Yet @engineer_comp_geek said above 50 volts will be enough.
I’m not arguing. I am confused.
It’s not as simple as that. With rare exceptions, it’s impossible to kill yourself with a car battery that supplies 600 A at 12 V. It is capable of supplying that amperage, but your body has a high enough resistance that at 12 V, you will never come close to that level.
A static shock may have a high voltage and amperage, but it is such a short duration (nanoseconds) that there is almost no energy in it (millijoules). It might lightly singe a hair on your arm. It can’t stop your heart because it doesn’t go on for long enough.
A source with high voltage and modest current very much can kill you. I have a neon sign transformer rated at 15,000 volts and 50 mA. That’s 750 W, so plenty of power, and also more than enough voltage to overcome the natural resistance of the skin. And it isn’t just for a few nanoseconds; it’s continuous.
120 or 240 V residential power can kill you if you’re unlucky. It’s not inherently energy-limited like the static shock. But it’s also a low enough voltage that you need a fairly long jolt to kill you. Long enough that you have a good chance of letting go before it does significant damage. But that doesn’t help if you have no means of letting go for whatever reason (the hairdryer in the bathtub, etc.).
Yes, but it’s complicated.
Voltage and current are not completely independent of each other. Generally speaking, the higher the voltage, the more current you’ll get. One of the first things you learn about electrical stuff is called Ohm’s Law.
V = IR
V is Voltage, measured in volts
I is current (from the French word “Intensitie”), measured in amps
R is Resistance, measured in ohms
The resistance of most materials is fairly constant. So if you know the resistance of the material and the applied voltage, you can very easily calculate how much current will flow. And if you double the voltage, you double the current. Triple the voltage, and you triple the current. Simple.
So what happens if you try to measure the “resistance” of the human body? You find out very quickly that the human body has a very non-linear response to voltage and current, so the above formula doesn’t work. At lower voltages like 12 volts, the “resistance” of the human body is going to be millions of ohms. It varies a bit from person to person and with how wet or sweaty your skin is, but let’s say in this particular example it’s 2 million ohms.
12 volts = I x 2,000,000
or I = 12 / 2,000,000 = 0.000006 amps
If you double the voltage, the current will also double, so at 24 volts you would get 0.000012 amps.
The “safe” current level for the purpose of most safety standards is 5 mA (0.005 amps), so you aren’t going to get anywhere close to enough current to cause harm. Notice that the “safe” level is defined with a current (amps) not a voltage. Below 5 mA shouldn’t be able to throw your heartbeat out of whack.
But here’s the thing. What if the voltage is 100 volts? This is high enough of a voltage where the electricity can now punch through the outer layer of your skin, and the effective “resistance” of the human body drops all the way down to something like 500 to 1000 ohms. Let’s say 1000 for this example. Now the current is 100 volts /1000 ohms = 0.1 amps. This is WAY above the “safe” level of 0.005 amps, so it’s well into the range where it can potentially screw up your heartbeat and kill you.
The point here is that the effective “resistance” of the human body varies a lot. Not only does it vary by the applied voltage, but it also varies with all sorts of things like your exact skin and how sweaty or wet you are. But there is a general thing going on here in that higher voltages generally result in higher currents, so low voltages like 12 and 24 volts generally can’t hurt you, but higher voltages (typically above 50 volts) can kill you.
But asking if it’s the volts that gets you or the amps isn’t a valid question, because volts and amps are both related to each other.
Figuring out voltage and current with respect to the human body is very complicated. In fact, it’s very common when dealing with safety type stuff to oversimplify the human body to a resistor in series with both a resistor and capacitor in parallel. But the thing is, the values of those components varies with the voltages that are being applied. Like I said, it’s complicated.
Because a Van de Graaff generator is naturally limited in current. Yes, it produces 100,000 volts or so, but you won’t get more than maybe 100 to 200 mA out of it, and that current mostly travels across the surface of your skin. The current doesn’t penetrate into your body and doesn’t cross your heart.
Lightning, on the other hand, is essentially just a very large Van de Graaff generator, but instead of being limited to 100 to 200 mA, it produces hundreds of thousands of amps. This is more than enough to cook you to death, even in the extremely short duration of a lightning bolt.
It doesn’t produce a continuous 100 kV.
The VDG generators used for educational purposes source a few tens of microamps.
Probably a system where high voltage AC is controlled by low voltage DC. It’s just a way to say “It’s fine. that’s the DC side of the system.” Not that DC is inherently safer.
Also, once you get to continental length scales, there are radiative losses with 50-60 Hz AC that simply aren’t present at all with DC.
You’ll see lots of folks saying “it’s not the volts, it’s the amps”, but the truth is, it’s not either, it’s the watts.
That said, a human body behaves at least approximately like a resistor, so there will be a one-to-one relationship, or close to it, between volts, amps, and watts. The real reason why a van de Graf generator doesn’t kill you is because absolute voltage doesn’t matter at all, only voltage difference, and when you’re touching the generator, your whole body is at the same millions of volts.
Well, time is definitely a factor, if that’s what you mean.
It’s not amps or watts that kill,
it’s a conductive path to ground that kills.
While (I believe) it’s true most shocks and electrocutions occur when a person is grounded, it is not a requirement. An isolated source can also zap you, but it requires contact with both terminals.
We recently acquired this power supply at work. Can source up to 42 A when set to 350 VDC. Deadly, for sure. But touching only the positive terminal or only the negative terminal shouldn’t hurt you. Touching both… will.
It should also be mentioned that you can receive a shock while messing with your home wiring even if you’re isolated from ground. Stand barefoot on Saran wrap, touch the hot conductor, and you’ll get shocked. This is due to capacitive coupling.
You don’t consider that grounding? Ok, a closed circuit that passes through your body with the right amount of amps and voltage and sometimes frequency is what kills. ‘Grounding’ is a bit pithier description though.
If by “pithier” you mean “wrong”. A conductive path to ground can be completely safe, and a situation without a conductive path to ground can be lethal. There’s no particular relationship between having a conductive path to ground and the danger of a situation.
I’ll never understand EEs’ (and armchair EEs’) obsession with the concept of a ground.
Isn’t that the correct answer to almost everything in life?
There is also that thing where AC cannot manage to use the whole wire, just the outside part.
Is that why DC is often used in ships? No issue with distribution over long distances.
Yep, there’s even a book on grounding that’s 1088 pages long. 
I’d think it’s because it’s pretty straightforward that if you holding two wires, there can be current through them, and it’s important to remember that you don’t need a second wire to complete a circuit, you just need to be connected to the ground.
Besides, in home wiring, that second wire is connected to the ground.
Does that mean it is literally a wire stuck in the dirt near your house?
I live in a hi-rise with 200+ units. Where do all our grounds go?
Yes.
Somewhere in your high rise all the grounds are tied together and then attached to some sort of metal object buried in the dirt.
Yep.
Go outside and look at the service entrance box on your home. You should see a rod in the ground, and a wire between the box and the rod.
The power for your home is being fed from the secondary windings of a nearby transformer. The center tap is connected to the earth: a copper rod is pounded into the earth, and a copper wire is connected between the center tap and rod.
It is necessary to do this. If this were not done, and the secondary windings were left “floating,” the secondary windings could “float up” to the voltage on the transformer’s primary windings (relative to earth). That would be bad.