Eli5: Regarding electricity, is the dangerous part the current or the voltage?

Question

Lots of time I’ve heard about electricity things like: the one that kills you is the current, don’t worry about large voltages (tasers for example have thousand of voltage). But using Ohm’s Law, if the voltage is big, the current is big. Then why it’s said that about current?

In: 4

Answer 1

The adage is often “it’s not voltage that kills you, it’s current”, but that’s a drastic over-simplification to the point that it’s pretty much incorrect.

As you noted, ohm’s law helps us understand the relationship between voltage and current. If voltage goes up, current goes up (assume for this discussion that resistance never changes), right?

Well, *kind of*. What about things like Van deGraaf generators, that can generate hundreds of thousands of volts, and give you a shock from several feet away? Or, as you noted, tasers?

Voltage alone is just sort of analogous to pressure- that’s how much the electricity “wants” to flow. Current is how much *actually* flows. You can’t measure current unless it’s flowing.

So consider a voltage source that provides HUGE pressure, but almost no current- like a Van deGraaf generator that makes massive static electricity discharges- when current begins flowing, the voltage “pressure” is massive, but it almost instantly drops to nothing because there’s not enough energy behind it to sustain that pressure. So you get a spark and a shock that stings a bit but does no damage, because the voltage dropped so fast the current was negligible.

But now consider a voltage source that’s very low voltage-like a car battery at about 12 volts. It can generate HUNDREDS of amperes. However, because the voltage “pressure” isn’t very high, it’s much harder to get a shock from it, because your body’s resistance is so high that almost no current can flow.

So, the real answer is that if the resistance of the circuit path is low enough and the voltage source can provide enough current, you can get hurt very badly. But you could get killed by any voltage source that can sustain enough current- which if it goes from hand to hand through your chest and across your heart, is not very large.