Stefan's Tesla-Pages (safety page)


Some words about safety:

CAUTION: Tesla coils use and produce high voltage electricity. Tesla coils can be very dangerous, even lethal! You can easily electrocute yourself with one of these machines. You assume all risk and liability for your creation. Make sure you know how to proceed safely before you start!
If you intend to show your devices in public think of having an insurance.

The author of this document is an amateur, not a professional. The information provided in this document should be interpreted with this distinction clearly in mind. The author hereby disclaim any liability for injury to persons or property that may result due to the construction and use of Tesla coils and other high voltage apparatus. This document is for informational purposes only, and makes no claims to its completeness or accuracy. While some of the dangers associated with the construction and the use of Tesla coils have been pointed out in this document, other potential hazards may exist. Tesla coils are inherently very dangerous devices and should only be constructed and operated by individuals familiar enough with these dangers!

This is a free site. I reserve the right to shut it down, display invalid results, and fail in any way possible. The descriptions are not fault tolerant in any way and should never be used without common sense. I am currently continually upgrading this site. I put in new stuff frequently. While I try to avoid problems, brand new discussions 'have bugs'. Please send me descriptions of any problems you encounter. You may not use this information for any purpose which is considered illegal in your country. The knowledge is intended for free use. Any type of using the images or text without permission is forbidden. The entire site content is copyright by STK with all rights reserved (see also end of page for details).

These pages are only for the purpose to show other people how my systems were built and the way they work, NOT for the purpose to advise anyone to make his own Tesla coil or do any other things described on these pages! Some images on my pages are trick photographies, so don't try anything you see here, it could be lethal! The following risks/problems are associated with Tesla Coils:

For detailed information about the risks associated with Tesla coils, you should read the safety-hints on the TCML website, at least before you attempt to do something with high voltage. In this case read as much as you can about it, e.g. join some of the email-lists. Use your head and if you don't have any idea on how to do things safely then get assistance (mail or other coilers). Please have also a look at Sam M. Goldwasser's HV safety page (which is part of the Sci.Electronics.Repair (S.E.R) FAQ). BUT BE SURE TO RETURN TO MY WEBSITE!

Yes, it looks very cool when somebody touches the output arc of a TC or performs such stunts like Robert Krampf does. But this is not as save as many coilers will tell you. Some hints about the special dangers in doing this with conventional TCs:
  • In case of a flash-over from the primary to the secondary, you are in direct contact (!) to dangerous line frequeny currents (CW-coils don't contain these line frequency currents because they are direct fed by high frequency => no danger of flash overs with line frequency)
  • The big toroid of a conventional coil collects a lot of charge. The discharge current of this capacitor (yes, the toroid is a capacitor with the second plate being the earth) is only determined by the resistance of our body (1kOhm). Big toroid => high current => deadly (the skin effect which does not really apply for humans at these frquencies only REDUCES the current inside you, that means that if the total current is too high you will die despite the skin effect!).
  • There is a DC field around TCs (I think this is because of different mobilities of the positive and negative charges). This means you will be charged when you are in the vincinity of the coil before touching it. Human body model is 150pF (plus 1kOhm and 10µH in series) so you'll get a BIG zap if you touch the arc and DISCHARGE yourself though the coil. So you'll feel pain and you will make some reflex movements and perhaps touch a high voltage line this way. But don't even think of earthing yourself to prevent the charge accumulation. Think of the difference between sparks in air and power arcs to a grounded wire...

So please don't try to touch a high power TC!!! (or have at least someone with a defibrillator with you although this might not help anymore in some cases...)

Terry Fritz wrote on this on the TCML (6'99):
I would not try to touch the output arcs. In an untuned system, no telling what is going on. In general, touching output arcs is avoided these days. The voltage does not go along the outside of the body as thought for many years. I goes right into you. The nerves don't react to the high frequency but all the heating and cooking is the same as if it were DC. It is not considered safe.

Christoph Baumann writes on his website (
The Skin Effect Myth
It is a very common belief that Tesla Currents won't harm you if you touch a Tesla Coil, because of the so called Skin Effect. This is not true! The Skin Effect is connected with the specific restistance of a electric conductor. The electric charges penetrate the deeper into a conductor the lower the frequency and the higher the specific resistance.
At Tesla frequencies the charges penetrate ca. 40cm! into a human body. The reason why you don't get an electrical shock is that the nerves can't react at such high frequencies. But the electrical power is nevertheless absorbed by your body. This probably won't hurt at 100-200W output, but touching a large coil will "fry" your nerves internally.
Another risc is an arc from the primary to the secondary coil which would connect you to the really hurting and lethal currents in the primary circuit.
So don't touch a running Tesla Coil unless you really know what you are doing! And don't blame anyone if it zapped you though, you have been warned!
Created by Christoph Baumann Sep 1999
Last change: Sep 17 1999

See also this website for clarification on the old myth "skin effect on humans":

Don calculates a skin depth of 0.75mm in his wrist (much less than Christoph states, I still have to check this for myself). But this is only based on theory for homogeous flesh, actual humans are very inhomogenous. Don gives some advise why this small skin depth is still not safe:

1. Blood in blood vessels is very conductive and could make more current reach your heart than you think. Resistivity of outer regions of the body may be higher, forcing more current to the interior. Resistivity may be higher than I think - this issue can make current flow less confined to the skin than predicted. The nerve system in the heart may not have the frequency response I described above.

2. Some Tesla coil shocks have some low frequency component - such as if there was a voltage peak and associated charge on the secondary when current starts flowing to you and there is no charge or opposite charge when current stops flowing through you. This can be worse should the oscillation be unreliable for any reason. Although such a shock here may be not much, it could jolt you into bumping something and causing damage or causing you to contact a more lethal current somewhere else.

3. Non-shocking high frequency AC can cause burns. Should the burn penetrate through the dermis, it can take many months or years to heal and the burned tissue might never be the same again. Do note that if any muscle cells are totalled, they are generally not replaced - same as nerve cells. Nerve cell damage is often (not always) non-total, although non-totally damaged nerve cells can take an awfully long time to regenerate a long dendrite or a long axon.

