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Tesla Coil Safety? Answered

My high school recently had an engineering fair, and my friend had built a tesla coil. Its has multiple spark gaps, an RF filter (I think thats what its called), a 120 to 20000v transformer, and toroid top-load, if any of that matters.
We/I would entertain ourselves by standing away from the coil and holding a fluorescent tube (by the glass with bare hands, not by the contacts) near the top-load and watching it light up. Even though I was well away from the coil, my forearm muscles would twitch, especially it the coil spark hit the contact on the other side of the tube. Then if anybody touched me, both of us would feel a shock and the same slight twitching (the same kind of twitching you feel from those electric muscle stimulators with the pads you put on sore muscles). We even set up a chain of about 5 people holding hands, and all of us would feel a shock, even though only the first person in the line (aka me)  was holding the fluorescent tube near the coil, with my hand on glass, no where within range of the streamers coming from the top-load.

Now for my question: is this dangerous? (I know its non-lethal, im talking about my nerves) And what exactly was happening? because it was not an incredibly large coil, and i know that the field of a coil is much larger than the actual streamers. I also read somewhere that insulators dont work the same at incredibly high voltages. I think what I was feeling was the skin effect, and the charge came from the excited electrons in the tube. If my ideas are correct, then wouldn't me holding the tube be just the same as if i had just put my hand near the top-load and let the streamers hit me?


Why could i feel shocks if I was only touching glass though?


"The operator and all spectators must maintain a distance of at least 20 feet (6 meters) from the Tesla Coil while it is connected to an electrical outlet, even if the main power switch is turned off. All persons must also maintain a distance of at least 10 feet (3 meters) away from the power transformer while it is connected to an electrical outlet, even if the main power switch is turned off. Note that under some conditions, the Tesla Coil is capable of producing arcs slightly longer than rated in the specifications."

This is from The Santa Cruz Institute for Particle Physics' Outreach Program, who do school demonstrations with a Tesla Coil which generates arcs about 5 feet (1.5 meters) in length.

The capacitance of the topload is going to be significant shock factors in larger coils.

Oh, and in every high voltage demo I have sen or done, objects waved near the device have been grounded by wires or chains.

Try a chain-mail glove with a length of cable trailing onto the floor.

I disagree with Frollard and Iceng. Tesla coil output is very high frequency, and simply doesn't pass into the body, due to something called the skin effect. You can however get RF burns if you do it too much.

The output current has to pass THROUGH your body to be harmful.

"Although skin effect limits Tesla currents to the outer fraction of an inch in metal conductors, the 'skin depth' of human flesh at typical Tesla coil frequencies is still of the order of 60 inches (150 cm) or more.[39][40][41][42][43] This means that high frequency currents will still preferentially flow through deeper, better conducting, portions of an experimenter's body such as the circulatory and nervous systems."


I take Steve's word on most everything, since he's read the reading, walked the walk, and now talks the talk (and probably been shocked by every type of electricity imaginable ;) ) but I must lean on the side of safety when it's called into question. Granted the info I linked is wikipedia, but it does cite MANY sources on this particular issue.
Rephrase from the site: you often don't feel the pain of 15-20khz current because your nerves are incapable of reacting before the current reverses, so you don't feel it but it's still there doing damage.

Like I said though, not a source of "fatal shocks", but potentially RF burns.

Also, the operating frequency makes a big difference. My experience is of systems operating in the Mhz.

Take the whole wiki article as a guide, and its instructive.


If suddenly one of the people in the chain became a good path to ground (easy to brush against a wall outlet), it quickly goes from 'not much current' because of the insane air resistance to A LOT OF CURRENT, with the voltage high enough to get into your body, and the current enough to stop your heart; yes, it is VERY DANGEROUS, and VERY POTENTIALLY lethal.

Don't take that as 'don't play with tesla coils' - but take it as, be safe. It is safe to be charged up to a bajillion volts -- its what you do with a van de graffe generator. Discharging that current through your body is what does damage.

The insides of a fluorescent tube conduct quite well, and while glass is a good insulator, a thin wall of it is nothing compared to 20kV.