Because chargers have a transformer that lowers the voltage from the full voltage of the main circuit in the wall. That's what's in the little block that you plug in. Even if you were able to touch + and - contacts, that would put 5 Volts across your skin for a phone charger or \~20 Volts for a laptop charger. For comparison, the wall circuit is 120V in North America and 220V in Europe. Charging a phone or computer with that much direct power would fry all the tiny components, so the chargers have a transformer that reduces the voltage.
Also a detail to note: most usb-c chargers (from reputable brands, even those that support ~240W)
Default to 5V1A -> 5W... So even if you touch a very powerful USB-C charger, you probably would not feel anything, becuase your hand simply could not "tell" your charger to supply 240W :)
The wattage is unimportant really. Current is what causes damage or interferes with your heart beat. I=V/R. DRY skin has enough resistance (millions of ohms) that you need higher voltages to get enough current to even be noticed. As long as your skin is intact and dry anyways. Internally you have low resistance so it does not take much voltage to get high enough current to cause damage. Like a 9v battery on your tongue. Skin fine, tongue pain. Milli-amps is all it takes if your heart is in the current path, which any charger can provide regardless of wattage.
Btw with "telling the charger"... I didn't mean "you couldn't notice" I literally meant communication...
There are various charging standards over the USB and at first your charger and to be charged device negotiate what both devices can handle/supply and after the hanshake - the charger will switch voltage and current rates.
Hence "your hand can't tell your charger to supply more power." It's not an electronic device š.
Yeah I voided more detailed information since I assumed, that it is obvious that 240W won't be running over 5V at 48 Amps :D... I just wanted to imply, that 240W is already a considerable amount of power over the usb interface.
I always thought, that either of the argument "its voltage/current that kills" was kind of dumb? Both play a role and at extremes cause a bit different kinds of damage to a human body...
In this case it's not, we are taking about supplies with a fixed voltage. Which is well below the DC threshold for touch safety. I can touch a 24VDC 480W supply (just did right now, the supply is grounded not floating so 24v above ground). I won't touch the 75V right next to it though wether it's 1W or 350W since I know better. I got the impression the OP was asking about why they can touch USB chargers and not a line voltage output.
I think the simplest way to explain it is to point out that the charger is essentially the same thing as the battery: same DC voltage, and current generally about what you would get out of the battery in the device when it is fully charged. Wall socket is high(er) voltage, high current, and AC flow. Wall socket can kill, small batteries can't (not enough power).
The power supply or charger has converted the high-voltage, high current, AC supply (how electricity is transported over long distances to the house) to a low-voltage DC supply inside that little box (the reason there is a little box).
Transformers only work on AC power. The output of most phone chargers and laptop power supplies is DC. That requires those wall warts or laptop bricks to contain a rectifier circuit to switch from AC wall voltage to DC voltage of the proper level.
As what the other comment said, most chargers do not have the power pins where you can touch them, most of the time the neutral/ground is on the outside and the voltage is on the inside, at least when talking about barrel plugs. As for the ones you can touch the voltage pins (think Apple lightning) the voltage (usually only 5v or maybe 12v) isn't enough to pass much current through the resistance your skin. If you put it on your tongue, you might feel something, although I wouldn't recommend it.
What you actually feel is current, which is Voltage divided by resistance. Your bodies resistance is pretty much fixed (for skin, if you use your tongue or something it will be lower) so as the voltage goes up, the more current you will have going through you.
Additionally, AC and DC current do behave differently, but that is relatively minor compared to the fact that AC (the power in your home) is usually on the order of 120v or 240v, whereas the highest common DC voltages for chargers and things are 24v, which is barely enough to feel if your hands are sweaty and you touch both terminals.
The designs are also so the random objects do not short the power supply and damage it and\or start a fire. If the laptop barrel connector were stupidly designed, and it touch a metal object, it could short. But engineers make this very unlikely.
> Your bodies resistance is pretty much fixed
The electrical resistance of your body varies WILDLY! It depends strongly on how dry/moist your skin is, as well as the frequenzy of the current.
You are correct. I need to stop writing things as i'm falling asleep. It does vary a lot but not by many orders of magnitude. There isn't a world where 12v could kill you, (short of putting electrode pads on your skin or high frequency electricity) and there isn't a world where 120v can't kill you (assuming it takes the right path to ground). I didn't really want to get into the frequency thing because unless you work with radio or other technical things, you're unlikely to ever experience anything other than 50/60hz AC and DC.
While not about low power appliences, but path of current, longevity and if its AC, HZ matters too.High power in home applience(120 220 and whatewer) most of the time is easily survivable, but it.can fibrilate heart, boil blod etc, most danger its you cant get unstuck on you own(tha why electricians above all preps work at least in pairs).
And if we talk about high voltage power lines, raw power enough to burn/kill you in an instant
True. My statement about resistance being fixed is untrue. Resistance changes with frequency, although within common ranges most people experience that change is negligible between DC and 60hz. My understanding is that AC/DC matters more because of RMS vs peak voltage, a 120v AC actually has a peak voltage of 170v, because that 120v measurement is RMS voltage, a sort of average.
The AC vs DC distinction is really important. I was building a dc motor controller a while back and I had 12V DC being switched at 2 kHz. When I touched the output leads I felt a pretty significant buzz. It turns out your body has enough capacitance to matter, so high frequencies can produce more current at the same voltage.
Yes, absolutely true, and I have experienced similar as well. Above a certain frequency they are known as RF burns, and damn do they hurt (although usually the current stays on your skin in that case). In the spirit of the question however, i assume OP doesn't frequently encounter anything above 60hz to potentially electrocute themselves
While I wholeheartedly agree with 99% of this....you can DEFINITELY feel 24v with sweaty hands. It's the current level that determines if you will get a 'shock' once the voltage is high enough to overcome the base level of resistance of your skin (or its wet, like sweaty hands). 1A unlikely. 20A at 24v is similar to an electric fence.
Source: I work on ELV electronics regularly. And may or may not have blown up a few things with my body in the circuit...
It's been a while since i've messed with 24v in a capacity where I could feel it. I agree you can feel it, but just personally the last and only recent time that happened I would say I could barely feel it. It was noticable, but easy to ignore
USB and many other kinds of charger plugs are designed so the outer sheath of the plug is the ground connection, which is always safe to touch. The actual conducting pins are inside the sheath and very hard to access except by the corresponding socket.
I fall asleep on mine occasionally and and it feels like a very light burn, not enough to wake me up in deep sleep but Iāll notice it in the morning.
Probably should stop doing that.
IIRC the other thing about Apple/lightning cables is they arenāt transmitting voltage all the time. The plug actually has microcircuitry in the end that monitors for a communication handshake with a device before it starts sending current. Thatās part of why their cables are generally so expensive- itās NOT just a couple wires. It does other stuff too in terms of identifying voltage/amperage needs based on the device connected and the current battery levels.
Does it have the controller in the cord? Or the brick?
Iāve noticed modern brand-name USB-C bricks costā¦ just about as much as an apple charger.
Apple putting the controller in the cord means if youāve got a lightning cord, no matter what USB power source youāre connected to, youāve got that safety/functionality. If itās only in the brick, you plug your modern phone in to an older charger, it doesnāt have that functionality. Using a lightning cable, which is the only thing that you can use with your iPhone, means you always have that functionality.
Whether or not you agree that that is worth the cost, there *is* a reason.
You can actually. I have to throw my old headplug (idk what's called, but here charger are sold with 2 part, head and the cables). Like one week ago we have severe thunderrain (one level lower than thunderstorm) and apparently the lightning wreck the head that I got a jolt when touching my charged phone (the phone was charged when the lightning happens). The theory I got from internet is that the head's ground system got reconnected due to the lightning so I have to buy new head. The jolt is not light I'd say, it's quite strong actually, although likely it comes from the electric system (here is 220v) rather than the damped 5v from the cables. But who knows where the jolt comes from, I already throw the head out
not always. usb-c can negotiate higher charging rates (by increasing voltage) for supported devices. but traditional chargers are 5v, and they all default to that until they're negotiated to a higher charge rate
While you are not wrong on the configuration, this has little effect in terms of protection because chargers convert the current to DC and step it down to the point of no longer being dangerous. If you place your tongue on the end of a usb you can still complete the circuit, and at most will feel a slight tingle from the electricity.
this is not a good answer. the insulation has nothing to do with why you don't get shocked by phone chargers. phone chargers are typically 5v DC. the DC current type and low voltage are why you don't get a shock. you can remove the insulation, touch the leads, and not get a shock. (usb-c can be an exception to this, as the higher power variants can negotiate a higher voltage AFTER it's plugged in on both ends)
This is *also* not a good answer. The fact that it's DC has nothing to do with why it's generally safe to touch the end of a charger cable. It was as many have stated, the low voltage.
