What is the maximum voltage a human can withstand?

  • I am surprised at the low quality of answers given here! Sorry to say, nearly all of the answers display a tenuous grasp of electronics and electrical nature, and use the age-old adage “it’s not the voltage, but the current that kills.” So I’ll clear things up, and hopefully save some people from misunderstanding this any further.


    Voltage is related to the electric force between two points. More specifically, it is the gradient of the electric field, which in turn is a description of electric force. It is a description of electric potential energy, the ability of the electric field to force a charged particle and move it (i.e. the ability to do work). Because electric force exists between electric charges, voltage can also be interpreted as related the difference in charge between two points. Any time there is a voltage between two points, there must also be an electric field, though the electric field will actually depend on the physical distance between the two points.

    When an electric field exists in an imperfect conductor, a current will flow in the conducting medium. Current is the movement of charged particles (electrons, ions, etc). In order for charges to circulate in a loop, a power source is required which might maintain the potential difference (the voltage) between two points by, we could say, ‘rearranging’ the charges: a voltage source. It could also maintain a constant flow of current: a current source. Either way, a potential difference (voltage) in an imperfect conductor will always cause a current. In imperfect conductors, the current will have many, many interactions with the conductor’s atoms. It’s like playing Plinko. This will then give more kinetic energy to the conductor’s atoms, and heat is generated. So any time a current flows in an imperfect conductor, heat is generated.

    With these simplified definitions of voltage and current, we can look at some scenarios that will help clear up some of the confusion. If there is a voltage between two points, it means there is a difference in the quantity of charge between those points. This applies anywhere. If the charge difference is between two conductors, say a human hand and a doorknob, the charge difference will cause an “equalization”. Many charges will be moved very quickly because they are under a great force (by nature of there being a voltage). This is a current, but it is limited to the difference in charge between the two points. Once all the charges are moved, there’s no more current.

    The voltage in this scenario is only dependent on the difference in the quantity of charges, but it can get into the thousands of volts, the kilovolts (kV). The limited quantity of charge that can possibly be moved, however, means this voltage is reduced to 0V very, very quickly, and the current flow is quite brief.

    If, on the other hand, you have a power source, such as a voltage source, the potential difference will be maintained. The current that flows will be proportional to the resistance of the path, as long as the power source can supply enough current. That is key: Every power source can only supply current up to a point, called the rated current. So a AA battery, for example, can supply currents up to, maybe, 1A (1 ampere). You have to put it across a resistance that will not exceed this. If the “load”, the conductive/resistive path between the + and the -, is too low resistance, the battery’s internal resistance will limit any more current from flowing.

    Voltage sources are much more common for the average consumer, so current sources we’ll leave by the wayside. Voltage sources include things like batteries and wall outlets. You can have constant voltage, which produces constant current, or direct current (DC), or voltage that changes continuously from a positive value to a negative value, producing a current that moves forwards and then back, over and over – an alternating current (AC). This is really only included in this description for completeness.

    Anyway, all voltage sources have a rated current. If you exceed it, the voltage will simply get lower instead of the current increasing any more. For the voltage of the source, V, and the maximum suppliable current, Imax, we say the power of the source is P = V*Imax.

    The power of a source is constant. Or at least ideally. If you convert the voltage to a higher voltage, the maximum current must decrease. If you want to convert the output to get more current, the voltage output will go down. Whatever you do, the product of the voltage and the max current will stay constant.

    For example, given a AA battery with a voltage of 1.5V and a rated max current of 1A, the power is 1.5*1 = 1.5W. We can know “step up” the voltage from the battery (using a clever circuit called a switch mode convert) from 1.5V to as high a voltage as we want. Let’s put the voltage to 5kV (5,000 V) because that’s a very high and seemingly dangerous voltage. But we know the power is constant, at 1.5W, so the maximum possible current our circuit will be able to supply will be 1.5/5000 = 0.0003 = 300uA (300 microamps). After 300uA, the supply voltage will simply drop instead of supplying any more current, just as before.

    This is a failure of the power supply, and the actual applied voltage will drop, so the load isn’t actually seeing the 1.5kV after you try to pass 300uA. Power supplies with higher power ratings will be able to source more current, supplies with lower ratings will be able to generate still less current, before they all hit their limit.

    Side note: switching converters, or any voltage converter for that matter, will always have an efficiency rating. If you supply it with 1.5W, it might only be able to supply 85% of that, 1.2W.


    Now we can talk about what happens when a current flows through a person. As was mentioned, current flow always generates heat. The more current, the more heat. The human body has a fairly high resistance, but not as high as one might think. To get current to flow requires a power source with a voltage that is fairly high, because we’re forcing the current through a lot of resistance. Here’s a familiar chart of what happens to a person at different currents.

    The current passing through your body will be generating a lot of heat, enough to burn your insides. It will also mess with your nervous system, limiting your ability to control your muscles. The amount of current that can kill is rather low, at around 100mA+. The resistance of the human body is roughly between 100k and 1k, or 100,000 and 1,000 ohms. In the chart you can see the voltage required to get the corresponding current levels to pass through a human body at either side of the spectrum.

    Now, knowing what we know about power, we see that a deadly amount of current will pass at between 100V and 10kV at 100–300mA, which would require a power supply that is not only at a voltage of 100V–10kV, but is also capable of supplying between 10W and 1kW (1,000W). If the power supply satisfies both conditions, you will be in danger. If it has a rated power of <10W, you’ll never be at risk, because either the voltage will drop (and thus the force causing the current is reduced, and the current will reduce) or the current will simply be too low to cause death. Assuming you fit in the 100mA part of the current survival threshold, anyway.


    So what voltage can a person survive? Well if we’re considering death from heat, burning, and tampering with vital organs, it’s going to be between 100V and 10kV, as long as the power supply can actually produce the current that would kill you. An ideal, limitless power supply will always be deadly between 100V and 10kV, but in the real world there are always power limits.

    This seems to imply that the human body can withstand any voltage, as long as the source of the potential difference (e.g. a difference in amount of charge) can’t produce currents high enough to burn you and disrupt your organs. Even if you have a voltage of 100MV (100,000,000V) between you and something else, you should be perfectly alright as long as no current can flow through you. Right?

    This is actually interesting because I can’t say for sure that the human body will always be alright as long as the voltage difference is caused by something that can’t really supply current. If, for example, there are two 10ft square plates with a voltage of 100MV between them, and there’s no arcing or anything, and you’re between them, your body resistance should allow for a significant potential difference across you from the side facing one plate to the side facing the other. When that happens, the charges in your body will naturally want to reorient themselves, and I don’t know what risks you would face when this happens. Maybe you would see no change, maybe you would lose brain function and your heart would stop, but I would think the former to be more likely. I’d have to really think about it.

    Anyway, let’s finish up by replacing “It’s not the voltage that kills you, it’s the amps!” with “Death by electrocution requires a high voltage power supply that has a rated power which allows for 100mA or more of current to flow under load.” It’s catchy, I guess.

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