Please read also:

Here is a measurement done for high frequency which depicts the skindepth in different human "material" (bones, fat, tissue, muscle flesh etc.):

The source of the measurement above can be found here:

Some data measured at my body:
wrist: diameter approx. 4cm => half diameter ~2cm
trunk (torso): "thickness" approx. 20cm => half thickness ~10cm

Even if we extrapolate the measurement benevolently, the skin depth at the wrist is 10 times the half diameter. Therefore the current will go completely through the whole "material" without any reduction in the inner parts! The same applies at the torso, where the skindepth is in the range of the half diameter.

Result: We can't really say the skin effect will apply to humans (or will have a significant effect on current distribution in critical parts of the body) at typical SGTCs frequencies (100-300kHz)! Even for plasma tweeters (27MHz), there will be no significant changes!

Remark #1: If the skin effect would have a significant effect on current distribution (skin depth in human skin in sub-mm range which in reality applies only at frequencies above 20GHz!), all the current will be distributed in a far smaller cross section: circumference of wrist is roughly 20cm, if we assume the current will flow only in the outermost 1mm, the cross section in which all the current is flowing is 200mm²; compare this with the total cross section of the wrist ~ 4*6cm = 2400mm². Without skin effect the current will distribute over a 10x higher area, therefore the current density without skin effect is only 1/10th, so the heating (P=I^2*R) is only roughly 1/100!

Remark #2: Skin depth should be proportional 1/SQR(f) in homogeneous materials as long as the diameter of the conductor is far bigger than the skin depth. The big decrease towards lower frequencies in the graph above (especially bones) gives a hint that the people who did the measurements took the sizes of humans already into account ;-)

A dangerous thing?

Subject: A dangerous thing?
From: Terry Fritz <>
Date: Thu, 13 May 1999 20:52:27 -0600

Hi All,

I don't mean to be morbid in our usually upbeat group but once in a while we need to stop and remember. Ours is a VERY dangerous hobby! Below are the brief accounts of the three people (that I am aware of) who have been killed...

Hernry L Transtrom - Electrocuted while working on a stage and using a large Tesla coil. He inadvertently allowed a power arc to go from his body to some metal framing that was part of the stage backdrop.

1992 - Graduate student intern working at McDonnell Douglas in St. Louis. A Tesla coil was being used to test aircraft parts against the effects of lightening. The intern got too close to the tank circuit and either bushed up against it or a spark left the circuit and stuck him. He never regained a heartbeat despite excellent CPR and paramedic responses.

March 29,1999 - An unsupervised 14 month old boy wandered into the poorly made AC line wiring of a Tesla coil. He was found some time later but could not be resuscitated. (see full article on bottom of this page)

It should be noted that the last two of these incidents may have gone unnoticed if it were not for the Internet. The possibility of there being others that we don't know about is very high.


A Tesla coil can be dangerous even in distances which were considered as save - if you wear a pacemaker. In February'00, the following posting appeared on the TCML at pupman:

Subject: Re: Pacmakers and Tesla coils = bad??
From: Terry Fritz <>
Date: Sun, 13 Feb 2000 20:14:43 -0700

Hi Stan,
WOW!!! When I was reading about pacemakers, it was implied that they could be accidently triggered by a number of things. I was not really "sure" a TC could do it but the things they described seemed like it would be very possible. However, this is proof that a 15/60 coil can trigger the defibrillator types at 25 feet. The people that have these are warned by their doctors what the jolt they give is like so they will be somewhat prepared. This is especially important if they are driving or something (Mark mentioned that they would normally be unconscious, but perhaps that can be programmed). Pacemakers can also be stunned into safe and default modes if their logic detects something is wrong. This may go unnoticed but they may not be able to operate as needed in such a fail safe state. The equipment that "talks" to these pacemakers may be able to detect and count the number of times they are affected.
There apparently are no official levels or standards of EM interference for these things. Different brands appear to be affected more or less. They are somewhat "hardened" against normal EMI but a Tesla coil is obviously quite abnormal in most EMI respects. CERN calls out 0.5mT but I am not sure that is well based.
It would be nice if we could come up with a "safe" distance or some maximum EM level but there appears to be no such data that would apply to all manufacturers of pacemakers. It looks like the only thing we can go by now is "Keep pacemakers FAR away from any TC!"
Many thank for this very important post on this subject!
Cheers, Terry

At 09:15 PM 02/13/2000 -0500, you wrote:
>I witnessed first-hand what a TC can do to a modern pacemaker. A fellow
>was about 20-25ft from a running 15/60 coil. It ran for maybe 30
>seconds then suddenly he shook violently and dropped down on to his
>knees. Apparently, the gap misfired or whatever and for a second the
>frequency of the output was abnormal and triggered his pacemaker. If I
>remember right his delivered 5J. Whatever it delivered, it scared the
>holy heck out of me and was very painful for him. Fortunately, the
>shock had no ill effects on his rhythm.
>Obviously this situation could have been disastrous. The TC could have
>triggered his pacemaker and sent his heart into an irregular beat, or
>perhaps worse could have quietly destroyed his pacemaker and would have
>never been noticed until it failed to shock when it was really needed.
>IMHO it's just not worth it. Keep pacemakers FAR away for any TC!