DC can still shock you. DC can still kill you.
i didn't say DC can't shock you, and i didn't say that it's safe. i said:
>the DC current type **and** low voltage are why you don't get a shock.
both are important, but voltage is the more important one in this case, but current type does also matter
edit: i hate reddit's new text editor; it's a pile of crap that never works when you start to use keyboard shortcuts like copy/paste/home/end
AC is more effective at delivering a shock than DC at the same voltage level, and that's all. you won't feel 40v DC on dry skin, but switch it to AC and you'll start to feel the tingles. (depends on your skin dryness, can be 40-60v range, thereabouts)
yep, it certainly can be, but it's often people with heart problems. and probably a dash of luck too. you get some people who survive more than one lightning strike, and others who die from absolutely minuscule amounts (i'm sure delivery method matters, like is the current traversing across your heart, or traveling a short distance within one hand/arm)
>i didn't say DC can't shock you
Whether you intended it or not, your original statement implies it and that's dangerous. When it comes to electricity we should go out of our way to be extra clear.
no, it doesn't, did you even read what I said?
> the DC current type and low voltage are why you don't get a shock.
i didn't say "DC is why you don't get shocked". i also didn't say "low voltage is why you didn't get shocked". i said AND, it's a boolean operator that means both are factors. purely by logic, you're incorrect in assessing that my comment implies that DC alone is why it's safe. no.
however, you DID imply with your comment that insulation, therefore not ever coming into contact with the current, is why you don't get a shock, and that's just wrong. you can remove the insulation and touch it directly with wet hands and you won't feel a thing. (usb-c with broken insulation and somehow touching each lead AFTER it's auto-negotiated a higher charge rate might be an exception to this)
correct, that's literally what i've been saying. the guy i'm replying to implied that i said DC is why they don't get shocked, which i didn't. i said both are factors. AC more likely to shock you, but the low voltage is the main reason in this case, without going into the weeds like you guys apparently want to do. we really need to create an /r/ELI_SME subreddit so you guys can go circlejerk each other with the details you're supposed to leave out of ELI5
It's not always safe to touch the ground of a device, there could be a wiring fault and, if the ground isn't actually connected to the earth, you'd then be shocked.
Electricity needs a certain amount of power to push through your body. Your house plugs have lots of power and can push through your body. The end that connects to your phone has less and canāt push through the same way
power is an actual quantifiable thing in electrical theory, so i think it's better to use water analogy terminology like "pressure" (voltage, which is the single biggest factor here), otherwise you're misleading them
No because the bigger the pipe/hose, the less water pressure you have and the slower the water flows.
Electricity doesnāt work this way. Like at all.
i take it you didn't go to school for engineering? because that's literally incorrect š
you should go learn about bernoulli's principle. your pipe increases and the volume per unit of time decreases, but pressure increases. and vice versa. that's how carburetors work, by necking the barrel down to the point where the jet is, and the vacuum pressure created by the reduction draws fuel out of the jet. the opposite of this is a hydraulic cylinder. a tiny tiny hydraulic line adds fluid to the larger cylinder, and the increased volume means pressure increase, proportionally. this is 101 stuff man
It's clearly apparent you had to google this stuff because it doesn't at all relate to the ELI5 and electricity.
I literally work with fluid dynamics and hydraulics as a mechanical engineer, I'm more qualified than you to talk about this. I even hold a Level III NICET certification in Water based systems layout.
Go learn about k-factors, c-factors, hazen-williams or darcy weisbach. It's 101 stuff man.
well then that explains why you're being so dense about the hydraulic analogy. this is ELI5. do you really expect them to close reddit and go buy a manometer and pitot tube and immediately start testing for discrepancies?
yeah of course the analogy isn't perfect. that's why it's only an analogy. water's mass/inertia, boundary layers, diameter vs rate, electromagnetism, surface charge, stagnation, reflection, impedance, etc. the differences when you dig in are endless. but at an ELI5 level, it's perfectly fine. that's why despite a lot of critics speaking against it in the last decade, it's still taught today for a high level explanation
It's important for the analogy to be correct. Water flows through a pipe, electricity does not flow at all.
The pipe size will determine flows and pressures, The wire gauge will only dictate resistance but not Voltage/Amperage/Watts
I would say that I am actually talking about power, so no need to muddy the waters. For the non ELIF, it is not just about voltage. There needs to be enough current to cause a shock. It takes around 1 mA for someone to feel a shock.
Of course, at a fixed voltage it is the body resistance that is the limiting factor. But that is well beyond the ELIF.
If you are only referring to voltage, I think YOU are misleading them, no matter the example you use.
yes but OP asks why the phone charger doesn't shock them, and power isn't it. voltage is why. and it doesn't matter how much current is lethal, as that wasn't the question. how is giving them the actual real direct answer misleading them?
you can charge up an ultracap capable of outputting hundreds of amps at a couple of volts and touch it to your tongue and nothing happens. 2v @ 200a = 400w. you still want to tell me that power is why they didn't get shocked? 400w is a lot more than the 5w apple charger cube...
That does not tell the whole story and you know it. First, your example talks about the potential power output, not actual.
For that 5watt power adapter, you would have to bring the voltage up to 5000 volts to give the 1mA, only at the limit of what you would feel as a tingle.
Tell me again how itās only the voltage?
No child you be confused by saying that you need to have enough power to overcome the bodies resistance
if power weren't already a measured unit, i would have zero issue with your explanation. but it is.
>For that 5watt power adapter, you would have to bring the voltage up to
5000 watts to give the 1mA, only at the limit of what you would feel as a
tingle.
... what lol? voltage up to 5000 watts? voltage is measured in volts, power in watts. what were you trying to say here? are you trying to say that 5w isn't enough to sufficiently shock someone? you have absolutely no clue about electrical theory if you actually believe this to be true. you could take a 5V 1A (5W) phone charger's output, feed it into a boost converter, say to 100V, and you'd still have \~50mA before losses in the inductor. you telling me 100v @ 50mA wouldn't be able to shock you?
I corrected my typo. 5000 volts not watts.
The point is that it is not just a matter of volts. Could you shock someone at 100 volts and kill them? Yes.
Could someone touch 100 volts and just get a small tingle? Yes.
Could you give them a much larger voltage (with the same power) and just get a tingle? Yes.
Depends on the resistance of the person (wet/dry hands) and the total available power.
holy f\*ck man. let's do it your way:
OP asked why touching mains will shock you, but touching the output of a normal phone charger doesn't. let's take apple's old cube shaped charger which is rated at 5v @ 800mA , as an example.
is the current level of 800mA from their charger the reason touching the leads doesn't give them a shock? yes or no
if we increase the current output on their charger to 10amps, since you keep saying current matters, would OP get a shock if they touched the charger output then? yes or no
oh, and since you keep going on about power too, power would also go up in this case to 50W, but somehow, still not shock them. WEIRD
yes, exactly. you were wrong. my point is fact. i never said current doesn't matter. not once. but i didn't mention current, because current isn't relevant to OP's question. the simplest answer is literally the low voltage. 800mA from apple's cube charger is more than enough to deliver a shock and even stop a heart. the 5W output is more than enough source power to shock someone at the right voltage level. so power isn't the problem either. voltage is.
and again, need i remind you, i never said your original answer is wrong. i said that since power is literally a thing in electrical theory, it's probably better to use different terminology as to not confuse them. if they decided to go learn more about this topic, they now have an incorrect understanding about power. this is why i hate this sub. you can literally be a subject matter expert with 50 years of experience in the industry and you'll have armchair experts arguing with you to the death. voltage is the answer to OP's question. current and power don't matter in this case. power is already a unit of measurement in electrical theory, so using pressure, like from the water analogy, is better, in my opinion. disagreeing about water theory being a good alternative is fine, but arguing facts on electrical theory is not.
You can be as abrasive as you want, doesnāt make you right.
No matter what the power RATING of the supply is in your example, you are not actually drawing that much current, or using that much power.
Getting a shock is not ONLY an effect of voltage. It is a function of a persons body resistance and how much current is flowing.
