Timeline for Safe current limit for human contact?
Current License: CC BY-SA 4.0
15 events
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| Apr 19, 2019 at 22:24 | history | edited | JYelton | CC BY-SA 4.0 |
Capitalization
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| Jan 13, 2019 at 0:32 | comment | added | neverMind9 | Say that in front of ElectroBOOM. | |
| Jan 21, 2011 at 21:23 | comment | added | Mark | @endolith for instance a Tazor may have an initial operating voltage of 600,000 volts, which will be applied for a split second to break down skin resistance before the current limiter kicks in and lowers the current (obviously by limiting voltage) by that time your body resistance has changed significantly as a result of the skin resistance break down. Again the body resistance is changing, you wouldn't build this as a fixed voltage limiter, but as a fixed current limiter to handle the change in body resistance. | |
| Jan 21, 2011 at 21:20 | comment | added | Mark | @endolith I'm really not going to argue about what a current limiting circuit is, obviously it lowers the voltage, its monitoring and reacting to current, i'm not going to call it a voltage limiter just because thats how it operates. As for the resistance, yes actually you can. Your body doesn't have a fixed resistance, your skin is the major source of resistance but its resistance tends to break down in response to application of voltage/current. Your skin may start out at 2M ohm and drop to maybe few hundred ohms in response to applied voltage/currents levels and duration of application. | |
| Jan 21, 2011 at 20:42 | comment | added | endolith | "2) X00,000+V at 1mA isn't dangerous, 500mA at 100V is dangerous." One of those is a resistance of 100,000,000 ohm, the other is a resistance of 200 ohm. You can't have both with the same human body. And a "current limiter" is just going to reduce the voltage. | |
| Jan 21, 2011 at 19:21 | comment | added | Mark | @bt2 If you wanted to build a safe "shock" device. You don't do so by limiting the voltage because we can't account for wide fluctuations in body resistance. We'd build it with a high voltage and a current limit as limiting the current is how we can guarantee limiting possible damage. As mentioned there may be a frequency component in the mix as well, depending on what you want to achieve. I doubt it matters much in a hand-shake shock device, matters more in something like a tazer if you want to lock muscles. | |
| Jan 21, 2011 at 19:15 | comment | added | Mark | @bt2 This is just a chicken and egg debate. My point is quite simply: 1) Current is the physical action that causes damage. 2) X00,000+V at 1mA isn't dangerous, 500mA at 100V is dangerous. You need some voltage to induce current flow but the functions of skin resistance breakdown means that body resistance can change massively. Ultimately the voltage that is applied to your body doesn't matter when it comes to damage, its the current that needs to be controlled to prevent damage. Again hundreds of thousands of volts current limited is not dangerous. 100V without a current limit is. | |
| Jan 21, 2011 at 19:07 | comment | added | Mark | @Endolith There are no losses in the loop, and the current in the loop doesn't perform work, but measuring that current requires work to be performed. Such loops are usually coupled to 'standard' circuits where losses are measured to determine the current in the loop. The loop pretty much useless without the ability to measure either its operation or its effect, measurement requires work. | |
| Jan 21, 2011 at 15:46 | comment | added | endolith | @Mark: Current in a superconducting loop isn't doing any work, either. :) | |
| Jan 21, 2011 at 5:04 | comment | added | Mark | while true, voltage is just a potential, that is voltage can do no work, only current can. | |
| Jan 21, 2011 at 0:30 | comment | added | bt2 | Current won't pass through your body without voltage. I've worked with continuity test equipment capable of flowing massive amounts of current and could safely hold the anode and cathode in my hands, due to the low voltage. So, saying it's the current that kills you, is like saying "It's not the lack of breathing that killed you, its the lack of O2 in your blood." Without a difference in potential, you aren't going to get any current. | |
| Jan 20, 2011 at 22:23 | comment | added | endolith | @Mark Meaning that 1 mA of DC has a different effect from 1 mA of 60 Hz AC, which has a different effect from large spikes at 2 Hz that average out to 1 mA. There isn't a magical voltage that kills people, and there's not a magical current, either. | |
| Jan 20, 2011 at 21:42 | comment | added | Mark | @endolith "It's not current that kills, it's the fibrillation." Considering that its current that causes the fibrillation i don't get what your point is. Thats like saying "It's not the lack of breathing that killed you, its the lack of O2 in your blood". I get what your saying on the voltage vs current issue, but honestly if someone is daft enough to look at a supply's current rating and grab on to it there isn't much you could say that would save them. Also, I don't often see a supply thats limited to currents below what i stated are dangerous that outputs enough V to pass through skin. | |
| Jan 20, 2011 at 20:52 | comment | added | endolith | It's not current that kills, it's the fibrillation. The path the current takes through your body and the presence of vibrations that interfere with the heart are important. Saying "voltage doesn't matter; it's the current that kills" will only encourage people to look at the current rating of a power supply and think that somehow has something to do with the danger of it. Power supplies are almost always voltage supplies. They don't force a specific current. The amount of current that goes through your heart depends on your resistance and the supply's voltage. | |
| Jan 20, 2011 at 1:46 | history | answered | Mark | CC BY-SA 2.5 |