# Electric shock at high voltage but low charge

Thread Starter

#### Benjamin Buemann

Joined Apr 17, 2015
1
My question relates to the statement "The electric shock applied by an electric fence is not letal despite the high voltage due to the fact that the current is very low. However ohms law must apply at the moment you touch the fence and the high voltage should therefore result in a high current through your body. As I understand it the electric pulse in the fence is very short and the amount of energy released during the shock corresponding low. But nevertheless, if only ohms law prevail for a very short time you must be exposed to a high current but how can the heart tolerate that? A similar situation could be that you connect to a heavely charged condensator with at low capacity or a generator creating a high voltage but at a very low power output.

#### WBahn

Joined Mar 31, 2012
26,398
There are a few factors at play. One is that the source has a fairly high impedance and so much of the voltage is dropped across the source as soon as current starts to flow. Second is the low energy available for the current and so the voltage drops very quickly as soon as current starts to flow. Your body's response comes in several ways, but a big one is related to the total charge that flows through sensitive areas as well as the time over which it flows. So even a fairly large current can be tolerated if it is sufficiently brief.

#### BR-549

Joined Sep 22, 2013
4,938
Ohms law is what saves your life.

The high voltage source has impedance. When you touch the fence, your body impedance is put in series with the source impedance.

That total impedance and the short duration......is what limits the current.

#### BR-549

Joined Sep 22, 2013
4,938
I never scoped an electric fence. At first, I would think like Wbahn, that the voltage would drop long before end of pulse.

But with a thick hide large animal standing on insulated hooves, maybe it's full voltage thru-out the pulse.

Any farmers out there?

#### joeyd999

Joined Jun 6, 2011
4,477
I lived on a farm for a bit when I was a kid. I *loved* touching the electric fence.

Hmmm....now that I think about it, this might explain a few things...

#### crutschow

Joined Mar 14, 2008
28,196
The heart is quite tolerant of DC shocks. For example, a defibrillator actually applies a DC (unidirectional) pulse through the heart to start it beating when it stops. So the voltage or current applied by the electric fence is not of particular concern since its a unipolar pulse, unless perhaps it's enough to cause loss of consciousness. Certainly many old TV repair guys have been zapped by the CRT anode voltage without dying (although they may have felt like they did), and that packs a lot more punch then any electric fence controller.

It's AC current through the heart of sufficient amount (something greater than 50mA I think) that can cause fibrillation and consequent death (if a defibrillator isn't quickly used).
That was the basis for the great AC versus DC war between Edison and Tesla.

(It's rather interesting that the natural heart pacemaker system seems to be a quasi-stable feedback loop oscillator. When disrupted by an AC current it becomes unstable and has to be reset by a DC current pulse to become operational again.)

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