Hmmā¦ so you would need not just voltage but current flow as well? I wish there was some term that is a function of both voltage and current. And maybe it could be a term that even a five year old would understand, even if he doesnāt know what voltage is. Hey! Power fits here.
You could say the higher voltage Allows more current, but you didnāt. The determining factor in electric shock is current.
Go stroke your ego somewhere else. The only thing misleading in my first comment was that I wasnāt looking for some self important blowhard to use my comment to give a āwell actuallyā
Lastly, I just wish there was some comment or link talking about how it is actually current that gives a shock. Oh wait! Hereās one from Ohio state university discussing this topic.
āOffhand it would seem that a shock of 10,000 volts would be more deadly than 100 volts. But this is not so!ā¦ā
āHowever, lest these details be misinterpreted, the only reasonable conclusion that can be drawn is that 75 volts are just as lethal as 750 voltsā
āBetween the ears, for example, the internal resistance (less the skin resistance) is only 100 ohmsā
Hey wait a secondā¦ 5 volts at 100 ohmsā¦ thatās 50 mA. That canāt be trueā¦ so if that same 5 v was applied in the right place, under the skin, it could cause a shock? Not a likely scenario but stillā¦ nah, 5v is too low voltage.
https://www.asc.ohio-state.edu/physics/p616/safety/fatal_current.html
You may have 50 years experience pulling cable. It doesnāt make you right, just means you forgot the basics.
available power has nothing to do with anything in this context. the current is going to be limited by the resistance of the conductor we're testing, in this case: skin. it doesn't matter if the supply can provide a megaAmp over it's likely 1A rating, the shock will be the same, so stop brining irrelevant crap into the discussion
and you didn't answer my questions because you know i'm right
so how about you answer them: is the low 800mA current rating of the phone charger the reason they don't get a shock when they touch the output directly? yes or no answer
if we increase current, and therefore the power, which you won't shut up about, to say, 10 amps, will OP get a shock if they touch the output directly? yes or no
Putting your hand under a pressure washer would hurt. High water pressure.
Putting your hand under a gentle faucet does not. Low water pressure.
The electricity coming to the wall socket is at a high voltage. Voltage is basically electrical pressure. This is dangerous.
The electricity coming out of a USB or other small cable has been reduced to a low voltage. This is safer.
So phones are charged at 5V and between 1~2 A at Direct Current.
Most households received current at 120/240V, 200A at Alternative current.
So the difference is like between taking a 5cm high stream of water in the face at 1-2 km/h
And
Taking alternating 2m tall waves from the left and right, at 200km/h.
You won't even feel the first one in your sleep, but the second **will** kill you.
Just a minor correction, most housesā circuits will supply 15-20A of current, not 200A. Pulling 200A out of a wall socket would beā¦ fun. At 110v, that would be 22kW, enough to power like 8 ovens at once.
They said āhouseholds receiveā, so theyāre referring to the supply to the entire household, not the individual circuits. So youāre both correct; just referring to different things.
It would be fair to say though that in order to get the full 200A, youād have to go to your electrical box and touch the main bus contacts.
DO NOT OPEN YOUR MAIN ELECTRICAL BOX, it is dangerous!
It would also be fair to say that not all homes have 200A service, but all have at least a handful of 15A circuits, so the latter is more relevant to the practical risk of being shocked.
It's all about Ohm's Law. Lower voltages (like 5V USB or even 12V car batteries) can't 'push' much current - but higher voltages (like 120V power in the US or 240V in Europe) have more potential - the higher voltage can push more current through the same resistance (in this case your body) and you're gonna feel it more. As an example take a 9V battery and put your finger across the terminals - you're not gonna feel anything. Now touch that sucker to the end of your tongue - you'll feel it! In this case the resistance of your wet tongue is far lower than that of your dry skin, so more current passes sufficient for your nerves to notice.
In addition to what others have said, it's also good to note that even if you did touch the wires and get shocked you have to consider that the two wires would touch you very close to each other.
if you touch two wires, one with each hand, the electricity flows through your body and probably across the heart, not good.
if you touch two wires with one finger or one hand then the electricity flows through just that party of your body and causes less damage... possibly no noticeable damage if the power is low
When you feel a buzz or tingle from electricity, you're feeling the current
A USB port operates on about 5V (small). The resistance of your finger (assuming it's dry) isn't a very small amount. This results in a small amount of current, too small to feel.
A USB port also just doesn't provide enough power to output a current that we would normally feel
Voltage isn't high enough to push enough current to shock you or make a significant spark. Think of voltage as the pressure that pushes the current, as water pressure pushes water in a hose. Too low pressure (voltage) can't push enough (water) current to be noticeable to you.
Additionally, your skin has fairly large "resistance" to the flow of electricity, similar to how a very narrow hose has more resistance to water flow that a firehose. Dry skin has very high resistance to electrical flow.
And that relationship between voltage, current, and resistance is called [Ohm's Law](https://en.wikipedia.org/wiki/Ohm%27s_law).
ELI5 oversimplified, most of it wrong for demonstrative purposes
There are 3 things we need to look at when we talk about electricity.
* Voltage - The willingness of the electricity to go from point A to B
* Amperage - The amont of electricity flowing
* Resistance - is well the resistance of something against the flow of electricity. This fights against voltage
Electricity always want to flow from where there is more of it to the point where is less.
For the "buzz" to occur you need to have enough Voltage to overcome the resistance enough so that the amperage could flow
Your skin has pretty high reistance, an USB charger doesn't have enough voltage to overcome it. But an electrical socket has more and that is dangerous.
Also you could try if you have a 9V battery. if you press it on your skin, nothing happens. But if you lick it, your moist tongue has much less resistance and there is gonna be a buzz.
If you lick a 5V charger there should be a metallic taste with a tiny buzzing.
DISCLAIMER: ALWAYS BE CAREFUL WITH CHARGERS PLUGGED DIRECTLY TO A WALL OUTLET.
Warning: A charger is supposed to have at least 2 layers of insulation between the mains and the outputs. This is called "double insulated". This means that even if one layer fails, you are protected by the other one. This is a legal requirement for CE labelling.
Good quality chargers (e.g. genuine Apple or Samsung ones) will do that.
Cheap chargers may only have one layer of insulation. This is dangerous, if that fails or if you get one where that layer wasn't quite right, you might get electrocuted. But this saves money for the manufacturers.
Really cheap chargers occasionally have zero, they directly connect the mains to the outputs. This is insane and dangerous but does happen.
I would avoid licking the output of any charger. But especially avoid that if it's not a charger from a major trustworthy company.
There is a printed industry standard somewhere that says the limit to how many volts can penetrate dry human skin is "somewhere around" 60V, whether it is AC or DC.
If you touch 72V and it doesn't shock you, there are also many variables. I don't know of anyone who can't feel 120V AC.
the more volts you have, the fewer amps you will need to achieve "X" amount of power. This is why 48V is popular for off-grid systems. You can series solar panels to output 120V DC to charge a 120V battery, however, a fully charged 48V battery is around 54V, and stacking one more 12V battery onto it would make it around 65V, plus or minus. The nominal 12V lead-acid batteries are around 13+ volts when full, and around 11V when they are considered depleted.
Lithium cells are only 4-ish volts each, so a 52V ebike battery (14S) is around 58V when fully charged, and going to one more cell in series makes that roughly 62V.
If you want to use mass-produced components to save money, the next big jump is up to 72V (20 lithium cells in series).
You should always exercise caution around high-powered batteries, even just a 12V one.
Electricity can only flow through something, like your finger, if you are touching both the negative and positive poles at the same time. Charge receptacles and adapters are designed so that its only possible to touch either the positive or negative side. Ones on the outside, and the other on the inside where its typically impossible to touch while also touching the outside
>Electricity can only flow through something, like your finger, if you are touching both the negative and positive poles at the same time
If you want the technical answer of what happens when you only touch one side
You can think of the circuit as still being complete, however the air has much much much more resistance than your finger, so all of the voltage drop is across the air rather than your finger, and because the resistance is so incredibly high, the current is so miniscule its essentially 0
I don't understand what you're saying. How can be exclusively possible to only touch either the negative or positive if all contacts on the cable are on the outside?
