[Besoeker]

I would never touch a 1F capacitor charged to say 30-40V.

Doesn't matter if it's a capacitor or the continuously rated 70kA heaxphase rectifier system I mentioned a few posts ago.

[Harmattan]

Current can definitely flow through vacuum where the voltage difference between any two points is zero.

Stop playing with words. Of course you are literally right. But there is no spontaneous electric current without a potential difference (which can be induced by applied voltage, different materials, different temperatures, etc). Ignoring quantum effects of course.

But sure you can always beam electrons. Which is irrelevant in the discussed context.

And Rancid is right: in normal conditions safety is about electric current, not voltage. As a proof you can hang yourself on a high-voltage power line: you will indifferently sustain a 50kV difference while there will be no current passing through. Just like a car crash's safety depends on speed, not gravitation, even though there is in some scenarios a relationship between gravitation and speed.

[Besoeker]

And Rancid is right: in normal conditions safety is about electric current, not voltage. As a proof you can hang yourself on a high-voltage power line: you will indifferently sustain a 50kV difference while there will be no current passing through.

Disagree. If you hang, like a bird on a single high voltage power line, there is no potential difference. That needs two points of contact to establish a voltage difference and you need that to get current flow.

[Harmattan]

That needs two points of contact to establish a voltage difference and you need that to get current flow.

Not at all: every point in space has an electric potential and the difference between any given couple of points is called a voltage and results in an electromagnetic force.

Just like every point in space has a gravitational potential and the difference between any given couple of points results in a gravitational force.

Joining two points of different potential with conductors simply results in those points' charges being allowed to move, which then bends the electric field, which then put in motion more charges and ends up bending the field to form a conduction path between the two electrodes. Just like moving masses (as a result of gravitational force for example) bends the gravitational field.

[Besoeker]

Not at all: every point in space has an electric potential and the difference between any given couple of points is called a voltage and results in an electromagnetic force.

So why don't we all experience electric shocks all the time?

[Harmattan]

So why don't we all experience electric shocks all the time?

Because thanks to the contact with the earth the difference of electric potential between our skins is usually not different enough. Usually charges' exchanges are not perceived. Shocks occur when there are thousands of volts of difference! There are too few charges to harm human beings but enough to damage some devices.

Shocks in daily life are typically caused by very insulating soles (not enough exchange with the earth) or clothes' friction that creates regions of opposite charges over your dielectric surface.

[Besoeker]

Because thanks to the contact with the earth the difference of electric potential between our skins is usually not different enough. Usually charges' exchanges are not perceived. Shocks occur when there are thousands of volts of difference!

An acceptance that voltage difference matters........but it doesn't need thousands to cause a fatality.

[Rancid]

An acceptance that voltage difference matters........but it doesn't need thousands to cause a fatality.

There are a lot of dependencies, which is why in some cases, a relatively small voltage can be fatal, and a much larger one isn't.

You're just going in circles now for the fuck of it, it seems.

[Harmattan]

An acceptance that voltage difference matters........but it doesn't need thousands to cause a fatality.

I just explained to you that if you feel a shock it means that there was a difference of thousands of volts! Which was harmless for you.

Voltage only matter indirectly because it can create a strong current in some conditions. Just like gravity does not harm you as long as you stand on the roof but will make you reach a high speed if you jump.

The speed will harm you, not the gravity. The current will harm you, not the voltage.

It is best to not put your fingers in a 220V electric plug, it is best to not jump from the roof. But gravity and voltage are directly harmless; you sustain them permanently without problem.

[Besoeker]

I just explained to you that if you feel a shock it means that there was a difference of thousands of volts

A difference of a hundred volts will make you feel a shock and it could be lethal.

[Besoeker]

An acceptance that voltage difference matters........but it doesn't need thousands to cause a fatality.

There are a lot of dependencies, which is why in some cases, a relatively small voltage can be fatal, and a much larger one isn't.

You're just going in circles now for the fuck of it, it seems.

