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Does a dangling wire really electrocute me if I'm standing in water?
The 2019 Stack Overflow Developer Survey Results Are InDoes this strategy for crossing electrified water work?Conductivity of water, and risk of shock? (fact checking)What are some cheap, reliable methods of water-proofing switches and buttons?How do I “cap” a wire so it doesn't short or electrocute someone?How does a “break” in the neutral wire enable it to reach the full line voltage?Resistance Wire Circuit Safety Around WaterCan a charged 120v high voltage capacitor really kill you?How does grounding the circuit provides safety?Water on Li-Ion battery fire: good idea, bad idea, or neutral?Why is touching the live wire of a socket dangerous inside an apartment few stories up?12v nichrome wire water heater. Is it safe?
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We've all seen this scenario in movies; somebody has to cross a room half filled with water and there is a dangling electric wire that shoots sparks everywhere. The poor person has to cross the room but cannot do so because if the wire hits the water he is obviously electrocuted since water is a conductor.
But is it so simple in real life? If I'm really standing in water in a room, and a high voltage wire hits the water, how does the electricity flow through me to electrocute me? Only my feet are touching the water, no other bodypart of mine is touching anywhere. And realistically there probably would be some piping etc. connected to ground somewhere that would conduct the current to ground. How would I be electrocuted if the current just flows past me?
I suspect this is similar to the well known situation of somebody dropping a hair dryer into a bathtub with a person in it. Why doesn't the current in this situation flow either from the live wire to the neutral wire or through the drain to the ground? Why does simply being in "high voltage water" electrocute me? (And yes, I know the scenario is not so likely with modern appliances but let's consider this in theory).
safety
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show 7 more comments
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We've all seen this scenario in movies; somebody has to cross a room half filled with water and there is a dangling electric wire that shoots sparks everywhere. The poor person has to cross the room but cannot do so because if the wire hits the water he is obviously electrocuted since water is a conductor.
But is it so simple in real life? If I'm really standing in water in a room, and a high voltage wire hits the water, how does the electricity flow through me to electrocute me? Only my feet are touching the water, no other bodypart of mine is touching anywhere. And realistically there probably would be some piping etc. connected to ground somewhere that would conduct the current to ground. How would I be electrocuted if the current just flows past me?
I suspect this is similar to the well known situation of somebody dropping a hair dryer into a bathtub with a person in it. Why doesn't the current in this situation flow either from the live wire to the neutral wire or through the drain to the ground? Why does simply being in "high voltage water" electrocute me? (And yes, I know the scenario is not so likely with modern appliances but let's consider this in theory).
safety
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38
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I seriously suggest that you don’t do any testing.
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– Solar Mike
2 days ago
7
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The answer is: it depends, there are many variables involved like: distance between you and the wire, voltage on the wire, conductivity of the water, water level, material of the bath, if the bath is metal or conductive: how well is it grounded, is it painted. I could go on for a while. All this determines the amount of current passing through the person. Also thin persons can handle less current than "less thin" persons. There can be no clear answer.
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– Bimpelrekkie
2 days ago
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Your ground symbol in the sketch implies that the power on the wire is referenced to ground. It may not be. The power on that line could be isolated from ground.
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– scorpdaddy
2 days ago
5
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This question reminded me of the following video on Youtube made by Electroboom: youtube.com/watch?v=dcrY59nGxBg Where he actually does an experiment to confirm this
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– Ferrybig
2 days ago
2
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"There's an exposed wire over the bathtub ... Oh yeah! Shock wire! I call it that 'cause if you take a shower and touch it.....YOU DIE!" - Ron Swanson / Andy Dwyer - Parks and Rec
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– NKCampbell
2 days ago
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show 7 more comments
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We've all seen this scenario in movies; somebody has to cross a room half filled with water and there is a dangling electric wire that shoots sparks everywhere. The poor person has to cross the room but cannot do so because if the wire hits the water he is obviously electrocuted since water is a conductor.
But is it so simple in real life? If I'm really standing in water in a room, and a high voltage wire hits the water, how does the electricity flow through me to electrocute me? Only my feet are touching the water, no other bodypart of mine is touching anywhere. And realistically there probably would be some piping etc. connected to ground somewhere that would conduct the current to ground. How would I be electrocuted if the current just flows past me?
I suspect this is similar to the well known situation of somebody dropping a hair dryer into a bathtub with a person in it. Why doesn't the current in this situation flow either from the live wire to the neutral wire or through the drain to the ground? Why does simply being in "high voltage water" electrocute me? (And yes, I know the scenario is not so likely with modern appliances but let's consider this in theory).
safety
$endgroup$
We've all seen this scenario in movies; somebody has to cross a room half filled with water and there is a dangling electric wire that shoots sparks everywhere. The poor person has to cross the room but cannot do so because if the wire hits the water he is obviously electrocuted since water is a conductor.
But is it so simple in real life? If I'm really standing in water in a room, and a high voltage wire hits the water, how does the electricity flow through me to electrocute me? Only my feet are touching the water, no other bodypart of mine is touching anywhere. And realistically there probably would be some piping etc. connected to ground somewhere that would conduct the current to ground. How would I be electrocuted if the current just flows past me?
I suspect this is similar to the well known situation of somebody dropping a hair dryer into a bathtub with a person in it. Why doesn't the current in this situation flow either from the live wire to the neutral wire or through the drain to the ground? Why does simply being in "high voltage water" electrocute me? (And yes, I know the scenario is not so likely with modern appliances but let's consider this in theory).
safety
safety
asked 2 days ago
S. RotosS. Rotos
8491814
8491814
38
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I seriously suggest that you don’t do any testing.
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– Solar Mike
2 days ago
7
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The answer is: it depends, there are many variables involved like: distance between you and the wire, voltage on the wire, conductivity of the water, water level, material of the bath, if the bath is metal or conductive: how well is it grounded, is it painted. I could go on for a while. All this determines the amount of current passing through the person. Also thin persons can handle less current than "less thin" persons. There can be no clear answer.
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– Bimpelrekkie
2 days ago
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Your ground symbol in the sketch implies that the power on the wire is referenced to ground. It may not be. The power on that line could be isolated from ground.
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– scorpdaddy
2 days ago
5
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This question reminded me of the following video on Youtube made by Electroboom: youtube.com/watch?v=dcrY59nGxBg Where he actually does an experiment to confirm this
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– Ferrybig
2 days ago
2
$begingroup$
"There's an exposed wire over the bathtub ... Oh yeah! Shock wire! I call it that 'cause if you take a shower and touch it.....YOU DIE!" - Ron Swanson / Andy Dwyer - Parks and Rec
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– NKCampbell
2 days ago
|
show 7 more comments
38
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I seriously suggest that you don’t do any testing.
$endgroup$
– Solar Mike
2 days ago
7
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The answer is: it depends, there are many variables involved like: distance between you and the wire, voltage on the wire, conductivity of the water, water level, material of the bath, if the bath is metal or conductive: how well is it grounded, is it painted. I could go on for a while. All this determines the amount of current passing through the person. Also thin persons can handle less current than "less thin" persons. There can be no clear answer.
$endgroup$
– Bimpelrekkie
2 days ago
$begingroup$
Your ground symbol in the sketch implies that the power on the wire is referenced to ground. It may not be. The power on that line could be isolated from ground.
$endgroup$
– scorpdaddy
2 days ago
5
$begingroup$
This question reminded me of the following video on Youtube made by Electroboom: youtube.com/watch?v=dcrY59nGxBg Where he actually does an experiment to confirm this
$endgroup$
– Ferrybig
2 days ago
2
$begingroup$
"There's an exposed wire over the bathtub ... Oh yeah! Shock wire! I call it that 'cause if you take a shower and touch it.....YOU DIE!" - Ron Swanson / Andy Dwyer - Parks and Rec
$endgroup$
– NKCampbell
2 days ago
38
38
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I seriously suggest that you don’t do any testing.
$endgroup$
– Solar Mike
2 days ago
$begingroup$
I seriously suggest that you don’t do any testing.
$endgroup$
– Solar Mike
2 days ago
7
7
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The answer is: it depends, there are many variables involved like: distance between you and the wire, voltage on the wire, conductivity of the water, water level, material of the bath, if the bath is metal or conductive: how well is it grounded, is it painted. I could go on for a while. All this determines the amount of current passing through the person. Also thin persons can handle less current than "less thin" persons. There can be no clear answer.
$endgroup$
– Bimpelrekkie
2 days ago
$begingroup$
The answer is: it depends, there are many variables involved like: distance between you and the wire, voltage on the wire, conductivity of the water, water level, material of the bath, if the bath is metal or conductive: how well is it grounded, is it painted. I could go on for a while. All this determines the amount of current passing through the person. Also thin persons can handle less current than "less thin" persons. There can be no clear answer.
$endgroup$
– Bimpelrekkie
2 days ago
$begingroup$
Your ground symbol in the sketch implies that the power on the wire is referenced to ground. It may not be. The power on that line could be isolated from ground.
$endgroup$
– scorpdaddy
2 days ago
$begingroup$
Your ground symbol in the sketch implies that the power on the wire is referenced to ground. It may not be. The power on that line could be isolated from ground.
$endgroup$
– scorpdaddy
2 days ago
5
5
$begingroup$
This question reminded me of the following video on Youtube made by Electroboom: youtube.com/watch?v=dcrY59nGxBg Where he actually does an experiment to confirm this
$endgroup$
– Ferrybig
2 days ago
$begingroup$
This question reminded me of the following video on Youtube made by Electroboom: youtube.com/watch?v=dcrY59nGxBg Where he actually does an experiment to confirm this
$endgroup$
– Ferrybig
2 days ago
2
2
$begingroup$
"There's an exposed wire over the bathtub ... Oh yeah! Shock wire! I call it that 'cause if you take a shower and touch it.....YOU DIE!" - Ron Swanson / Andy Dwyer - Parks and Rec
$endgroup$
– NKCampbell
2 days ago
$begingroup$
"There's an exposed wire over the bathtub ... Oh yeah! Shock wire! I call it that 'cause if you take a shower and touch it.....YOU DIE!" - Ron Swanson / Andy Dwyer - Parks and Rec
$endgroup$
– NKCampbell
2 days ago
|
show 7 more comments
6 Answers
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Oh yes. The phenomenon is called "Electrical Drowning".
In this tragic case, a girl decided to dance in a fountain, unawares that the underwater lights had a ground fault. Her muscles contracted and she fell down. One friend went in to try to grab her, and she too lost control of her leg muscles and fell down. Her two other friends tried to rescue the first two.
Firefighters showed up, one tiptoed in, lost it and his friends yanked him out. The firefighters spent 15 minutes trying to find the shutoff switch.
The problem with falling down in water is that you drown. All four girls did.
In fact, multiple victims is often the only clue to an electrical drowning.
This is why any beachside installations now require GFCI and shutoff switches, and why you should not swim near a boat on shore power.
