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voltage=1000V,current=1/1000Amps, so power=1watt now is this the same as 1V with 1Amp which is not dangerous to humans.

Does voltage not have any any effect if the current is too low?

Because voltage is energy consumed /charge , so voltage is dangerous independently or not? why/why not?

Or is it current that is dangerous, regardless of voltage?

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    \$\begingroup\$ If you apply 1000V to a human, there's no way the current will be 1mA. \$\endgroup\$ – Dmitry Grigoryev Sep 12 '16 at 8:29
  • \$\begingroup\$ no it can be in a circuit, dont you know that. If the power output is low,that can easily happen. its like saying if mass is too high acceleration cant be low. F=ma it can be any real number,both in theory and practice. \$\endgroup\$ – koe Sep 12 '16 at 8:31
  • \$\begingroup\$ Obvious counterexample: static charge. It's quite easy to charge yourself up to several kilovolts, at which point you feel only a mild discomfort when it discharges. Because it's a very short pulse, and doesn't cross internal organs. \$\endgroup\$ – pjc50 Sep 12 '16 at 8:31
  • \$\begingroup\$ how could you say its several Kilovolts? \$\endgroup\$ – koe Sep 12 '16 at 8:32
  • \$\begingroup\$ @pjc50 how do you know the current will be limited to 1mA during a discharge? Read Chupacabras answer. \$\endgroup\$ – Dmitry Grigoryev Sep 12 '16 at 8:35
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Current limited high voltage is indeed not dangerous. Static electricity is a good example.

According to IEC 62368, up to 2mA DC or 0.7mA peak AC is considered safe regardless of voltage. On the other hand 48VDC is normally considered safe but in hospital environment SELV is max 24V. 48VDC can kill you when you have probes inserted inside your body where the electricity can conduct directly through blood vessels.

With regard to unrestricted current, up to 60VDC or 42.4VAC peak is considered safe.

The key word here is current limited i.e. the current of a high voltage source is limited by means such as series resistor or an active current limiting device. For a capacitor charged to a given voltage there are voltage/capacitance charts that define safe charge level. At 2kV safe capacitance is quite small.

And, yes, a big electrolytic charged to 1kV will kill you so better stick to small ceramics.

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  • \$\begingroup\$ Different jurisdictions pick different voltages in the 40 to 60v region for 'safe', so I generally hedge that number when I answer this sort of thing \$\endgroup\$ – Neil_UK Sep 12 '16 at 8:56
  • \$\begingroup\$ @Neil_UK defining specific IEC standard is pretty unambiguous, it's up to the engineer to know if it applies or not. In this case it is a relatively new standard mostly implemented in EU countries. Rest of the world is still mostly using IEC 60950 derived standards that can amend it with national regulations. \$\endgroup\$ – Barleyman Sep 12 '16 at 9:09
  • \$\begingroup\$ Ah! I'd missed the IEC reference, probably as it was in a different paragraph. It is my bad for not reading, but consider me a canary in the coal mine, and the posibility it's a UX thang. \$\endgroup\$ – Neil_UK Sep 12 '16 at 9:56
  • \$\begingroup\$ Note that the 2 mA figure is for externally applied voltage. Many years ago I read of a case of an externally powered, implanted pacemaker whose power supply was improperly grounded. Patient touched the metal bed frame and was killed by leakage. Current was estimated at 47 uA. \$\endgroup\$ – WhatRoughBeast Sep 12 '16 at 14:44
  • \$\begingroup\$ @Barleyman "... up to 60VDC or 42.4VAC peak is considered safe ..." - Did you mean "60VAC peak", or "42.4VAC RMS" (which are the same for sine wave AC)? If not, could you explain why the limit for AC is lower? \$\endgroup\$ – marcelm Sep 12 '16 at 14:52
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Human body has some resistance. This resistance can be 100kΩ or can be as low as 500Ω if you have wet hands (human body resistance is not a constant, it depends on many factors).

If you apply 1000V voltage source on your skin, the current will be much higher that 1mA! (no matter you have dry or wet hands)
If you apply 1V voltage source on your skin, the current will not be 1A. Even you have wet hands, and your body has 500Ω resistance, the current would be 2mA.

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  • \$\begingroup\$ Chupacabras, if current is high, that is dangerous to the body, regardless? It should be as too much charge goes to the body in too less time? \$\endgroup\$ – koe Sep 12 '16 at 8:39
  • \$\begingroup\$ irrespective of voltage? \$\endgroup\$ – koe Sep 12 '16 at 8:40
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    \$\begingroup\$ @koe, do you know what is the relation between voltage, current and resistance? \$\endgroup\$ – Chupacabras Sep 12 '16 at 9:48
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It all depends on the details of the damage mechanism.

It's generally accepted that to cause cardiac fibrillation, a current of more than 30mA is needed across the chest, for a certain significant amount of time. In which case, a current limited to 1mA would be unlikely to kill a healthy adult that way. Somebody with compromised health, or very young or old, might be more fragile.

Let's say that you were standing on top of a ladder, attaching wires to a battery powered door-bell, or modifying a telephone connection. An unexpected 1kV could concentrate your attention so much on the surprise and discomfort, you could fall off the ladder.

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Voltage is just a mean to apply current. Professors used to tell us that we're just a bunch of 1kΩ resistors, but actual resistance depends on conditions like wear, type of skin, humidity etc.

If the voltage is too low then you cannot apply high enough current. So high enough voltage is a condition but not a guarantee. Guarantee is high voltage with provided current. Good example of safe high voltage is static electricity - the overall electric charge is very low, so despite extremely high voltage, the current produced is minuscule and all it does is maybe sting a bit(or destroy electric equipment).

Now if you have high voltage source which can provide high current, then you're getting in trouble. Hight current with enough exposure time is what causes the danger. Here's a chart showing how long you can stay safe with certain current flowing through you, this particular one is for AC in frequency from 15Hz to 100Hz:

http://www.elektro.info.pl/images/photos/24/5072/__b_5cdb7b7a846bba3ad8ace544bb08e3c7.jpg

Keep in mind that this is for AC. For DC current, the thresholds are generally 2-4 times higher.

Anywhere in AC-1 area is completely safe(for people without cardiac problems or pacemaker) and generally barely noticeable.

AC-2 is still safe but not recommended, and generally lets you set yourself free from the source on your own.

Anything above is potentially fatal. Line b marks the end of area where you still have control on your body and can potentially deattach yourself, anything more means you need help.

AC-3 marks an area where there are very likely pathophysiological symptoms such as muscle contractions, problems with breathing, cardiac disorders etc. Still not fatal but really dangerous and the longer you stay the higher possibility of long term damages.

AC-4 is pretty much guaranteed one or many of the following: respiratory arrest, cardiac arrest, burns, and the higher you get, the higher % probability of Ventricular fibrillation. 1A has a 50% probability of VF. AC-4 pretty much means near-certain death if not helped in an instant.

Aside from the pure reaction of your body, there's also an aspect of surroundings. If you happen to be on a ladder, then even AC-2 can suprise you enough to make you jump back and cause a dangerous fall. AC-3 is very likely to cause muscle contractions so it can literally sweep you off your feet and make you lose your balance, again causing another type of danger.

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