>Tesla List wrote:
>> Original Poster: Terry Fritz <>
>> Hi Mark,
>> I just want to thank you for adding this sort of expert addition to all
>> this. I got onto this pacemaker thing by accident, but the stuff I saw
>> really worried me!!
>> Having a pacemaker zap someone would be sort of unpleasant. However,
>> having it do ANYTHING it is not supposed to be doing is a real concern.
>> Tesla coils would be almost a worst case situation to find these ultra high
>> tech gizmos dealing with.
>> When they were just simply bipolar devices they were probably pretty immune
>> to a lot of things. However, the are now really sophisticated and they
>> could do a lot of harm if they were to get "confused". I think we need to
>> be extra careful of these things now!
>> Cheers, Terry

Another first-hand info comes from Dr. Resonance in his TCML-posting

Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>
I have a pacemaker in me. 4 x the strike distance has always worked for me.
Dr. Resonance

In the same posting, Peter Terren wrote:

Original poster: "Peter Terren" <>
<SNIP> Electric fields are not likely to be great under the skin. Pacemakers have to be noise tolerant and any dysfunction is likely to be only for the duration that the TC is running. Note that we use radiofrequency diathermy without problems in patients with pacemakers and this is applying RF voltages enough to burn, directly to the skin.

And another posting concerning people with a hearing aid:
Subject: Re: Pacmakers and Tesla coils = bad??
From: "Dr. Resonance" <> (by way of Terry Fritz <>)
Date: Mon, 14 Feb 2000 16:53:08 -0700

Already did some testing in that area with Medtronics (the large pacemaker mfgr in Minneapolis). At a reasonable distance of 6-8 feet nothing shows up that represents any danger to people with these devices. It did make a lot of noise in a hearing aid so we tend to warn them as well. We usually specify a distance of not less than 30-40 feet for all our shows with a 1 MEV coil operating at fundamental of 170 KHZ. Smaller coils running at 500 KHZ presented even less due to their lower power levels.

Dr. Resonance
Subject: Re: Damages to Electronic Equipment
From: Terry Fritz <>
Date: Mon, 14 Feb 2000 21:16:02 -0700

I have blown a telephone answering machine (AT&T) about 20 feet away. I can set off a CO2 detector 25 feet away. So the EMI off a Tesla coil can go far. It does not matter if there are walls or floors in the way.
Cheers, Terry
Subject: Re: Damages to Electronic Equipment
From: (by way of Terry Fritz <>)
Date: Tue, 15 Feb 2000 11:59:14 -0700

Coils eat computers for breakfast. My first coil killed a computer of mine last year. By the way keep your digital wristwatch away form them also.
Happy coiling, Leslie

A Tesla coil can be dangerous when used inside the house. In November'00, the following posting appeared on the TCML at pupman:

Subject: Apartment coilers beware! (1)
From: "Tesla list" <tesla@xxxxxxxxxx>
Date: Thu, 30 Nov 2000 16:52:06 -0700
Original poster: "Rick" <>

I thought I'd share this entertaining experience with you guys...

I've got a nice medium-size coil at home, in my town house / apartment. I've run it many times in the living room without too many problems. Sometimes I have to go around the house and toggle the power on my answering machine, computer, and stereo to get them to work again after a good run. That's a pretty good indication that I'm running out of room for an inside coil, but hey--I don't have a yard. What's a guy to do?

So, one day someone broke my coil by trying to lift the secondary while it was attached to its heavy plywood base. I had just fixed it a couple weeks ago when my friends came to visit who've never seen a well built coil before. They'd seen maybe 12" discharges, but I was getting at least 36". I was getting two streamers, so I decided to put all the topload I could find on it and retune. I tapped about three more turns out--the most I've ever done before. Unfortunately, the thick streamer coming off the top toroid ran out of room! It decided that it was just close enough to the ceiling to go up, instead of coming out horizontally. It must have been putting out a lot of energy because someone who was upstairs informed me that it lit up florescent tube propped against my bed and that a nearby metal can was giving off sparks.

Well wouldn't you know it, the coil springs in my mattress must have been arcing too, because my bed caught fire--big time. No direct hits, it was 100% induction that started the fire. I noticed also that a couple devices around the house were permanently dead, so I decided that my apartment coiling days are over =( I've got to find a new place to run my coil...

My fire extinguisher took care of the flames and my friends helped me drag the queen size mattress down the stairs and onto the sidewalk while we searched for one terrified pet. Someone drove by and decided to call the fire department--Doh! Just as we're pouring a little water on the smoldering mattress, we hear some sirens in the background, followed by the arrival of the police and a huge fire truck. The firemen jumped out with pitchfork-like things and wend to town on my mattress, then hosed it off... Took a look around the house, laughed, took some pictures, laughed, called their friends to come over and laugh at me, then told me to have a nice day and left.

I kept wondering how things would be different if the fire had started inside the walls... Just beware of the forces of induction, I guess. Put chicken-wire on the walls of your living room, or something =)

A Tesla coil can be dangerous when used inside the house. In December'00, the following posting appeared on the TCML at pupman:

Subject: Re: Apartment coilers beware! (2)
Date: Fri, 01 Dec 2000 08:05:01 -0700
Original poster: "Rick" <>

On 01-Dec-00 Tesla list wrote:
> Original poster: "Garry Freemyer" <>
> You got off lucky with the fire department. Here in the town I live in, they
> can make YOU pay $250 if the fire department has to come to your house.
> I too live in an apartment but I'm pretty lucky so far. I get sparks about 2
> feet long, I got filters on the chord to the wall. I cannot sink a grounding
> rod. They would have a cow and kittens if I tried.
> I cannot unpot an NST either. Flammable materials are not allowed.
> I cannot even do work on my car, not even so much as an oil change.
> I cannot wash my car either!!
> However, I'm lucky that nothing needs resetting when I run my coil, I don't
> even see interference on my TV in the next room. Not a snowflake.
> I run it little but I sure well understand your desire to move.

I'm not allowed to do any of that stuff either, but that doesn't stop me =) I've got 2 cats, which is 2 more than I'm allowed to have... hmm..

You see, the sad thing is that some dude driving by freaked and called the FD, not me!!! They really didn't need to come out and shred the remains of my mattress. It was all dandy and taken care of! Oh well.

I think the FD might try to collect a little money from property management, but it doesn't look like anything has come of it yet.

We actually threw the waterlogged mattress in the dumpster... Uh, "temporarily" until I could arrange to take it to the dump.