Why electrical drownings happen
You've seen problems involving grids of resistors. That's what water is, a 3-D grid of resistors, and you also are some of the resistors.
Electrical current travels all available paths in proportion to their conductance (1/resistance). 1-10 mA is enough to start causing problems for a sensitive person; 100 mA is lethal in its own right.
Electricity wants to get back to source (the pole transformer's neutral), and the NEC standard for a grounding rod is 25 ohms. You can do the math here.
Well, I get 120 V through a 24 ohm resistor = 5 amperes. So only a tiny fraction of that current need go through you to nail you. If we rely on that article's 20 mA, then 1/250 of the current is enough to drown you.
Note also: this is not nearly enough to trip a typical 13, 15, 16 or 20 A branch circuit breaker.
However, a GFCI breaker will trip at 6-8 mA. That greatly improves the prognosis. This narrows it down to a highly improbable combination of events where the current is naturally limited to less than 6 mA, and almost all goes through you, and you're ultra-sensitive.
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Many such cases, like this one, don't involve drowning. The current stops the heart (and other things).
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– Brock Adams
yesterday
5
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"That's what water is, a 3-D grid of resistors, and you also are some of the resistors." Best analogy I have ever seen to describe this issue. Bravo!
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– J. Raefield
yesterday
3
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One additional point: Compared to fresh water, the human body is a particularly low resistance path, so the current will preferentially go through you.
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– Martin Bonner
16 hours ago
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Then how do you explain this? youtube.com/watch?v=dcrY59nGxBg
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– Chloe
8 hours ago
add a comment |
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In something like water electricity does not "flow to ground" in a neat straight line. There is a potential difference between sections of water radiating out from the HV contact point. That might also mean that your feet are at different potentials, and there will be current flow which could be fatal. This is one reason why cows in fields can be electrocuted by a nearby lightning strike. The voltage difference between their feet can be thousands of volts.
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It also might not flow to ground at all. If the dangling wire, for example, was connected to a UK shaver outlet (powered by an isolation transformer) then the only available path is back the other wire to the other side of the transformer.
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– J...
2 days ago
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Yes, this. There is currently flowing out in all directions to different grounding points. If somehow floor was non-conducting and very well isolated except for a single very good ground very near the wire then most of the room might be safe, but I’m not gonna be the one to verify that.
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– John Hascall
2 days ago
3
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Even humans can be electrocuted by a nearby lightning strike. Paradoxically, there are many aspects of a strike that are worse if it hits the ground near you than if it hits you directly (the former can stop your heart if the electrical potential is great enough, whereas the latter "just" causes burns and lung damage).
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– forest
2 days ago
1
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Especially considering that most water you encounter day-to-day is fresh water. The human body is saltwater, which has a lower resistance, so electricity will preferentially flow through you.
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– skyler
yesterday
2
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Regarding potential differences on the ground in a lightning strike: That's why you should have your feet close together (to minimize the potential difference between them and hence the current flowing through them) while you squat (to minimize the chances of a direct hit which would at least give you an instant new tatoo).
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– Peter A. Schneider
17 hours ago
add a comment |
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I think that the answer is pretty simple - you are a better conductor than fresh water. I read this somewhere and it made me giggle then: "Humans are just big bags of salt water", which is true. A current of 1 mA through the heart is enough to cause a heart attack, so at 220 V, 220 kΩ resistance is not enough. You are less than 220 kΩ, especially when in water. Skin is the only insulator we have.
Just don't try it.
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Yup, this is how you can get electrocuted--you have a considerably lower resistance than fresh water so if your body can be used to go to the ground it will--the current is happy to flow up one leg and down the other.
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– Loren Pechtel
yesterday
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Actually this is wrong: the worst shock will happen in a slightly salty water with the same conductance as a human body. Think about impedance matching: maximum power transfer happens when Zload=Zsource.
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– Dmitry Grigoryev
yesterday
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@DmitryGrigoryev You are right.
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– Atizs
yesterday
1
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@DmitryGrigoryev: Maximum power transfer when the voltage is regulated happens for a matched load. Therefore, replace the source by its Thevenin equivalent, and the load should be the conjugate of the Thevenin-equivalent series impedance. That's totally unrelated to impedance equaling that of the water it displaces -- you're matching to the wrong part of the circuit. (Another statement of the issue, you are matching resistivity when you should be matching resistance)
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– Ben Voigt
21 hours ago
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"Ugly bags of mostly water!" You made me remember a little bit of Star Trek humor.
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– enorl76
9 hours ago
add a comment |
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how does the electricity flow through me to electrocute me?
I already posted that picture once in a question about electric eels:
Source: phys.org Credit: Kenneth Catania
Electricity doesn't flow along a single preferred path, it flows in the entire water body with different intensities. If you happen to be in a path with high enough current, you'll get electrocuted.
An interesting corollary to this fact is that you'll get the worst shock when you and the water have comparable conductance. If the water is much more conductive than you, even high currents will only create a small voltage difference, which may not be harmful. If the water is much less conductive, the voltage difference may be huge, but the current will be limited.
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That's a nice illustration of a tricky concept.
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– Wossname
yesterday
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The current flowing through a body in water depends solely on its resistance and the sustained voltage, not (directly) on the resistance of the sorrounding water. The caveat "directly" is because a high resistance surrounding makes the potential difference at your body collapse (it happens in the high resistance part, and the current through your body making that drop happen may not be harmful). But the case that your body has a higher resistance than the surrounding won't have any benefit at all. (You'd need a power source though which can sustain the voltage in spite of the high currents.)
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– Peter A. Schneider
17 hours ago
add a comment |
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Just being in "high voltage water" won't electrocute you, just as birds can happily perch on 10+kV power lines (and linemen can be dropped onto live lines for maintenance work), since there's no path, but as you say, there's always going to be a path to ground somewhere in that water, and so there'll be currents flowing through the water. Since that means that there's potential differences across the water at different points, you'd experience that between your feet, and since the human body is a good conductor, other than the skin, which reduces greatly in resistance when wet, that would allow possibly lethal current to flow through the torso. People can and do get electrocuted standing in salty bilge water on 24V systems on boats, it doesn't take a lot of voltage if the resistance is low enough.
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I'm pretty sure birds are safe because of their low capacitance (from their small size). It ensures very little AC current can flow through them.
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– forest
2 days ago
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Electrocuted by 24V? Do you have a case reference?
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– Peter A. Schneider
17 hours ago
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@forest They are safe because the potential difference between their feet is minimal and they are not touching any grounded objects. OK, if they had a high capacitance some initial current would flow into them upon contact, but nothing "flows through them" unless they touch something else.
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– Peter A. Schneider
17 hours ago
add a comment |
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Definitely don't try any of these things. This is definitely not intended to imply you should be complacent about any of the dangers of electricity, but there are numerous things that are often extremely wrong in movie handling of electricity, particularly in this type of scene. Often effects are used to simply make the electricity do what the story requires, so a few things:
- Overcurrent and other fault protection: In most of the world, every circuit has over current protection and many circuits have ground fault or arc fault protection. As manufacturing capability increases, we've been able to add more ways to protect electrical installations and make them safe. In a futuristic scenario with improved technology, there is usually no reason this would have changed. Faults damage equipment, so even in a scenario where disregard for human life is written in, systems would have advanced precautions to limit property damage. At any rate, often the conductor you see creating the danger is actually a cable, with visible wires sticking out of the end, whatever the prop department thought would look cool. In many of these cases, the conductor, as presented, would have shorted between it's own conductors and tripped its overcurrent device or GFCI. In order for the conductor to stay live, something else must go wrong, like it miraculously not shorting out when being pulled loose from what it was connected to, falling, and or jiggling without shorting out on itself or touching something made of metal, or the breaker welding closed(which does occasionally happen).
- Electricity flows more on paths of less resistance. You could place large copper wire, a wet log and a strip of asphalt side by side, and connect the same voltage at once to the ends of all three. Most of the current would flow through the copper wire, much less would flow through the wet log, and a negligible amount through the asphalt, though there would be current flow in all three. If the conductors on a broken cable have enough voltage to create CGI arcs to nearby fixtures/water/whatever things that are far away, they have enough voltage to arc to its own return conductor or ground, which is sometimes mistakenly portrayed as inches away. For its own return conductor or ground to not be the target of most arcs, a second thing has to go wrong. Those conductors have to be broken somewhere between the arcing cable and the source, somehow without damaging a single high voltage cable more than would allow it to function. Electricity will not tend to travel through a meter of air to establish an arc when a 20mm arc establishes a low impedance return path.
- Electricity is often much more brutal and much less flashy than in the movies, and movies often portray a greater(or smaller) margin for survival than actually exists. As part of your training in electrical industries, especially in power distribution, there's a good likelihood you'll see a video of someone dying working with or around electricity. It's utterly terrible. Brutal, merciless, and not always quick. The actual speed that electricity can "change" and propagate at is fast enough to need quality examples to make it easy to comprehend. There are situations where high voltage is portrayed in movies as something that great dexterity, strength and skill can just deal with, and inevitably characters are sometimes shown doing something that would have killed or vaporized them. Sometimes with low voltage wires a character is shown killed by something that, as presented, would have a relatively low probability of being lethal. In the latter case I'm comfortable with that as laymen and professionals should treat something with a very good chance of killing them as something that will.
- Electricity flows in loops. Each molecule, depending on bonding, nuclei, and electron shells, tends to keep roughly a certain amount of electron in each area around it. The electrons themselves are bouncing around, and when they are not held too tightly where they are, they fly freely between nearby molecules, and the limiting factor is that when/as an electron moves out of an area that "needs" an electron, forces will be exerted on other nearby electrons as well as the one flying away to pull them in and fill the gap. Depending on structure of molecule and nuclei, different materials either bind their electrons tightly(insulators) or allow them to flow more freely(conductors). When you cause electrons to flow along a wire, new ones must replace the ones that flow away. The area you are pumping the electrons to will have too many and the area you are pumping them from will not have enough. There is nowhere for the flow to go other than back to where there are too few, as all of the other molecules around have exactly enough. No loop, no current.
- Water isn't really a good conductor. Dirty water, particularly salty water is. Pure water is not (tap water is not pure). Aside from that, if you put a generator on the shore of an ocean and strung a wire across the surface of the water to a point far out where the tip of the wire was bare, 1 meter underwater, and connected the generator to that wire and a ground rod, the generator would work to pass a current down that wire, into the water, along the earth, through the ground rod, and back to the generator, where the electrons you're pumping out need to be replaced. Because of the high(ish) conductivity of salt water, there wouldn't be high voltages/currents for too high a distance in most directions around the tip of that wire, as the flow of electrons is "attempting" to return on the shortest path possible to its source. voltage will spread out in other directions somewhat as the flowing electrons spread out to travel more freely. This is not to say that the water around the electrode is not dangerous, but to point that movies are often not specifically accurate with where current is flowing.