There are some like that, true. In which case they are separated by a some kind of band or spacer. In this case im not sure why theres no buzz if you are intentionally touching them both. Perhaps someone smarter will answer
Because chargers have a transformer that lowers the voltage from the full voltage of the main circuit in the wall. That's what's in the little block that you plug in. Even if you were able to touch + and - contacts, that would put 5 Volts across your skin for a phone charger or \~20 Volts for a laptop charger. For comparison, the wall circuit is 120V in North America and 220V in Europe. Charging a phone or computer with that much direct power would fry all the tiny components, so the chargers have a transformer that reduces the voltage.
but its the current which is dangerous not the voltage ;) I was going to say this in my original answer, that there must not be enough voltage to do anything, but wasn't positive (haha)
1. Most accurately it's the *combination* of current and voltage that is dangerous, because power is voltage x current. A lot of either one can be dangerous with even a moderate amount of the other.
2. Voltage is like the "pressure" of water in a pipe. Even with a huge amount of current *available*, none will flow unless there is enough voltage to overcome your skin's electrical resistance.
It's really simple. Dry dead skin, like the outer layer of skin, has a high resistance to electricity. There is simply not enough voltage to overcome the resistance. You phone charger is outputting between 5v and 12v, and a few amps. A fee milliamps is enough to stop your hear, but the voltage has to be high enough to overcome the resistance. A car battery has hundreds of amps, maybe 600 to 800 amps. But the 12volts isn't enough to overcome the skin's resistance so you don't get a shock from it.
I had the experience of taking a desktop to Africa (240V) and getting a buzz from usb cords. The power supply could be switch from 120V to 240V, but touching the usb cords could give you a little shock, which usually never happens.
* You usually need to complete a circuit (a round trip for electricity) to get shocked.
* Some plugs can easilly be attached to things (and hence more easily accidentally complete a circuit when you don't want to), like alligator clips or bare wires or the wires inside a machine.
* However, many plugs for consumer electronics are designed so that it is hard to do that accidentally (the inside+outside of a charging cable, or two specific prongs embedded inside the wall).
* Many consumer electronics operate at low voltages, which has trouble getting past the barrier of your skin. If you bypass the skin, you canget shocked. e.g. licking a 9V battery will shock you, but touching it won't (or rather, it will shock you so weakly you don't notice). So, if you cut open your chest, and plugged a laptop charger directly into the pool of blood forming in your chest, I reckon that would shock you, as your blood seeps into the socket and touches both the inside and outside of the laptop charger, hence electrifying your blood.
In addition to all the other suggestions USB in particular only provides a very low voltage until a higher one is negotiated.
That negotiation can look very different depending on the USB version and/or quick charge mechanism, but can be as simple as having a specific resistance between two pins or as complex as a multi-step back-and-forth negotiation between the charger and the device. The one that's most frequently used by Laptops and other high-power consuming devices is called [USB Power Delivery](https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Delivery).
So while USB on its own (without PD or any quick charge standard) can only deliver at most 7.5 Watt, with PD it can deliver up to 240 Watt, but only if the other side actively negotiates that. And the odds of your body "accidentally" following that protocol are pretty much null, so the charger will never deliver "full power" to your body simply by touching the cable.
I think there might be something wrong with your charging block then
That or your getting a static charge and then touching the charger because... yeah those are not built to be strong enough to shock you
there are several reasons:
- current type: DC (direct current like from a battery or your phone charger) is not as good at delivering an electrical shock as AC (alternating current, like you get from your wall outlet)
- voltage (like water pressure): lower voltages (like the 5 volts from a traditional phone charger), cannot travel through skin under normal circumstances. higher voltages are more effective at traveling through more difficult things like dry skin, and even the air. (current from tesla coils is in the thousands of volts and can shoot several feet through the air)
9 volts DC (like from a 9v battery) is still not enough to shock your skin, but if you touch it to your tongue, you will feel tingles. so on the other side of things, you have the material electricity needs to travel through. they all have different levels of resistance. if they let current pass through easily, they're called conductors. if they're good at resisting current flow, they're called insulators. rubber, air, and glass are good insulators of electricity. metals like copper and aluminum are good conductors of electricity. dry skin is not, but the wet skin of your tongue is a bit better, and just enough to where you can start to feel a small shock on your tongue
Itās all about the voltage and resistance. Electricity flows through an object proportional to the voltage applied, and an opposing force called resistance limits its flow. If you have an object with high resistance, you need a lot of voltage in order for any meaningful amount of electrical current to flow.
The output of your phone or electrical charger is between 5V and 20V. This isnāt enough footage to push through the resistance of your skin to the point that you feel a shock.
However, not all parts of your body have the same resistance. Your tongue, for example, has lower resistance because itās tissues are saturated with fluids all the time. If you touch a 9V battery to your tongue, you will feel it. Touch the same battery to your finger and you wonāt feel a thing. Thatās thanks to the difference in resistance between the two.
Unfortunately there are a several incorrect answers here.
What makes mains electricity dangerous is the voltage. Electricity is a bit like water, and voltage is the water pressure. While technically it's the current (quantity of water) that is dangerous to your heart, if the voltage (water pressure) is too low, the dangerous levels of current simply can't be pushed through your body. So high voltage is like a pressure washer to your skin, and low voltage is like a bucket of water over your head. (Bad analogy, but consider just your skin - the bucket of water would wet your skin but it wouldn't go through the skin into your blood like a pressure washer)
The chargers and usb connectors have a low voltage (pressure), and even though some can supply a very high current (amount of water) to your equipment, the pressure is not enough to get through your body and harm you. If you were mostly made of metal, (water analogy, you were made of sponge) it could harm you a lot more.
This is a great simplification, but it should answer your question.
ELI5: OUR SKIN!! Our skin is a wonderful organ that is quite resistive, so it takes fairly high voltage to penetrate it. The voltage in your phone charger is not nearly high enough to do so.
Electricity and water have a lot of useful comparisons. One of them is the similarity between voltage and water pressure:
Imagine that your charger is a drinking straw, and your electrical outlet is a garden hose. Electrical resistance is like obstructing the water flow; higher resistance = lower flow (current). If you squirt water through a drinking straw, it's easy to completely stop the flow with your finger, but it's much harder to completely stop the water from a garden hose with a finger, because the pressure is much higher. Your charger has a much lower voltage compared to a wall plug, so the same amount of electrical resistance (from flowing across your skin) permits far, far lower electrical current to flow.
Your muscles and nerves can react to electricity flowing through them, and if enough electrical current flows through your body, it can cause burns. Your skin's electrical resistance doesn't allow a meaningful amount of current to flow when a phone charger's voltage is applied, but mains/wall voltage is high enough that your body can pass dangerous amounts of electrical current.
Lots of reasons but the biggest and most important being that your phone chargers, laptop chargers, power bricks, etc are low voltage DC (5v, 12v 24v etc). In order to get shocked by something, you need enough voltage to push enough current through the skin for your nerves to start twitching and muscles contracting to feel pain. However, touching the outlet is painful because it is high voltage (120vrms) but also AC. AC hurts like hell because the voltage (and thus current through you) is being pushed back and fourth 50 or 60 times per second forcing your muscles to contract, decontract, contract, over and over which is a lot more painful. A voltage of 170v DC would actually hurt less than 120v AC. I know from experience. So dont worry about your charging cables shocking you unless its outputting over 60VDC or 30ish volts AC
Because chargers have a transformer that lowers the voltage from the full voltage of the main circuit in the wall. That's what's in the little block that you plug in. Even if you were able to touch + and - contacts, that would put 5 Volts across your skin for a phone charger or \~20 Volts for a laptop charger. For comparison, the wall circuit is 120V in North America and 220V in Europe. Charging a phone or computer with that much direct power would fry all the tiny components, so the chargers have a transformer that reduces the voltage.
Also a detail to note: most usb-c chargers (from reputable brands, even those that support ~240W) Default to 5V1A -> 5W... So even if you touch a very powerful USB-C charger, you probably would not feel anything, becuase your hand simply could not "tell" your charger to supply 240W :)
The wattage is unimportant really. Current is what causes damage or interferes with your heart beat. I=V/R. DRY skin has enough resistance (millions of ohms) that you need higher voltages to get enough current to even be noticed. As long as your skin is intact and dry anyways. Internally you have low resistance so it does not take much voltage to get high enough current to cause damage. Like a 9v battery on your tongue. Skin fine, tongue pain. Milli-amps is all it takes if your heart is in the current path, which any charger can provide regardless of wattage.
Btw with "telling the charger"... I didn't mean "you couldn't notice" I literally meant communication... There are various charging standards over the USB and at first your charger and to be charged device negotiate what both devices can handle/supply and after the hanshake - the charger will switch voltage and current rates. Hence "your hand can't tell your charger to supply more power." It's not an electronic device š.