I woke up the next morning to the sound of the garbage truck and thought that they might refuse to collect our trash on account of a queen size mattress poking out of the dumpster. I peeked out my back-door peep-hole and watched as the overfilled dumpster went up and over the truck, then came back down empty.

Saved me the dump fee!

That last run also fried my stereo and my laptop modem... Both of which were also upstairs.

I remember my friend laughing as he said "And you wanted to hook up another transformer!" Well I guess if I had gone for another transformer instead of increased topload, my arcs might not have been so close to the ceiling....

Well, I'll pray on my stocks, cross my fingers, and hope for a 5acre plot of land in a few years. I've got a 15KVA 14,400v pole pig sitting in a closet downstairs =) I'm glad I don't have a 240 outlet here because I surely would have killed myself by now.

A Tesla coil can be dangerous when used inside an appartment. In December'00, the following posting appeared on the TCML at pupman:

Subject: Re: Apartment coilers beware! (3)
Date: Sat, 02 Dec 2000 14:17:15 -0700
Original poster: "Garry F." <>

>That last run also fried my stereo and my laptop modem... Both of which were also upstairs.

What I am worried about is what if you fry a neighbor's stereo or computer. You could end up evicted and also be paying to have someone else's computer fixed.

Try getting two of those magnetic rf filters that slip over your power cable. Maybe just maybe you will eliminate your problem. It sounds like some RF is getting into the ground wiring. If you can sink a rod or better yet, hook to a metal cold water pipe, that would be better.

A Tesla coil can be dangerous when used near flamable substances. In November'00, the following posting appeared on the TCML at pupman:

Subject: Re: Apartment coilers beware! (4)
From: "Tesla list" <tesla@xxxxxxxxxx>
Date: Thu, 30 Nov 2000 23:11:38 -0700
Original poster:

In a message dated 11/30/00 9:14:54 PM Pacific Standard Time, writes:

<< I always switch that light off when operating the coil, but one time while the coil was running I noticed a sudden "pop" and small explosion in the light switch on the wall. >>

Hi all,

I have another little accident story to add to this thread. I had already been firing my pole pig system for a few months when one day I was firing some pretty hot spark runs from it. Of course I had my earplugs in place while firing, but I happened to notice a "popping" noise above the noisy sparks thru my earplugs. I turned off the system and started to investigate. I found that a spark had struck a gallon jug of windshield washer fluid (methanol based) and also found that I had a nearly invisible fire going from the fluid scattered by the little explosion. The spark had penetrated the plastic wall of the jug and ignited the mehtanol based blue windshield wiper fluid inside. Fortunately, I didn't have much trouble extinguishing it once I discovered it, but I certainly could have burned down my shop, had I not been alert. Be sure to keep flammable materials away from sparking Tesla coils!

Sparkin' in Memphis, David Rieben

Man pleads guilty in son's death

The 14-month-old was killed by an electricity experiment built by his father, who is sentenced to one year, eight months in prison
Oregon News, Saturday, January 16 1999

By David R. Anderson of The Oregonian staff

A Southeast Portland man whose 14-month-old son was electrocuted when he played with the man's electricity experiment pleaded guilty Friday to criminally negligent homicide.

Ronald A. Turek, 33, agreed with prosecutors to a sentence of one year and eight months in prison. However, if Turek is accepted into the Shutter Creek boot camp, he could be released in seven months. By making the agreement, Turek avoided a second-degree manslaughter charge and a possible Measure 11 sentence of five years and 10 months in prison.

Multnomah County Circuit Judge Julie Frantz accepted the plea and sentence, saying it was a just resolution to the case.

Turek's lawyer said after the hearing that the case was tragic.

"He's in his own private prison for life," said Mark Smolak. "This was his only child, and that's something he's never going to forget. He's extremely remorseful."

Turek declined an opportunity to speak during the hearing.

Prosecutors agreed that Turek should be eligible for boot camp, in part because he has no prior criminal record.

"I feel very comfortable with this resolution," said Chuck Sparks, a deputy district attorney. "This man was not an uncaring human being who didn't love his son. He did something that was very reckless and negligent."

On March 29, Turek drank six 16-ounce beers over the course of four hours, the equivalent of three quarts, Sparks said. Turek, a single father, fell asleep on his living room couch with his son.

While he slept, the boy, Ronald Turek Jr., apparently got past barriers that Turek had placed in his living room around an electrical apparatus that appears to create an arc of homemade lightning.

Turek built the device from a manual but did not completely follow the directions, Sparks said. For example, Turek used an ungrounded source and kept it plugged in. Two electrical engineers hired by prosecutors said the device was "highly dangerous," Sparks said.

When Turek awoke after sleeping about four hours, he found his son and tried to resuscitate him, but the boy was dead.

Smolak said the device was a Tesla coil, which produces an arcing high-voltage discharge from a low-voltage source.

Smolak said his client did not dispute the major points of the prosecutor's case but maintained that a faulty extension cord that Turek had modified, not the electrical apparatus itself, caused the boy's death when he spilled saltwater from the experiment.

The boy showed no signs of prior abuse, said Portland Police Detective Sgt. Jon Rhodes, who investigated the death.

"It's a sad case," Rhodes said.

Be careful with high voltage or you will end like the Furby in this test <>!

How NOT to build and operate a Tesla coil... (part 1)

A Christmas Story for Coilers
by Fr. Tom McGahee
(Originally written Christmas of 1998)
(Slightly Modified for Christmas, 1999)

The story begins innocently enough... Meanwhile, out in the garage, Bill the Frankfurter was busily lashing together his latest concoction: In keeping with the Christmas Spirit, Bill was building a rather large Christmas Decoration for the front yard. To the uninitiated it looked simply like a large aluminum Christmas tree mounted on a pedestal of some sort. In reality, the aluminum Christmas tree was merely the Topload on Bill's latest Tesla Coil. Bill knew full well that the geometry of the tree did not really lend itself well to being an EFFICICIENT topload. But that was all-right. Bill was more interested in shock value than he was in efficiency. Actually, the pedestal was the "extra" coil of Bill's experimental Magnifier Tesla Coil. According to his calculations the "extra" coil should be capable of throwing arcs at least 6 feet long. One of these days, if he could manage to scrape up the necessary cash, he would try building one of those as yet untried polymorphic toroid structures designed by that guy who was advertising plans for them on the Tesla List. But not today.

