Post by: talanum1 on 01/06/2020 14:13:14
Post by: Colin2B on 01/06/2020 14:37:48
You don’t need the door knob to be connected to ground, just neutral and then it will collect some of the excess electrons.
Post by: Bored chemist on 01/06/2020 14:52:47
So how is this allowed if the door handle is not connected to ground.The door handle is connected to ground- via the door.
Things like wood are normally considered insulators, but at high voltages it is clear that they are poor conductors.
Post by: talanum1 on 01/06/2020 17:54:10
at high voltages it is clear that they are poor conductors.
Then I would get shocked by just touching the door too. This is not the case.
Post by: Bored chemist on 01/06/2020 17:57:37
It also may also add significant capacitance.
Post by: Colin2B on 01/06/2020 18:07:16
It also may also add significant capacitance.I almost suggested the op read up on capacitors, but assumed from his username s/he already knew about them. Just realised I had misread the name as tantalum.
Post by: talanum1 on 03/06/2020 11:38:04
Post by: talanum1 on 03/06/2020 11:43:28
Post by: PmbPhy on 03/06/2020 12:14:49
I noticed that there is no shock when touching the door, also no conduction, because if I touch the door and directly afterwards I touch the handle I get a shock from the handle. So the handle really is isolated from ground by the door, so I don't understand why I get shocked.Noting is connected to ground unless its connected by a conductor. And just because you don't see or hear it doesn't mean that charge isn't being transferred. On a cold winter day rub your feet along the ground and then touch the doorknob, then you'll get zapped.
Post by: Yahya A.Sharif on 03/06/2020 13:56:59
Post by: Petrochemicals on 03/06/2020 21:49:39
To make a current/spark/transfer of electons all you need is a "potential difference", not ground, a voltage drop, not dissipation, even thought ground seems like ground, a big enough pd and electricity runs from the ground to the clouds up the lightning rod.
As an alternate example 110v potential difference safety power system has only a 55v risk to ground due to the fact they have 55+ and 55-, where as mains is only to neutral thus a 240v risk is present,
Post by: vhfpmr on 03/06/2020 23:01:41
When any two conductors are separated by an insulator (a dielectric) the combination forms a capacitor, which stores energy in the form of an electrostatic field. If you connect a capacitor to a battery a current will flow into it despite the fact that it's electrodes are separated by an insulator, because the capacitor is storing electric charge on the dielectric. Once the capacitor has charged to the same voltage as the battery the current will stop. The ratio of the charge stored to the voltage is the capacitance, a larger capacitor will store more charge for any given voltage. Since capacitance C = Q/V, then Q=CV, so if you have a very high voltage it only takes a small capacitance to create a noticeable charge. Current is rate of change of charge, so if the charge transfers in a very short space of time as the insulation of the air breaks down, the current can be quite high.
Post by: PmbPhy on 04/06/2020 01:46:17
The handle in fact is connected to the ground through the door .Unless the door is metal and that metal as a conductor leading into the grown then its not grounded. Since your door is wooden then doorknob its not grounded. But still there there can be a spark between body and ground. Discharge doesn't only happen between a body and a grounded object.
Post by: hamdani yusuf on 04/06/2020 09:34:01
Alternatively, the electrical connection can be provided by the latch through strike plate, frame, and finally to the floor.The handle in fact is connected to the ground through the door .Unless the door is metal and that metal as a conductor leading into the grown then its not grounded. Since your door is wooden then doorknob its not grounded. But still there there can be a spark between body and ground. Discharge doesn't only happen between a body and a grounded object.
Post by: Yahya A.Sharif on 04/06/2020 10:35:17
Both wood and soil and anything else can represent ground .So it is not the handle is connect to the ground through the door , it is the handle connected to the ground and ground here is the door.There is not difference in this case between wood and soil both are insulators.The handle in fact is connected to the ground through the door .Unless the door is metal and that metal as a conductor leading into the grown then its not grounded.