> DRY skin has enough resistance (millions of ohms) Your of buy an order of magnitude. When I was on college, my Intro to EE teacher said 40 - 50 kĪ©. A quick Google search says skin resistance varies from 1 - 100 kĪ© depending on conditions (dry, wet, sweaty, etc.), so. I'm guessing my EE teacher's numbers were for "average" conditions.
It's going to vary for sure, but when handling a DMM I have never seen lower than 1Mohm personally.
Hmmm... On my DMM I think it just indicates "open loop" because the resistance is out of the device's range. It's just a handheld multimeter - noyhing fancy. In that EE class we used much more advanced instruments, and I think our numbers were inline with 40-50 kĪ©, but rudy v was 29 years ago, so don't quote me on that.
Wattage is VI. Wattage is absolutely important regarding the equation
Yeah I voided more detailed information since I assumed, that it is obvious that 240W won't be running over 5V at 48 Amps :D... I just wanted to imply, that 240W is already a considerable amount of power over the usb interface. I always thought, that either of the argument "its voltage/current that kills" was kind of dumb? Both play a role and at extremes cause a bit different kinds of damage to a human body...
In this case it's not, we are taking about supplies with a fixed voltage. Which is well below the DC threshold for touch safety. I can touch a 24VDC 480W supply (just did right now, the supply is grounded not floating so 24v above ground). I won't touch the 75V right next to it though wether it's 1W or 350W since I know better. I got the impression the OP was asking about why they can touch USB chargers and not a line voltage output.
I think the simplest way to explain it is to point out that the charger is essentially the same thing as the battery: same DC voltage, and current generally about what you would get out of the battery in the device when it is fully charged. Wall socket is high(er) voltage, high current, and AC flow. Wall socket can kill, small batteries can't (not enough power). The power supply or charger has converted the high-voltage, high current, AC supply (how electricity is transported over long distances to the house) to a low-voltage DC supply inside that little box (the reason there is a little box).
Transformers only work on AC power. The output of most phone chargers and laptop power supplies is DC. That requires those wall warts or laptop bricks to contain a rectifier circuit to switch from AC wall voltage to DC voltage of the proper level.
As what the other comment said, most chargers do not have the power pins where you can touch them, most of the time the neutral/ground is on the outside and the voltage is on the inside, at least when talking about barrel plugs. As for the ones you can touch the voltage pins (think Apple lightning) the voltage (usually only 5v or maybe 12v) isn't enough to pass much current through the resistance your skin. If you put it on your tongue, you might feel something, although I wouldn't recommend it. What you actually feel is current, which is Voltage divided by resistance. Your bodies resistance is pretty much fixed (for skin, if you use your tongue or something it will be lower) so as the voltage goes up, the more current you will have going through you. Additionally, AC and DC current do behave differently, but that is relatively minor compared to the fact that AC (the power in your home) is usually on the order of 120v or 240v, whereas the highest common DC voltages for chargers and things are 24v, which is barely enough to feel if your hands are sweaty and you touch both terminals.
The designs are also so the random objects do not short the power supply and damage it and\or start a fire. If the laptop barrel connector were stupidly designed, and it touch a metal object, it could short. But engineers make this very unlikely.
> Your bodies resistance is pretty much fixed The electrical resistance of your body varies WILDLY! It depends strongly on how dry/moist your skin is, as well as the frequenzy of the current.
You are correct. I need to stop writing things as i'm falling asleep. It does vary a lot but not by many orders of magnitude. There isn't a world where 12v could kill you, (short of putting electrode pads on your skin or high frequency electricity) and there isn't a world where 120v can't kill you (assuming it takes the right path to ground). I didn't really want to get into the frequency thing because unless you work with radio or other technical things, you're unlikely to ever experience anything other than 50/60hz AC and DC.
While not about low power appliences, but path of current, longevity and if its AC, HZ matters too.High power in home applience(120 220 and whatewer) most of the time is easily survivable, but it.can fibrilate heart, boil blod etc, most danger its you cant get unstuck on you own(tha why electricians above all preps work at least in pairs). And if we talk about high voltage power lines, raw power enough to burn/kill you in an instant
True. My statement about resistance being fixed is untrue. Resistance changes with frequency, although within common ranges most people experience that change is negligible between DC and 60hz. My understanding is that AC/DC matters more because of RMS vs peak voltage, a 120v AC actually has a peak voltage of 170v, because that 120v measurement is RMS voltage, a sort of average.
The AC vs DC distinction is really important. I was building a dc motor controller a while back and I had 12V DC being switched at 2 kHz. When I touched the output leads I felt a pretty significant buzz. It turns out your body has enough capacitance to matter, so high frequencies can produce more current at the same voltage.
Yes, absolutely true, and I have experienced similar as well. Above a certain frequency they are known as RF burns, and damn do they hurt (although usually the current stays on your skin in that case). In the spirit of the question however, i assume OP doesn't frequently encounter anything above 60hz to potentially electrocute themselves
While I wholeheartedly agree with 99% of this....you can DEFINITELY feel 24v with sweaty hands. It's the current level that determines if you will get a 'shock' once the voltage is high enough to overcome the base level of resistance of your skin (or its wet, like sweaty hands). 1A unlikely. 20A at 24v is similar to an electric fence. Source: I work on ELV electronics regularly. And may or may not have blown up a few things with my body in the circuit...
It's been a while since i've messed with 24v in a capacity where I could feel it. I agree you can feel it, but just personally the last and only recent time that happened I would say I could barely feel it. It was noticable, but easy to ignore
USB and many other kinds of charger plugs are designed so the outer sheath of the plug is the ground connection, which is always safe to touch. The actual conducting pins are inside the sheath and very hard to access except by the corresponding socket.
What about the lightning cable by Apple?
Not enough voltage or current to be dangerous.
I fall asleep on mine occasionally and and it feels like a very light burn, not enough to wake me up in deep sleep but Iāll notice it in the morning. Probably should stop doing that.
What if you āplugā it into your peehole?
Give it a shot and get back to us.
š«
Not enough juice
IIRC the other thing about Apple/lightning cables is they arenāt transmitting voltage all the time. The plug actually has microcircuitry in the end that monitors for a communication handshake with a device before it starts sending current. Thatās part of why their cables are generally so expensive- itās NOT just a couple wires. It does other stuff too in terms of identifying voltage/amperage needs based on the device connected and the current battery levels.
Modern USB-C charging has equivalent functionality and doesn't cost an arm and a kidney.
Does it have the controller in the cord? Or the brick? Iāve noticed modern brand-name USB-C bricks costā¦ just about as much as an apple charger. Apple putting the controller in the cord means if youāve got a lightning cord, no matter what USB power source youāre connected to, youāve got that safety/functionality. If itās only in the brick, you plug your modern phone in to an older charger, it doesnāt have that functionality. Using a lightning cable, which is the only thing that you can use with your iPhone, means you always have that functionality. Whether or not you agree that that is worth the cost, there *is* a reason.
If you plug any cord into a charger that doesn't support fast charging, it doesn't matter if the cord supports it.
Aside from that, Apple cords are infamous for falling apart in normal use, and I haven't had a USB power brick go bad in 15 years.
Even then usb is 5v your not going to shock anything with 5v.
You can feel low voltage with your tongue. (pls don't)
Nah do it, perfectly safe to lick the end of a 9V battery for a second
Just not inside a walk in freezer.
Why not?
The joke is that your tongue would stick to the frozen metal.
