Author Topic: what's the current of a static shock?  (Read 553 times)

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Offline Beamin

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what's the current of a static shock?
« on: March 17, 2020, 10:23:28 pm »
Volts is 1000 per inch or centimeter?  But what is the current? What would be the current of shocks you can't feel like the ones that kill electronics? Is the a rule of thumb for estimating  like with volts?  PS forums on a tablet suck! Damn broken charger on my MS surface.
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Offline jmelson

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Re: what's the current of a static shock?
« Reply #1 on: March 18, 2020, 08:26:17 pm »
Volts is 1000 per inch or centimeter?  But what is the current? What would be the current of shocks you can't feel like the ones that kill electronics? Is the a rule of thumb for estimating  like with volts?  PS forums on a tablet suck! Damn broken charger on my MS surface.
The ones you can't feel are a few mA, but last only for us.  The ones you feel are 10's of mA and last for hundreds of us.  The ones that make you jump are maybe 100 mA and last for a ms or more.

You can look up the human body model for ESD testing devices for a reference on what sort of discharges are available in the real world.

Jon
 

Offline Zero999

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Re: what's the current of a static shock?
« Reply #2 on: March 18, 2020, 10:36:43 pm »
Volts is 1000 per inch or centimeter?  But what is the current? What would be the current of shocks you can't feel like the ones that kill electronics? Is the a rule of thumb for estimating  like with volts?  PS forums on a tablet suck! Damn broken charger on my MS surface.
The ones you can't feel are a few mA, but last only for us.  The ones you feel are 10's of mA and last for hundreds of us.  The ones that make you jump are maybe 100 mA and last for a ms or more.

You can look up the human body model for ESD testing devices for a reference on what sort of discharges are available in the real world.

Jon
I'd say a good few orders of magnitude higher than that. The electrical resistance of the human body (the skin can be ignored at this high voltages) between say the hand and foot is around 500 Ohm and if the voltage is 10kV, then we have around 20A, in theory. If the capacitance it around 100pF, the RC time constant will be around 50ns, so the shock doesn't last for very long. I haven't looked at the inductance, because I don't know what the inductance of a human is. Anyone know? Even so, the peak current will still be way over 10s of mA.
http://yagitech.blogspot.com/2011/10/electrical-hazards.html

As far as static electricity is concerned, it doesn't make much sense to think of voltage and current. Energy is a far better indicator of how bad the shock is.
 

Online blueskull

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Re: what's the current of a static shock?
« Reply #3 on: March 19, 2020, 03:16:26 am »
A few to a few tens of amps, for a few to a few tens of us, at around 55kv/in (22400V/cm).
 

Offline amyk

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Re: what's the current of a static shock?
« Reply #4 on: March 21, 2020, 08:56:44 pm »
It's not the volts nor amps that kills, it's the joules...
 

Offline GlennSprigg

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Re: what's the current of a static shock?
« Reply #5 on: March 25, 2020, 12:51:43 pm »
Volts is 1000 per inch or centimeter?  But what is the current? What would be the current of shocks you can't feel like the ones that kill electronics? Is the a rule of thumb for estimating  like with volts?  PS forums on a tablet suck! Damn broken charger on my MS surface.
The ones you can't feel are a few mA, but last only for us.  The ones you feel are 10's of mA and last for hundreds of us.  The ones that make you jump are maybe 100 mA and last for a ms or more.

You can look up the human body model for ESD testing devices for a reference on what sort of discharges are available in the real world.

Jon
I'd say a good few orders of magnitude higher than that. The electrical resistance of the human body (the skin can be ignored at this high voltages) between say the hand and foot is around 500 Ohm and if the voltage is 10kV, then we have around 20A, in theory. If the capacitance it around 100pF, the RC time constant will be around 50ns, so the shock doesn't last for very long. I haven't looked at the inductance, because I don't know what the inductance of a human is. Anyone know? Even so, the peak current will still be way over 10s of mA.
http://yagitech.blogspot.com/2011/10/electrical-hazards.html

As far as static electricity is concerned, it doesn't make much sense to think of voltage and current. Energy is a far better indicator of how bad the shock is.

