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I am aware that current is very dangerous and only 0.2 amps is enough to stop a heart. However I always see that high voltage is dangerous. Tasers produce a high voltage but since there is low current it is considered safe. How is it possible? According to Ohm's law, Current is equal to voltage divided by resistance (I=E/R). So if you are being tased by 10,000 volts and your resistance is only 1000 ohms, wouldn't there be 10 amps flowing through you and killing you? (10,000/1000= 10)

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  • \$\begingroup\$ The voltage drops as soon as you touch it. \$\endgroup\$ – immibis Mar 5 '18 at 3:53
  • \$\begingroup\$ There's more than just the Ohm's law to the interaction between current and human nervous system. Here's one of my favorite posts on that subject. \$\endgroup\$ – Nick Alexeev Mar 5 '18 at 3:59
  • \$\begingroup\$ @immibis. Not if there is enough current. I smell skin burning... \$\endgroup\$ – Sparky256 Mar 5 '18 at 3:59
  • \$\begingroup\$ @Sparky256 For a safe high voltage, the voltage drops as soon as you touch it. Otherwise it is not safe. \$\endgroup\$ – immibis Mar 5 '18 at 4:04
  • \$\begingroup\$ 10ma can stop a heart, if that heart is up a ladder or falls in water. \$\endgroup\$ – Harper Mar 5 '18 at 4:05
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Safety standards are different for a taser from an ordinary electrical appliance.

The whole point of a taser is to have an adverse effect on the human body, and a small fraction of people who get tased do die from it. This risk is considered acceptable (by some people), since the alternative is for the taser user to use a gun or nightstick instead, either of which has risk of death.

However, if you are designing a kitchen appliance or a television set, if it has the same effect on its user as a taser, that would be a gross failure, and an unacceptable risk.

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  • \$\begingroup\$ A Taser over the heart or the back of the neck is considered possibly fatal. It may stop the heart. \$\endgroup\$ – Sparky256 Mar 5 '18 at 4:02
  • \$\begingroup\$ Note that my above comment is about abusing the proper use of a Taser. \$\endgroup\$ – Sparky256 Mar 5 '18 at 4:33
  • \$\begingroup\$ Ahh so that's how to abuse a taser eh LOL @Sparky256 - the cat is out of the bag so to speak! \$\endgroup\$ – Andy aka Mar 5 '18 at 11:42
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Let's look at other things which work this same way. A metal-halide light is a type of arc-discharge light. Like most arc-discharge lights, it is practically a dead short once the arc is struck. So why doesn't a metal-halide light basically explode once it ignites?

Because it is fed from a current-limiting power supply.

Most HID lights use a magnetic wound-transformer ballast, which is rigged to limit current. But HID ballasts do exist which are electronic, and do the same thing with semiconductors. These are similar to LED driver modules, except with additional features to strike the arc and warm up the bulb.

Similarly, taser control modules hit the victim with enough voltage to strike the arc, then limit current to "correct" values.

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  • \$\begingroup\$ How does this answer the OP's question? \$\endgroup\$ – Sparky256 Mar 5 '18 at 4:14
  • \$\begingroup\$ @Sparky256 "taser control modules hit the victim with enough voltage to strike the arc, then limit current to "correct" values. " \$\endgroup\$ – immibis Mar 5 '18 at 4:23
  • \$\begingroup\$ @immibis. Thanks for pointing that out in the answer. +1 \$\endgroup\$ – Sparky256 Mar 5 '18 at 4:26
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wouldn't there be 10 amps ?

Maybe for the 1st few nanoseconds, but

No

Your question is too vague to answer all conditions to make it safe.

Make what safe? A taker?

Most of the Electro muscular currents bypass the heart from external dielectric mass. So they might use 10k more energy to start a heart in Emergency than in open heart surgery.

The source impedance limits the current to desired levels, while high initial voltage ionized the contact to lower contact impedance.

Safety of insulation depends on medium (3kV/mm for clean air) and electrode or bushing geometry which has 5:1 effect from smooth donut to sharp needle for E field gradient stress.

Distribution capable of 10kA *600V is capable of human arc flash is many orders of magnitude more unsafe than 100kV @ 10mA.

But a transformer substation with 200kV basic impulse limit (BIL200) protection will protect yet fail with 60kV at line f on a 40kV grid due to insulation strength raised by source rise time from ionization delays.

All line powered products Must be factory tested to safety Hipot leakage tests in each country in the range of 3kV with <100uA expected except for line filters up to 250 uA per power supply.

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V does equal IR... Have you ever picked up a 1.5V AA battery like this? enter image description here

If the resistance between the terminals, was say 10 Ohms then we would potentially have 0.15 amps flowing... getting close to that "heart stopping 0.2amps" right?

Well, the thing is that the current is always going to take the shortest (lowest impedance) path, which in this case would be from the second finger to the thumb, which is a long way from the heart.

According to this article https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2763825/ The resistance of dry skin is about 100,000 ohms and "internal body resistance" is about 300Ohms..

So putting these two facts together: 1) resistance of skin is quite high 2) current will take the shortest (or lowest impedance) path between two points

we can see that being short by a taser is not likely to stop the heart (unless the probes end up either side of it).

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    \$\begingroup\$ Would you bet your life on that assumption? \$\endgroup\$ – Sparky256 Mar 5 '18 at 4:15
  • \$\begingroup\$ Many things don't act like resistors when high voltages are involved. \$\endgroup\$ – immibis Mar 5 '18 at 4:16
  • \$\begingroup\$ This does not answer the OP's question. \$\endgroup\$ – Sparky256 Mar 5 '18 at 4:20
  • \$\begingroup\$ The lowest impedance path between the two taser prongs is unlikely to be through the heart. I thought the picture helped show that? \$\endgroup\$ – AugustCrawl Mar 5 '18 at 4:27
  • \$\begingroup\$ This does not answer the OP's question. \$\endgroup\$ – Sparky256 Mar 5 '18 at 4:31

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