A small electric shock

[5614]

So without a complete circuit there is no flow and thus no power.

Expansion: As shown in the equation P=IV

 

As the human body mostly consists of water with low resistanse,

Although the human body does have a lot of water in it overall the body still has a high resistance.

[YT2095]

200k for dry hands and well below 20k for a wound, that`s not what i`de call High resistance at all, we`re as conductive as 7% salt water!

[5614]

OK, I wouldn't really call that high resistance either, but still, it means that if you get a 240V shock it's only like 0.0012A going through you, and you need 0.5A to kill, that'd be more like a 100KV electric shock... that's interesting, then why can 240V kill? I suppose a long exposure or wound or when you have a wet hand it does make a difference (from personal experience!).

[Primarygun]

I forget which, ampere or voltage, reaches a particular level would kill a person.

Probably voltage. Above the level does not stop heart beating but just inhibit.

[Lance]

OK, I wouldn't really call that high resistance either, but still, it means that if you get a 240V shock it's only like 0.0012A going through you, and you need 0.5A to kill, that'd be more like a 100KV electric shock... that's interesting, then why can 240V kill?

 

There is no set current to kill. Nobody said that you must have 0.5A to kill, people can and have died from much much lower currents than that. I have heard this number quoted anywhere from 10ma to 9 amps for a woman and 10 amps for a man (no joke).

[Primarygun]

I'd think electrostatics charges are more dangerous than a current.

Current requires a complete circuit but the former does not.

[5614]

I forget which, ampere or voltage, reaches a particular level would kill a person.

That would be the current... ampere.

 

I'd think electrostatics charges are more dangerous than a current.

I wouldn't! It's pretty hard to kill yourself with electrostatics, it's a lot easier to kill yourself with a current.

 

There is no set current to kill.

OK, but I once read somewhere that a sustained (no idea for how long) 0.5A current would kill the average human.

[YT2095]

to kill requires the P=IV equasion, it`s the Power that kills, not Voltage or Amperage alone.

 

I`ll gladly spend a day between 2 plates of 1 volt at a million amps potential or several kilovolts arcing at me at virtualy no amps.

[Callipygous]

i have heard that if there is enough voltage a closed circuit can still give you a shock. even if it doesnt have enough voltage to bridge the gap to the ground or anything like that, i was told you could still get shocked if the voltage was high. any truth to that?

[Lance]

to kill requires the P=IV equasion' date=' it`s the Power that kills, not Voltage or Amperage alone.

 

I`ll gladly spend a day between 2 plates of 1 volt at a million amps potential or several kilovolts arcing at me at virtualy no amps.[/quote']

 

Thats why I say flowing current rather than just current. Obviously if you stand between 1 two plates charged to 1V almost 0 current will flow.

 

Electrostatics are not dangerous because the discharge times are so low. a hundred amps may flow but its only lasting for a short amount of time.

[Lance]

i have heard that if there is enough voltage a closed circuit can still give you a shock. even if it doesnt have enough voltage to bridge the gap to the ground or anything like that, i was told you could still get shocked if the voltage was high. any truth to that?

 

It depends on the power supply and your bodies potential. If your body is charged to +1kV then touching a similarly charged object wont do anything. But if your body does not have a charge or is charged to -1kv then you will get a 1-2kv shock.

 

The shock wont be as high because the capacitance of your body is relatively low. Current will flow into your body until you reach the same potential as the power supply then current will cease to flow.

[Spyman]

From my understanding the internal body resistance between random different points of induvidial human bodys can be as low as 100 Ohms.

The skin when dry and clean can have a resistance up to 2 M Ohms.

 

From my safetybook of "Working with Electricity":

 

Loss of muscle control between 10-20 mA.

 

Difficulty with breathing between 20-30 mA.

 

Possible heart fibrillation between 50-100 mA.

 

Internal burning damage above 1 A.

 

Time dependency for severe damage of body:

 

<50 V 30 mA 5 s

125 V 80 mA 330 ms

230 V 155 mA 180 ms

400 V 280 mA 70 ms

 

So, an electrical shock can be lethal in three ways:

 

1) Heart stops pumping. (The current overtakes control signals for the heart.)

 

2) Breathing stops - suffocation. (The current overtakes control signals for breathing.)

 

3) Severe internal burning degres. (The power from the current transformes to heat.)

 

Most people die of no:1 because AC, (which is normal power supply in houses for most people), causes spasms in Your muscles, thus You problably lose contact fast, but the heart may not restart again.

I have never heard of anyone get hurt or dying from an electrostatic charge.

[J.C.MacSwell]

From my understanding the internal body resistance between random different points of induvidial human bodys can be as low as 100 Ohms.

The skin when dry and clean can have a resistance up to 2 M Ohms.

 

From my safetybook of "Working with Electricity":

 

Loss of muscle control between 10-20 mA.

 

Difficulty with breathing between 20-30 mA.

 

Possible heart fibrillation between 50-100 mA.

 

Internal burning damage above 1 A.

 

Time dependency for severe damage of body:

 

<50 V 30 mA 5 s

125 V 80 mA 330 ms

230 V 155 mA 180 ms

400 V 280 mA 70 ms

 

So' date=' an electrical shock can be lethal in three ways:

 

1) Heart stops pumping. (The current overtakes control signals for the heart.)

 

2) Breathing stops - suffocation. (The current overtakes control signals for breathing.)

 

3) Severe internal burning degres. (The power from the current transformes to heat.)

