http://www.youtube.com/watch?v=SlNGKly09CQ&feature=related

So ummm yea. Why is he not dead eh?

I was reading how Tesla coils work recently. As I understand its just a huge induction transformer with a very high voltage output.

I also read how lightning works on howstuffworks.com to try and understand this better.

So Tesla coils produce as much voltage as lightning more or less right? The resistance of the human body becomes nothing compared to such voltages. So yea. Why is this guy not dead. Also why does he not look like a piece of burned toast?

My only thought is maybe the secondary coil is not able to source a lot of current. If this is correct, why not? Look at that step leader that is more or less striking the guy. That has to be kilo-amps.

I am interested in this because well I'm an EE no further questions needed. But also my friend and I are going to visit the Carnegie Science Center where they have a live tesla coil show and personally I want to sit close to it. Its my duty as an EE.

So can you guys guarantee me that I won't die unless I encase myself in rubber and glass?

 

The man is inside a faraday cage
http://en.wikipedia.org/wiki/Faraday_cage

 

So thats what that is. Okay I will give him that.

But I saw some portable tesla coils you can buy online that say, "safe, low current", and yet they still produce lightning and have a high voltage output.

I guess my question really is, how can a Tesla coil have a high voltage output, create lightning, and yet have currents safe enough that it won't kill you without a Faraday cage?

If the secondary coil cannot source a lot of current then why can't it electrically? And why does the lightning look so big if the current is so low?

I admit you can get some sparks with a 9 volt battery but come on.

 

The man is inside a faraday cage
http://en.wikipedia.org/wiki/Faraday_cage

That is one fah-ree-key pair of shoes to be in !!!

 

Because the voltage is so high. I don't really know too much about Tesla Coils, but what you are looking at is the ionized air created by the electric field (which is another way of saying high voltage).

There has been a back and forth on the forum, which some folks saying you can't have alternating electric fields without magnetic fields (in other words, RF), and visa versa. Me, I tend to point to the Tesla Coil as the counter argument. They also make electromagnets in junk yards that use alternating current to generate counter EMF in non ferrous materials, which allows the electromagnet to pick them up anyhow.

 

Current is what kills.. Voltage does not.

 

Yes and no. Voltage is what delivers the current. I have never seen anyone try to take a Tesla bolt unprotected.

 

Hmm, I don't know much about ionized air, except what I read in the lightning article. Also from wiki.

http://en.wikipedia.org/wiki/High_voltage

Voltages below about 500–700 volts cannot produce easily visible sparks or glows in air at atmospheric pressure, so by this rule these voltages are "low"

From the same article....

Voltages of greater than 50 V applied across dry unbroken human skin are capable of producing heart fibrillation if they produce electric currents in body tissues that happen to pass through the chest area

And this

Low-energy exposure to high voltage may be harmless, such as the spark produced in a dry climate when touching a doorknob after walking across a carpeted floor.

What exactly does the "low-energy" mean in the last quote?

Another article

http://en.wikipedia.org/wiki/Electric_shock

60 mA of AC (rms, 60 Hz) or 300–500 mA of DC can cause fibrillation.[2][3]

he NIOSH states "Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms.

So taking all these quotes together...

500V can produce ionized air.

I = V/R.... I = 500/(100,000) = 5mA.

Hmm so it seems not all ionized air will kill you, although it will hurt like hell. That is my conclusion. Of course I am taking ideal values and totally dry skin into consideration.

But this is a very interesting topic. I wonder how they determine their title of "safe portable Tesla coil". And how much we can trust them?

Please never say, current kills not voltage. I swear that phrase makes me go crazy with rage. Its not an answer, unless you explain what you mean. Actually power and energy kills. My friend who doesn't know much about electricity once said this phrase to me, and said oh well that means 500,000 volts wont hurt me. I facepalmed. So Please. Think what you are saying.

 

I just noticed something. How do these 3 quotes from wiki make sense when taken together? According to ohm's law they don't.

Voltages of greater than 50 V applied across dry unbroken human skin are capable of producing heart fibrillation if they produce electric currents in body tissues that happen to pass through the chest area

60 mA of AC (rms, 60 Hz) or 300–500 mA of DC can cause fibrillation.[2][3]

The NIOSH states "Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms.

I = 50/100,000 = 0.5mA

How the heck does 0.5mA kill you?

