Comment by atoav | Hacker News Reader

Comment by atoav | Hacker News Reader

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> A 2000V .001A power supply might give quite a shock on the other hand, and depending upon any capacitance in the supply might just as well prove fatal.

What does the capacitor supply, that the PSU can't? Could it be discharge current?

Before you accuse me of repeating dangerous tropes, please consider making sure to discuss it with the folks at VDE, because this is what it says in their (and the equivalent european) product norms and norms for electrical installations.

When touching the positive pole of a 1V 1000A PSU (I assume DC) you won't have 1000A flowing through your body. It is not the rating current of the PSU that kills you, but the actual current going through your body. And how well that current will flow through your body depends on many things, including voltage, frequency (if we are talking AC), contact resistances, skin resistance, the internal resistance of your body, how big you are, your ground connection resistance, the duration of the current flow, etc.

There is a reason we use high AC voltage for transportation of currents for long distances.

I do see where the general objection to the "current kills" comes from, even if their reasoning got a bit muddled.

All else equal, twice the voltage yields twice the current (and 4x the power).

So while yes, it's the current that kills you, in the majority of circumstances high voltage = high current. Outside of explicitly current-limited setups (e.g. a Van de Graaff generator or a desktop ionizer), most higher voltage devices will kill you more easily.

And so the "voltage doesn't kill" meme more often than not (IMO) gives laymen an undue sense of safety when working with higher voltages, at the benefit of appealing to the more electrically-inclined crowds sense of "being precisely correct".

Just look at the dozens deaths a year from people messing with microwave transformers, trying to make some pretty wood lightning art, for an example of this.

> in the majority of circumstances high voltage = high current

To be debated. Most of the visible (air-arcing) shocks I tend to get happen when I wear the wrong textile and given the length of the arc the voltage is well above 1 kV. So in most of the circumstances I personally encounter the current did not kill me.

What kills you is the current flow through your body. Voltage and frequency helps to produce that flow. RCDs and other protective devices help to limit that flow.

High voltage is dangerous if it has the current to back it. High voltage is also dangerous in the hands of people who don't understand the difference between current and voltage.

Ohm's law says:

I = V/R

It's as simple as that. A high enough voltage will find a current path ionizing the air or whatever is in it's way. A high current doesn't doesn't do that by itself.

Your use of the pedantic trope is trying to win the argument, but destroys the causal effect of why people die which is high voltage. It's like saying "No, he didn't die because he jumped off the building. He died because his body hit the ground." Pedantic, sure, but completely ignores the cause of death.

That's why you see warning signs for "HIGH VOLTAGE" but not "HIGH CURRENT".

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