 

Most people die of no:1 because AC, (which is normal power supply in houses for most people), causes spasms in Your muscles, thus You problably lose contact fast, but the heart may not restart again.

[b']I have never heard of anyone get hurt or dying from an electrostatic charg[/b]e.

 

A capacitor with an electrostatic charge can kill, although it is the current it creates that is lethal.

[YT2095]

<50 V 30 mA 5 s

 

the only problem I have with that (and I`ve chosen that particular one deliberately to illustrate my P=IV statement) is that when I was working as a welder, 50v at 90A whas the setting for the wrought Iron welding trans, often you`de be leaning on the jig changing a rod over and get a shock (tickle), we used to wet our hands and see who could hold on the longest, just for a giggle, 30 seconds + was about min, some incl myself could hold on all lunch break if need be.

the point being that although the voltage is at 50 and the current at 90 Amps (enough to melt 1/8" steel rods with), non of us died, and the reason is that the 90A is the POTENTIAL! on a dead short, factor in skin resistance then the amps drop, now factor that into the P=IV equasion and you`ll get a wattage rating, it`s the WATTAGE across the body that kills you, saying Volts or Amps is silly, it`s a mere PART of the whole

[Spyman]

A capacitor with an electrostatic charge can kill, although it is the current it creates that is lethal.

If only touching one of the poles of the capacitor, thus not creating a complete cicuit ?

it`s the WATTAGE across the body that kills you, saying Volts or Amps is silly

I agree that it's the wattage across-inside-through the body that causes the harm.

 

The examples from my safetybook is rough and a worst case scenario, simply to give an estimate how dangerous electricity is.

 

Thus 50 V could give 30 mA across-inside-through Your body, in a worst case scenario, which is enough wattage, (1.5 W), to cause harm to Your body, after 5 seconds the harm is considered to be severe from some standard safety level.

[J.C.MacSwell]

If only touching one of the poles of the capacitor' date=' thus not creating a complete cicuit ?

.[/quote']

 

Do capacitors have poles?

 

Capacitor contact to any ground would create current flow. (??)

[YT2095]

well you only need to look at a cardiac resucitator that uses 200 to 300 joules to shock the heart back into sinus rythm, the same can kill when in a normal rythm.

and that has to overcome skin resistance even though the conductive gell is used, it`s far from a "perfect" contact, a pacemaker sends out milli watts of power to keep the heart ticking over.

 

the key here is indeed the Intimate contact and thus lower resistance

[YT2095]

Do capacitors have poles?

 

Capacitor contact to any ground would create current flow.

 

of course they do, that`s how we charge them, and no contact with "ground" will not discharge a cap

[Spyman]

Do capacitors have poles?

Typical designs consist of two electrodes or plates' date=' each of which stores an opposite charge.[/quote']http://en.wikipedia.org/wiki/Capacitor

[Lance]

of course they do, that`s how we charge them, and no contact with "ground" will not discharge a cap

 

Unless the other side is grounded.

[YT2095]

LOL, yeah a dead short will do it

[jdurg]

Capacitors can easily kill a human. Inside CRTs there are very highly charged capacitors which have given off lethal shocks to people unfortuneate enough to touch them before they had discharged. Hence all the warnings on the outside of TVs and computer monitors.

 

Typically speaking, however, it is the amperages that need to be looked at when investigating a possible 'shock'. A simple 'rub your feet on the carpet and touch a metal door knob in the winter' type of shock is about 200,000 volts, yet the amperage is so low that it only causes a minor 'sting'. Typical household electrical lines (here in the USA at least) carry about 110 volts and I forget the amperage. However the amperage is sufficiently high enough that you can quite readily be killed by receiving a full shock. In the end, it's the combination of volts and amps that kills you. High volts and low amps will kill just as effectively as low volts and high amps. It's just that voltages are generally sufficently high enough that small fluctuations in amperage can be the difference between a lethal shock and annoying zap.

[J.C.MacSwell]

[url']http://en.wikipedia.org/wiki/Capacitor[/url]

 

So a capacitor is a pair (or more) of oppositely charged conductors. I had it pictured as a single charged (positive or negative) conductor.

 

So either pole won't discharge to ground due to the proximity and opposite charge on the other?

[YT2095]

for this instance, we can ignore it being a capacitor, and think of it as a battery instead with a + and - pole.

you need both poles in use to complete a circuit to draw power, touching any single pole to ground or anything else will not draw current.

same with a cap

[Spyman]

So either pole won't discharge to ground due to the proximity and opposite charge on the other?

The charge inside a capacitor is between the poles, like in a battery.

 

More, the charge is not a potential, it is electrical energy which includes a potential. A capacitor charged with X Volt is not charged with a potential, it's charged with so much energy that the potential between the poles has raised to X Volt.

 

Lets say a capacitor is charged to (with) 100 Volt:

 

- If the negative pole is connected to the ground then the positive pole will have a potential of +100 V with respect to the ground.

 

- If the positive pole is connected to the ground then the negative pole will have a potential of -100 V with respect to the ground.

 

- If both poles are connected to the ground, then the capacitor will discharge it's energy storage through the ground.

 

- If non of the poles are connected to the ground, then the capacitor will still hold it's energy with the potential of 100 V between the poles.

 

So when touching/connecting to both poles I view the capacitor as an power source and not a electrostatic charge.

 

Capacitors in power applications, like frequency converters, can easily store enough energy to seriously harm or kill a human, if connected to both poles.