Discharge doesn't only happen between a body and a grounded object.The idea of connecting to the ground is that earth is neutral.As everything is ground then everything is neutral unless it is charged with positive or negative charge.Metal on earth is also neutral.Neutral metal when touching by charged object will give the spark and as I said metal can absorb charge.For a metal not touching earth also will be neutral and give the spark
Post by: PmbPhy on 04/06/2020 14:05:07
The handle in fact is connected to the ground through the door .That is incorrect. Please look up the definition of grounded.
Post by: Bored chemist on 04/06/2020 15:13:37
Since three of us have said it's grounded- and given reasons, perhaps you should look up the definition.The handle in fact is connected to the ground through the door .That is incorrect. Please look up the definition of grounded.
The door handle could be connected to ground by the door frame.
The door handle is connected to ground- via the door.
The handle in fact is connected to the ground through the doo
Post by: PmbPhy on 04/06/2020 15:59:00
Since three of us have said it's grounded- and given reasons, perhaps you should look up the definition.
You just couldn't look it up, could you? You may be a good chemist but you make a lousy physicist. Any physicist would know I am right.
Definition of electrically grounded
Quote
Grounding is a principle of electricity that sometimes puzzles homeowners. In essence, the grounding system in a residential wiring system serves a "backup" pathway that provides an alternate route for electrical current to follow back to "ground" in the case of a problem in the wiring system.Also: https://en.wikipedia.org/wiki/Ground_(electricity)
Quote
A typical earthing electrode (left of gray pipe), consisting of a conductive rod driven into the ground, at a home in Australia. Most electrical codes specify that the insulation on protective earthing conductors must be a distinctive color (or color combination) not used for any other purpose.Wood is NOT an insulator and therefore is not an alternate route for electrical current. No insulator is a direct physical connection to the earth
In electrical engineering, ground or earth is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the earth.
Physics is NOT voted upon. Leave the physics to the physicists, bc. Stick to what you know, not to what you have a warm fuzzy feeling for.
Do you want the definition from a physics text?
Post by: Bored chemist on 04/06/2020 19:34:43
Wood is NOT an insulator and therefore is not an alternate route for electrical current.Pardon?
Post by: Bored chemist on 04/06/2020 19:44:37
You just couldn't look it up, could you?I didn't need to.
Definition of electrically groundedI see what the problem is.
You have muddled up grounding with a safety Earth connections.
And then you made things worse by missing out the important bit of what that wiki page says
"In electrical engineering, ground or earth is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the earth."
And the thing is, that a doorknob in't electrical engineering, is it.
But, fundamentally, you have missed the point.
It's called a ground, or earth, because that's what it's connected to.
But, like wood, earth isn't a great conductor.
So, you really can't need a good conductivity to earth something.
Do you want the definition from a physics text?No, but it looks like you should check it out.
Post by: PmbPhy on 04/06/2020 22:56:21
From Physics for Scientists and Engineers with Modern Physics -- A Strategic Approach by Randall D. Knight, (2004), pages 793-94
Quote
Any object which is physically connected to the earth through a conductor is said to be grounded. The effect of being grounded is that the object shares any excess charge it has with the earth. But the earth is so enormous that any conductor attached to the earth will be completely discharged.Whomever is saying otherwise is quite wrong. Ignore them!
The purpose of grounding objects such as circuits and appliances. is to prevent the build up of any charge on objects.
Post by: Bored chemist on 04/06/2020 23:03:48
Whomever is saying otherwise is quite wrong. Ignore them!OK
You just told everyone to ignore you.
"Any object which is physically connected to the earth through a conductor is said to be grounded."
So, for example, a door handle, which is connected to earth via the timber door (timber is a poor conductor, but good enough if there's a high voltage, and a large contact area- like a doorknob) is grounded.
Now, lets see who
.
is saying otherwise
The handle in fact is connected to the ground through the door .That is incorrect. Please look up the definition of grounded.
