Interesting reading and supports my comment about resistance of the human body. Interesting that you note 30mA but I could only find reference to 90mA in the calculation put forward here. 100mA appears to be the listed minimum
threshold in this and other references.
Another that I found was:
http://www.elec-toolbox.com/Safety/safety.htm which provided a good description of how a
GFCI (
RCD) works. It also cites a similar lethal
current.
Most of the RCDs that are available here are 35mA rated but you can get them up to 100mA so it would seem strange that these devices would not break the
circuit until a lethal
current was detected.
If you look at his calculation for a 9V battery and the average human having a resistance of 500K, you can calculate the required
voltage battery required to produce the 100mA
shock that is considered to be fatal.
x = 100mA and 9V = 0.018mA (18 microampares)
Thus, x = (100 x 9)/0.018 which equals 50,000
Therefore, you would require a 50,000V
shock to be fatal. I think that most stun guns that the police use are 20,000 to 50,000V
To check, E=IR so 50,000V=I x 500,000ohms
I=50,000V/500,000ohms, which equals 0.1A (100mA)
Whilst the math is correct on paper, something doesn’t seem correct to me and I am sure it is more complicated that this. The ability of a
power source to actually be capable of delivering the
current has to be a factor. I believe that low
voltage DC welders have killed people due to the reduced skin resistance form perspiration and the high
current at which they operate.
I have not yet been able to find out the
current generated by a defibrillator but I know that 300J to 360J are the standard ‘shocks’ that are delivered during a cardiac arrest.
Regardless of this fact however is the importance of
electrical safety as whilst this debate is interesting, I wonder if people will simply think, “That couldn’t possibly deliver enough
current to kill me” when we should be thinking that any electrical device has the potential to cause us harm (even death).