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I've had this debate with some coworks. What voltage (rough order of magnitute) is used to safely shock people?

"Safe" is a vague term, but as an example, there are arcade games where you hold onto two rods and you are hit with a jolt that grows in intensity (the challenge being to hold on until the end). I've also seen this sort of thing at museum where you touch two contacts to "feel the jolt of an electric eel". Not painful, but you definatley feel some force going through you.

Right now, due to different interpretations of some fundamental laws of electricity, we have guesses of "about 40 volts" and "about 40,000 volts", so please explain why one value is used over another.

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up vote 4 down vote accepted

We get electric shock due to current and not due to voltage. The electrical shock is actually dependent on the magnitude of current and the time of flow. That means we can withstand a high value of current for a short duration (like in case of lightning). Many people survive despite being struck by lightning. Whereas smaller amount of current may be detrimental if it flows for a long time.

The empirical formula for the tolerable magnitude of current=0.116/sqrt(t) for 50 kg body weight (t = 0.03 s to 3.0 s) (refer IEEE80). You can refer to IEEE80 which discusses the above in great detail.

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Ignoring the connection between current and potential difference makes this kind of answer misleading to the lay reader. It is correct if you understand all the background and the connections between current and potentials, but it is almost custom built to fool people. – dmckee Nov 8 '13 at 19:52

In general there is not any safe voltage. The danger mostly depends on the current flowing through your body, especially the heart and the duration of the current flow.

So for any kind of trick device you want to use a relatively high voltage, so that wet or dry hands do not make a large difference and limit the duration of the pulse to less than a few milliseconds. Here is a diagram on p. 7 (Code of Practice for The Safe Use of Electricity) that illustrates this. For less than a few milliseconds a few mA are considered safe but it decreases rapidly for longer pulses.

To be on the safe side I would do quite a bit of background research into local regulations and similar devices before trying something like this on other people. Especially the taser should be a warning example, it was considered relatively safe but a few people died from the application, so be cautious.

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There are several values for several different situations. But one of the important factors in the amount of effect (pain, injury, ...) is (according to my labsafety book) the current that flows through the body, which is determined by Ohm's law. The conductivity (and thus the resistance) of the body isn't constant, it will decrease with longer exposure to the current. Thus the maximum voltage depends on the exposure time. Other differences might occur from the conditions like how wet it is or the location of the contacts.

40V DC is, in my (dutch) safety booklet, between the maximum allowed voltage for contact in poor (60V) and very poor environments (30V). Which probably assumes longer exposure to the current and quite a safety margin.

The wikipedia article on Tasers states that most weapons use 50 kV up to 6800 kV. While the agricultural fences use between 5-20 kV and pulses of about 10 microseconds.

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It is best to go by the standard that there is no safety in electricity. One Volt in the right place will kill you. An Australian submarine sailor was killed by 64 volts DC which a lot of people would regard as safe. I have been hit by voltages from 1 to 1,000,000. Lucky.

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For the arcade game, where you are holding rods for many seconds, I think 40V is a good guess (perhaps a bit too low). Why? Take a 9V battery and touch the two terminals with dry hands, you won't feel anything. With sweaty hands you can get a slight tingle, and with your tongue you get a zap. So 9V is too low, but getting towards the right order of magnitude. But it is EXTREMELY unlikely that everyone who uses the machine gets the same voltage. It certainly has both a voltage and a current limit. Someone with very sweaty hands will be delivered a lower voltage than someone with dry hands.

40kV over many seconds is most certainly fatal ... even with dry hands it will fry you with tens of thousands of watts while also stopping your heart for good measure!!

For the museum demo, the way you describe it it sounds like it's creating a static electricity shock. This is neither a predetermined voltage nor a predetermined current, but a predetermined charge. 40 kV is not unusual when rubbing a balloon on your hair in the winter, I believe. It is not dangerous because the current flows over an extremely short period of time. So it is possible that the museum demo is in that range, if my guess is correct.


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protected by Qmechanic Feb 15 '13 at 18:26

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