He chuckled to himself as he struggled to move the "extra" coil and Christmas tree topload out of the garage and onto the front lawn. His wife was currently curled up in front of the fireplace with a romance book and two cats. Bill hated cats, but for the sake of his wife he tolerated their presence in his home. Bill strapped the coil/tree assembly to the top of the little American Flyer sled, and wrestled it into position on the front lawn. The final position was about 7 feet away from the shoveled walkway that led from the street to his front door. Bill always used the side door, but he had In-Laws coming over tonight, and *they* always used the Front Door. He figured the 6 foot arcs would be hurled mostly upward, and there would be no chance of the arcs actually coming any where near the In-Laws as they came down the little shoveled path that he had prepared.

He carefully positioned a couple of dozen old polyethylene buckets to hold the transmission line, which was several lengths of 1/2 inch copper tubing that he had brazed together. He giggled to himself deliriously as he fastened the transmission line in place and attached it to the base of the "extra" coil. Then he attached the other end of the transmission line to the anti-corona ring of his secondary coil.

The secondary coil consisted of a single layer of high voltage test prod wire wrapped in a solenoid fashion around a fair-sized plastic garbage can. The test prod wire was "on loan" from Bill's employer. The employer was unaware of this fact, but Bill appreciated his generosity all the same. The garbage can was a slightly used Rubber-Maid garbage can that Bill had swiped from the kitchen earlier in the day. The garage was permeated with the odor of aging tuna fish. The plastic garbage can was nestled inside a piece of slightly damp cardboard sonotube that was several inches larger in diameter than the garbage can. Bill had "borrowed" the sonotube from a construction site a few blocks away that was not very heavily guarded. One of these days he would return it. If he managed to remember, of course... The primary consisted of several turns of heavy battery cable that Bill had found laying around in the back of one of his buddies' trucks. (All of Bill's buddies drive trucks...)

Most of the high voltage capacitors were homebrew poly caps in sections of PVC pipe and under mineral oil (actually an off-brand of cattle laxative that he had seen mentioned by Gary Weaver on the Tesla List.) Not being able to find any decent clear poly, Bill had managed to scrape up a mixture of "construction" grade poly (that had lots of interesting things imbedded in it), and some smooth and shiny BLACK poly that he thought might work well, despite his fleeting concern that it might contain large quantities of carbon in the form of lampblack. What the heck, what did he have to lose by trying???

Dozens of these capacitors were wired in series - parallel to achieve the required voltage and capacitance rating. Just a few days before, he had discovered a mistake in his calculations and had realized that he still needed more capacitance. Remembering a series of posts on the Tesla List about MMC and EMMC caps, Bill had decided to try his hand at making EDEMMCB caps. (Extremely Dangerous Extended Monolithic Modular Capacitor Banks) Let's see, now, he was sure that Terry Fritz or one of those guys had posted something about being able to run them at something like 3 times their rated DC voltage. So with his 14.4KV One Eared Pole Pig he would need about a 4.8KV rating on the caps. Being a somewhat conservative kind of a guy (at least when it comes to things electrical), he decided to round that up to a 5KV DC rating. He smiled broadly at the thought of all the extra margin of safety he had engineered into this EDEMMCB capacitor.

He had purchased one hundred .1 microfarad 500 volt DC off-brand snubber caps at the local Radio Shack for a buck a piece. What the heck. It was Christmas. He could afford to splurge a little. He didn't have any of that printed circuit board stuff to mount the capacitors onto, so he just spot soldered strings of ten capacitors together. He kept the leads the full length and just spot soldered the very ends of the capacitors together. That way if a capacitor were to accidentally fail he could just snip off the very end and turn them back into Radio Shack for a full refund. The only problem with leaving the leads so long was that the strings of capacitors were quite long. Fifty inches to be exact. He wasn't about to waste any precious money on high megohm resistors, so there were no bleeder resistors across any of the caps. The ten strings of capacitors were laid out side by side on the concrete floor. As was his custom, Bill lashed all the capacitor strings together using Radio Shack clip leads.

Imagine Bill's consternation when he measured the total capacitance of his poly caps and EDEMMCB capacitor only to discover that he was still off by .01001 microfarad from the magic capacitor value that TESLAC had spit out.

Not wanting to spend any more money and time on poly caps or more strings of EDEMMCB caps, he decided to revert to making the tried and true Beer Bottle Caps. He had tried making Soda Bottle Caps once, but they were not nearly so much *fun* to make as Beer Bottle Caps.

Bill had invited a couple dozen of his closest friends over for a Bring Your Own Booze - Beer Bash. His wife finally busted up the party at 4 AM Sunday morning. Bill emptied out whatever beer still remained in the bottles (I leave it to your own imagination to figure out just how he did this). After many many trips to the bathroom he finally had all the empty beer bottles he needed. There were a fair number of aluminum cans as well. These he put in the plastic garbage bag in the kitchen. While his wife wasn't looking he stole all the aluminum foil and corn oil and salt that he could find and proceeded to build a couple of tub-fulls of beer bottle caps, which he then wired into the existing capacitor grid using his few remaining Radio Shack clip leads.

