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Comment by GuB-42 | Hacker News Reader

- Japan runs at 100V, the lowest and therefore safest voltage in the world. At least when it comes to electrocution. I suppose that it is also the reason why in Europe, where the standard voltage goes up to 240V, electrical safety is much more strict.

- As it is already mentioned, Japan is backwards in several domains and that may just be one of these. That's despite their technological advance in others.

- I have a feeling that there are more "perfect electricians" in Japan than anywhere else, because of their culture.

- Some 2-prong devices are perfectly safe because they are double insulated. This is also called Class II and the symbol for it is a square inside another square.

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Japan runs at 100V, the lowest and therefore safest voltage in the world.

100V, 240V, if 15 amps runs through you, you’re having a really bad day either way. That’s another way of saying, “it ain’t the volts, it’s the amperage.”

I = V/R

So given relatively constant resistance, voltage is linearly proportional to amperage. Double the volts, double the amps.

The resistance of the human body can vary, for instance, if you're sweating, your resistance drops, therefore the amperage increases. Dry skin has high resistance, so if you stab electrodes through your skin and into your flesh, the low resistance of your mostly salt water body will carry a high amperage. But with all environmental factors being equal, if one person gets zapped by 100V and another person gets zapped by 240V, the person zapped by 240V will have 2.4x the amps running through them, and their day will be roughly 2.4x worse.

In other words, sure, guns don't kill people, bullets kill people. But you'll find that whenever a bullet kills sometime, there was probably a gun involved.

I was always taught “volts jolt; mills kill”. i.e. high voltage will knock you across the room but a few milliamps of current across the heart will easily kill you.

A 12V car battery can kill if you’re not careful.

So much misinformation in this thread. Voltage, current, and resistance are physical properties entirely dependent on each other -- increasing one affects the value of others. That's like saying that the mass of bullets kills people, without any regard for velocity.

A 12 V car battery can kill you, if it has a low-resistance path that goes through your heart. Touching the terminals will do nothing. Maybe if you applied that voltage to conductive spikes inserted into specific points of the body, there would be some effect.

A voltage source, like a car battery, does not determine how much current passes through a circuit. That is determined by the circuit's resistance, and the source's upper limits (i.e. internal resistance for batteries, rated current for power supplies).

As voltage increases, so does current. High-voltage supplies will absolutely kill you, as long as they're able to supply the required current. Which, to harm a human heart, is quite low (tens to hundreds of milliamps). Aside from fringe sources like static electricity and tasers, most HV sources are entirely capable.

But voltage is what matters to pass through the skin. 12v can kill if it's applied below the skin into the highly conductive inside of the body. But to get through skin you need at least 30v.

Path (through the body) and frequency also matter. See generally:

https://hypertextbook.com/facts/2000/JackHsu.shtml

I recall a story, late 1990's to early oughts, of a solo researcher found dead in his lab of apparent heart failure whilst working with very low voltage- and amperage currents, but at critical frequencies. I cannot find an online reference presently.

It also depends on path of travel: hand to foot, probably not too bad. Across your chest / heart: probably worse.

Voltage always kills. It's always voltage.

Amps are a side effect of the thing that is killing you - volts.

The only time a voltage sufficient enough to kill you, doest kill you, is when it is only present for an extremely small amount of time and/or not traversing your heart.

> The only time a voltage sufficient enough to kill you, doest kill you, is when it is only present for an extremely small amount of time and/or not traversing your heart.

The reason this is the case is because your initial premise is incorrect. Power kills you. Power equals work divided by time. This is why huge voltages over short periods of time don’t kill you.

> Some 2-prong devices are perfectly safe because they are double insulated. This is also called Class II and the symbol for it is a square inside another square.

Interesting. FWIW, besides the UL logo, my rice cooker has no safety or regulatory markings, and the Zojirushi webpage makes no mention of double insulation or any extra safety features.

Japan runs at 100V, the lowest and therefore safest voltage in the world.

That's not really how electricity works is it?

My understanding is that with the resistance of the human body, once you exceed a certain voltage AC (much lower than 100 V), yes, current increases, but you're going to be severely electrocuted regardless.

Voltage does matter. If you have thick skin or touch cable through something (like layer of paint) it might be enough to save you if the voltage is 100V but not if it's 240V.

ElectroBoom has a great video on how the interplay between current and voltage works with lethality in the human body. As he shows, even 150A in your mouth can be safe:

https://www.youtube.com/watch?v=XDf2nhfxVzg

To be totally clear here: DO NOT ATTEMPT AT HOME.

Similarly, lowest voltage ever to kill someone was 48V.

I don’t disagree, but my assumption is the difference between 100V and 240V is pretty minor under most scenarios.

This is entirely "stuff I absorbed growing up", but I was very firmly given the impression that I shouldn't mess with the 240V outlets, because the 120V outlets might kill me but the 240V outlets will kill me (of course, in the US, the 120V outlets are 15+/-5A, and the 240V outlets are 30A).

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