what's the current of a static shock? - Page 1
Forum section: electronics / general

author: Beamin
author_rank: Super Contributor
timestamp: March 17, 2020, 10:23:28 pm
content: 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.

author: jmelson
author_rank: Super Contributor
timestamp: March 18, 2020, 08:26:17 pm
content: Quote from: Beamin on March 17, 2020, 10:23:28 pmThe 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

author: Zero999
author_rank: Super Contributor
timestamp: March 18, 2020, 10:36:43 pm
content: Quote from: jmelson on March 18, 2020, 08:26:17 pmI'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.htmlAs 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.

author: amyk
author_rank: Super Contributor
timestamp: March 21, 2020, 08:56:44 pm
content: It's not the volts nor amps that kills, it's the joules...

author: GlennSprigg
author_rank: Super Contributor
timestamp: March 25, 2020, 12:51:43 pm
content: Quote from: Zero999 on March 18, 2020, 10:36:43 pm500 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 obviouslynotrecommending 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!!

author: Zero999
author_rank: Super Contributor
timestamp: March 25, 2020, 01:43:13 pm
content: Quote from: GlennSprigg on March 25, 2020, 12:51:43 pmYes, 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.

author: Beamin
author_rank: Super Contributor
timestamp: November 18, 2020, 04:48:02 am
content: This thread reminds me of "electro Booms" videos on youtube where he gets shocked in every video.

author: Psi
author_rank: Super Contributor
timestamp: November 18, 2020, 07:16:55 am
content: Average prolonged current is what's dangerous.A static shock can have very high peak current, well over 100mA, but it's over so fast it doesn't affect you.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 18, 2020, 02:10:38 pm
content: ESD in the low 10s of A, yes. Duration is some tens of nanoseconds, nothing your body can respond to, electrochemically speaking, only the average effect many milliseconds later. You feel a little jump, or maybe a lot.And yes, the resistance is that low. Two things: one, the voltage is high enough to pierce the skin, which has relatively high resistance. Two, the frequency is high, and skin and flesh has a high dielectric constant (it's mostly water), so the reactance is relatively low, and this carries current into and through the body as well. (The exact figure is a mixture of resistance and capacitance -- you're a lossy circuit.) If you hold onto a piece of metal and take the spark, the current distributes itself over your hand or whatever, and you don't feel it; but the electrical response is very much the same (with a small, extra sharp edge where the discharge strikes the metal bit), and those currents are indeed still passing through, or over, your body.If you stick your DMM probes into your fingers I think you'll find it's quite a low lower than the surface resistance... if you're stupid enough to actually do that, but please don't, it hurts?Incidentally, it's sometimes said that you can do this (take sparks while holding metal objects) with Tesla coils and the skin effect protects your insides; alas, this is false, as a simple calculation shows those frequencies (100s kHz) have no problem going all the way through you. For ESD, the average frequency content is in the 10s to 100s MHz, significantly higher -- enough that it may not go to your core, but it's still not something you want applied between corners of your body. Only by the GHz, is the skin depth shallow enough to begin to avoid vital parts -- think microwaving a roast on high power, only the outer inch or two is heated. Finally by several 10s of GHz, only the surface of the skin is affected -- as used by the military's ADS weapon for instance.Tim

author: ConKbot
author_rank: Super Contributor
timestamp: November 18, 2020, 02:31:02 pm
content: Quote from: GlennSprigg on March 25, 2020, 12:51:43 pmQuick sanity-check on this, if the 2meg resistance that a meter shows held up, then 240v would only pass 120 uA through you and should be a tiny tingle, and 5kv from the output of the doubler on a microwave oven transformer would only pass 2.5mA, and be painful to touch, but not pose that much of a risk to a person. Both of these are obviously incorrect.

author: TimFox
author_rank: Super Contributor
timestamp: November 18, 2020, 02:41:03 pm
content: Technically, a static shock is a certain amount ofcharge, and the current is limited by the resistances discussed above.

author: amyk
author_rank: Super Contributor
timestamp: November 19, 2020, 02:23:09 am
content: Quote from: Beamin on November 18, 2020, 04:48:02 amDid you mean his videos reminded you of this thread so you bumped it?

author: GlennSprigg
author_rank: Super Contributor
timestamp: November 19, 2020, 01:31:33 pm
content: Quote from: TimFox on November 18, 2020, 02:41:03 pmWhat people forget, is that such 'low power' static charges VERY quickly collapse in voltage, due to their nature.This often happens faster than any bodily response to such contact. And to others, 100-mA???... I don't know aboutthe USA, but Earth-Leakage Breakers here usually trip at about 20-mA, (very short duration!) as 30-mA will kill you!!

author: bsfeechannel
author_rank: Super Contributor
timestamp: November 19, 2020, 09:25:32 pm
content: https://en.wikipedia.org/wiki/Electrical_injury

author: S. Petrukhin
author_rank: Super Contributor
timestamp: November 20, 2020, 01:19:00 am
content: Static charge flows away at a speed close to the speed of light. The peak value, which decreases very sharply, obeys Ohm's law. These are very large currents, but small Coulombs (1 coulombs = 1 ampere per second). That is, the charge can perform very little work despite a very high voltage.However, a static charge can damage without generating a current. p-n junctions are formed by doping: in one region there is a lack of electrons, in the second - extra ones. To damage the p-n junction, you can apply a current to mix these areas, but you can also apply a field. A rough example: you have a bunch of screws and nuts on the table next to you. You can mix them by pushing them with your hand-this is the current. But you can mix them without touching them with a magnet. A static charge can suck out electrons or put them where they don't need to be. This is how the electromagnetic pulse from a nuclear explosion damages semiconductors.