- Flashy arcs and sparks - Electricity is invisible. All we can see are the effects on objects as electricity passes through them. Heat, light, motion, the occasional smell. In order to draw attention to them, arcs, sparks and flashes are often brighter than they might be in real life, or of the wrong type (explosive rather than plasma, for example). The resistivity of air is around 2100V/mm, meaning to start an arc through room temperature air, you need 2100V for every mm you want the arc to jump. Once the air starts conducting and becomes a plasma, it conducts quite well, but it takes quite a voltage to start an arc.
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"•Electricity follows the path of least resistance" Not true. Give it two paths, 1000 and 1001 ohm. Does all current flow in the 1000 ohm path and no current in the 1001 ohm path?
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– winny
yesterday
2
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@Winny Good point. I spouted off a safety axiom in my effort to keep things simple =P. Corrected now. Please check the rephrase if you have the time =).
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– K H
yesterday
add a comment |
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6 Answers
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6 Answers
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Oh yes. The phenomenon is called "Electrical Drowning".
In this tragic case, a girl decided to dance in a fountain, unawares that the underwater lights had a ground fault. Her muscles contracted and she fell down. One friend went in to try to grab her, and she too lost control of her leg muscles and fell down. Her two other friends tried to rescue the first two.
Firefighters showed up, one tiptoed in, lost it and his friends yanked him out. The firefighters spent 15 minutes trying to find the shutoff switch.
The problem with falling down in water is that you drown. All four girls did.
In fact, multiple victims is often the only clue to an electrical drowning.
This is why any beachside installations now require GFCI and shutoff switches, and why you should not swim near a boat on shore power.
Why electrical drownings happen
You've seen problems involving grids of resistors. That's what water is, a 3-D grid of resistors, and you also are some of the resistors.
Electrical current travels all available paths in proportion to their conductance (1/resistance). 1-10 mA is enough to start causing problems for a sensitive person; 100 mA is lethal in its own right.
Electricity wants to get back to source (the pole transformer's neutral), and the NEC standard for a grounding rod is 25 ohms. You can do the math here.
Well, I get 120 V through a 24 ohm resistor = 5 amperes. So only a tiny fraction of that current need go through you to nail you. If we rely on that article's 20 mA, then 1/250 of the current is enough to drown you.
Note also: this is not nearly enough to trip a typical 13, 15, 16 or 20 A branch circuit breaker.
However, a GFCI breaker will trip at 6-8 mA. That greatly improves the prognosis. This narrows it down to a highly improbable combination of events where the current is naturally limited to less than 6 mA, and almost all goes through you, and you're ultra-sensitive.
$endgroup$
1
$begingroup$
Many such cases, like this one, don't involve drowning. The current stops the heart (and other things).
$endgroup$
– Brock Adams
yesterday
5
$begingroup$
"That's what water is, a 3-D grid of resistors, and you also are some of the resistors." Best analogy I have ever seen to describe this issue. Bravo!
$endgroup$
– J. Raefield
yesterday
3
$begingroup$
One additional point: Compared to fresh water, the human body is a particularly low resistance path, so the current will preferentially go through you.
$endgroup$
– Martin Bonner
16 hours ago
$begingroup$
Then how do you explain this? youtube.com/watch?v=dcrY59nGxBg
$endgroup$
– Chloe
8 hours ago
add a comment |
$begingroup$
Oh yes. The phenomenon is called "Electrical Drowning".
In this tragic case, a girl decided to dance in a fountain, unawares that the underwater lights had a ground fault. Her muscles contracted and she fell down. One friend went in to try to grab her, and she too lost control of her leg muscles and fell down. Her two other friends tried to rescue the first two.
Firefighters showed up, one tiptoed in, lost it and his friends yanked him out. The firefighters spent 15 minutes trying to find the shutoff switch.
The problem with falling down in water is that you drown. All four girls did.
In fact, multiple victims is often the only clue to an electrical drowning.
This is why any beachside installations now require GFCI and shutoff switches, and why you should not swim near a boat on shore power.
Why electrical drownings happen
You've seen problems involving grids of resistors. That's what water is, a 3-D grid of resistors, and you also are some of the resistors.
Electrical current travels all available paths in proportion to their conductance (1/resistance). 1-10 mA is enough to start causing problems for a sensitive person; 100 mA is lethal in its own right.
Electricity wants to get back to source (the pole transformer's neutral), and the NEC standard for a grounding rod is 25 ohms. You can do the math here.
Well, I get 120 V through a 24 ohm resistor = 5 amperes. So only a tiny fraction of that current need go through you to nail you. If we rely on that article's 20 mA, then 1/250 of the current is enough to drown you.
Note also: this is not nearly enough to trip a typical 13, 15, 16 or 20 A branch circuit breaker.
However, a GFCI breaker will trip at 6-8 mA. That greatly improves the prognosis. This narrows it down to a highly improbable combination of events where the current is naturally limited to less than 6 mA, and almost all goes through you, and you're ultra-sensitive.
$endgroup$
1
$begingroup$
Many such cases, like this one, don't involve drowning. The current stops the heart (and other things).
$endgroup$
– Brock Adams
yesterday
5
$begingroup$
"That's what water is, a 3-D grid of resistors, and you also are some of the resistors." Best analogy I have ever seen to describe this issue. Bravo!
$endgroup$
– J. Raefield
yesterday
3
$begingroup$
One additional point: Compared to fresh water, the human body is a particularly low resistance path, so the current will preferentially go through you.
$endgroup$
– Martin Bonner
16 hours ago
$begingroup$
Then how do you explain this? youtube.com/watch?v=dcrY59nGxBg
$endgroup$
– Chloe
8 hours ago
add a comment |
$begingroup$
Oh yes. The phenomenon is called "Electrical Drowning".
In this tragic case, a girl decided to dance in a fountain, unawares that the underwater lights had a ground fault. Her muscles contracted and she fell down. One friend went in to try to grab her, and she too lost control of her leg muscles and fell down. Her two other friends tried to rescue the first two.
Firefighters showed up, one tiptoed in, lost it and his friends yanked him out. The firefighters spent 15 minutes trying to find the shutoff switch.
The problem with falling down in water is that you drown. All four girls did.
In fact, multiple victims is often the only clue to an electrical drowning.
This is why any beachside installations now require GFCI and shutoff switches, and why you should not swim near a boat on shore power.
Why electrical drownings happen
You've seen problems involving grids of resistors. That's what water is, a 3-D grid of resistors, and you also are some of the resistors.
Electrical current travels all available paths in proportion to their conductance (1/resistance). 1-10 mA is enough to start causing problems for a sensitive person; 100 mA is lethal in its own right.
Electricity wants to get back to source (the pole transformer's neutral), and the NEC standard for a grounding rod is 25 ohms. You can do the math here.
Well, I get 120 V through a 24 ohm resistor = 5 amperes. So only a tiny fraction of that current need go through you to nail you. If we rely on that article's 20 mA, then 1/250 of the current is enough to drown you.
Note also: this is not nearly enough to trip a typical 13, 15, 16 or 20 A branch circuit breaker.
However, a GFCI breaker will trip at 6-8 mA. That greatly improves the prognosis. This narrows it down to a highly improbable combination of events where the current is naturally limited to less than 6 mA, and almost all goes through you, and you're ultra-sensitive.
$endgroup$
Oh yes. The phenomenon is called "Electrical Drowning".
In this tragic case, a girl decided to dance in a fountain, unawares that the underwater lights had a ground fault. Her muscles contracted and she fell down. One friend went in to try to grab her, and she too lost control of her leg muscles and fell down. Her two other friends tried to rescue the first two.
Firefighters showed up, one tiptoed in, lost it and his friends yanked him out. The firefighters spent 15 minutes trying to find the shutoff switch.
The problem with falling down in water is that you drown. All four girls did.
In fact, multiple victims is often the only clue to an electrical drowning.
This is why any beachside installations now require GFCI and shutoff switches, and why you should not swim near a boat on shore power.
Why electrical drownings happen
You've seen problems involving grids of resistors. That's what water is, a 3-D grid of resistors, and you also are some of the resistors.
Electrical current travels all available paths in proportion to their conductance (1/resistance). 1-10 mA is enough to start causing problems for a sensitive person; 100 mA is lethal in its own right.
Electricity wants to get back to source (the pole transformer's neutral), and the NEC standard for a grounding rod is 25 ohms. You can do the math here.
Well, I get 120 V through a 24 ohm resistor = 5 amperes. So only a tiny fraction of that current need go through you to nail you. If we rely on that article's 20 mA, then 1/250 of the current is enough to drown you.
Note also: this is not nearly enough to trip a typical 13, 15, 16 or 20 A branch circuit breaker.
However, a GFCI breaker will trip at 6-8 mA. That greatly improves the prognosis. This narrows it down to a highly improbable combination of events where the current is naturally limited to less than 6 mA, and almost all goes through you, and you're ultra-sensitive.
edited yesterday
Peter Mortensen
1,60031422
1,60031422
answered 2 days ago
HarperHarper
6,837927
6,837927
1
$begingroup$
Many such cases, like this one, don't involve drowning. The current stops the heart (and other things).
$endgroup$
– Brock Adams
yesterday
5
$begingroup$
"That's what water is, a 3-D grid of resistors, and you also are some of the resistors." Best analogy I have ever seen to describe this issue. Bravo!
$endgroup$
– J. Raefield
yesterday
3
$begingroup$
One additional point: Compared to fresh water, the human body is a particularly low resistance path, so the current will preferentially go through you.
$endgroup$
– Martin Bonner
16 hours ago
$begingroup$
Then how do you explain this? youtube.com/watch?v=dcrY59nGxBg
$endgroup$
– Chloe
8 hours ago
add a comment |
1
$begingroup$
Many such cases, like this one, don't involve drowning. The current stops the heart (and other things).
$endgroup$
– Brock Adams
yesterday
5
$begingroup$
"That's what water is, a 3-D grid of resistors, and you also are some of the resistors." Best analogy I have ever seen to describe this issue. Bravo!
$endgroup$
– J. Raefield
yesterday
3
$begingroup$
One additional point: Compared to fresh water, the human body is a particularly low resistance path, so the current will preferentially go through you.
$endgroup$
– Martin Bonner
16 hours ago
$begingroup$
Then how do you explain this? youtube.com/watch?v=dcrY59nGxBg
$endgroup$
– Chloe
8 hours ago
1
1
$begingroup$
Many such cases, like this one, don't involve drowning. The current stops the heart (and other things).
$endgroup$
– Brock Adams
yesterday
$begingroup$
Many such cases, like this one, don't involve drowning. The current stops the heart (and other things).
$endgroup$
– Brock Adams
yesterday
5
5
$begingroup$
"That's what water is, a 3-D grid of resistors, and you also are some of the resistors." Best analogy I have ever seen to describe this issue. Bravo!