The spark gap was an old circular saw blade that was missing a couple of teeth. Why bother to pay big bucks to that Wingate guy for a precision built and properly balanced tungsten gapped rotary spark gap with G-10 fiberglass wheel when you could make your own for next to nothing? Bill's own rotary spark gap was powered by an ancient single phase AC motor that Bill had scrounged from the local dump for a few bucks. The motor and circular saw blade were connected via a belt and pulley arrangement, since the shaft of the AC motor was somewhat bent, and could not reliably direct-drive the saw blade. As it was, when the spark gap motor was powered on, the wooden base to which the entire Spark Gap assembly was bolted would shake all over the place and make an awful racket. Bill had jerry-rigged a device that allowed him to vary the phasing on the spark gap by rotating the motor by pulling on a four foot long two-by-four. Bill had wanted to use a ten-foot-pole, but Malcolm Watts told him that nobody would want to come near it with a ten-foot pole. That seems to have convinced him.

Looking through the archives, Bill had found a posting by John Freau on how to convert small AC motors into fully synchronous motors. Oblivious to the fact that the conversion pertained only to SMALL AC motors, Bill modified his motor anyhow, and found that after filing away large chunks of his rotor that the modification only made his motor lopsided. Now it REALLY jumped around when he turned on the power. So he held the rotary spark gap assembly wooden base plate as still as he could by temporarily holding it down with a couple of old lawn mower engines that he had hanging around. He made a mental note to drop John a nasty note telling him how useless his modification had been.

Back a few feet from the spark gap was the one eared pole pig. Thick high voltage cables snaked across the floor from the Pig to the Spark Gap and the rest of the Tesla Coil. Not wanting to cut the cables, (which he had borrowed from work without asking) Bill had left each cable its original length of fifty feet.

The pig was fed a diet of 220 VAC from a 100 amp service line. Now, the pole piggie was only rated at 10KVA, but Bill had read somewhere on the List that you could actually push a pig to two or three times its rated power capacity if you kept the run short, (so that you didn't boil off all the oil). Bill planned to test out this theory tonight.

Now, Bill SHOULD have had a number of things that he didn't. Such as common sense, an ON/OFF switch, and adequate fuses. Bill just couldn't bring himself to pay good money for something that was designed to self-destruct. Instead of fuses he had placed large metal bolts in the fuse holders. Much more robust, don't you think??

Being something of a cheapskate, Bill had decided not to bother with installing a silly little thing like an ON/OFF switch, because the guy at the dump wanted more than two bucks for the ones he had in the big box marked "Electrical Stuff". He knew that he needed something to limit the current to the pole pig, so he decided to wire a couple of defective toaster ovens and a couple of strings of Christmas tree bulbs in *parallel* with the primary of the pole pig. He could have SWORN that he had read a post somewhere (maybe on the Tesla-2 List) about putting some sort of a load in series or parallel or something or other with the transformer primary.

Bill knew that a variac was really a "must", but he didn't have one. He was originally going to use a 5 amp Triac that was on sale at Radio Shack, but when he got there they were all out. But then he remembered having read a post that seemed to imply that you could modify a three phase AC motor to act as some kind of a variable transformer. Sneaking into the dump under cover of darkness, he liberated a 400 pound three phase AC motor that had once seen service in an office building as the elevator motor. Luckily for him he owned a truck with a crane attached. Heh heh. A few whacks with an axe in just the right places and he had de-commisioned one set of windings. He knew he only needed two. But which two? He hoped it was the two that still remained. He welded two metal stubs to the casing and then welded a three foot length of one inch diameter solid steel rod to the rotor shaft. Now the motor shaft could only turn 90 degrees.

It was still a minute or two before the In-Laws were scheduled to arrive. One last check and Bill was ready for an operational test. He turned on the rotary spark gap motor. Whump! Whump! Whump! Whump! Whump WhumpWHUMPwhumpawhumpawumpawupa... Yes, the spark gap assembly was a bit, uh, vibrational, but seemed to be holding together OK. Bill lined the plug up with the socket (remember, he had no ON/OFF switch), and rammed the plug into the socket. BZZZZSHHHT! The spark gap lit up with bright actinic light and would have fried Bill's eyeballs in no time at all if not for the fact that Bill (always safety conscious) had quickly put on a pair of welding goggles. Now he could look at the spark gap arc with impunity. Which he did. Unfortunately, the goggles were so dark that that was ALL that Bill could see.

Carefully shielding his eyes with his left hand, he used his right hand to gingerly lift the goggles and look at the Christmas tree on the front lawn.

Outside, the Christmas tree came to life with a pale glow of pink and blue corona that fuzzed out for about two feet. But no arcs. No streamers. What a bummer! He stuffed another wad of cotton in each ear so that he could think again, and taking a deep breath of the ozone-soaked air, he groped his way over towards the modified three phase motor. Grabbing a hold of the metal rod, he strained to change the angle of the rotor. Suddenly a forest of fierce white arcs as thick as his arm broke out between the primary and the secondary. DARN!

He released the control rod. TWANG!!!! The rod slammed itself into the short stub that acted as a stop. Bill yanked the plug out of the socket. This was not an easy task, as the plug was sort of welded into the socket. But a few good whacks with a monkey wrench and the plug came loose. The only sound was the whappawhappawhapa of the rotary gap assembly, and the insistent buzzing that was only in Bill's ears. DARN! The secondary was arcing to the primary. Maybe if he added a capacitive load to the secondary he could get this sucker to stop arcing. He looked around for something... anything... to use as a capacitive load. His eyes came to rest on the leering sharp-toothed smile of his butane tank work of art, the Halloween Tank-O-Lantern. To amuse the neighbors and anyone else foolish enough to approach his house at Halloween, he had fashioned a gruesome Tank-O-Lantern by using a cutting torch to fashion leering eyes and drooling teeth from the once-smooth surface of the butane tank. The various burn marks from the cutting torch operations made the tank look even more sinister when the light played on it just right.

Grabbing the Tank-O-Lantern, he managed to get it to sit on top of the existing anti-corona ring. It wobbled a bit, but what the heck.