Post by: Bored chemist on 04/06/2020 23:05:39
Quote from: PmbPhy on Today at 15:59:00No, but it looks like you should check it out.[/quote]
Do you want the definition from a physics text?
Looks like I was right.
You checked it out and found you were wrong.
Post by: Bored chemist on 04/06/2020 23:06:21
I choose not to see his posts.Great way to stay uninformed there.
Hows it working out for you?
Post by: evan_au on 04/06/2020 23:58:42
Quote from: bored chemist
But, like wood, earth isn't a great conductor.It's true that some rock types like granite have low conductivity, and safety earth connections in granite country need alternative methods (eg relying more on the Neutral wire). But most rock types give reasonable protection.
So, you really can't need a good conductivity to earth something.
I agree that rock would not be good to make long, thin wires. But in its protective/electrical safety role, it is used to make short, really fat wires, and it's not too bad at this - 1 Ohm resistance is often achievable, especially in areas using "Multiple Earthed Neutral", where every house has its own earth stake.
The other important role of "Earth" is as a capacitor.
- This is why the old-fashioned "wireless" had a terminal for an antenna wire and an earth wire - the Earth is able to absorb the radio-frequency currents picked up by the antenna wire.
- Most of the capacitors we put in electronics have two plates, spaced very close together. This allows high capacitance in a small volume.
- But there is another form of capacitor which has just a single conductive element. It doesn't pack nearly as much capacitance into the same volume as a two-plate capacitor.
- A doorknob insulated by the door can act as a small capacitor, and can cause a spark when you touch it
- A car, somewhat insulated by its tyres can act as a larger capacitor, and can cause a spark when you touch it
- An earthed object is connected to the Earth as a much larger capacitor, and can cause a significant spark when you touch it
- I remember at university calculating the capacitance of the Earth - I don't remember the technique, but I do remember that I wasn't impressed with the comparison with what I could get at my local electronics store...
Of course, the Earth, insulated by the vacuum of space, has a higher breakdown voltage compared to a capacitor I could hold in my hand!
Even for an "Earthed" object, the inductance of the Earth wire and skin effect in the wire significantly reduces the current in an impulse with a fast rise and fall time, like an electrostatic discharge.
PS: These MIT lecture notes calculate that the Earth has a capacitance of around 0.0007 Farads, or 700 microFarads.
http://web.mit.edu/sahughes/www/8.022/lec06.pdf
Post by: Petrochemicals on 05/06/2020 03:16:57
When I wear shoes and spent time on the bed, I get an electric shock when touching the metal door-handle. I must be positively charged. So how is this allowed if the door handle is not connected to ground.
Try touching a wired earth object when you get out of bed , my understanding of electrical regulations is any wired 240v appliance with a metal case.
Post by: PmbPhy on 05/06/2020 03:18:31
It's true that some rock types like granite have low conductivity, and safety earth connections in granite country need alternative methods (eg relying more on the Neutral wire). But most rock types give reasonable protection.That's beside the point. Whenever an electric circuit is grounded or a conductor is grounded it can't build up a charge. Try. It won't work. The earth is a charge sink. I used to be an electronics technician. That was when I was first acquainted with the subject. Every time I worked on an electronic device I always grounded the chassis. Not once in those years did I ever get zapped. You won't get sapped from a conductor which is conducted to ground with a conductor. - Just as the text said.
Post by: Bored chemist on 05/06/2020 09:33:48
These MIT lecture notes calculate that the Earth has a capacitance of around 0.0007 Farads, or 700 microFarads.Which is pretty small if you are considering impedance at 50 or 50 Hz,
But it's huge compared to a person- have a look at fig 2
https://incompliancemag.com/article/human-body-model-and-electrostatic-discharge-esd-tests/.
Now, let's get some order of magnitude for the capacitance of the doorknob (on its own)
The capacitance of an isolated sphere is proportional to the diameter.
The Earth is about 13 million metres across a doorknob is about 0.065 metres So it's about 200 million times smaller.
So the capacitance is about 3.5 pF.