$endgroup$
– J. Raefield
yesterday
$begingroup$
"That's what water is, a 3-D grid of resistors, and you also are some of the resistors." Best analogy I have ever seen to describe this issue. Bravo!
$endgroup$
– J. Raefield
yesterday
3
3
$begingroup$
One additional point: Compared to fresh water, the human body is a particularly low resistance path, so the current will preferentially go through you.
$endgroup$
– Martin Bonner
16 hours ago
$begingroup$
One additional point: Compared to fresh water, the human body is a particularly low resistance path, so the current will preferentially go through you.
$endgroup$
– Martin Bonner
16 hours ago
$begingroup$
Then how do you explain this? youtube.com/watch?v=dcrY59nGxBg
$endgroup$
– Chloe
8 hours ago
$begingroup$
Then how do you explain this? youtube.com/watch?v=dcrY59nGxBg
$endgroup$
– Chloe
8 hours ago
add a comment |
$begingroup$
In something like water electricity does not "flow to ground" in a neat straight line. There is a potential difference between sections of water radiating out from the HV contact point. That might also mean that your feet are at different potentials, and there will be current flow which could be fatal. This is one reason why cows in fields can be electrocuted by a nearby lightning strike. The voltage difference between their feet can be thousands of volts.
$endgroup$
4
$begingroup$
It also might not flow to ground at all. If the dangling wire, for example, was connected to a UK shaver outlet (powered by an isolation transformer) then the only available path is back the other wire to the other side of the transformer.
$endgroup$
– J...
2 days ago
$begingroup$
Yes, this. There is currently flowing out in all directions to different grounding points. If somehow floor was non-conducting and very well isolated except for a single very good ground very near the wire then most of the room might be safe, but I’m not gonna be the one to verify that.
$endgroup$
– John Hascall
2 days ago
3
$begingroup$
Even humans can be electrocuted by a nearby lightning strike. Paradoxically, there are many aspects of a strike that are worse if it hits the ground near you than if it hits you directly (the former can stop your heart if the electrical potential is great enough, whereas the latter "just" causes burns and lung damage).
$endgroup$
– forest
2 days ago
1
$begingroup$
Especially considering that most water you encounter day-to-day is fresh water. The human body is saltwater, which has a lower resistance, so electricity will preferentially flow through you.
$endgroup$
– skyler
yesterday
2
$begingroup$
Regarding potential differences on the ground in a lightning strike: That's why you should have your feet close together (to minimize the potential difference between them and hence the current flowing through them) while you squat (to minimize the chances of a direct hit which would at least give you an instant new tatoo).
$endgroup$
– Peter A. Schneider
17 hours ago
add a comment |
$begingroup$
In something like water electricity does not "flow to ground" in a neat straight line. There is a potential difference between sections of water radiating out from the HV contact point. That might also mean that your feet are at different potentials, and there will be current flow which could be fatal. This is one reason why cows in fields can be electrocuted by a nearby lightning strike. The voltage difference between their feet can be thousands of volts.
$endgroup$
4
$begingroup$
It also might not flow to ground at all. If the dangling wire, for example, was connected to a UK shaver outlet (powered by an isolation transformer) then the only available path is back the other wire to the other side of the transformer.
$endgroup$
– J...
2 days ago
$begingroup$
Yes, this. There is currently flowing out in all directions to different grounding points. If somehow floor was non-conducting and very well isolated except for a single very good ground very near the wire then most of the room might be safe, but I’m not gonna be the one to verify that.
$endgroup$
– John Hascall
2 days ago
3
$begingroup$
Even humans can be electrocuted by a nearby lightning strike. Paradoxically, there are many aspects of a strike that are worse if it hits the ground near you than if it hits you directly (the former can stop your heart if the electrical potential is great enough, whereas the latter "just" causes burns and lung damage).
$endgroup$
– forest
2 days ago
1
$begingroup$
Especially considering that most water you encounter day-to-day is fresh water. The human body is saltwater, which has a lower resistance, so electricity will preferentially flow through you.
$endgroup$
– skyler
yesterday
2
$begingroup$
Regarding potential differences on the ground in a lightning strike: That's why you should have your feet close together (to minimize the potential difference between them and hence the current flowing through them) while you squat (to minimize the chances of a direct hit which would at least give you an instant new tatoo).
$endgroup$
– Peter A. Schneider
17 hours ago
add a comment |
$begingroup$
In something like water electricity does not "flow to ground" in a neat straight line. There is a potential difference between sections of water radiating out from the HV contact point. That might also mean that your feet are at different potentials, and there will be current flow which could be fatal. This is one reason why cows in fields can be electrocuted by a nearby lightning strike. The voltage difference between their feet can be thousands of volts.
$endgroup$
In something like water electricity does not "flow to ground" in a neat straight line. There is a potential difference between sections of water radiating out from the HV contact point. That might also mean that your feet are at different potentials, and there will be current flow which could be fatal. This is one reason why cows in fields can be electrocuted by a nearby lightning strike. The voltage difference between their feet can be thousands of volts.
answered 2 days ago
Dirk BruereDirk Bruere
5,82353063
5,82353063
4
$begingroup$
It also might not flow to ground at all. If the dangling wire, for example, was connected to a UK shaver outlet (powered by an isolation transformer) then the only available path is back the other wire to the other side of the transformer.
$endgroup$
– J...
2 days ago
$begingroup$
Yes, this. There is currently flowing out in all directions to different grounding points. If somehow floor was non-conducting and very well isolated except for a single very good ground very near the wire then most of the room might be safe, but I’m not gonna be the one to verify that.
$endgroup$
– John Hascall
2 days ago
3
$begingroup$
Even humans can be electrocuted by a nearby lightning strike. Paradoxically, there are many aspects of a strike that are worse if it hits the ground near you than if it hits you directly (the former can stop your heart if the electrical potential is great enough, whereas the latter "just" causes burns and lung damage).
$endgroup$
– forest
2 days ago
1
$begingroup$
Especially considering that most water you encounter day-to-day is fresh water. The human body is saltwater, which has a lower resistance, so electricity will preferentially flow through you.
$endgroup$
– skyler
yesterday
2
$begingroup$
Regarding potential differences on the ground in a lightning strike: That's why you should have your feet close together (to minimize the potential difference between them and hence the current flowing through them) while you squat (to minimize the chances of a direct hit which would at least give you an instant new tatoo).
$endgroup$
– Peter A. Schneider
17 hours ago
add a comment |
4
$begingroup$
It also might not flow to ground at all. If the dangling wire, for example, was connected to a UK shaver outlet (powered by an isolation transformer) then the only available path is back the other wire to the other side of the transformer.
$endgroup$
– J...
2 days ago
$begingroup$
Yes, this. There is currently flowing out in all directions to different grounding points. If somehow floor was non-conducting and very well isolated except for a single very good ground very near the wire then most of the room might be safe, but I’m not gonna be the one to verify that.
$endgroup$
– John Hascall
2 days ago
3
$begingroup$
Even humans can be electrocuted by a nearby lightning strike. Paradoxically, there are many aspects of a strike that are worse if it hits the ground near you than if it hits you directly (the former can stop your heart if the electrical potential is great enough, whereas the latter "just" causes burns and lung damage).
$endgroup$
– forest
2 days ago
1
$begingroup$
Especially considering that most water you encounter day-to-day is fresh water. The human body is saltwater, which has a lower resistance, so electricity will preferentially flow through you.
$endgroup$
– skyler
yesterday
2
$begingroup$
Regarding potential differences on the ground in a lightning strike: That's why you should have your feet close together (to minimize the potential difference between them and hence the current flowing through them) while you squat (to minimize the chances of a direct hit which would at least give you an instant new tatoo).
$endgroup$
– Peter A. Schneider
17 hours ago
4
4
$begingroup$
It also might not flow to ground at all. If the dangling wire, for example, was connected to a UK shaver outlet (powered by an isolation transformer) then the only available path is back the other wire to the other side of the transformer.
$endgroup$
– J...
2 days ago
$begingroup$
It also might not flow to ground at all. If the dangling wire, for example, was connected to a UK shaver outlet (powered by an isolation transformer) then the only available path is back the other wire to the other side of the transformer.
$endgroup$
– J...
2 days ago
$begingroup$
Yes, this. There is currently flowing out in all directions to different grounding points. If somehow floor was non-conducting and very well isolated except for a single very good ground very near the wire then most of the room might be safe, but I’m not gonna be the one to verify that.
$endgroup$
– John Hascall
2 days ago
$begingroup$
Yes, this. There is currently flowing out in all directions to different grounding points. If somehow floor was non-conducting and very well isolated except for a single very good ground very near the wire then most of the room might be safe, but I’m not gonna be the one to verify that.
$endgroup$
– John Hascall
2 days ago
3
3
$begingroup$
Even humans can be electrocuted by a nearby lightning strike. Paradoxically, there are many aspects of a strike that are worse if it hits the ground near you than if it hits you directly (the former can stop your heart if the electrical potential is great enough, whereas the latter "just" causes burns and lung damage).
$endgroup$
– forest
2 days ago
$begingroup$
Even humans can be electrocuted by a nearby lightning strike. Paradoxically, there are many aspects of a strike that are worse if it hits the ground near you than if it hits you directly (the former can stop your heart if the electrical potential is great enough, whereas the latter "just" causes burns and lung damage).
$endgroup$
– forest
2 days ago
1
1
$begingroup$
Especially considering that most water you encounter day-to-day is fresh water. The human body is saltwater, which has a lower resistance, so electricity will preferentially flow through you.
$endgroup$
– skyler
yesterday
$begingroup$
Especially considering that most water you encounter day-to-day is fresh water. The human body is saltwater, which has a lower resistance, so electricity will preferentially flow through you.
$endgroup$
– skyler
yesterday
2
2
$begingroup$
Regarding potential differences on the ground in a lightning strike: That's why you should have your feet close together (to minimize the potential difference between them and hence the current flowing through them) while you squat (to minimize the chances of a direct hit which would at least give you an instant new tatoo).
$endgroup$
– Peter A. Schneider
17 hours ago
$begingroup$
Regarding potential differences on the ground in a lightning strike: That's why you should have your feet close together (to minimize the potential difference between them and hence the current flowing through them) while you squat (to minimize the chances of a direct hit which would at least give you an instant new tatoo).
$endgroup$
– Peter A. Schneider
17 hours ago
add a comment |
$begingroup$
I think that the answer is pretty simple - you are a better conductor than fresh water. I read this somewhere and it made me giggle then: "Humans are just big bags of salt water", which is true. A current of 1 mA through the heart is enough to cause a heart attack, so at 220 V, 220 kΩ resistance is not enough. You are less than 220 kΩ, especially when in water. Skin is the only insulator we have.
Just don't try it.
$endgroup$
$begingroup$
Yup, this is how you can get electrocuted--you have a considerably lower resistance than fresh water so if your body can be used to go to the ground it will--the current is happy to flow up one leg and down the other.
