos are not a good way to learn about electrical safety.

Your first question: what if you touch a bare wire connected to an electrical outlet? If it's the neutral (often white in USA) or ground (green) wire, nothing, because these are at ground potential. If it's a hot (black) wire, then you're at risk of a shock, because that wire is at a potential of 110V or 220V relative to ground.

The effects will depend how much current flows through your body, and the path it takes. If you're insulated from ground (rubber sneakers) and just touch the wire, you may feel a strong tingle, and your arm may jerk, disconnecting yourself. If you're holding a metal water pipe with the other hand, and you grab the uninsulated hot wire, you are at risk of being electrocuted, because the current will be flowing across your chest and potentially affecting your heart.

I'm not going to go into the medical details unless you want them. Suffice it to say it can send your heart into a fatal bad rhythm (arrhythmia) and you could die. If a great deal of current flows, it can burn tissues.

Now, if an appliance has a metal case which is grounded, that provides some protection, but it's not perfect. If the hot conductor touches the case, a large short-circuit current will flow, and that should open the circuit breaker in the distribution panel. If it doesn't, then the appliance case may be at a potential of about half the line voltage, and could still shock you. This is rarely the case.

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First of all it's important to be clear that being electrocuted means death by electrical shock where a shock may cause injury but is not fatal. You seem to be mixing these two terms.

As far as what would happen if you touched a closed circuit, the answer is that it depends. Keep in mind that electricity tends to follow the path of least resistance back to its source. If YOU are that path with a low enough resistance, you will get shocked and possibly electrocuted. If you are not that path, some electricity may still flow through your body and shock or electrocution may still result. It just depends on how much current flows through your body and what parts of your body are in the path.

The very best approach is to take precautions to avoid electric current flowing through your body.

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    \$\begingroup\$ Please don't say "electricity follows the path of least resistance" - Electricity follows all possible paths - more current will flow in the path with the lowest resistance, but current flows in all other paths as well. \$\endgroup\$ Commented Jan 21, 2021 at 0:31
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Let's say I have some electrical appliance plugged into the wall outlet and turned on. If one of the wires coming from the plug is stripped bare and I touch it, what would happen?

Well, please don't do that. If it is the hot wire, you will probably get a shock. If it is the neutral wire you probably won't get a shock (but don't do it anyway, because you still could get shocked from the neutral wire, or you might THINK it is neutral but it is really hot).

But if you are touching that metal casing which is connected to both hot and ground, how are you protected? Would you still not be in contact with a closed circuit and potentially get electrocuted?

Well, you are protected two ways. First, if the hot wire is touching ground, and assuming the electrical system was all wired correctly, a very large current should flow through the hot wire and ground, and blow the fuse or trip the breaker. So that condition is not what I would consider to be a stable condition. This type of fault should clear itself very quickly.

But, even if it didn't self-clear, the resistance through the ground wire should be much, much lower than through you, so if you receive any shock at all it should be mild and non-lethal.

So quite a few things have to go wrong or be done incorrectly before you get shocked. Also, nowadays there is a special type of circuit breaker (GFCI or RCD) that can detect when small ground faults occur and trip the breaker. This is even one more layer of protection that may be in place depending on where you live and when the electrical system was done.

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