I don't think that's big enough to transfer enough charge to give much of a shock.
So I still think it's connected to Earth. How good does that connection need to be?
Well, the body is something like 100pF of capacitance. And the spark duration is something less than a tenth of a second- it's hard to say how much less.
That implies that the resistance of the circuit must be small enough that RC is less than about 0.1.
C is about 10^-10
So R must be a gigohm or less.
There are some values here
https://link.springer.com/chapter/10.1007%2F978-3-642-73683-4_6
for the resistance measured between two needles in a piece of wood. They vary from about 0.6 Meg to about 5 Gig.
So, it's in the right ballpark, especially considering that doorknobs are not just held in with needles.
Post by: Bored chemist on 05/06/2020 09:35:03
You won't get sapped from a conductor which is conducted to ground with a conductor. - Just as the text said.You will if you are charged to a high voltage- which is the relevant case for the OP's circumstances.
Post by: alancalverd on 05/06/2020 10:00:04
Walking across a carpet in insulating shoes generally charges the body to around 15,000 V - the value assumed for most ESD protection systems, though 50 kV is possible with really dry shoes.
This is enough to give you a very nasty surprise when discharged. Remember the door knob is not isolated but connected through a few megohms to a very large surface (the door) with roughly the same capacitance as your body, so you will lose half of your accumulated charge on contact. The duration of the discharge depends pretty much on how well the doorknob is connected to the surface of the door.
One of my more entertaining clashes between engineering and accountancy was in specifying the carpet to be fitted in a mammographic x-ray room. We had designed a special unit accessible to wheelchair users, and the radiographers worked on their knees. The superintendent asked for a pure wool carpet treated with industrial antistatic solution, but having paid over the odds for a special x-ray machine the finance department insisted on tendering for the carpet (the bit they could understand) and supplied a domestic wool-nylon mix without telling us. The first radiographer knelt down, shuffled across the carpet, and touched the first patient's nipple. The noise was unbelievable and the carpet was replaced the next day.
Post by: Bored chemist on 05/06/2020 10:12:15
Post by: PmbPhy on 05/06/2020 10:31:57
The doorknob spends 24/7 connected to ground through the bulk and surface resistivity of the door, so it is reasonable to assume that it is at earth potential first thing in the morning. You could measure its resistance to true earth and it is unlikely to exceed a gigohmThe door is not a conductor so the doorknob is not grounded and therefore the doorknob can have static charge built up upon it.
Post by: Bored chemist on 05/06/2020 10:49:50
In particular, could someone quote the reference I gave showing that the resistance of a piece of wood can be less than a megohm.
https://link.springer.com/chapter/10.1007%2F978-3-642-73683-4_6
That might stop him repeatedly posting this sort of tosh.
The door is not a conductor
Post by: Bored chemist on 05/06/2020 10:57:47
It's about 400 Mohm.
So, about 200M per door handle.
That's only a fact; I don't see it changing Pmbphy's mind.
(Again, I'd be grateful if someone would quote this, otherwise it won't reach the eyes of the "man who will not see".)
Post by: evan_au on 05/06/2020 12:14:40
ESD=ElectroStatic Discharge
Quote from: PmbPhy
Try touching a wired earth object when you get out of bedThe recommended way to discharge yourself to Earth is through a resistor of several hundred kilohms to a Megohm.
This limits the discharge current to something that humans can't feel - and also won't damage sensitive electronic components.
Don't use a single 1MΩ resistor from the local electronics store - they arc over at high voltages. Put 10x 100KΩ in series for better protection against high voltages.
Quote from: BC
I just measured the resistance between the front and back door handles of my house,How did you measure that? My multimeter only goes up to 10 MΩ - and the leads aren't nearly long enough!
It's about 400 Mohm.
So, about 200M per door handle.
Post by: Bored chemist on 05/06/2020 12:22:30
The recommended way to discharge yourself to Earth is through a resistor of several hundred kilohms to a Megohm.A megohm at 20KV "limits" the current to 20mA. That's enough to give you a shock.
