# Why do I get a shock if I touch a live wire and my feet are on the ground?

I understand that there is a large potential difference but I guess we humans offer a very large resistance. So, shouldn't the current be very small - small enough not to kill us?

• possible duplicate of How does insulating footwear prevent an electric shock? – innisfree Mar 27 '15 at 14:48
• You're performing a silly, dangerous experiment – innisfree Mar 27 '15 at 14:49
• I'm voting to close this question as off-topic because it is about physiological effects of electricity. – ACuriousMind Mar 27 '15 at 15:24
• I'm voting to keep it open: The shock here can be seen as using the body as a measurement instrument to indicate current flow, not as a question about why the body reacts this way to electrical currents. – pyramids Mar 27 '15 at 16:08
• It doesn't take much current to kill you, and the electrical resistance between two electrodes touching your sweaty hands and/or feet may not be as much as you think. physics.ohio-state.edu/~p616/safety/fatal_current.html en.wikipedia.org/wiki/Electric_shock – Solomon Slow Mar 27 '15 at 20:13

Your body is a somewhat sensitive current detector because it uses electricity internally and is sensitive to disturbances; a few mA passing through the body can be felt and a few tens can start to cause more serious problems than mere sensations. The large resistivity you suspect your body to have is not supported by facts. Even just for fingering electric components, the human body model (a model meant to reflect what is important to the electronics, not to people!) only assumes 1.5 $\mathrm{k}\Omega$ resistance (albeit as worst case), presumably for dry fingers. Most of the resistance is provided by dry skin; wet skin or larger contact area can decrease it below that value.

Being in contact with the ground closes the circuit. Even if the ground is not sufficiently conductive to close the DC current path, its capacitance may suffice to let enough current pass for the shock experience/hazard. Your body's capacitance of (from the same human body model) 100 pF alone is not enough to be problematic even with mains voltage. But if you contact anything with a thousand times as much capacitance to an AC voltage of 110 V at 60 Hz, it would lead to a current in the mA range just for charging and discharging the capacitance.

Your question is very vague. "large" "very large" "small" Yet you ask for a certain threshold being exceeded or not.

First of all, what is "small enough"? (aka What is the threshold current for electrocuted humans if you want them "well done"?)

It depends on the frequency. For AC you often find the number 50 mA or0.05A. (Trust me, you don't want to know where this number comes from, the phrase "the resistance of a wet baby..." still gives me the creeps)

What is a "large potential difference"? It depends on where you live, let's say AC is 200V.

What is a "very large resistance"? As you probably now, people don't follow their own rules. It comes to no surprise that Ohm wasn't following his own law, because he was a human. Humans are not linear resistors.

The more voltage one applies, the lower the resistance is. I found this table on wikipedia:

U in V      R in kΩ

25          67,3
50          44,9
75          24,8
100         10,9
125         8
150         5,2
175         4,3
200         3,8


(It's from this book: ISBN 3-8007-2603-3, which is German, but I have the Sauerkraut to read and translate it)

Admittedly this is "measured" (creeeepy) from arm to arm, which is not what you asked for. But still, it gives an idea of what's going on. Let's assume it is the same for arm to leg resistance that you asked for.

And finally, what is the current?

I = U / R = 200V / 3800Ω = 0.053A


This is not very precise. You could touch a wire with a different voltage at a different frequency. Some estimations for human resistance are different: as low as 500Ω, others are higher. The amount of current that kills varies, depending on your body, etc. If the current actually kills you also depends on the time the current is flowing.

As you can see, there's a lot going on here. The key thing to understand is: if it's electrons that are going on and if there are enough of them going through you in a certain amount of time, you die.