For the second time that evening, Bill rammed the plug into the socket. Again the spark gap burst into life. The horrendous roar of the spark gap beat against his ears as he grabbed the control rod and pulled. A fierce blue corona outlined the eyes and teeth of the leering Tank-O-Lantern, and as he gleefully peeked out from under the welding goggles, Bill could plainly see that beautiful two to three foot arcs were issuing forth from the branches of the aluminum Christmas tree. Not bad. The system was obviously a little out of tune, and he didn't have much more time before the In-Laws would arrive, so he would just have to run it the way it was. But he wanted the tree to look a bit more Christmas-sy so he whacked the plug with the monkey wrench again and turned off the high voltage. Then he made a quick surreptitious trip to the attic and got some really awful Christmas ornaments, (the ones that his In-Laws had given him and his wife years ago), and used them to decorate the tree.

Unknown to Bill, while he was out decorating the tree, his wife came out to the garage with a bag full of garbage that she didn't want in her kitchen for her parents to see. Looking around in the garage she spied what she knew was a plastic garbage can sitting inside what looked like a cardboard container of some kind. Seeing no other garbage container around, she decided to dump the load of trash into the plastic garbage can. So she did. And with interesting results.

Bill was totally unaware that the coupling and inductance of his coil had been changed slightly by the addition of various beer cans and tuna fish containers that had been dumped into the core of his beloved experimental Magnifier Coil.

The addition of the gaudy glass Christmas tree ornaments had little effect on the capacitance of the Christmas Tree Topload, but Bill's last-minute addition of a large copper toilet ball to the very *top* of the tree had changed the isotropic capacitance of the total topload just enough that the "extra" coil and topload were in perfect tune.

When Bill saw his In-Laws exit their car and begin their trip down the shoveled walkway that led within a few feet of the Christmas Coil, he stationed himself next to the power outlet and waited until they were at just the right spot.

His face twitched nervously, and he made a strange gurgling sound as he waited anxiously for his In-Laws to reach the perfect spot. And then they were there.

Gleefully he jammed the plug into the socket and then ran excitedly over to the control rod. Little beads of sweat broke out on his forehead as he grasped the rod firmly with both hands and pulled madly back on the control rod.

Meanwhile, inside the garbage can secondary, RF induction heating was taking place on the cat food tin cans. The heat caused the garbage to shift suddenly, and in that instant a wonderful serendipity took place. For a few fleeting cycles, PERFECT resonance was achieved! Megawatts of energy happily surged back and forth in the slipshod tank circuit of the amazing Christmas Coil. Phase angles slipped past one another invisibly and fell in-synch. Due to a couple of missing teeth on the makeshift rotary spark gap's circular saw blade the caps ceased to fire for a moment, and the capacitor bank experienced an Anomalous Resonant Rise. An instant later the excessive voltage caused a particularly massive dump of energy into the primary circuit at precisely the right phase angle, and the resulting surge in energy passed from the base of the wildly glowing Tank-O- Lantern down the copper tubing transmission line, which looked as though it were ringed with fire. The transmission line was just exactly the right length to allow the electrical wave travelling down it to slam into the base of the "extra" coil precisely at a zero voltage, MAX current node. Richard Hull would have been proud. The "extra" coil and the Christmas Tree Topload with round copper toilet ball were exactly matched to the impedance required, and the massive driving force of megawatts of resonant energy caused the "extra" coil to react like a spring that had been hit hard with a hammer. The resulting jump in energy caused the voltage at the Christmas Tree to exceed the breakdown voltage of the winter air. With a mad, screeching KaBOOOM the air broke down, and a single solitary streamer launched itself into the cold night air. Up, UP, *UP* it surged, sending a seething, writhing, liquid bolt of pure white electricity stabbing through the darkness. Then, seeking the path of least resistance, it arched over and began its lethal descent. Escaping the intense electrostatic forces that existed at the surface of the aluminum tree, the mighty bolt of man-made lightning swerved around and headed straight for the nearest conductive object it could find!!!

The In-Laws would have been toasted alive were it not for the one object that caught the Arc's attention. Beyond the In-Laws, a good twenty feet from where the Lightning Bolt had launched itself from the infamous Copper Toilet Ball, was an old fashioned lamp post. It put out a dim but somewhat cheery quantity of light that seemed to beckon to the Wayward Lightning Bolt. Like a giant white arm, the lightning bolt swerved around from its upward climb and slammed full force into the cheery lamp post.

PHHHHHHHT! KABLAMMMMM! Like a gigantic flash lamp the lightning bolt lit up the night with an instant of blinding whiteness and a deafening BLAM that reverberated in the In-Law's ears long after their knees had stopped shaking. Where the mighty arc hit, the metal of the lamp-post went incandescent and exploded into a shower of hot sparks that rained through the air and burnt their way through the snow.

The momentary surge of primary current was too much for the EDEMMCB capacitor strings. One moment they were as cool as the night air, then the next instant they exploded like 100 Chinese firecrackers. When the EDEMMCB caps exploded this placed too much of an electrical burden on the other capacitors in the system. First the Beer Bottle caps shattered and sent shards of glass whizzing in all directions. Then the once-sturdy home-made rolled caps exploded like a bunch of defective cannon. They all burst at once and spewed hot liquid laxative throughout the garage, and all over poor Bill, who was already feeling pretty sh***y as it was.

A flash of light. A moment of raw, awesome beauty, a might explosion, and then DARKNESS as all the electricity for blocks around ceased to flow.

It is a Christmas that Bill will always remember. It is a Christmas that his wife and In-Laws will never let him forget.

