You know what kills you is the current that flows through affecting your heart, not the voltage. But the amount of current that goes through your body depends on the voltage, hence the concept of “higher voltage is more dangerous than lower voltage”.
The tricky part is that the current also depends on the resistance of your body, as per Current = Voltage / Body Resistance. This is the reason you can wear plastic gloves and touch any voltage and you will be ok, since the resistance is practically infinite, the current is practically zero. This doesn’t hold at very high voltages as other factors come in play but let’s forget that for now.
The safe limit for DC voltage is any voltage that when applied to your body will generate less than lethal current. As per various sources (you can easily google them), any current over 10 mA will produce a severe shock whereas current over 100 mA is lethal. I think 1mA you feel quite a bit.
To determine the safe voltage requires that you know your body resistance, which unfortunately (or fortunately, not sure) depends on many factors and will also change as current flows through the skin. Which body part is involved is important as well as moisture on your skin. There is also the issue of the path between the two contact points and if it goes through your heart. Hand to hand is worse than sticking your tongue on two contact points as current will go mostly through your tongue (although some current will still go through your heart as there is a circuit).
If I measure the resistance between my two hands (with somewhat moist skin) I read about 200kOhm, but if I actually attach my instrument alligator clips to my skin (amazing what people do for a Quora answer), it falls to 100kOhm - ouch!. Does that mean that I can touch 1000V and only get 10mA shocking me? Nope, because it turns out that as current starts flowing, it actually breaks down your skin reducing skin resistance. This is why it gets complicated.
So practically, what is the answer? Well, it’s like price of luxury goods, if you have to ask, you probably shouldn’t depend on the answer. But here are some of my own experiences (which will not apply to you and I am not suggesting you try them)
Anything over that, I’d stay away and treat it very carefully.
The tricky part is that the current also depends on the resistance of your body, as per Current = Voltage / Body Resistance. This is the reason you can wear plastic gloves and touch any voltage and you will be ok, since the resistance is practically infinite, the current is practically zero. This doesn’t hold at very high voltages as other factors come in play but let’s forget that for now.
What is the safe limit of DC voltage for humans to touch?
The safe limit for DC voltage is any voltage that when applied to your body will generate less than lethal current. As per various sources (you can easily google them), any current over 10 mA will produce a severe shock whereas current over 100 mA is lethal. I think 1mA you feel quite a bit.
To determine the safe voltage requires that you know your body resistance, which unfortunately (or fortunately, not sure) depends on many factors and will also change as current flows through the skin. Which body part is involved is important as well as moisture on your skin. There is also the issue of the path between the two contact points and if it goes through your heart. Hand to hand is worse than sticking your tongue on two contact points as current will go mostly through your tongue (although some current will still go through your heart as there is a circuit).
If I measure the resistance between my two hands (with somewhat moist skin) I read about 200kOhm, but if I actually attach my instrument alligator clips to my skin (amazing what people do for a Quora answer), it falls to 100kOhm - ouch!. Does that mean that I can touch 1000V and only get 10mA shocking me? Nope, because it turns out that as current starts flowing, it actually breaks down your skin reducing skin resistance. This is why it gets complicated.
So practically, what is the answer? Well, it’s like price of luxury goods, if you have to ask, you probably shouldn’t depend on the answer. But here are some of my own experiences (which will not apply to you and I am not suggesting you try them)
- 9V battery - yeah, I use my tongue to see if they are ok - not recommended but what can I say. Hand to hand touch, no problem.
- 12V battery - in working with 12–14V batteries for years, I have never had issues including touching them with wet hands. The fact that they are in all vehicles also indicates that in most normal circumstances, 12V is ‘safe’.
- 24V batteries - worked with the extensively as well but not as often with wet hands. Never felt anything.
- 48V batteries - these I can feel and avoid contact. I suspect wet hands would cause a rather uncomfortable feeling.
Anything over that, I’d stay away and treat it very carefully.
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