$endgroup$
– Loren Pechtel
yesterday
$begingroup$
Actually this is wrong: the worst shock will happen in a slightly salty water with the same conductance as a human body. Think about impedance matching: maximum power transfer happens when Zload=Zsource.
$endgroup$
– Dmitry Grigoryev
yesterday
$begingroup$
@DmitryGrigoryev You are right.
$endgroup$
– Atizs
yesterday
1
$begingroup$
@DmitryGrigoryev: Maximum power transfer when the voltage is regulated happens for a matched load. Therefore, replace the source by its Thevenin equivalent, and the load should be the conjugate of the Thevenin-equivalent series impedance. That's totally unrelated to impedance equaling that of the water it displaces -- you're matching to the wrong part of the circuit. (Another statement of the issue, you are matching resistivity when you should be matching resistance)
$endgroup$
– Ben Voigt
21 hours ago
$begingroup$
"Ugly bags of mostly water!" You made me remember a little bit of Star Trek humor.
$endgroup$
– enorl76
9 hours ago
add a comment |
$begingroup$
I think that the answer is pretty simple - you are a better conductor than fresh water. I read this somewhere and it made me giggle then: "Humans are just big bags of salt water", which is true. A current of 1 mA through the heart is enough to cause a heart attack, so at 220 V, 220 kΩ resistance is not enough. You are less than 220 kΩ, especially when in water. Skin is the only insulator we have.
Just don't try it.
$endgroup$
$begingroup$
Yup, this is how you can get electrocuted--you have a considerably lower resistance than fresh water so if your body can be used to go to the ground it will--the current is happy to flow up one leg and down the other.
$endgroup$
– Loren Pechtel
yesterday
$begingroup$
Actually this is wrong: the worst shock will happen in a slightly salty water with the same conductance as a human body. Think about impedance matching: maximum power transfer happens when Zload=Zsource.
$endgroup$
– Dmitry Grigoryev
yesterday
$begingroup$
@DmitryGrigoryev You are right.
$endgroup$
– Atizs
yesterday
1
$begingroup$
@DmitryGrigoryev: Maximum power transfer when the voltage is regulated happens for a matched load. Therefore, replace the source by its Thevenin equivalent, and the load should be the conjugate of the Thevenin-equivalent series impedance. That's totally unrelated to impedance equaling that of the water it displaces -- you're matching to the wrong part of the circuit. (Another statement of the issue, you are matching resistivity when you should be matching resistance)
$endgroup$
– Ben Voigt
21 hours ago
$begingroup$
"Ugly bags of mostly water!" You made me remember a little bit of Star Trek humor.
$endgroup$
– enorl76
9 hours ago
add a comment |
$begingroup$
I think that the answer is pretty simple - you are a better conductor than fresh water. I read this somewhere and it made me giggle then: "Humans are just big bags of salt water", which is true. A current of 1 mA through the heart is enough to cause a heart attack, so at 220 V, 220 kΩ resistance is not enough. You are less than 220 kΩ, especially when in water. Skin is the only insulator we have.
Just don't try it.
$endgroup$
I think that the answer is pretty simple - you are a better conductor than fresh water. I read this somewhere and it made me giggle then: "Humans are just big bags of salt water", which is true. A current of 1 mA through the heart is enough to cause a heart attack, so at 220 V, 220 kΩ resistance is not enough. You are less than 220 kΩ, especially when in water. Skin is the only insulator we have.
Just don't try it.
edited yesterday
Peter Mortensen
1,60031422
1,60031422
answered 2 days ago
AtizsAtizs
580313
580313
$begingroup$
Yup, this is how you can get electrocuted--you have a considerably lower resistance than fresh water so if your body can be used to go to the ground it will--the current is happy to flow up one leg and down the other.
$endgroup$
– Loren Pechtel
yesterday
$begingroup$
Actually this is wrong: the worst shock will happen in a slightly salty water with the same conductance as a human body. Think about impedance matching: maximum power transfer happens when Zload=Zsource.
$endgroup$
– Dmitry Grigoryev
yesterday
$begingroup$
@DmitryGrigoryev You are right.
$endgroup$
– Atizs
yesterday
1
$begingroup$
@DmitryGrigoryev: Maximum power transfer when the voltage is regulated happens for a matched load. Therefore, replace the source by its Thevenin equivalent, and the load should be the conjugate of the Thevenin-equivalent series impedance. That's totally unrelated to impedance equaling that of the water it displaces -- you're matching to the wrong part of the circuit. (Another statement of the issue, you are matching resistivity when you should be matching resistance)
$endgroup$
– Ben Voigt
21 hours ago
$begingroup$
"Ugly bags of mostly water!" You made me remember a little bit of Star Trek humor.
$endgroup$
– enorl76
9 hours ago
add a comment |
$begingroup$
Yup, this is how you can get electrocuted--you have a considerably lower resistance than fresh water so if your body can be used to go to the ground it will--the current is happy to flow up one leg and down the other.
$endgroup$
– Loren Pechtel
yesterday
$begingroup$
Actually this is wrong: the worst shock will happen in a slightly salty water with the same conductance as a human body. Think about impedance matching: maximum power transfer happens when Zload=Zsource.
$endgroup$
– Dmitry Grigoryev
yesterday
$begingroup$
@DmitryGrigoryev You are right.
$endgroup$
– Atizs
yesterday
1
$begingroup$
@DmitryGrigoryev: Maximum power transfer when the voltage is regulated happens for a matched load. Therefore, replace the source by its Thevenin equivalent, and the load should be the conjugate of the Thevenin-equivalent series impedance. That's totally unrelated to impedance equaling that of the water it displaces -- you're matching to the wrong part of the circuit. (Another statement of the issue, you are matching resistivity when you should be matching resistance)
$endgroup$
– Ben Voigt
21 hours ago
$begingroup$
"Ugly bags of mostly water!" You made me remember a little bit of Star Trek humor.
$endgroup$
– enorl76
9 hours ago
$begingroup$
Yup, this is how you can get electrocuted--you have a considerably lower resistance than fresh water so if your body can be used to go to the ground it will--the current is happy to flow up one leg and down the other.
$endgroup$
– Loren Pechtel
yesterday
$begingroup$
Yup, this is how you can get electrocuted--you have a considerably lower resistance than fresh water so if your body can be used to go to the ground it will--the current is happy to flow up one leg and down the other.
$endgroup$
– Loren Pechtel
yesterday
$begingroup$
Actually this is wrong: the worst shock will happen in a slightly salty water with the same conductance as a human body. Think about impedance matching: maximum power transfer happens when Zload=Zsource.
$endgroup$
– Dmitry Grigoryev
yesterday
$begingroup$
Actually this is wrong: the worst shock will happen in a slightly salty water with the same conductance as a human body. Think about impedance matching: maximum power transfer happens when Zload=Zsource.
$endgroup$
– Dmitry Grigoryev
yesterday
$begingroup$
@DmitryGrigoryev You are right.
$endgroup$
– Atizs
yesterday
$begingroup$
@DmitryGrigoryev You are right.
$endgroup$
– Atizs
yesterday
1
1
$begingroup$
@DmitryGrigoryev: Maximum power transfer when the voltage is regulated happens for a matched load. Therefore, replace the source by its Thevenin equivalent, and the load should be the conjugate of the Thevenin-equivalent series impedance. That's totally unrelated to impedance equaling that of the water it displaces -- you're matching to the wrong part of the circuit. (Another statement of the issue, you are matching resistivity when you should be matching resistance)
$endgroup$
– Ben Voigt
21 hours ago
$begingroup$
@DmitryGrigoryev: Maximum power transfer when the voltage is regulated happens for a matched load. Therefore, replace the source by its Thevenin equivalent, and the load should be the conjugate of the Thevenin-equivalent series impedance. That's totally unrelated to impedance equaling that of the water it displaces -- you're matching to the wrong part of the circuit. (Another statement of the issue, you are matching resistivity when you should be matching resistance)
$endgroup$
– Ben Voigt
21 hours ago
$begingroup$
"Ugly bags of mostly water!" You made me remember a little bit of Star Trek humor.
$endgroup$
– enorl76
9 hours ago
$begingroup$
"Ugly bags of mostly water!" You made me remember a little bit of Star Trek humor.
$endgroup$
– enorl76
9 hours ago
add a comment |
$begingroup$
how does the electricity flow through me to electrocute me?
I already posted that picture once in a question about electric eels:
Source: phys.org Credit: Kenneth Catania
Electricity doesn't flow along a single preferred path, it flows in the entire water body with different intensities. If you happen to be in a path with high enough current, you'll get electrocuted.
An interesting corollary to this fact is that you'll get the worst shock when you and the water have comparable conductance. If the water is much more conductive than you, even high currents will only create a small voltage difference, which may not be harmful. If the water is much less conductive, the voltage difference may be huge, but the current will be limited.
$endgroup$
$begingroup$
That's a nice illustration of a tricky concept.
$endgroup$
– Wossname
yesterday
$begingroup$
The current flowing through a body in water depends solely on its resistance and the sustained voltage, not (directly) on the resistance of the sorrounding water. The caveat "directly" is because a high resistance surrounding makes the potential difference at your body collapse (it happens in the high resistance part, and the current through your body making that drop happen may not be harmful). But the case that your body has a higher resistance than the surrounding won't have any benefit at all. (You'd need a power source though which can sustain the voltage in spite of the high currents.)
$endgroup$
– Peter A. Schneider
17 hours ago
add a comment |
$begingroup$
how does the electricity flow through me to electrocute me?
I already posted that picture once in a question about electric eels:
Source: phys.org Credit: Kenneth Catania
Electricity doesn't flow along a single preferred path, it flows in the entire water body with different intensities. If you happen to be in a path with high enough current, you'll get electrocuted.
An interesting corollary to this fact is that you'll get the worst shock when you and the water have comparable conductance. If the water is much more conductive than you, even high currents will only create a small voltage difference, which may not be harmful. If the water is much less conductive, the voltage difference may be huge, but the current will be limited.
$endgroup$
$begingroup$
That's a nice illustration of a tricky concept.
$endgroup$
– Wossname
yesterday
$begingroup$
The current flowing through a body in water depends solely on its resistance and the sustained voltage, not (directly) on the resistance of the sorrounding water. The caveat "directly" is because a high resistance surrounding makes the potential difference at your body collapse (it happens in the high resistance part, and the current through your body making that drop happen may not be harmful). But the case that your body has a higher resistance than the surrounding won't have any benefit at all. (You'd need a power source though which can sustain the voltage in spite of the high currents.)
$endgroup$
– Peter A. Schneider
17 hours ago
add a comment |
$begingroup$
how does the electricity flow through me to electrocute me?
I already posted that picture once in a question about electric eels:
Source: phys.org Credit: Kenneth Catania
Electricity doesn't flow along a single preferred path, it flows in the entire water body with different intensities. If you happen to be in a path with high enough current, you'll get electrocuted.
