5 ms·

A basic knowledge of electricity. 100-200mA will kill you. https://academic.oup.com/ptj/article-abstract/46/9/968/4637975?redirectedFrom=PDF https://academic.o

A basic knowledge of electricity. 100-200mA will kill you. https://academic.oup.com/ptj/article-abstract/46/9/968/4637975?redirectedFrom=PDF https://academic.oup.com/ptj/article-abstract/46/9/968/46379... I have heard people say "that can't be right, because a car battery can source 100+ amps and touching those terminals doesn't kill me!" The reason is because you have a high enough impedance that 100mA doesn't flow from a 12V source through your body.

james400 5y ago
"It's not the voltage that kills you, it's the amps!" Wouldn't power (W) (or joules) be a better way to phrase it? Because as you said, you can't have 100mA flowing through your heart unless you ALSO have stiff enough source to actually supply that current - which implies a high compliance voltage, can't escape ohms law.
- kortex 5y ago
  No, it's not the power, either, as low resistant paths can be extremely dangerous (such as wet skin). Really, it's a 2 dimensional space that makes for a less catchy aphorism. "It's not the voltage that kills you, it's the combination of voltage and conductivity". Honestly I kinda hate that saying. It's like "it's not the fall that kills you, it's the sudden decelleration on impact." For most situations people encounter, it's high voltage sources with more than enough power which are dangerous.
  - jfrunyon 5y ago
    "The combination of voltage and conductivity" is ... current, no?
- aaronmdjones 5y ago
  GP mentioned impedance, not resistance. You won't feel anything touching the 12/24V terminals in your car because they're DC. Your skin has a high resistance, but when faced with AC, has a low impedance. This makes AC much more dangerous, as you conduct 120V AC much better than 120V DC. Even 50mA will likely kill you, as outlined on the "death graph" as we electricians call it. This is independent of voltage. https://upload.wikimedia.org/wikipedia/commons/7/7f/IEC_TS_60479-1_electric_shock_graph.svg https://upload.wikimedia.org/wikipedia/commons/7/7f/IEC_TS_6... Blue is harmless and imperceptible, green is harmless, yellow is harmful, red is fibrillation. Edit: This illustrates why 30mA (or less) RCD protection is common (and required) in various jurisdictions, depending on the kind of circuits you're serving.
  - Reason077 5y ago
    Right, and in particular, "Type B" RCD protection is required for solar inverters in various jurisdictions. These provide protection against DC fault currents.
  - jhgb 5y ago
    > This makes AC much more dangerous, as you conduct 120V AC much better than 120V DC. But at higher frequencies, you should experience the skin effect, right?
    - aaronmdjones 5y ago
      I can't answer that question, as I'm only an electrician, not an electrical or RF engineer. That said, we're referring to power delivery here, and the highest frequency I'm aware of in this space is the 400 Hz power distribution systems used on warships.
- joncrocks 5y ago
  "It's the volts that jolt, but the mills (mA) that kills" - The phrase a schoolteacher used when I was a lad.
  - jrockway 5y ago
    V = I * R
- jhgb 5y ago
  The voltage across the heart will be rather bounded if you fix the current at 100mA, though. Hearts will not differ significantly from each other.
- Johnny555 5y ago
  Not really, whether it takes 50V with wet skin or 500V with dry skin, it's the current that kills you, not the watts
- jackweirdy 5y ago
  Here is medhi sadaghdar (electro boom) putting 11v at 150A through his tongue https://www.youtube.com/watch?v=XDf2nhfxVzg https://www.youtube.com/watch?v=XDf2nhfxVzg
Reason077 5y ago
Embarrassingly, I have managed to shock myself several times during my life on 240V mains. Once quite recently while working on a light fitting at a friend's flat and not realising that someone had flipped the circuit back on at the circuit breaker! That shock was certainly quite unpleasant, but despite touching my sweaty skin against live wires, it seems to have been far from fatal. Surely the dangerous situations are live-to-earth shocks, which could potentially run across your whole body (rather than just a hand or finger, as in my case). But that's why we have RCD/GFCI protection, right? Those will trip with tiny fault currents, certainly much less than 300 mA. Secondly, aren't "Type B" RCDs required on solar inverters? Those will detect and trip on DC fault currents as low as 30 mA, not 300!
- nielsbot 5y ago
  you need "Lock Out Tag Out" lol https://en.wikipedia.org/wiki/Lockout–tagout https://en.wikipedia.org/wiki/Lockout–tagout
- quickthrowman 5y ago
  > Embarrassingly, I have managed to shock myself several times during my life on 240V mains. Once quite recently while working on a light fitting at a friend's flat and not realising that someone had flipped the circuit back on at the circuit breaker! Next time, I suggest using a breaker lockout [0] in conjunction with the local disconnecting means (light switch, which you can also lock out! [1]) to do it safely :) [0] https://www.walmart.com/ip/MASTER-LOCK-493B-Circuit-Breaker-Lockout-Standard-Single-and-Double-Toggles/25461421?wmlspartner=wlpa&selectedSellerId=7646 https://www.walmart.com/ip/MASTER-LOCK-493B-Circuit-Breaker-... [1] https://www.homedepot.com/p/Ideal-Wall-Switch-Lockout-44-789/100004613 https://www.homedepot.com/p/Ideal-Wall-Switch-Lockout-44-789...
  - Reason077 5y ago
    > "light switch, which you can also lock out!" No you can't! Ceiling light fittings (in the UK, at least) are often always live regardless of the switch setting. This is because they are typically wired in a "loop" arrangement with separate loop and switch cables. Example: https://www.practicaldiy.com/electrics/lighting-wiring/light-wiring-loop.php https://www.practicaldiy.com/electrics/lighting-wiring/light...