500 Ohms??  A 'typical' resistance from fingers on one hand, to fingers on the other, can vary greatly but be as high as 2 to 5 Meg Ohms!  As some people said, it IS the Current that kills. Around 20 to 30 mA is usually considered as being fatal, and is why Earth Leakage protection devices are generally made to 'Trip' at that current. However, the 'time' one is connected plays an important part too!!

If the Shock duration was only say 1 to 5 milliSecs, then you are generally ok. In fact, as an Elect/Tech over many years, I've probably had literally thousands of shocks, deliberately! with a split second flick with the back of a finger! (I'm obviously not recommending this).
Sometimes, in circuits, the energy is so weak that the voltage collapses immediately & there is virtually non-existent Current to cause damage. For instance, the 'old' cranked up Mega-Testers putting out 500/1000 Volts would give you a playful jolt, but the newer Electronic versions don't give you any feeling at all!! while still able to test a high impedance circuit with actual high voltage.

'Static' is really the same as that. Lots of volts, but no real energy. (And I'm not talking about the likes of Lightning here!).  We safely touch the top of a Van De Graaff Generator and 'zap' other people with between 50,000 & 150,000 Volts! Negligible current can be drawn.

That being said!...  CMOS Technology Chips can be easily damaged, (unlike TTL Chips), by mere static. Internally, the components/traces/layering is so small (and other factors) that the mere fraction of a second & very low mA current can destroy them. You can find photos through microscopes of destroyed junctions etc., that look like they have been hit with an Oxy-Accetelene Torch!!   8)
 

Offline Zero999

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Re: what's the current of a static shock?
« Reply #6 on: March 25, 2020, 01:43:13 pm »
Volts is 1000 per inch or centimeter?  But what is the current? What would be the current of shocks you can't feel like the ones that kill electronics? Is the a rule of thumb for estimating  like with volts?  PS forums on a tablet suck! Damn broken charger on my MS surface.
The ones you can't feel are a few mA, but last only for us.  The ones you feel are 10's of mA and last for hundreds of us.  The ones that make you jump are maybe 100 mA and last for a ms or more.

You can look up the human body model for ESD testing devices for a reference on what sort of discharges are available in the real world.

Jon
I'd say a good few orders of magnitude higher than that. The electrical resistance of the human body (the skin can be ignored at this high voltages) between say the hand and foot is around 500 Ohm and if the voltage is 10kV, then we have around 20A, in theory. If the capacitance it around 100pF, the RC time constant will be around 50ns, so the shock doesn't last for very long. I haven't looked at the inductance, because I don't know what the inductance of a human is. Anyone know? Even so, the peak current will still be way over 10s of mA.
http://yagitech.blogspot.com/2011/10/electrical-hazards.html

As far as static electricity is concerned, it doesn't make much sense to think of voltage and current. Energy is a far better indicator of how bad the shock is.

500 Ohms??  A 'typical' resistance from fingers on one hand, to fingers on the other, can vary greatly but be as high as 2 to 5 Meg Ohms!  As some people said, it IS the Current that kills. Around 20 to 30 mA is usually considered as being fatal, and is why Earth Leakage protection devices are generally made to 'Trip' at that current. However, the 'time' one is connected plays an important part too!!
Yes, 500Ohms is the typical figure of electrical resistance between the hand and foot ignoring the resistance of the skin, which will simply breakdown at these high voltages. The figures you sight, of 2M to 5M, include the skin are only correct at low voltages. In other words, once the voltage goes above 1kV or so, the resistance of the skin can be ignored, because it arcs over, becoming conductive leaving only the resistance of the flesh left.

I agree, I might have overestimated the current and underestimated the pulse duration, but that will be because I didn't take into account the inductance in quick my calculation, rather than the resistance.

Time is important. If the current pulse is short enough, the nerves won't respond to it.
« Last Edit: March 25, 2020, 06:57:57 pm by Zero999 »
 


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