An interesting corollary to this fact is that you'll get the worst shock when you and the water have comparable conductance. If the water is much more conductive than you, even high currents will only create a small voltage difference, which may not be harmful. If the water is much less conductive, the voltage difference may be huge, but the current will be limited.
$endgroup$
how does the electricity flow through me to electrocute me?
I already posted that picture once in a question about electric eels:
Source: phys.org Credit: Kenneth Catania
Electricity doesn't flow along a single preferred path, it flows in the entire water body with different intensities. If you happen to be in a path with high enough current, you'll get electrocuted.
An interesting corollary to this fact is that you'll get the worst shock when you and the water have comparable conductance. If the water is much more conductive than you, even high currents will only create a small voltage difference, which may not be harmful. If the water is much less conductive, the voltage difference may be huge, but the current will be limited.
edited yesterday
answered yesterday
Dmitry GrigoryevDmitry Grigoryev
18.5k22778
18.5k22778
$begingroup$
That's a nice illustration of a tricky concept.
$endgroup$
– Wossname
yesterday
$begingroup$
The current flowing through a body in water depends solely on its resistance and the sustained voltage, not (directly) on the resistance of the sorrounding water. The caveat "directly" is because a high resistance surrounding makes the potential difference at your body collapse (it happens in the high resistance part, and the current through your body making that drop happen may not be harmful). But the case that your body has a higher resistance than the surrounding won't have any benefit at all. (You'd need a power source though which can sustain the voltage in spite of the high currents.)
$endgroup$
– Peter A. Schneider
17 hours ago
add a comment |
$begingroup$
That's a nice illustration of a tricky concept.
$endgroup$
– Wossname
yesterday
$begingroup$
The current flowing through a body in water depends solely on its resistance and the sustained voltage, not (directly) on the resistance of the sorrounding water. The caveat "directly" is because a high resistance surrounding makes the potential difference at your body collapse (it happens in the high resistance part, and the current through your body making that drop happen may not be harmful). But the case that your body has a higher resistance than the surrounding won't have any benefit at all. (You'd need a power source though which can sustain the voltage in spite of the high currents.)
$endgroup$
– Peter A. Schneider
17 hours ago
$begingroup$
That's a nice illustration of a tricky concept.
$endgroup$
– Wossname
yesterday
$begingroup$
That's a nice illustration of a tricky concept.
$endgroup$
– Wossname
yesterday
$begingroup$
The current flowing through a body in water depends solely on its resistance and the sustained voltage, not (directly) on the resistance of the sorrounding water. The caveat "directly" is because a high resistance surrounding makes the potential difference at your body collapse (it happens in the high resistance part, and the current through your body making that drop happen may not be harmful). But the case that your body has a higher resistance than the surrounding won't have any benefit at all. (You'd need a power source though which can sustain the voltage in spite of the high currents.)
$endgroup$
– Peter A. Schneider
17 hours ago
$begingroup$
The current flowing through a body in water depends solely on its resistance and the sustained voltage, not (directly) on the resistance of the sorrounding water. The caveat "directly" is because a high resistance surrounding makes the potential difference at your body collapse (it happens in the high resistance part, and the current through your body making that drop happen may not be harmful). But the case that your body has a higher resistance than the surrounding won't have any benefit at all. (You'd need a power source though which can sustain the voltage in spite of the high currents.)
$endgroup$
– Peter A. Schneider
17 hours ago
add a comment |
$begingroup$
Just being in "high voltage water" won't electrocute you, just as birds can happily perch on 10+kV power lines (and linemen can be dropped onto live lines for maintenance work), since there's no path, but as you say, there's always going to be a path to ground somewhere in that water, and so there'll be currents flowing through the water. Since that means that there's potential differences across the water at different points, you'd experience that between your feet, and since the human body is a good conductor, other than the skin, which reduces greatly in resistance when wet, that would allow possibly lethal current to flow through the torso. People can and do get electrocuted standing in salty bilge water on 24V systems on boats, it doesn't take a lot of voltage if the resistance is low enough.
$endgroup$
2
$begingroup$
I'm pretty sure birds are safe because of their low capacitance (from their small size). It ensures very little AC current can flow through them.
$endgroup$
– forest
2 days ago
$begingroup$
Electrocuted by 24V? Do you have a case reference?
$endgroup$
– Peter A. Schneider
17 hours ago
$begingroup$
@forest They are safe because the potential difference between their feet is minimal and they are not touching any grounded objects. OK, if they had a high capacitance some initial current would flow into them upon contact, but nothing "flows through them" unless they touch something else.
$endgroup$
– Peter A. Schneider
17 hours ago
add a comment |
$begingroup$
Just being in "high voltage water" won't electrocute you, just as birds can happily perch on 10+kV power lines (and linemen can be dropped onto live lines for maintenance work), since there's no path, but as you say, there's always going to be a path to ground somewhere in that water, and so there'll be currents flowing through the water. Since that means that there's potential differences across the water at different points, you'd experience that between your feet, and since the human body is a good conductor, other than the skin, which reduces greatly in resistance when wet, that would allow possibly lethal current to flow through the torso. People can and do get electrocuted standing in salty bilge water on 24V systems on boats, it doesn't take a lot of voltage if the resistance is low enough.
$endgroup$
2
$begingroup$
I'm pretty sure birds are safe because of their low capacitance (from their small size). It ensures very little AC current can flow through them.
$endgroup$
– forest
2 days ago
$begingroup$
Electrocuted by 24V? Do you have a case reference?
$endgroup$
– Peter A. Schneider
17 hours ago
$begingroup$
@forest They are safe because the potential difference between their feet is minimal and they are not touching any grounded objects. OK, if they had a high capacitance some initial current would flow into them upon contact, but nothing "flows through them" unless they touch something else.
$endgroup$
– Peter A. Schneider
17 hours ago
add a comment |
$begingroup$
Just being in "high voltage water" won't electrocute you, just as birds can happily perch on 10+kV power lines (and linemen can be dropped onto live lines for maintenance work), since there's no path, but as you say, there's always going to be a path to ground somewhere in that water, and so there'll be currents flowing through the water. Since that means that there's potential differences across the water at different points, you'd experience that between your feet, and since the human body is a good conductor, other than the skin, which reduces greatly in resistance when wet, that would allow possibly lethal current to flow through the torso. People can and do get electrocuted standing in salty bilge water on 24V systems on boats, it doesn't take a lot of voltage if the resistance is low enough.
$endgroup$
Just being in "high voltage water" won't electrocute you, just as birds can happily perch on 10+kV power lines (and linemen can be dropped onto live lines for maintenance work), since there's no path, but as you say, there's always going to be a path to ground somewhere in that water, and so there'll be currents flowing through the water. Since that means that there's potential differences across the water at different points, you'd experience that between your feet, and since the human body is a good conductor, other than the skin, which reduces greatly in resistance when wet, that would allow possibly lethal current to flow through the torso. People can and do get electrocuted standing in salty bilge water on 24V systems on boats, it doesn't take a lot of voltage if the resistance is low enough.
answered 2 days ago
Phil GPhil G
2,9651412
2,9651412
2
$begingroup$
I'm pretty sure birds are safe because of their low capacitance (from their small size). It ensures very little AC current can flow through them.
$endgroup$
– forest
2 days ago
$begingroup$
Electrocuted by 24V? Do you have a case reference?
$endgroup$
– Peter A. Schneider
17 hours ago
$begingroup$
@forest They are safe because the potential difference between their feet is minimal and they are not touching any grounded objects. OK, if they had a high capacitance some initial current would flow into them upon contact, but nothing "flows through them" unless they touch something else.
$endgroup$
– Peter A. Schneider
17 hours ago
add a comment |
2
$begingroup$
I'm pretty sure birds are safe because of their low capacitance (from their small size). It ensures very little AC current can flow through them.
$endgroup$
– forest
2 days ago
$begingroup$
Electrocuted by 24V? Do you have a case reference?
$endgroup$
– Peter A. Schneider
17 hours ago
$begingroup$
@forest They are safe because the potential difference between their feet is minimal and they are not touching any grounded objects. OK, if they had a high capacitance some initial current would flow into them upon contact, but nothing "flows through them" unless they touch something else.
$endgroup$
– Peter A. Schneider
17 hours ago
2
2
$begingroup$
I'm pretty sure birds are safe because of their low capacitance (from their small size). It ensures very little AC current can flow through them.
$endgroup$
– forest
2 days ago
$begingroup$
I'm pretty sure birds are safe because of their low capacitance (from their small size). It ensures very little AC current can flow through them.
$endgroup$
– forest
2 days ago
$begingroup$
Electrocuted by 24V? Do you have a case reference?
$endgroup$
– Peter A. Schneider
17 hours ago
$begingroup$
Electrocuted by 24V? Do you have a case reference?
$endgroup$
– Peter A. Schneider
17 hours ago
$begingroup$
@forest They are safe because the potential difference between their feet is minimal and they are not touching any grounded objects. OK, if they had a high capacitance some initial current would flow into them upon contact, but nothing "flows through them" unless they touch something else.
$endgroup$
– Peter A. Schneider
17 hours ago
$begingroup$
@forest They are safe because the potential difference between their feet is minimal and they are not touching any grounded objects. OK, if they had a high capacitance some initial current would flow into them upon contact, but nothing "flows through them" unless they touch something else.
$endgroup$
– Peter A. Schneider
17 hours ago
add a comment |
$begingroup$
Definitely don't try any of these things. This is definitely not intended to imply you should be complacent about any of the dangers of electricity, but there are numerous things that are often extremely wrong in movie handling of electricity, particularly in this type of scene. Often effects are used to simply make the electricity do what the story requires, so a few things:
- Overcurrent and other fault protection: In most of the world, every circuit has over current protection and many circuits have ground fault or arc fault protection. As manufacturing capability increases, we've been able to add more ways to protect electrical installations and make them safe. In a futuristic scenario with improved technology, there is usually no reason this would have changed. Faults damage equipment, so even in a scenario where disregard for human life is written in, systems would have advanced precautions to limit property damage. At any rate, often the conductor you see creating the danger is actually a cable, with visible wires sticking out of the end, whatever the prop department thought would look cool. In many of these cases, the conductor, as presented, would have shorted between it's own conductors and tripped its overcurrent device or GFCI. In order for the conductor to stay live, something else must go wrong, like it miraculously not shorting out when being pulled loose from what it was connected to, falling, and or jiggling without shorting out on itself or touching something made of metal, or the breaker welding closed(which does occasionally happen).