Post by: PmbPhy on 05/06/2020 12:41:01
The recommended way to discharge yourself to Earth is through a resistor of several hundred kilohms to a Megohm.That's so you don't electrocute yourself with a high current. You are neither an electric appliance or an electric circuit. High current destroys circuits. There's a good reason to ground circuits as you may know.
I'm tired of this thread. Think what you want but don't come asking questions if you won't accept the answer - From a legitimate source like a physics text.
This limits the discharge current to something that humans can't feel - and also won't damage sensitive electronic components.
Don't use a single 1MΩ resistor from the local electronics store - they arc over at high voltages. Put 10x 100KΩ in series for better protection against high voltages.
Quote from: BC
I just measured the resistance between the front and back door handles of my house,How did you measure that? My multimeter only goes up to 10 MΩ - and the leads aren't nearly long enough!
It's about 400 Mohm.
So, about 200M per door handle.
[/quote]
Post by: alancalverd on 05/06/2020 15:40:05
Back in the day I used to design electrometers with >1015 ohm input impedance. No big deal measuring 400MΩ if you know what you are doing (a standard "Megger" insulation tester runs to 200 GΩ). We occasionally used reformed amber as an insulator (non-triboelectric, non-piezoelectric, and more dimensionally stable than polyethylene) but never wood.
Post by: alancalverd on 05/06/2020 15:43:20
I hope someone in finance ended up paying for the useless carpet.Knowing the way of the world, I suspect he was promoted for challenging the "experts" and saving money, long before the carpet was delivered. 'Twas ever thus.
Post by: Bored chemist on 05/06/2020 15:52:01
That's so you don't electrocute yourself with a high current. You are neither an electric appliance or an electric circuit. High current destroys circuits. There's a good reason to ground circuits as you may know.Would it be better if you stopped talking bollocks?
The OP is talking about static from moving round the room.
That's not gong to electrocute anyone, is it?
(BTW, the word electrocute might not mean what you think it does. It's derived from "execute").
How did you measure that? My multimeter only goes up to 10 MΩ - and the leads aren't nearly long enough!A long bit of wire (of sufficiently small resistance as not to matter), and a better meter than yours.
A maplin wg020 with a 2 gig range.
I did check it against a couple of 1 gig resistors. If anything, it seems to over-read.
Post by: Bored chemist on 05/06/2020 15:59:11
Think what you want but don't come asking questions if you won't accept the answer - From a legitimate source like a physics text.I did accept what your physics book said.
Any object which is physically connected to the earth through a conductor is said to be grounded.And I even accepted what you said about it.
Whomever is saying otherwise is quite wrong. Ignore them!(Though the word, in this case is "whoever".)
And then I pointed out that but someone else's measurements.
https://link.springer.com/chapter/10.1007%2F978-3-642-73683-4_6
and mine
I just measured the resistance between the front and back door handles of my house,
It's about 400 Mohm.
So, about 200M per door handle.
show that a doorknob is connected to ground.
On the other hand, you said
Since your door is wooden then doorknob its not grounded.
So, you are quite simply wrong.
If you are bored of the discussion, that's fine, just accept that you were wrong, and bow out gracefully.
Post by: Colin2B on 05/06/2020 16:42:15
The door handle could be connected to ground by the door frame.If it is a wooden door, then unlikely, but if it is a metal door then definitely.
As as been said before, you don’t need any earth connection to get a discharge.
Post by: evan_au on 06/06/2020 10:07:17
Quote
I get an electric shock when touching the metal door-handleI find that a large part of the shocking sensation actually comes from the heat and current density of the spark.
I've never tried to measure the dimensions of an electrostatic discharge, but they can be several mm long, and appear to have a diameter of well under a mm. This ionizes the air, so we are talking about temperatures of thousands of degrees, and a high current through a very small area of skin.
Instead of touching the doorknob or grounded appliance with your fingers, try discharging yourself through the ring on your finger or some other piece of metal held in your fingers.
