static electricity
- Thread starter sparky j
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Re: static electricity
Static electricity has a very high voltage. It can be millions of volts. But the current is usually very low. That is why it only hurts a little.
How much will kill you? Can lightning be considered a form of static electricity? It can have very large currents due to the buildup of charge over a very large area (maybe a few square miles of clouds).
But someone may survive a large lightning strike, and someone else may get killed by a smaller strike. So you can't really say X amount will kill someone. There are a lot of different variables that come into play.
Static electricity has a very high voltage. It can be millions of volts. But the current is usually very low. That is why it only hurts a little.
How much will kill you? Can lightning be considered a form of static electricity? It can have very large currents due to the buildup of charge over a very large area (maybe a few square miles of clouds).
But someone may survive a large lightning strike, and someone else may get killed by a smaller strike. So you can't really say X amount will kill someone. There are a lot of different variables that come into play.
B
bthielen
Guest
Re: static electricity
I believe I am correct that static discharge is probably dc. I read a document that roughly 100mA of dc current will usually cause trouble breathing and 500mA dc will likely cause heart fibrillation.
**NOTE** The amount of current required to hurt or kill someone varies considerably from person to person and under various circumstances. It is ALWAYS best to assume it is all dangerous and to be treated with respect.
I was told one time that it takes roughly 100KV to jump an air gap of 1/4". Seems reasonable considering spark plugs in my old '67 were gapped at about .028" and the coil delivered about 30KV. A much wider gap and the spark plug failed to ignite the fuel.
I know one thing for sure. The electric fencer around my pasture will knock you on your can if you touch the wire with bare feet on a damp morning. Another example of a high voltage, low current charge. It hurts!!
Bob
I believe I am correct that static discharge is probably dc. I read a document that roughly 100mA of dc current will usually cause trouble breathing and 500mA dc will likely cause heart fibrillation.
**NOTE** The amount of current required to hurt or kill someone varies considerably from person to person and under various circumstances. It is ALWAYS best to assume it is all dangerous and to be treated with respect.
I was told one time that it takes roughly 100KV to jump an air gap of 1/4". Seems reasonable considering spark plugs in my old '67 were gapped at about .028" and the coil delivered about 30KV. A much wider gap and the spark plug failed to ignite the fuel.
I know one thing for sure. The electric fencer around my pasture will knock you on your can if you touch the wire with bare feet on a damp morning. Another example of a high voltage, low current charge. It hurts!!
Bob
- Location
- Lockport, IL
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- Semi-Retired Electrical Engineer
Re: static electricity
Static electricity is DC, and lightning is an example of static electricity. All the term "static" tells you is that it originated by the buildup of charge on one object, and that charge flows into a second object when the two come into contact (or are close enough to permit charge to jump the gap between them). Static electricity does not require a complete electrical circuit; current flows only long enough to equalize the charge on two separate objects. As to how much is present, in terms of amps or volts, that is dependent on the source.
Static electricity is DC, and lightning is an example of static electricity. All the term "static" tells you is that it originated by the buildup of charge on one object, and that charge flows into a second object when the two come into contact (or are close enough to permit charge to jump the gap between them). Static electricity does not require a complete electrical circuit; current flows only long enough to equalize the charge on two separate objects. As to how much is present, in terms of amps or volts, that is dependent on the source.
Re: static electricity
I remember watching my uncle work on an electric fence. The fence was usually ran with insulators on metal posts. He had a thing that would short the wire to the fence post. Then he could work on the fence downstream of the short.
Of course, if the shorting device didn't make good contact, or if the fence post wasn't grounded really good, it could be fairly painful.
Steve
I remember watching my uncle work on an electric fence. The fence was usually ran with insulators on metal posts. He had a thing that would short the wire to the fence post. Then he could work on the fence downstream of the short.
Of course, if the shorting device didn't make good contact, or if the fence post wasn't grounded really good, it could be fairly painful.
Steve
B
bthielen
Guest
Re: static electricity
Good to be corrected. I was either misinformed or my memory isn't too reliable. But actually looks like I missed it by more like 4x10^2.
Thanks for the info.
Bob
Good to be corrected. I was either misinformed or my memory isn't too reliable. But actually looks like I missed it by more like 4x10^2.
Thanks for the info.
Bob
bphgravity
Senior Member
- Location
- Florida
Re: static electricity
The interesting thing about a "static" or "separation discharge" event like lightning is that the current level is independent of the circuit impedance. For example, if you have a 75,000 amp lighnting discharge, this will be the current that flows regardless if the circuit impedance is 1 ohm or 1,000 ohms. However, the transient voltage across the path will increase or decrease in magnitude.
The interesting thing about a "static" or "separation discharge" event like lightning is that the current level is independent of the circuit impedance. For example, if you have a 75,000 amp lighnting discharge, this will be the current that flows regardless if the circuit impedance is 1 ohm or 1,000 ohms. However, the transient voltage across the path will increase or decrease in magnitude.
physis
Senior Member
Re: static electricity
I'm not questioning your understanding, I know that lightning's one of your specialties. I'm not aware of this phenomenon, so I have at least a couple questions.
Are you saying that the current is constant because the voltage is dynamic in response to some natural balance of current and impedance?
If I consider that the impedance comes from only ionized air and try to imagine a conductor made from that, is the width or diameter of the air column constantly changing so that the current is maintained?
What determines the current's magnitude? I'm guessing it's different in every case.
That's more than interesting.
I'm not questioning your understanding, I know that lightning's one of your specialties. I'm not aware of this phenomenon, so I have at least a couple questions.
Are you saying that the current is constant because the voltage is dynamic in response to some natural balance of current and impedance?
If I consider that the impedance comes from only ionized air and try to imagine a conductor made from that, is the width or diameter of the air column constantly changing so that the current is maintained?
What determines the current's magnitude? I'm guessing it's different in every case.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: static electricity
I see lightning as being a current source: same current regardless of voltage drop along its path. Once lightning hits something (roof, tree, antenna, whatever), then if there is a high impedance path from that point to planet Earth, there will be a high voltage drop as measured from the point of impact to the dirt. That is a key reason for bonding metal structures, even if they are not at risk of becoming energized from an internal fault of some nearby electrical device. You want a low impedance path for the lightning to follow, so that the structure does not build up a high voltage to earth.
The amount of current should be dependent only on the amount of charge that had built up in the cloud, by the time conditions are right for the discharge to occur.
I see lightning as being a current source: same current regardless of voltage drop along its path. Once lightning hits something (roof, tree, antenna, whatever), then if there is a high impedance path from that point to planet Earth, there will be a high voltage drop as measured from the point of impact to the dirt. That is a key reason for bonding metal structures, even if they are not at risk of becoming energized from an internal fault of some nearby electrical device. You want a low impedance path for the lightning to follow, so that the structure does not build up a high voltage to earth.
The amount of current should be dependent only on the amount of charge that had built up in the cloud, by the time conditions are right for the discharge to occur.
Re: static electricity
I see lightning as a capacitive discharge which is by no means a constant current event. Does anyone have a reference to an article that makes that claim?
Then again, the length of the lightning bolt may create significant inductance which would tend to maintain a constant current??
[ January 06, 2006, 08:42 PM: Message edited by: rattus ]
I see lightning as a capacitive discharge which is by no means a constant current event. Does anyone have a reference to an article that makes that claim?
Then again, the length of the lightning bolt may create significant inductance which would tend to maintain a constant current??
[ January 06, 2006, 08:42 PM: Message edited by: rattus ]
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