> And why is it that if you touch a 120 V source, you die - yet a 15000
> V static shock merely stings?

The 120V source can deliver current for an unlimited amount of time (or unt=
il =

the circuit is broken) while the static charge is just as its name implies =
- =

static. As soon as current begins to flow, the voltage is rapidly decreased=
 and =

all the stored enery in it is used up.

You can think of static charge as a charged capacitor (with a very low =

capacitance). When the capacitor is discharged it can no longer deliver a =

current through the load (your body, for instance). For normal static charg=
es, =

the capacitance is very low which means that the charge will be discharged =

through your body in a matter of pico seconds.

If you touch a 10nF capacitor charged to 15000V - It will do a lot more tha=
n =

merly sting.  =


When dealing whith static charges (charged capacitors), the charged voltage=
 in =

combination with the capacitance tells you how much energy the capacitor =

stores. IEC/EN 61010 states that maximum permissible limits for a capacitan=
ce =

charged to a voltage above 15000V is 350mJ. Above that it is considered to =
be =

hazardous live. The energy in a charged capacitor is C*V*V/2 so a capacitor =

with a capacitance of more than around 3nF charged to 15000V is considered =

unsafe for a human to touch. When you have seen the discharge spark from a =
10nF =

capacitor charged to around 15kV and heard the bang it makes, you make sure=
 to =

keep the fingers away.

For sources of continuous currents (as opposed to charged capacitors), IEC/=
EN =

61010 says that potentials higher than 33VAC rms, 46.7V peak or 70VDC that =
can =

deliver a current of 0.5mA rms for sinusoidal waveforms, 0.7mA peak for non =

sinusoidal waveforms or mixed frequencies or 2mADC when measured through a =

circuit representing the impedance of a human body, is concidered to be =

hazardous live. So in this sence it is the current that kills and not the =

voltage as long as the voltage is above the values above. And in this case =
it =

doesn't matter if the voltage is 100V or 100000V.

/Ruben



=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
Ruben J=F6nsson
AB Liros Electronic
Box 9124, 200 39 Malm=F6, Sweden
TEL INT +46 40142078
FAX INT +46 40947388
ruben@pp.sbbs.se
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D

-- =

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