- The high temperature arc does not touch your skin, but occurs between the ring and earth
- Instead of the current being concentrated in an area of perhaps 0.1mm x 0.1mm, it is now distributed over an area of perhaps 2 x 20 mm, so the current density is way down.
- So although the spark is just as big (and just as loud), it doesn't feel nearly as bad.
Standard ESD wrist-straps have an electrical contact button with a diameter of 7-10mm, enough to spread the current over a wide area.
- You put on the wrist-strap first
- then you touch the strap to an Earthed discharge point with an alligator clip (preferably while holding a plastic part of the strap)
- You are then discharged through the resistor of the wrist strap, and it doesn't cause an electric shock (as it would if you touched the discharge point with your finger).
See: https://en.wikipedia.org/wiki/Antistatic_device#Antistatic_wrist_strap
Post by: Bored chemist on 06/06/2020 11:51:36
If it is a wooden door, then unlikely,Just to clarify.
The experiment was done with wooden doors and the door handles foud to be connected to eachother via the ground.
So I don't see why you think it's "unlikely"
As as been said before, you don’t need any earth connection to get a discharge.Given that there is an Earth connection- via the door- this is irrelevant.
But it's easy enough to test.
Ask the OP to get another door handle (or some similar sized + shaped metal object- a coke can is probably similar enough), and put it on a good insulator- say a sheet of clear perspex or a plastic lunchbox and see if touching it give him a shock in the same way that touching the door handle does.
If it does then the effect is due to the capacitance of the knob, if not, it's due to conduction via the door.
But, in any event, wood is not a very good insulator.
Post by: Petrochemicals on 06/06/2020 20:06:31
If you get no shock from the wood but get a shock from the handle this is just a static discharge to the metal handle and the wood an insulator to the static charge.
If you fail to get a shock the door is an conductor (water content 15%) to the point of a non noticeable dissipation of charge.
Post by: yor_on on 07/06/2020 16:51:25
Well, it's chicks for me
Post by: talanum1 on 07/06/2020 17:24:37
Post by: Bored chemist on 07/06/2020 17:32:56
I get no shock from the wooden door. Also not from a metal spoon in a mug.That makes sense if the door conducts, but sufficiently poorly that you need a good contact with it, like a door handle fixed in place with screws or something like that.
Post by: Petrochemicals on 07/06/2020 21:04:46
I get no shock from the wooden door. Also not from a metal spoon in a mug.
To check whether the wood provides a sufficient insulation medium to your charge, just for us, touch the wood first then the handle second.
Post by: Bored chemist on 07/06/2020 22:03:36
And...?I get no shock from the wooden door. Also not from a metal spoon in a mug.To check whether the wood provides a sufficient insulation medium to your charge, just for us, touch the wood first then the handle second.
Post by: hamdani yusuf on 08/06/2020 04:16:26
Petrochemicals suggested a 2 steps experiment, but talanum1 had done the first step only.And...?I get no shock from the wooden door. Also not from a metal spoon in a mug.To check whether the wood provides a sufficient insulation medium to your charge, just for us, touch the wood first then the handle second.
Post by: talanum1 on 08/06/2020 08:30:23
Ground acts like a source/sink of electrons. I don't believe the door is large enough to act like a sink/source.
Post by: alancalverd on 08/06/2020 17:34:25
A conductor does not need to be at any particular potential to share charge, only a different potential from the one your finger is at.
If you want to pit belief against physics, try shuffling across the carpet and discharging your finger several times in quick succession. You should find the shock gradually diminishes as the door acquires more charge. Then wait a couple of hours and do it again, by which time the charge on the door will have leaked away.
Post by: Bored chemist on 08/06/2020 18:05:34
If you want to pit belief against physics, try shuffling across the carpet and discharging your finger several times in quick succession. You should find the shock gradually diminishes as the door acquires more charge. Then wait a couple of hours and do it again, by which time the charge on the door will have leaked away.That's just mean. :-)
Post by: Petrochemicals on 08/06/2020 21:24:41
.Not if its grounded alan, he will just get multiple electric shocks. Sort of like wylie coyote (genius).