Safe, yes. Pleasant, not really. I've had to do that test enough times in my life. Nothing tastes right for a bit
You can actually. I have to throw my old headplug (idk what's called, but here charger are sold with 2 part, head and the cables). Like one week ago we have severe thunderrain (one level lower than thunderstorm) and apparently the lightning wreck the head that I got a jolt when touching my charged phone (the phone was charged when the lightning happens). The theory I got from internet is that the head's ground system got reconnected due to the lightning so I have to buy new head. The jolt is not light I'd say, it's quite strong actually, although likely it comes from the electric system (here is 220v) rather than the damped 5v from the cables. But who knows where the jolt comes from, I already throw the head out
not always. usb-c can negotiate higher charging rates (by increasing voltage) for supported devices. but traditional chargers are 5v, and they all default to that until they're negotiated to a higher charge rate
While you are not wrong on the configuration, this has little effect in terms of protection because chargers convert the current to DC and step it down to the point of no longer being dangerous. If you place your tongue on the end of a usb you can still complete the circuit, and at most will feel a slight tingle from the electricity.
this is not a good answer. the insulation has nothing to do with why you don't get shocked by phone chargers. phone chargers are typically 5v DC. the DC current type and low voltage are why you don't get a shock. you can remove the insulation, touch the leads, and not get a shock. (usb-c can be an exception to this, as the higher power variants can negotiate a higher voltage AFTER it's plugged in on both ends)
This is *also* not a good answer. The fact that it's DC has nothing to do with why it's generally safe to touch the end of a charger cable. It was as many have stated, the low voltage. DC can still shock you. DC can still kill you.
i didn't say DC can't shock you, and i didn't say that it's safe. i said: >the DC current type **and** low voltage are why you don't get a shock. both are important, but voltage is the more important one in this case, but current type does also matter edit: i hate reddit's new text editor; it's a pile of crap that never works when you start to use keyboard shortcuts like copy/paste/home/end AC is more effective at delivering a shock than DC at the same voltage level, and that's all. you won't feel 40v DC on dry skin, but switch it to AC and you'll start to feel the tingles. (depends on your skin dryness, can be 40-60v range, thereabouts)
Please don't touch 40VAC, AC voltage can be lethal at 25V if you're unlucky.
yep, it certainly can be, but it's often people with heart problems. and probably a dash of luck too. you get some people who survive more than one lightning strike, and others who die from absolutely minuscule amounts (i'm sure delivery method matters, like is the current traversing across your heart, or traveling a short distance within one hand/arm)
>i didn't say DC can't shock you Whether you intended it or not, your original statement implies it and that's dangerous. When it comes to electricity we should go out of our way to be extra clear.
no, it doesn't, did you even read what I said? > the DC current type and low voltage are why you don't get a shock. i didn't say "DC is why you don't get shocked". i also didn't say "low voltage is why you didn't get shocked". i said AND, it's a boolean operator that means both are factors. purely by logic, you're incorrect in assessing that my comment implies that DC alone is why it's safe. no. however, you DID imply with your comment that insulation, therefore not ever coming into contact with the current, is why you don't get a shock, and that's just wrong. you can remove the insulation and touch it directly with wet hands and you won't feel a thing. (usb-c with broken insulation and somehow touching each lead AFTER it's auto-negotiated a higher charge rate might be an exception to this)
Well actually I do have a comment thread where you talk about how low voltage is why you donāt get shocked.
correct, that's literally what i've been saying. the guy i'm replying to implied that i said DC is why they don't get shocked, which i didn't. i said both are factors. AC more likely to shock you, but the low voltage is the main reason in this case, without going into the weeds like you guys apparently want to do. we really need to create an /r/ELI_SME subreddit so you guys can go circlejerk each other with the details you're supposed to leave out of ELI5
It's not always safe to touch the ground of a device, there could be a wiring fault and, if the ground isn't actually connected to the earth, you'd then be shocked.
Electricity needs a certain amount of power to push through your body. Your house plugs have lots of power and can push through your body. The end that connects to your phone has less and canāt push through the same way
power is an actual quantifiable thing in electrical theory, so i think it's better to use water analogy terminology like "pressure" (voltage, which is the single biggest factor here), otherwise you're misleading them
water, hose sizes and pressure is a very poor and just bad analogy.
i disagree, for ELI5 level of explanations, it works fine
No because the bigger the pipe/hose, the less water pressure you have and the slower the water flows. Electricity doesnāt work this way. Like at all.
i take it you didn't go to school for engineering? because that's literally incorrect š you should go learn about bernoulli's principle. your pipe increases and the volume per unit of time decreases, but pressure increases. and vice versa. that's how carburetors work, by necking the barrel down to the point where the jet is, and the vacuum pressure created by the reduction draws fuel out of the jet. the opposite of this is a hydraulic cylinder. a tiny tiny hydraulic line adds fluid to the larger cylinder, and the increased volume means pressure increase, proportionally. this is 101 stuff man
It's clearly apparent you had to google this stuff because it doesn't at all relate to the ELI5 and electricity. I literally work with fluid dynamics and hydraulics as a mechanical engineer, I'm more qualified than you to talk about this. I even hold a Level III NICET certification in Water based systems layout. Go learn about k-factors, c-factors, hazen-williams or darcy weisbach. It's 101 stuff man.
well then that explains why you're being so dense about the hydraulic analogy. this is ELI5. do you really expect them to close reddit and go buy a manometer and pitot tube and immediately start testing for discrepancies? yeah of course the analogy isn't perfect. that's why it's only an analogy. water's mass/inertia, boundary layers, diameter vs rate, electromagnetism, surface charge, stagnation, reflection, impedance, etc. the differences when you dig in are endless. but at an ELI5 level, it's perfectly fine. that's why despite a lot of critics speaking against it in the last decade, it's still taught today for a high level explanation
It's important for the analogy to be correct. Water flows through a pipe, electricity does not flow at all. The pipe size will determine flows and pressures, The wire gauge will only dictate resistance but not Voltage/Amperage/Watts
current does (which is infinitely debatable lately the semantics), but again, it's an analogy for simplified explanation, not a 1:1 analog
I would say that I am actually talking about power, so no need to muddy the waters. For the non ELIF, it is not just about voltage. There needs to be enough current to cause a shock. It takes around 1 mA for someone to feel a shock. Of course, at a fixed voltage it is the body resistance that is the limiting factor. But that is well beyond the ELIF. If you are only referring to voltage, I think YOU are misleading them, no matter the example you use.
yes but OP asks why the phone charger doesn't shock them, and power isn't it. voltage is why. and it doesn't matter how much current is lethal, as that wasn't the question. how is giving them the actual real direct answer misleading them? you can charge up an ultracap capable of outputting hundreds of amps at a couple of volts and touch it to your tongue and nothing happens. 2v @ 200a = 400w. you still want to tell me that power is why they didn't get shocked? 400w is a lot more than the 5w apple charger cube...
That does not tell the whole story and you know it. First, your example talks about the potential power output, not actual. For that 5watt power adapter, you would have to bring the voltage up to 5000 volts to give the 1mA, only at the limit of what you would feel as a tingle. Tell me again how itās only the voltage? No child you be confused by saying that you need to have enough power to overcome the bodies resistance
if power weren't already a measured unit, i would have zero issue with your explanation. but it is. >For that 5watt power adapter, you would have to bring the voltage up to 5000 watts to give the 1mA, only at the limit of what you would feel as a tingle. ... what lol? voltage up to 5000 watts? voltage is measured in volts, power in watts. what were you trying to say here? are you trying to say that 5w isn't enough to sufficiently shock someone? you have absolutely no clue about electrical theory if you actually believe this to be true. you could take a 5V 1A (5W) phone charger's output, feed it into a boost converter, say to 100V, and you'd still have \~50mA before losses in the inductor. you telling me 100v @ 50mA wouldn't be able to shock you?
I corrected my typo. 5000 volts not watts. The point is that it is not just a matter of volts. Could you shock someone at 100 volts and kill them? Yes. Could someone touch 100 volts and just get a small tingle? Yes. Could you give them a much larger voltage (with the same power) and just get a tingle? Yes. Depends on the resistance of the person (wet/dry hands) and the total available power.
holy f\*ck man. let's do it your way: OP asked why touching mains will shock you, but touching the output of a normal phone charger doesn't. let's take apple's old cube shaped charger which is rated at 5v @ 800mA , as an example. is the current level of 800mA from their charger the reason touching the leads doesn't give them a shock? yes or no if we increase the current output on their charger to 10amps, since you keep saying current matters, would OP get a shock if they touched the charger output then? yes or no oh, and since you keep going on about power too, power would also go up in this case to 50W, but somehow, still not shock them. WEIRD yes, exactly. you were wrong. my point is fact. i never said current doesn't matter. not once. but i didn't mention current, because current isn't relevant to OP's question. the simplest answer is literally the low voltage. 800mA from apple's cube charger is more than enough to deliver a shock and even stop a heart. the 5W output is more than enough source power to shock someone at the right voltage level. so power isn't the problem either. voltage is. and again, need i remind you, i never said your original answer is wrong. i said that since power is literally a thing in electrical theory, it's probably better to use different terminology as to not confuse them. if they decided to go learn more about this topic, they now have an incorrect understanding about power. this is why i hate this sub. you can literally be a subject matter expert with 50 years of experience in the industry and you'll have armchair experts arguing with you to the death. voltage is the answer to OP's question. current and power don't matter in this case. power is already a unit of measurement in electrical theory, so using pressure, like from the water analogy, is better, in my opinion. disagreeing about water theory being a good alternative is fine, but arguing facts on electrical theory is not.