- Electricity flows more on paths of less resistance. You could place large copper wire, a wet log and a strip of asphalt side by side, and connect the same voltage at once to the ends of all three. Most of the current would flow through the copper wire, much less would flow through the wet log, and a negligible amount through the asphalt, though there would be current flow in all three. If the conductors on a broken cable have enough voltage to create CGI arcs to nearby fixtures/water/whatever things that are far away, they have enough voltage to arc to its own return conductor or ground, which is sometimes mistakenly portrayed as inches away. For its own return conductor or ground to not be the target of most arcs, a second thing has to go wrong. Those conductors have to be broken somewhere between the arcing cable and the source, somehow without damaging a single high voltage cable more than would allow it to function. Electricity will not tend to travel through a meter of air to establish an arc when a 20mm arc establishes a low impedance return path.
- Electricity is often much more brutal and much less flashy than in the movies, and movies often portray a greater(or smaller) margin for survival than actually exists. As part of your training in electrical industries, especially in power distribution, there's a good likelihood you'll see a video of someone dying working with or around electricity. It's utterly terrible. Brutal, merciless, and not always quick. The actual speed that electricity can "change" and propagate at is fast enough to need quality examples to make it easy to comprehend. There are situations where high voltage is portrayed in movies as something that great dexterity, strength and skill can just deal with, and inevitably characters are sometimes shown doing something that would have killed or vaporized them. Sometimes with low voltage wires a character is shown killed by something that, as presented, would have a relatively low probability of being lethal. In the latter case I'm comfortable with that as laymen and professionals should treat something with a very good chance of killing them as something that will.
- Electricity flows in loops. Each molecule, depending on bonding, nuclei, and electron shells, tends to keep roughly a certain amount of electron in each area around it. The electrons themselves are bouncing around, and when they are not held too tightly where they are, they fly freely between nearby molecules, and the limiting factor is that when/as an electron moves out of an area that "needs" an electron, forces will be exerted on other nearby electrons as well as the one flying away to pull them in and fill the gap. Depending on structure of molecule and nuclei, different materials either bind their electrons tightly(insulators) or allow them to flow more freely(conductors). When you cause electrons to flow along a wire, new ones must replace the ones that flow away. The area you are pumping the electrons to will have too many and the area you are pumping them from will not have enough. There is nowhere for the flow to go other than back to where there are too few, as all of the other molecules around have exactly enough. No loop, no current.
- Water isn't really a good conductor. Dirty water, particularly salty water is. Pure water is not (tap water is not pure). Aside from that, if you put a generator on the shore of an ocean and strung a wire across the surface of the water to a point far out where the tip of the wire was bare, 1 meter underwater, and connected the generator to that wire and a ground rod, the generator would work to pass a current down that wire, into the water, along the earth, through the ground rod, and back to the generator, where the electrons you're pumping out need to be replaced. Because of the high(ish) conductivity of salt water, there wouldn't be high voltages/currents for too high a distance in most directions around the tip of that wire, as the flow of electrons is "attempting" to return on the shortest path possible to its source. voltage will spread out in other directions somewhat as the flowing electrons spread out to travel more freely. This is not to say that the water around the electrode is not dangerous, but to point that movies are often not specifically accurate with where current is flowing.
- Flashy arcs and sparks - Electricity is invisible. All we can see are the effects on objects as electricity passes through them. Heat, light, motion, the occasional smell. In order to draw attention to them, arcs, sparks and flashes are often brighter than they might be in real life, or of the wrong type (explosive rather than plasma, for example). The resistivity of air is around 2100V/mm, meaning to start an arc through room temperature air, you need 2100V for every mm you want the arc to jump. Once the air starts conducting and becomes a plasma, it conducts quite well, but it takes quite a voltage to start an arc.
$endgroup$
12
$begingroup$
"•Electricity follows the path of least resistance" Not true. Give it two paths, 1000 and 1001 ohm. Does all current flow in the 1000 ohm path and no current in the 1001 ohm path?
$endgroup$
– winny
yesterday
2
$begingroup$
@Winny Good point. I spouted off a safety axiom in my effort to keep things simple =P. Corrected now. Please check the rephrase if you have the time =).
$endgroup$
– K H
yesterday
add a comment |
$begingroup$
Definitely don't try any of these things. This is definitely not intended to imply you should be complacent about any of the dangers of electricity, but there are numerous things that are often extremely wrong in movie handling of electricity, particularly in this type of scene. Often effects are used to simply make the electricity do what the story requires, so a few things:
- Overcurrent and other fault protection: In most of the world, every circuit has over current protection and many circuits have ground fault or arc fault protection. As manufacturing capability increases, we've been able to add more ways to protect electrical installations and make them safe. In a futuristic scenario with improved technology, there is usually no reason this would have changed. Faults damage equipment, so even in a scenario where disregard for human life is written in, systems would have advanced precautions to limit property damage. At any rate, often the conductor you see creating the danger is actually a cable, with visible wires sticking out of the end, whatever the prop department thought would look cool. In many of these cases, the conductor, as presented, would have shorted between it's own conductors and tripped its overcurrent device or GFCI. In order for the conductor to stay live, something else must go wrong, like it miraculously not shorting out when being pulled loose from what it was connected to, falling, and or jiggling without shorting out on itself or touching something made of metal, or the breaker welding closed(which does occasionally happen).
- Electricity flows more on paths of less resistance. You could place large copper wire, a wet log and a strip of asphalt side by side, and connect the same voltage at once to the ends of all three. Most of the current would flow through the copper wire, much less would flow through the wet log, and a negligible amount through the asphalt, though there would be current flow in all three. If the conductors on a broken cable have enough voltage to create CGI arcs to nearby fixtures/water/whatever things that are far away, they have enough voltage to arc to its own return conductor or ground, which is sometimes mistakenly portrayed as inches away. For its own return conductor or ground to not be the target of most arcs, a second thing has to go wrong. Those conductors have to be broken somewhere between the arcing cable and the source, somehow without damaging a single high voltage cable more than would allow it to function. Electricity will not tend to travel through a meter of air to establish an arc when a 20mm arc establishes a low impedance return path.
- Electricity is often much more brutal and much less flashy than in the movies, and movies often portray a greater(or smaller) margin for survival than actually exists. As part of your training in electrical industries, especially in power distribution, there's a good likelihood you'll see a video of someone dying working with or around electricity. It's utterly terrible. Brutal, merciless, and not always quick. The actual speed that electricity can "change" and propagate at is fast enough to need quality examples to make it easy to comprehend. There are situations where high voltage is portrayed in movies as something that great dexterity, strength and skill can just deal with, and inevitably characters are sometimes shown doing something that would have killed or vaporized them. Sometimes with low voltage wires a character is shown killed by something that, as presented, would have a relatively low probability of being lethal. In the latter case I'm comfortable with that as laymen and professionals should treat something with a very good chance of killing them as something that will.
- Electricity flows in loops. Each molecule, depending on bonding, nuclei, and electron shells, tends to keep roughly a certain amount of electron in each area around it. The electrons themselves are bouncing around, and when they are not held too tightly where they are, they fly freely between nearby molecules, and the limiting factor is that when/as an electron moves out of an area that "needs" an electron, forces will be exerted on other nearby electrons as well as the one flying away to pull them in and fill the gap. Depending on structure of molecule and nuclei, different materials either bind their electrons tightly(insulators) or allow them to flow more freely(conductors). When you cause electrons to flow along a wire, new ones must replace the ones that flow away. The area you are pumping the electrons to will have too many and the area you are pumping them from will not have enough. There is nowhere for the flow to go other than back to where there are too few, as all of the other molecules around have exactly enough. No loop, no current.
- Water isn't really a good conductor. Dirty water, particularly salty water is. Pure water is not (tap water is not pure). Aside from that, if you put a generator on the shore of an ocean and strung a wire across the surface of the water to a point far out where the tip of the wire was bare, 1 meter underwater, and connected the generator to that wire and a ground rod, the generator would work to pass a current down that wire, into the water, along the earth, through the ground rod, and back to the generator, where the electrons you're pumping out need to be replaced. Because of the high(ish) conductivity of salt water, there wouldn't be high voltages/currents for too high a distance in most directions around the tip of that wire, as the flow of electrons is "attempting" to return on the shortest path possible to its source. voltage will spread out in other directions somewhat as the flowing electrons spread out to travel more freely. This is not to say that the water around the electrode is not dangerous, but to point that movies are often not specifically accurate with where current is flowing.
- Flashy arcs and sparks - Electricity is invisible. All we can see are the effects on objects as electricity passes through them. Heat, light, motion, the occasional smell. In order to draw attention to them, arcs, sparks and flashes are often brighter than they might be in real life, or of the wrong type (explosive rather than plasma, for example). The resistivity of air is around 2100V/mm, meaning to start an arc through room temperature air, you need 2100V for every mm you want the arc to jump. Once the air starts conducting and becomes a plasma, it conducts quite well, but it takes quite a voltage to start an arc.
$endgroup$
12
$begingroup$
"•Electricity follows the path of least resistance" Not true. Give it two paths, 1000 and 1001 ohm. Does all current flow in the 1000 ohm path and no current in the 1001 ohm path?
$endgroup$
– winny
yesterday
2
$begingroup$
@Winny Good point. I spouted off a safety axiom in my effort to keep things simple =P. Corrected now. Please check the rephrase if you have the time =).
$endgroup$
– K H
yesterday
add a comment |
$begingroup$
Definitely don't try any of these things. This is definitely not intended to imply you should be complacent about any of the dangers of electricity, but there are numerous things that are often extremely wrong in movie handling of electricity, particularly in this type of scene. Often effects are used to simply make the electricity do what the story requires, so a few things:
- Overcurrent and other fault protection: In most of the world, every circuit has over current protection and many circuits have ground fault or arc fault protection. As manufacturing capability increases, we've been able to add more ways to protect electrical installations and make them safe. In a futuristic scenario with improved technology, there is usually no reason this would have changed. Faults damage equipment, so even in a scenario where disregard for human life is written in, systems would have advanced precautions to limit property damage. At any rate, often the conductor you see creating the danger is actually a cable, with visible wires sticking out of the end, whatever the prop department thought would look cool. In many of these cases, the conductor, as presented, would have shorted between it's own conductors and tripped its overcurrent device or GFCI. In order for the conductor to stay live, something else must go wrong, like it miraculously not shorting out when being pulled loose from what it was connected to, falling, and or jiggling without shorting out on itself or touching something made of metal, or the breaker welding closed(which does occasionally happen).
- Electricity flows more on paths of less resistance. You could place large copper wire, a wet log and a strip of asphalt side by side, and connect the same voltage at once to the ends of all three. Most of the current would flow through the copper wire, much less would flow through the wet log, and a negligible amount through the asphalt, though there would be current flow in all three. If the conductors on a broken cable have enough voltage to create CGI arcs to nearby fixtures/water/whatever things that are far away, they have enough voltage to arc to its own return conductor or ground, which is sometimes mistakenly portrayed as inches away. For its own return conductor or ground to not be the target of most arcs, a second thing has to go wrong. Those conductors have to be broken somewhere between the arcing cable and the source, somehow without damaging a single high voltage cable more than would allow it to function. Electricity will not tend to travel through a meter of air to establish an arc when a 20mm arc establishes a low impedance return path.