If you want to pit belief against physics, try shuffling across the carpet and discharging your finger several times in quick succession. You should find the shock gradually diminishes as the door acquires more charge. Then wait a couple of hours and do it again, by which time the charge on the door will have leaked away.
Post by: Petrochemicals on 08/06/2020 21:34:34
I did touch the door, then the handle and I did touch a spoon.Well its either a sink or a ground, try shuffling across the carpet and discharging your finger several times in quick succession.
Ground acts like a source/sink of electrons. I don't believe the door is large enough to act like a sink/source.
Post by: Bored chemist on 08/06/2020 21:46:33
I presume Alan was kidding..Not if its grounded alan, he will just get multiple electric shocks. Sort of like wylie coyote (genius).
If you want to pit belief against physics, try shuffling across the carpet and discharging your finger several times in quick succession. You should find the shock gradually diminishes as the door acquires more charge. Then wait a couple of hours and do it again, by which time the charge on the door will have leaked away.
On the timescale of shuffling across the floor- call it ten seconds, the leakage resistance would have to be something like a few terohms or more to stop the charge leaking away from the few pF capacitance of an isolated doorknob.
So, maybe with a really clean PVC or glass door.
Anyway, we can possibly get the OP to measure the resistance to earth of the door-handle if he has the inclination, a cheap and cheerful digital volt meter some wire and a battery.
It's not as if it's difficult, or needs great precision..
Post by: alancalverd on 08/06/2020 22:52:46
Anyway I'm inspired by this thread to make a Van der Graaff generator from some plastic drainpipe and an old saucepan. All good fun!
Post by: Colin2B on 09/06/2020 04:00:03
Ground acts like a source/sink of electrons. I don't believe the door is large enough to act like a sink/source.Problem is you are not touching the ground.
With wired electricity from mains or battery you have a constant supply of electrons fed into a wire, analogy a hosepipe. With static it’s as if you have a cupful of water. That cupful can either drain away very slowly or you can tip it out all at once, and in order to feel the static in your scenario you usually need to let it out all at once.
To feel a dc electric current you need about 5mA through the fingers. Static discharge is usually over 3kV, but in extreme cases you can build up to 15-30kV, but sitting on the bed is likely to be generating towards the lower end.
The next question is whether you are ‘connected’ to earth. The the conductor/insulator scale is continuous and even the best insulators have some leakage current even if it is negligible. As @Petrochemicals says wood with a water content of 15%+ will be considered a conductor, But dry timber <12% is considered an insulator (usually as good as some rubbers) so we would not usually consider it to provide an adequate earth connection. The standard insulation test quotes a minimum resistance of 1MΩ, although no electrician would be happy with a value under 4-5MΩ. If you look at the measurement taken by @b 200MΩ would be considered a good level of insulation and not an adequate earth connection, but not, as has been pointed out, full isolation - dry wood is also a dielectric with a dielectric constant of 2-6.
If you consider that the minimum level of current for sensation in the finger is 5mA for dc, if we take an upper level of 30kV with 200MΩ the earth leakage would be 150μA, not enough to be felt. So earth leakage is not the direct cause of your shock, it is static discharge to even up the excess electrons on you, as Alan says, it’s a leaky capacitor which will reset ready for your next tingle.
Post by: Petrochemicals on 09/06/2020 21:47:24
If i chuck a cotton towel between my cotton trousers and t shirt and the chair it stops, but why ?
Post by: Bored chemist on 09/06/2020 22:12:28
https://en.wikipedia.org/wiki/Electrical_resistivity_measurement_of_concrete
Plastic chairs are notorious.
To generate static, you usually need a couple of insulators rubbing.
Cotton is hygroscopic enough not to be good at the job.
(Hair is less conductive.)