james400 5y ago

"It's not the voltage that kills you, it's the amps!" Wouldn't power (W) (or joules) be a better way to phrase it? Because as you said, you can't have 100mA flowing through your heart unless you ALSO have stiff enough source to actually supply that current - which implies a high compliance voltage, can't escape ohms law.

kortex 5y ago
No, it's not the power, either, as low resistant paths can be extremely dangerous (such as wet skin). Really, it's a 2 dimensional space that makes for a less catchy aphorism. "It's not the voltage that kills you, it's the combination of voltage and conductivity". Honestly I kinda hate that saying. It's like "it's not the fall that kills you, it's the sudden decelleration on impact." For most situations people encounter, it's high voltage sources with more than enough power which are dangerous.
- jfrunyon 5y ago
  "The combination of voltage and conductivity" is ... current, no?
aaronmdjones 5y ago
GP mentioned impedance, not resistance. You won't feel anything touching the 12/24V terminals in your car because they're DC. Your skin has a high resistance, but when faced with AC, has a low impedance. This makes AC much more dangerous, as you conduct 120V AC much better than 120V DC. Even 50mA will likely kill you, as outlined on the "death graph" as we electricians call it. This is independent of voltage. https://upload.wikimedia.org/wikipedia/commons/7/7f/IEC_TS_60479-1_electric_shock_graph.svg https://upload.wikimedia.org/wikipedia/commons/7/7f/IEC_TS_6... Blue is harmless and imperceptible, green is harmless, yellow is harmful, red is fibrillation. Edit: This illustrates why 30mA (or less) RCD protection is common (and required) in various jurisdictions, depending on the kind of circuits you're serving.
- Reason077 5y ago
  Right, and in particular, "Type B" RCD protection is required for solar inverters in various jurisdictions. These provide protection against DC fault currents.
- jhgb 5y ago
  > This makes AC much more dangerous, as you conduct 120V AC much better than 120V DC. But at higher frequencies, you should experience the skin effect, right?
  - aaronmdjones 5y ago
    I can't answer that question, as I'm only an electrician, not an electrical or RF engineer. That said, we're referring to power delivery here, and the highest frequency I'm aware of in this space is the 400 Hz power distribution systems used on warships.
joncrocks 5y ago
"It's the volts that jolt, but the mills (mA) that kills" - The phrase a schoolteacher used when I was a lad.
- jrockway 5y ago
  V = I * R
jhgb 5y ago
The voltage across the heart will be rather bounded if you fix the current at 100mA, though. Hearts will not differ significantly from each other.
Johnny555 5y ago
Not really, whether it takes 50V with wet skin or 500V with dry skin, it's the current that kills you, not the watts
jackweirdy 5y ago
Here is medhi sadaghdar (electro boom) putting 11v at 150A through his tongue https://www.youtube.com/watch?v=XDf2nhfxVzg https://www.youtube.com/watch?v=XDf2nhfxVzg

Reason077 5y ago

Embarrassingly, I have managed to shock myself several times during my life on 240V mains. Once quite recently while working on a light fitting at a friend's flat and not realising that someone had flipped the circuit back on at the circuit breaker! That shock was certainly quite unpleasant, but despite touching my sweaty skin against live wires, it seems to have been far from fatal. Surely the dangerous situations are live-to-earth shocks, which could potentially run across your whole body (rather than just a hand or finger, as in my case). But that's why we have RCD/GFCI protection, right? Those will trip with tiny fault currents, certainly much less than 300 mA. Secondly, aren't "Type B" RCDs required on solar inverters? Those will detect and trip on DC fault currents as low as 30 mA, not 300!

nielsbot 5y ago
you need "Lock Out Tag Out" lol https://en.wikipedia.org/wiki/Lockout–tagout https://en.wikipedia.org/wiki/Lockout–tagout
quickthrowman 5y ago
> Embarrassingly, I have managed to shock myself several times during my life on 240V mains. Once quite recently while working on a light fitting at a friend's flat and not realising that someone had flipped the circuit back on at the circuit breaker! Next time, I suggest using a breaker lockout [0] in conjunction with the local disconnecting means (light switch, which you can also lock out! [1]) to do it safely :) [0] https://www.walmart.com/ip/MASTER-LOCK-493B-Circuit-Breaker-Lockout-Standard-Single-and-Double-Toggles/25461421?wmlspartner=wlpa&selectedSellerId=7646 https://www.walmart.com/ip/MASTER-LOCK-493B-Circuit-Breaker-... [1] https://www.homedepot.com/p/Ideal-Wall-Switch-Lockout-44-789/100004613 https://www.homedepot.com/p/Ideal-Wall-Switch-Lockout-44-789...
- Reason077 5y ago
  > "light switch, which you can also lock out!" No you can't! Ceiling light fittings (in the UK, at least) are often always live regardless of the switch setting. This is because they are typically wired in a "loop" arrangement with separate loop and switch cables. Example: https://www.practicaldiy.com/electrics/lighting-wiring/light-wiring-loop.php https://www.practicaldiy.com/electrics/lighting-wiring/light...