- Electricity is often much more brutal and much less flashy than in the movies, and movies often portray a greater(or smaller) margin for survival than actually exists. As part of your training in electrical industries, especially in power distribution, there's a good likelihood you'll see a video of someone dying working with or around electricity. It's utterly terrible. Brutal, merciless, and not always quick. The actual speed that electricity can "change" and propagate at is fast enough to need quality examples to make it easy to comprehend. There are situations where high voltage is portrayed in movies as something that great dexterity, strength and skill can just deal with, and inevitably characters are sometimes shown doing something that would have killed or vaporized them. Sometimes with low voltage wires a character is shown killed by something that, as presented, would have a relatively low probability of being lethal. In the latter case I'm comfortable with that as laymen and professionals should treat something with a very good chance of killing them as something that will.
- Electricity flows in loops. Each molecule, depending on bonding, nuclei, and electron shells, tends to keep roughly a certain amount of electron in each area around it. The electrons themselves are bouncing around, and when they are not held too tightly where they are, they fly freely between nearby molecules, and the limiting factor is that when/as an electron moves out of an area that "needs" an electron, forces will be exerted on other nearby electrons as well as the one flying away to pull them in and fill the gap. Depending on structure of molecule and nuclei, different materials either bind their electrons tightly(insulators) or allow them to flow more freely(conductors). When you cause electrons to flow along a wire, new ones must replace the ones that flow away. The area you are pumping the electrons to will have too many and the area you are pumping them from will not have enough. There is nowhere for the flow to go other than back to where there are too few, as all of the other molecules around have exactly enough. No loop, no current.
- Water isn't really a good conductor. Dirty water, particularly salty water is. Pure water is not (tap water is not pure). Aside from that, if you put a generator on the shore of an ocean and strung a wire across the surface of the water to a point far out where the tip of the wire was bare, 1 meter underwater, and connected the generator to that wire and a ground rod, the generator would work to pass a current down that wire, into the water, along the earth, through the ground rod, and back to the generator, where the electrons you're pumping out need to be replaced. Because of the high(ish) conductivity of salt water, there wouldn't be high voltages/currents for too high a distance in most directions around the tip of that wire, as the flow of electrons is "attempting" to return on the shortest path possible to its source. voltage will spread out in other directions somewhat as the flowing electrons spread out to travel more freely. This is not to say that the water around the electrode is not dangerous, but to point that movies are often not specifically accurate with where current is flowing.
- Flashy arcs and sparks - Electricity is invisible. All we can see are the effects on objects as electricity passes through them. Heat, light, motion, the occasional smell. In order to draw attention to them, arcs, sparks and flashes are often brighter than they might be in real life, or of the wrong type (explosive rather than plasma, for example). The resistivity of air is around 2100V/mm, meaning to start an arc through room temperature air, you need 2100V for every mm you want the arc to jump. Once the air starts conducting and becomes a plasma, it conducts quite well, but it takes quite a voltage to start an arc.
$endgroup$
Definitely don't try any of these things. This is definitely not intended to imply you should be complacent about any of the dangers of electricity, but there are numerous things that are often extremely wrong in movie handling of electricity, particularly in this type of scene. Often effects are used to simply make the electricity do what the story requires, so a few things:
- Overcurrent and other fault protection: In most of the world, every circuit has over current protection and many circuits have ground fault or arc fault protection. As manufacturing capability increases, we've been able to add more ways to protect electrical installations and make them safe. In a futuristic scenario with improved technology, there is usually no reason this would have changed. Faults damage equipment, so even in a scenario where disregard for human life is written in, systems would have advanced precautions to limit property damage. At any rate, often the conductor you see creating the danger is actually a cable, with visible wires sticking out of the end, whatever the prop department thought would look cool. In many of these cases, the conductor, as presented, would have shorted between it's own conductors and tripped its overcurrent device or GFCI. In order for the conductor to stay live, something else must go wrong, like it miraculously not shorting out when being pulled loose from what it was connected to, falling, and or jiggling without shorting out on itself or touching something made of metal, or the breaker welding closed(which does occasionally happen).
- Electricity flows more on paths of less resistance. You could place large copper wire, a wet log and a strip of asphalt side by side, and connect the same voltage at once to the ends of all three. Most of the current would flow through the copper wire, much less would flow through the wet log, and a negligible amount through the asphalt, though there would be current flow in all three. If the conductors on a broken cable have enough voltage to create CGI arcs to nearby fixtures/water/whatever things that are far away, they have enough voltage to arc to its own return conductor or ground, which is sometimes mistakenly portrayed as inches away. For its own return conductor or ground to not be the target of most arcs, a second thing has to go wrong. Those conductors have to be broken somewhere between the arcing cable and the source, somehow without damaging a single high voltage cable more than would allow it to function. Electricity will not tend to travel through a meter of air to establish an arc when a 20mm arc establishes a low impedance return path.
- Electricity is often much more brutal and much less flashy than in the movies, and movies often portray a greater(or smaller) margin for survival than actually exists. As part of your training in electrical industries, especially in power distribution, there's a good likelihood you'll see a video of someone dying working with or around electricity. It's utterly terrible. Brutal, merciless, and not always quick. The actual speed that electricity can "change" and propagate at is fast enough to need quality examples to make it easy to comprehend. There are situations where high voltage is portrayed in movies as something that great dexterity, strength and skill can just deal with, and inevitably characters are sometimes shown doing something that would have killed or vaporized them. Sometimes with low voltage wires a character is shown killed by something that, as presented, would have a relatively low probability of being lethal. In the latter case I'm comfortable with that as laymen and professionals should treat something with a very good chance of killing them as something that will.
- Electricity flows in loops. Each molecule, depending on bonding, nuclei, and electron shells, tends to keep roughly a certain amount of electron in each area around it. The electrons themselves are bouncing around, and when they are not held too tightly where they are, they fly freely between nearby molecules, and the limiting factor is that when/as an electron moves out of an area that "needs" an electron, forces will be exerted on other nearby electrons as well as the one flying away to pull them in and fill the gap. Depending on structure of molecule and nuclei, different materials either bind their electrons tightly(insulators) or allow them to flow more freely(conductors). When you cause electrons to flow along a wire, new ones must replace the ones that flow away. The area you are pumping the electrons to will have too many and the area you are pumping them from will not have enough. There is nowhere for the flow to go other than back to where there are too few, as all of the other molecules around have exactly enough. No loop, no current.
- Water isn't really a good conductor. Dirty water, particularly salty water is. Pure water is not (tap water is not pure). Aside from that, if you put a generator on the shore of an ocean and strung a wire across the surface of the water to a point far out where the tip of the wire was bare, 1 meter underwater, and connected the generator to that wire and a ground rod, the generator would work to pass a current down that wire, into the water, along the earth, through the ground rod, and back to the generator, where the electrons you're pumping out need to be replaced. Because of the high(ish) conductivity of salt water, there wouldn't be high voltages/currents for too high a distance in most directions around the tip of that wire, as the flow of electrons is "attempting" to return on the shortest path possible to its source. voltage will spread out in other directions somewhat as the flowing electrons spread out to travel more freely. This is not to say that the water around the electrode is not dangerous, but to point that movies are often not specifically accurate with where current is flowing.
- Flashy arcs and sparks - Electricity is invisible. All we can see are the effects on objects as electricity passes through them. Heat, light, motion, the occasional smell. In order to draw attention to them, arcs, sparks and flashes are often brighter than they might be in real life, or of the wrong type (explosive rather than plasma, for example). The resistivity of air is around 2100V/mm, meaning to start an arc through room temperature air, you need 2100V for every mm you want the arc to jump. Once the air starts conducting and becomes a plasma, it conducts quite well, but it takes quite a voltage to start an arc.
edited yesterday
answered yesterday
K HK H
2,410315
2,410315
12
$begingroup$
"•Electricity follows the path of least resistance" Not true. Give it two paths, 1000 and 1001 ohm. Does all current flow in the 1000 ohm path and no current in the 1001 ohm path?
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– winny
yesterday
2
$begingroup$
@Winny Good point. I spouted off a safety axiom in my effort to keep things simple =P. Corrected now. Please check the rephrase if you have the time =).
$endgroup$
– K H
yesterday
add a comment |
12
$begingroup$
"•Electricity follows the path of least resistance" Not true. Give it two paths, 1000 and 1001 ohm. Does all current flow in the 1000 ohm path and no current in the 1001 ohm path?
$endgroup$
– winny
yesterday
2
$begingroup$
@Winny Good point. I spouted off a safety axiom in my effort to keep things simple =P. Corrected now. Please check the rephrase if you have the time =).
$endgroup$
– K H
yesterday
12
12
$begingroup$
"•Electricity follows the path of least resistance" Not true. Give it two paths, 1000 and 1001 ohm. Does all current flow in the 1000 ohm path and no current in the 1001 ohm path?
$endgroup$
– winny
yesterday
$begingroup$
"•Electricity follows the path of least resistance" Not true. Give it two paths, 1000 and 1001 ohm. Does all current flow in the 1000 ohm path and no current in the 1001 ohm path?
$endgroup$
– winny
yesterday
2
2
$begingroup$
@Winny Good point. I spouted off a safety axiom in my effort to keep things simple =P. Corrected now. Please check the rephrase if you have the time =).
$endgroup$
– K H
yesterday
$begingroup$
@Winny Good point. I spouted off a safety axiom in my effort to keep things simple =P. Corrected now. Please check the rephrase if you have the time =).
$endgroup$
– K H
yesterday
add a comment |
protected by Nick Alexeev♦ 1 hour ago
Thank you for your interest in this question.
Because it has attracted low-quality or spam answers that had to be removed, posting an answer now requires 10 reputation on this site (the association bonus does not count).
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-safety
38
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I seriously suggest that you don’t do any testing.
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– Solar Mike
2 days ago
7
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The answer is: it depends, there are many variables involved like: distance between you and the wire, voltage on the wire, conductivity of the water, water level, material of the bath, if the bath is metal or conductive: how well is it grounded, is it painted. I could go on for a while. All this determines the amount of current passing through the person. Also thin persons can handle less current than "less thin" persons. There can be no clear answer.
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– Bimpelrekkie
2 days ago
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Your ground symbol in the sketch implies that the power on the wire is referenced to ground. It may not be. The power on that line could be isolated from ground.
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– scorpdaddy
2 days ago
5
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This question reminded me of the following video on Youtube made by Electroboom: youtube.com/watch?v=dcrY59nGxBg Where he actually does an experiment to confirm this
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– Ferrybig
2 days ago
2
$begingroup$
"There's an exposed wire over the bathtub ... Oh yeah! Shock wire! I call it that 'cause if you take a shower and touch it.....YOU DIE!" - Ron Swanson / Andy Dwyer - Parks and Rec
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– NKCampbell
2 days ago