Post by: talanum1 on 10/06/2020 16:52:13
Post by: alancalverd on 10/06/2020 22:24:44
Until V exceeds the breakdown potential of air, Q depends on the area of contact between the static-generating surfaces, the nature of the surfaces, and the precise movement of rubbing and separating them. C is a constant, so the dependent variable is V. You can see this clearly in any controllable static generator like a Van der Graaff or Wimshurst machine - or even the adhesive tape generator depicted in this website https://www.thenakedscientists.com/get-naked/experiments/glowing-tape (https://www.thenakedscientists.com/get-naked/experiments/glowing-tape). The initial voltage is zero and increases as more charges are separated and the separation is increased.
Post by: Bored chemist on 10/06/2020 23:21:56
:-)
I'm fairly sure that the "lumped element" version's not up to the job.
Post by: vhfpmr on 11/06/2020 23:59:48
Post by: alancalverd on 12/06/2020 09:18:53
The IEC assumption of human body impedance for shock protection purposes is 1kΩ in parallel with 0.1μF for hand-to-hand full contact (normally damp hands). However for single finger dry touch the measured value is in the range 100 kΩ - 10 MΩ. This will give you more realistic i and t values for the discharge characteristic, but the curves will look the same.
Post by: Bored chemist on 12/06/2020 10:29:05
Does the (order of 2µH) inductance make a difference?
https://www.qsl.net/in3otd/ind1calc.html
I suspect it must
You have 20Kv to play with and that's going to change the current in the inductor by 20,000 = 0.000002 dI/dT
About 10^10 A/sec
You have something like 10^-9 seconds to change it, so that limits the current to about 10A.
That's roughly the same as the current you calculated, so the effect of the inductor will be comparable with that of the "resistor" used to model the arc. (And an established arc has a negative incremental resistance).
The approximate value calculated for the inductance might be more accurate than the guessed value of the resistance.
Post by: vhfpmr on 15/06/2020 14:26:47
I've seen mention of IEC standard and 'human body' standard, but no detail of the difference. There's also mention of air discharge vs contact discharge, but no detail. The waveform I'm getting into a short circuit matches the published one in all but peak amplitude. It refers to 30A, but I'm getting 24A (8kV/330Ω)
ESD Snip 2.JPG (249.14 kB . 1917x853 - viewed 2520 times)2μH is quite a lot of inductance, it's about right for a 2m loop of wire, but I'm not sure how representative that is. Inductance is dependent on conductor cross section, but I'm not sure quite how you'd go about quantifying that when the dielectric for the body capacitance amounts to the whole room volume. A 2μH inductor gives a very slow risetime and is significantly underdamped, but that brings us back to the need to know what load the test circuit is calibrated into.
ESD 2u.JPG (258.3 kB . 1915x856 - viewed 2363 times)
Post by: Bored chemist on 15/06/2020 15:29:17
I'm fairly sure that the "lumped element" version's not up to the job.The "single turn inductor calculator I found on line does take account of the conductor diameter.
I think I put 5 cm in as representative of a wrist and a 3m perimeter.
Apparently people have a resistivity of about 200 ohm cm.
https://pubmed.ncbi.nlm.nih.gov/10593226/
And if this calculator
https://www.allaboutcircuits.com/tools/skin-depth-calculator/
is right, that means we have an electrical skin depth of about 5cm at 0.2 GHz
So I think we can pretty much ignore that.
I'm not sure how one would model the whole lossy capacitive inductive system.
One quick sanity check, If you have a current of 20A in an inductor of 2 µH then you have as stored energy of 0.5*20*20*0.000002 J
That's 400 µJ
And the capacitor stores 0.5* 150 E-12 * 20,000*20,000
about 30mJ
So there's plenty of energy available to drive the current.
Post by: talanum1 on 15/06/2020 16:40:54
Post by: Bored chemist on 15/06/2020 19:09:13
The resistance between the door handle and the door frame is 10k - 175 k Ohm.That's interesting to know.
Are you able to measure the resistance to Earth- perhaps a metal water pipe?