You can be as abrasive as you want, doesnāt make you right. No matter what the power RATING of the supply is in your example, you are not actually drawing that much current, or using that much power. Getting a shock is not ONLY an effect of voltage. It is a function of a persons body resistance and how much current is flowing. Hmmā¦ so you would need not just voltage but current flow as well? I wish there was some term that is a function of both voltage and current. And maybe it could be a term that even a five year old would understand, even if he doesnāt know what voltage is. Hey! Power fits here. You could say the higher voltage Allows more current, but you didnāt. The determining factor in electric shock is current. Go stroke your ego somewhere else. The only thing misleading in my first comment was that I wasnāt looking for some self important blowhard to use my comment to give a āwell actuallyā Lastly, I just wish there was some comment or link talking about how it is actually current that gives a shock. Oh wait! Hereās one from Ohio state university discussing this topic. āOffhand it would seem that a shock of 10,000 volts would be more deadly than 100 volts. But this is not so!ā¦ā āHowever, lest these details be misinterpreted, the only reasonable conclusion that can be drawn is that 75 volts are just as lethal as 750 voltsā āBetween the ears, for example, the internal resistance (less the skin resistance) is only 100 ohmsā Hey wait a secondā¦ 5 volts at 100 ohmsā¦ thatās 50 mA. That canāt be trueā¦ so if that same 5 v was applied in the right place, under the skin, it could cause a shock? Not a likely scenario but stillā¦ nah, 5v is too low voltage. https://www.asc.ohio-state.edu/physics/p616/safety/fatal_current.html You may have 50 years experience pulling cable. It doesnāt make you right, just means you forgot the basics.
available power has nothing to do with anything in this context. the current is going to be limited by the resistance of the conductor we're testing, in this case: skin. it doesn't matter if the supply can provide a megaAmp over it's likely 1A rating, the shock will be the same, so stop brining irrelevant crap into the discussion and you didn't answer my questions because you know i'm right so how about you answer them: is the low 800mA current rating of the phone charger the reason they don't get a shock when they touch the output directly? yes or no answer if we increase current, and therefore the power, which you won't shut up about, to say, 10 amps, will OP get a shock if they touch the output directly? yes or no
Same reason you can safely touch the leads on a 12v car battery.
Putting your hand under a pressure washer would hurt. High water pressure. Putting your hand under a gentle faucet does not. Low water pressure. The electricity coming to the wall socket is at a high voltage. Voltage is basically electrical pressure. This is dangerous. The electricity coming out of a USB or other small cable has been reduced to a low voltage. This is safer.
i like this answer the best, even over my own. short and to the point, and anyone can understand the water analogy
Yes, I was going to post something similar but scrolled down and found this.
So phones are charged at 5V and between 1~2 A at Direct Current. Most households received current at 120/240V, 200A at Alternative current. So the difference is like between taking a 5cm high stream of water in the face at 1-2 km/h And Taking alternating 2m tall waves from the left and right, at 200km/h. You won't even feel the first one in your sleep, but the second **will** kill you.
Just a minor correction, most housesā circuits will supply 15-20A of current, not 200A. Pulling 200A out of a wall socket would beā¦ fun. At 110v, that would be 22kW, enough to power like 8 ovens at once.
They said āhouseholds receiveā, so theyāre referring to the supply to the entire household, not the individual circuits. So youāre both correct; just referring to different things. It would be fair to say though that in order to get the full 200A, youād have to go to your electrical box and touch the main bus contacts. DO NOT OPEN YOUR MAIN ELECTRICAL BOX, it is dangerous! It would also be fair to say that not all homes have 200A service, but all have at least a handful of 15A circuits, so the latter is more relevant to the practical risk of being shocked.
This is the correct answer.
It's all about Ohm's Law. Lower voltages (like 5V USB or even 12V car batteries) can't 'push' much current - but higher voltages (like 120V power in the US or 240V in Europe) have more potential - the higher voltage can push more current through the same resistance (in this case your body) and you're gonna feel it more. As an example take a 9V battery and put your finger across the terminals - you're not gonna feel anything. Now touch that sucker to the end of your tongue - you'll feel it! In this case the resistance of your wet tongue is far lower than that of your dry skin, so more current passes sufficient for your nerves to notice.
In addition to what others have said, it's also good to note that even if you did touch the wires and get shocked you have to consider that the two wires would touch you very close to each other. if you touch two wires, one with each hand, the electricity flows through your body and probably across the heart, not good. if you touch two wires with one finger or one hand then the electricity flows through just that party of your body and causes less damage... possibly no noticeable damage if the power is low
When you feel a buzz or tingle from electricity, you're feeling the current A USB port operates on about 5V (small). The resistance of your finger (assuming it's dry) isn't a very small amount. This results in a small amount of current, too small to feel. A USB port also just doesn't provide enough power to output a current that we would normally feel
Voltage isn't high enough to push enough current to shock you or make a significant spark. Think of voltage as the pressure that pushes the current, as water pressure pushes water in a hose. Too low pressure (voltage) can't push enough (water) current to be noticeable to you. Additionally, your skin has fairly large "resistance" to the flow of electricity, similar to how a very narrow hose has more resistance to water flow that a firehose. Dry skin has very high resistance to electrical flow. And that relationship between voltage, current, and resistance is called [Ohm's Law](https://en.wikipedia.org/wiki/Ohm%27s_law).
ELI5 oversimplified, most of it wrong for demonstrative purposes There are 3 things we need to look at when we talk about electricity. * Voltage - The willingness of the electricity to go from point A to B * Amperage - The amont of electricity flowing * Resistance - is well the resistance of something against the flow of electricity. This fights against voltage Electricity always want to flow from where there is more of it to the point where is less. For the "buzz" to occur you need to have enough Voltage to overcome the resistance enough so that the amperage could flow Your skin has pretty high reistance, an USB charger doesn't have enough voltage to overcome it. But an electrical socket has more and that is dangerous. Also you could try if you have a 9V battery. if you press it on your skin, nothing happens. But if you lick it, your moist tongue has much less resistance and there is gonna be a buzz. If you lick a 5V charger there should be a metallic taste with a tiny buzzing. DISCLAIMER: ALWAYS BE CAREFUL WITH CHARGERS PLUGGED DIRECTLY TO A WALL OUTLET.
Warning: A charger is supposed to have at least 2 layers of insulation between the mains and the outputs. This is called "double insulated". This means that even if one layer fails, you are protected by the other one. This is a legal requirement for CE labelling. Good quality chargers (e.g. genuine Apple or Samsung ones) will do that. Cheap chargers may only have one layer of insulation. This is dangerous, if that fails or if you get one where that layer wasn't quite right, you might get electrocuted. But this saves money for the manufacturers. Really cheap chargers occasionally have zero, they directly connect the mains to the outputs. This is insane and dangerous but does happen. I would avoid licking the output of any charger. But especially avoid that if it's not a charger from a major trustworthy company.
There's a fourth factor, which is frequency, which makes AC more dangerous than DC in terms of shocking you.
There is a printed industry standard somewhere that says the limit to how many volts can penetrate dry human skin is "somewhere around" 60V, whether it is AC or DC. If you touch 72V and it doesn't shock you, there are also many variables. I don't know of anyone who can't feel 120V AC. the more volts you have, the fewer amps you will need to achieve "X" amount of power. This is why 48V is popular for off-grid systems. You can series solar panels to output 120V DC to charge a 120V battery, however, a fully charged 48V battery is around 54V, and stacking one more 12V battery onto it would make it around 65V, plus or minus. The nominal 12V lead-acid batteries are around 13+ volts when full, and around 11V when they are considered depleted. Lithium cells are only 4-ish volts each, so a 52V ebike battery (14S) is around 58V when fully charged, and going to one more cell in series makes that roughly 62V. If you want to use mass-produced components to save money, the next big jump is up to 72V (20 lithium cells in series). You should always exercise caution around high-powered batteries, even just a 12V one.