Your erudite, polite, and most constructive post is noted.
I just deal with the realities.

[Harmattan]

A difference of a hundred volts will make you feel a shock and it could be lethal.

No: if you feel a little shock it means that there was a difference of thousands of volts between your hand and the ground! You can have thousands of volts of difference between your shirt and your pants. No problem, you do not feel it.

But when you do touch a conductor you allow the charges that created this difference to finally move according to this voltage. By moving they create a current. This current can have a high intensity and you can feel a little pain as a result. But because there were few charges on your skin and clothes, it is very brief and this is no big deal.

What matters if you put your fingers in a 220V plug is that there are many charges awaiting behind the plug (and on the power lines and such). In other words the plug can deliver a high intensity current (will deliver as much as your body's resistance allows). And there is the fact that it is AC.

But again voltage is exactly like gravity. This is why physicians talk about electric potential and gravitational potential, those are similar things. Voltage is just a potential difference, something that can dangerously put things in motion, not the thing that harm.

[Besoeker]

There are a lot of dependencies, which is why in some cases, a relatively small voltage can be fatal, and a much larger one isn't.

Care to cite numerical values for what you consider to be a relatively small voltage that could result in a fatality?

[Besoeker]

No: if you feel a little shock it means that there was a difference of thousands of volts between your hand and the ground!

That's absolute nonsense that no electrical engineer would accept.
That's why we have door interlocked isolators on 400V panels.

[Harmattan]

That's absolute nonsense that no electrical engineer would accept.

This is a fact, whether you accept it or not. Trust me.

That's why we have door interlocked isolators on 400V panels.

What matters is not the fact that there is a 400V voltage, what matters is that there are many charges provided by the power plant that would be accelerated by those 400V. And those charges would form a high and persistent current, which is the danger. Whereas there are only a few charges over your body, forming a not so high and very brief current.

This is why we keep telling you that voltage is not what matters. It only does if we are talking about something with plenty of charges behind it, that could be accelerated by this high voltage. Such as circuit connected to a power plant ready to provide a lot of charges.

In this case and in this case only, then those 400V become an indirect threat even if they are harmless alone. Gravity alone does not matter, but it does if you have three tons of rocks hanging over your head.

[Rancid]

Care to cite numerical values for what you consider to be a relatively small voltage that could result in a fatality?

How about you take a 1F capacitor, charge it up to different levels of voltage, and touch the leads. Then repeat that process. Start at 5V and increment up by 5V with every test run. If you want the voltage to be lower, then scrape off the top layer of your skin (the top layer is where most of the resistance in the human body is), and wet your hands in salt water.

Let us know when you find the lethal voltage. To keep this a bit more scientific, please calculate the amount of energy you are dissipating through your body with the following formula:




You can't be a power engineer. You simply cannot if you are not understanding this. Actually, that's not true, I've met many so called electrical engineers that don't really understand electricity/power/current/potential/etc. well, and could still do their job well. Sometimes you don't need a deep understanding if what you're working on is limited in scope, and doesn't require a lot of innovative thinking.

Do you really have a professional engineering license?

[Istanbuller]

Rancid's logic: Having deep understanding of engineering = engineering license

[Rancid]

Rancid's logic: Having deep understanding of engineering = engineering license

Well, I would hope that is the case.... I guess that's not really true.

Shit, this is one time where I can agree with Istanbuller. Just because you have a license and/or degree, doesn't really mean shit. It just means you studied for the test(s).

[Orestes]

Fucking nerds. I'm angry that I don't understand any of the above discussion.

The reason why earlier I asked about Leonardo is because he's mentioned in this article I've been reading, which argues against seeing Renaissance as that big of a breakthrough in scientific thought.

Also, all of the lists lack the Person of Jesus Christ - the greatest scientist of the human heart.

[mikema63]

I have to learn some of this now, neurons are apparently modeled the same way cables are. Except they are way more complicated than cables.