Is it duration? If you hold 50V over the part of the skin that is 100,000ohms long enough, the resistance will become lower?

 

If the man were not inside of the faraday cage he would be quite unhappy. Tesla coils produce high frequency-high voltage at low output currents. Obviously the output current and voltages increase with the size of the coil and streamer length.
The reason why you generally will not feel the shock from the small coils is due in part to skin effect, the resistivity of the human body and the inabuity of your nerves to register frequencies exceeding 20kHz.
Be warned, from personal experience with tesla coils... radio frequency burns can still occur and are extremely painful!

Here is a link I found explaining a bit about tesla coils and the human body. I cannot vouch for the information listed but at a glance it appears sound. http://members.misty.com/don/skin.html

Also, there is some information here as well. http://en.m.wikipedia.org/wiki/Tesla_coil

 

How the heck does 0.5mA kill you?
It can cause your heart to fibrillate (not function correctly).

 

It is indeed the current that kills. It takes voltage to deliver the current. However, the reason we don't drop dead from a ESD event is duration. But even then you have to allow for extremes, lightning qualifies as an ESD event. Sort of.

If I were to stick needles in your skin to your blood supply a nine volt battery would probably work, if the current went through your heart. But lets not experiment and say we did.

 

How the heck does 0.5mA kill you?
It can cause your heart to fibrillate (not function correctly).

Ahhh I notice wiki got their 50V value for the parts of your body that connect to the heart in some way.

Voltages of greater than 50 V applied across dry unbroken human skin are capable of producing heart fibrillation if they produce electric currents in body tissues that happen to pass through the chest area

60 mA of AC (rms, 60 Hz) or 300–500 mA of DC can cause fibrillation.[2][3]

The NIOSH states "Under dry conditions, the resistance offered by the human body may be as high as 100,000 Ohms.

So the summary of all this is, if you got 100mA going through your ass it wont kill you.

But 0.5mA going through your chest will kill you. Interesting.

No Bill we won't try to connect a 9V battery to my heart using a wire in my bloodstream. I'm crazy, but not that crazy.

But yea I'm going to sit close to the tesla coil in the science center. Will be awesome. Will take pictures.

 

This won't answer your question about tesla coils but you may find it useful. It is a photograph from my essentials of electricity text book. http://www.flickr.com/photos/51714097@N05/5662177682/

 

The resistance of the body (neglecting skin resistance) can be very low. Hence why they mention unbroken skin.. remove skin or soak yourself in water and those numbers vary greatly from the 100k ohms stated above down to as little as 50 ohms or less between organs/body parts.

And it is current kills.
You can have quite a high power number with high voltage but the current can still be very low and you may not die..

 

Please never say, current kills not voltage. I swear that phrase makes me go crazy with rage. Its not an answer, unless you explain what you mean. Actually power and energy kills. My friend who doesn't know much about electricity once said this phrase to me, and said oh well that means 500,000 volts wont hurt me. I facepalmed. So Please. Think what you are saying.

I've always heard "It's the volts that jolt but the mils that kills." In this case, 500,000 volts CAN hurt, but will not necessarily kill you. The idea is that usually higher voltage comes with a higher current. Tesla coils work in a way (with a very high frequency) that creates a very high voltage but has a low current that, due to the skin effect, often travels along the surface of your body. However, it is still not a good idea to touch a tesla coil's output directly for a couple reasons. One: If the frequency is low enough, the current can pass through muscles and nerves and cause serious health issues. Two: you never really know exactly how much current is put out by a tesla coil. I know some people who built tesla coils that had a fair amount of current on the output, and they were hurt badly when they accidentally came in contact with the arc. Either way, it is quite dangerous. I, personally, think getting in the way of the output should not be attempted in any way, unless you are in a faraday cage.
Der Strom

 

No bueno.

Mas pain.

 

Observe closely the man ALSO has hearing protection.

Tesla coils can be VERY loud, when you are only inches from the spark origin

 

I think may be due to low current even though their is high resistance will reduce the heating up of the conductor. I guess that might be the reason that we are not toasts...

 

I've had the spark from a small Tesla Coil go to a metal spoon I was holding (to avoid an RF burn from the spark) and I felt absolutely nothing.
The spark is such a high frequency that it mostly travels on the skin so is does no harm (due to the apply named "skin effect" and is not felt by your nerves.
Here's an interesting "fight" between two guys and a large Tesla coil.