author: amyk
author_rank: Super Contributor
timestamp: November 20, 2020, 04:25:41 am
content: Quote from: bsfeechannel on November 19, 2020, 09:25:32 pmThe lowest time on that graph is 10ms - a static shock (ESD event) is in the us/ns range.Some interesting reading:http://ntuemc.tw/theme/design/EC_lecture%2010.pdf

author: Psi
author_rank: Super Contributor
timestamp: November 20, 2020, 10:45:34 am
content: That's an interesting graph, i've never seen it shown like that before.

author: bsfeechannel
author_rank: Super Contributor
timestamp: November 20, 2020, 10:56:42 am
content: Quote from: amyk on November 20, 2020, 04:25:41 amIt is also for AC current, but it seems to imply that above a certain current intensity, no matter how short the shock is, it can potentially cause some irreversible effect.

author: amyk
author_rank: Super Contributor
timestamp: November 21, 2020, 03:15:11 am
content: If you really want to extrapolate it, then to me it seems AC-2 area would continue expanding to the right --- meaning "perceptible but no muscle reaction" occurs at very high current and very short durations.

author: bsfeechannel
author_rank: Super Contributor
timestamp: November 21, 2020, 04:29:57 am
content: Well, in that case the lines will cross each other. But since the line separating AC-3 from AC-4 flattens out way before 10ms (which by the way is half a cycle for 50Hz AC), this may suggest that there is a limit for inoffensive currents running through your body no matter how short their duration is. I'd rather bet on that.

author: Zero999
author_rank: Super Contributor
timestamp: November 21, 2020, 11:07:29 am
content: Quote from: bsfeechannel on November 20, 2020, 10:56:42 amThat chart is completely irrelevant to a static shock, which is several orders of magnitude shorter.

author: bsfeechannel
author_rank: Super Contributor
timestamp: November 21, 2020, 01:44:42 pm
content: Quote from: Zero999 on November 21, 2020, 11:07:29 amMaybe.But do you believe that if you have a current of arbitrary intensity running through your body, as long as it is as short as, say, 10μs, it will do you no harm?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 21, 2020, 03:17:43 pm
content: Of course not. A strong enough current will cause spot heating, or even vaporization. The effect is used to detonate high explosives (exploding bridgewire, slapper). Granted, it's easier to generate that kind of power into metals using capacitors, than it is into much higher-resistance flesh. But a high enough voltage, on a correspondingly smaller capacitor, ought to do it. (Be careful around your Marx generator experiments, people?)Amazingly enough, people have survived direct lightning strikes. That's the biggest possible shock, and it's literally electrostatic in origin. Offhand I don't know the chances of survival, or how much internal damage is usually sustained. Certainly, one does not escape with no physical marks at all; the skin burn patterns are... incredible.It seems likely that ESD causes such damage, simply in a very thin area; maybe this damages very few cells, or perhaps it even slips by living cells, burning just intercellular matrix, easily repaired in either case, and not enough damage to cause pain or physical problems. RF burns are notorious for a similar effect but sustained over a long enough period that a plug of flesh is literally burned out; which is supposed to hurt quite a lot, I forget if immediately or later on as toxins diffuse into surrounding healthy tissue...Tim

author: DrG
author_rank: Super Contributor
timestamp: November 21, 2020, 04:34:44 pm
content: So, instead of doing "work", I spent a few hours looking into the topic with the specific goal of seeing what kind of laboratory studies were out there...and there are many.This reviewhttps://ehjournal.biomedcentral.com/articles/10.1186/s12940-017-0248-ywas pretty interesting, including the table of studies with humanshttps://ehjournal.biomedcentral.com/articles/10.1186/s12940-017-0248-y/tables/1Of course, along the way, I came across the ignition liability (yes, a different issue)...like this case reporthttps://www.ejmi.org/pdf/Facial%20burn%20due%20to%20static%20electricity%20induced%20fire%20%20A%20rare%20clinical%20entity%20Case%20Report-02886.pdfand this one, that seems to suggest a liability for ignition of hand sanitizer!https://pubmed.ncbi.nlm.nih.gov/29322859/Alas, they have thwarted all of my usual methods for quickly getting the actual article, so all I can see is the abstract.Remember a while ago when the "cell phones cause fires at fuel pumps" was a thing, debunked to static electricity, but how does one decide the actual odds of a cell phone (not static electricity) has a 1 in 10 billion chance (assuming normal uses) of causing a fire at a fuel pump?https://www.ctvnews.ca/canada/one-in-10-billion-chance-cell-phone-could-ignite-vapours-at-gas-station-report-1.4332547

author: Zero999
author_rank: Super Contributor
timestamp: November 21, 2020, 06:04:20 pm
content: Of course static electricity isn't completely harmless. Not only is there the potential for ignition, but involuntary movements could result in injuries. I suppose one could argue that the shock itself will cause an injury, but it's very mild and will quickly repair itself.By the way, has anyone zapped insects with a piezo BBQ ignition before? That's one of the first things I did, when I got hold of one, as a child, after zapping myself and my siblings of course! Sometimes it would just stun the insect for awhile, but more often it one shock was fatal. Obviously it takes much less energy to harm a tiny insect, than a human.