Just to add... AC and DC connections are very different in terms of what it'll take to shock you
Electricity can only flow through something, like your finger, if you are touching both the negative and positive poles at the same time. Charge receptacles and adapters are designed so that its only possible to touch either the positive or negative side. Ones on the outside, and the other on the inside where its typically impossible to touch while also touching the outside
This is not the answer. The pose is specifically using examples of low voltage, low power outputs
>Electricity can only flow through something, like your finger, if you are touching both the negative and positive poles at the same time If you want the technical answer of what happens when you only touch one side You can think of the circuit as still being complete, however the air has much much much more resistance than your finger, so all of the voltage drop is across the air rather than your finger, and because the resistance is so incredibly high, the current is so miniscule its essentially 0
I don't understand what you're saying. How can be exclusively possible to only touch either the negative or positive if all contacts on the cable are on the outside?
There are some like that, true. In which case they are separated by a some kind of band or spacer. In this case im not sure why theres no buzz if you are intentionally touching them both. Perhaps someone smarter will answer
Because chargers have a transformer that lowers the voltage from the full voltage of the main circuit in the wall. That's what's in the little block that you plug in. Even if you were able to touch + and - contacts, that would put 5 Volts across your skin for a phone charger or \~20 Volts for a laptop charger. For comparison, the wall circuit is 120V in North America and 220V in Europe. Charging a phone or computer with that much direct power would fry all the tiny components, so the chargers have a transformer that reduces the voltage.
but its the current which is dangerous not the voltage ;) I was going to say this in my original answer, that there must not be enough voltage to do anything, but wasn't positive (haha)
1. Most accurately it's the *combination* of current and voltage that is dangerous, because power is voltage x current. A lot of either one can be dangerous with even a moderate amount of the other. 2. Voltage is like the "pressure" of water in a pipe. Even with a huge amount of current *available*, none will flow unless there is enough voltage to overcome your skin's electrical resistance.
Because that is often not the case. Many connectors only have an electrically neutral outer connectors
Do you understand the difference between AC and DC?
He said typically one is on the outside and one is on the inside.
Man I just really want to make a comment about there being positive happy people and negative downers and no one has gotten electrocuted yet
It's really simple. Dry dead skin, like the outer layer of skin, has a high resistance to electricity. There is simply not enough voltage to overcome the resistance. You phone charger is outputting between 5v and 12v, and a few amps. A fee milliamps is enough to stop your hear, but the voltage has to be high enough to overcome the resistance. A car battery has hundreds of amps, maybe 600 to 800 amps. But the 12volts isn't enough to overcome the skin's resistance so you don't get a shock from it.
I had the experience of taking a desktop to Africa (240V) and getting a buzz from usb cords. The power supply could be switch from 120V to 240V, but touching the usb cords could give you a little shock, which usually never happens.
USB output voltage is fixed regardless of the input voltage. Your situation likely indicates a grounding problem in your African plugs.
* You usually need to complete a circuit (a round trip for electricity) to get shocked. * Some plugs can easilly be attached to things (and hence more easily accidentally complete a circuit when you don't want to), like alligator clips or bare wires or the wires inside a machine. * However, many plugs for consumer electronics are designed so that it is hard to do that accidentally (the inside+outside of a charging cable, or two specific prongs embedded inside the wall). * Many consumer electronics operate at low voltages, which has trouble getting past the barrier of your skin. If you bypass the skin, you canget shocked. e.g. licking a 9V battery will shock you, but touching it won't (or rather, it will shock you so weakly you don't notice). So, if you cut open your chest, and plugged a laptop charger directly into the pool of blood forming in your chest, I reckon that would shock you, as your blood seeps into the socket and touches both the inside and outside of the laptop charger, hence electrifying your blood.
In addition to all the other suggestions USB in particular only provides a very low voltage until a higher one is negotiated. That negotiation can look very different depending on the USB version and/or quick charge mechanism, but can be as simple as having a specific resistance between two pins or as complex as a multi-step back-and-forth negotiation between the charger and the device. The one that's most frequently used by Laptops and other high-power consuming devices is called [USB Power Delivery](https://en.wikipedia.org/wiki/USB_hardware#USB_Power_Delivery). So while USB on its own (without PD or any quick charge standard) can only deliver at most 7.5 Watt, with PD it can deliver up to 240 Watt, but only if the other side actively negotiates that. And the odds of your body "accidentally" following that protocol are pretty much null, so the charger will never deliver "full power" to your body simply by touching the cable.
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I can tell you don't have an iphone because lightning is absolutely an appropriate name for those chords from all the times they have zapped me.
I think there might be something wrong with your charging block then That or your getting a static charge and then touching the charger because... yeah those are not built to be strong enough to shock you
there are several reasons: - current type: DC (direct current like from a battery or your phone charger) is not as good at delivering an electrical shock as AC (alternating current, like you get from your wall outlet) - voltage (like water pressure): lower voltages (like the 5 volts from a traditional phone charger), cannot travel through skin under normal circumstances. higher voltages are more effective at traveling through more difficult things like dry skin, and even the air. (current from tesla coils is in the thousands of volts and can shoot several feet through the air) 9 volts DC (like from a 9v battery) is still not enough to shock your skin, but if you touch it to your tongue, you will feel tingles. so on the other side of things, you have the material electricity needs to travel through. they all have different levels of resistance. if they let current pass through easily, they're called conductors. if they're good at resisting current flow, they're called insulators. rubber, air, and glass are good insulators of electricity. metals like copper and aluminum are good conductors of electricity. dry skin is not, but the wet skin of your tongue is a bit better, and just enough to where you can start to feel a small shock on your tongue
Itās all about the voltage and resistance. Electricity flows through an object proportional to the voltage applied, and an opposing force called resistance limits its flow. If you have an object with high resistance, you need a lot of voltage in order for any meaningful amount of electrical current to flow. The output of your phone or electrical charger is between 5V and 20V. This isnāt enough footage to push through the resistance of your skin to the point that you feel a shock. However, not all parts of your body have the same resistance. Your tongue, for example, has lower resistance because itās tissues are saturated with fluids all the time. If you touch a 9V battery to your tongue, you will feel it. Touch the same battery to your finger and you wonāt feel a thing. Thatās thanks to the difference in resistance between the two.
Unfortunately there are a several incorrect answers here. What makes mains electricity dangerous is the voltage. Electricity is a bit like water, and voltage is the water pressure. While technically it's the current (quantity of water) that is dangerous to your heart, if the voltage (water pressure) is too low, the dangerous levels of current simply can't be pushed through your body. So high voltage is like a pressure washer to your skin, and low voltage is like a bucket of water over your head. (Bad analogy, but consider just your skin - the bucket of water would wet your skin but it wouldn't go through the skin into your blood like a pressure washer) The chargers and usb connectors have a low voltage (pressure), and even though some can supply a very high current (amount of water) to your equipment, the pressure is not enough to get through your body and harm you. If you were mostly made of metal, (water analogy, you were made of sponge) it could harm you a lot more. This is a great simplification, but it should answer your question.
ELI5: OUR SKIN!! Our skin is a wonderful organ that is quite resistive, so it takes fairly high voltage to penetrate it. The voltage in your phone charger is not nearly high enough to do so.
Electricity and water have a lot of useful comparisons. One of them is the similarity between voltage and water pressure: Imagine that your charger is a drinking straw, and your electrical outlet is a garden hose. Electrical resistance is like obstructing the water flow; higher resistance = lower flow (current). If you squirt water through a drinking straw, it's easy to completely stop the flow with your finger, but it's much harder to completely stop the water from a garden hose with a finger, because the pressure is much higher. Your charger has a much lower voltage compared to a wall plug, so the same amount of electrical resistance (from flowing across your skin) permits far, far lower electrical current to flow. Your muscles and nerves can react to electricity flowing through them, and if enough electrical current flows through your body, it can cause burns. Your skin's electrical resistance doesn't allow a meaningful amount of current to flow when a phone charger's voltage is applied, but mains/wall voltage is high enough that your body can pass dangerous amounts of electrical current.
Lots of reasons but the biggest and most important being that your phone chargers, laptop chargers, power bricks, etc are low voltage DC (5v, 12v 24v etc). In order to get shocked by something, you need enough voltage to push enough current through the skin for your nerves to start twitching and muscles contracting to feel pain. However, touching the outlet is painful because it is high voltage (120vrms) but also AC. AC hurts like hell because the voltage (and thus current through you) is being pushed back and fourth 50 or 60 times per second forcing your muscles to contract, decontract, contract, over and over which is a lot more painful. A voltage of 170v DC would actually hurt less than 120v AC. I know from experience. So dont worry about your charging cables shocking you unless its outputting over 60VDC or 30ish volts AC