***** This is just a story. Any resemblance to any persons living or dead named Bill is merely coincidental.

  • As the author of this tale I want to say that the story is not meant to be a plan for how to build your own Arcstarter -er- I mean, Magnifier Coil.
  • The theory contained herein is only partially believeable, and is not meant to be a factual accounting of what actually happens in a Tesla Coil.
  • This is not an endorsement of Radio Shack or any of their products.
  • Cat lovers will please refrain from sending nasty e-mails to either Bill or myself.
  • Plans for the Christmas Coil may be made available if enough persons are interested. I should mention that the plans are purely experimental, which is why I will only be charging a token $25 for the plans.
  • I hope that all of you enjoy this little romp in the spirit in which it was written. I hope that none of those mentioned by name or otherwise implicated in the plot take offense at what has been written.
  • I wrote it especially for my good friend (at least he WAS my good friend), Bill the Arcstarter Pollack. But, as the disclaimer said, it is not actually ABOUT him. Even though he does hate cats and builds Tank-O-Lanterns, and dabbles in Tesla Coils. This story is just about a Bill who happens to be an awful lot LIKE Bill Pollack. The real Bill would *never* borrow anything from work without asking. He is beyond reproach. He is my friend.

Written by Fr. Tom McGahee
(reposted on the TCML in November2000)

How NOT to build and operate a Tesla coil... (part 2)

Subject: Re: What do you use for ballasting?
From: "Tesla list" <>
Date: Tue, 09 Jan 2001 08:02:33 -0700
Original poster: "Bert Hickman by way of Terry Fritz <>" <>


As long as you rectify the HV and use diodes to prevent backfeeding into the supply this approach should work. However, there is a problem with doing this directly from an AC source, especially with an ASRG. The difficulty arises when the tank cap has been partially charged but the voltage is insufficient to fire the main gap on the next presentation. If, on the next charging presentation, the voltage on the partially charged tank capacitor is significantly greater than the incoming HV charging voltage, the capacitor will discharge back through the secondary of the transformer, driving high energy pulses back INTO your 240 volt mains supply... and to those being served from the same distribution transformer!

One of the coilers who used to be on this list this some years back, tried this approach without backfeed prevention - the resulting voltage spikes blew out incandescent lights in his NEIGHBOR's house... :^)

-- Bert --

Bert Hickman
Stoneridge Engineering
Web Site:

Tesla list wrote:

> Original poster: "Steve & Jackie Young by way of Terry Fritz <>" <>

> Mike,
> Well, if you want to be a pioneer and adventurous, try the following version
> of "8) Other", which may not need any ballast at all!?

> Since you have an SRSG, consider adding more stationary contacts so the SRSG
> acts like a SPDT switch. In position one, it will charge your tank cap
> completely independent of the primary. In the next position, the tank cap
> discharges only into your primary. And the cycle repeats, repeats, re...

> In this arrangement, you never have the spark gap directly across your PT,
> so no power arcs. And the secondary tank circuit is entirely isolated from
> the PT (position 2 bangs), so no RF protection circuits are needed.

> I know this will work well with DC, and I am hoping you or someone will try
> it with AC and a properly phased SPDT SRSG. PT current will be proportional
> to and limited by the break rate (and your voltage controller variac, of
> course), so you may need little or no ballasting. (If I am overlooking
> something, someone please jump in and set us straight.)

> --Steve

Some more thoughts on grounding and a defined "target" for the sparks:

Good grounding is essential even when playing with DC cascades!

GTL-member Björn played with his 8 stage cascade when a spark went into the concrete floor of his attic (160kV, 10J). The cascade was driven without any connection to the line but from a battery instead and earthed at the water pipe. The spark resulted in an instant power outage and a destroyed 100W lightbulb. It was not the GFI which interrupted the current, but the 16A circuit breaker! Seemed as if the HV which entered the line has arced across the socket of the light bulb. Luckily this place was found easily, but think if this damage was done inside the wall where it could have started a fire some days later...!

So use a good ground and prepare a defined discharge path, be it for AC, RF or DC!

TCs and cameras:

On 25.02.03, GTL-member Stefan B. asked, how dangerous TC sparks and arcs will be to digicams. Jens R. replied that he hasn't lost a digicam yet but the automatic exposure of two conventional cameras! The first one in 3m distance to 80cm arcs, the second one in 6m distance to 2.5m arcs.

TCs compared to electrical fences:

Electrical fences (at least in the EU) dump up to 10J into the poor cow touching the fence. But, different to a TC-capacitor, the internal impedance of the generator is quite high in the range of 300-600Ohms. Therefore an electrical fence is far less dangerous than a TC system with the same energy.

Dave Sharpe reported about a good safety training he got in summer 2004 (

NFPA 70E Training outcomes (Ref: Safety Training...)
To: tesla-at-pupman-dot-com
Subject: NFPA 70E Training outcomes (Ref: Safety Training...)
Date: Thu, 26 Aug 2004 07:35:20 -0600
Original poster: Sparktron01-at-comcast-dot-net

I attended this training several weeks ago (2 days). There were many videos of severe injuries and fatalities arising from "Arc Flash/ Electrical Explosions", and several videos of staged electrical explosions (up to 15kV -at- 5kA) that were frightening to say the least (see Bert Hickman's video of the substation catastrophic KABOOM to have a similar reality check). The interesting take homes and statistics from this training are:

  1. 80% of nationwide electrical fatalities involved qualified electrical personnel (i.e. they had multiple years experience in electrical trade).
  2. Many fatalities involved "gettting comfortable" in your job, and eventually leads to shortcuts being taken (complacency). On HV gear this is an invitation for disaster.
  3. HV and high power LV equipment can have equipment failure, and if you are near it when it lets go, all bets are off unless you have PPE on. Water expands from liquid to vapor 1700 times it's liquid volume. Copper vapor / plasma expands 64,000 times (!!!!!) its original solid volume. Under a high energy fault condition, this will result in a violent thermal explosion with molten debris, and electrical plasma being ejected at high velocity, with a time duration of 0.5 sec or less. Impact energies can be suffciently high to shear 3/8" steel bolts. Imagine several thermite grenades and sticks of dynamite going off in confined quarters simultaneously...
  4. Many folks have died by bad meters, meter leads, or making an ASSumption that the power was turned off and no back feed path existed. If a DVM is not rated for class III (CB panelboard) service, and a high energy HV transient causes an arc over internal to meter; can result in a meter explosion. The moral of the story is DO NOT risk your life using a $3.00 Harbor Freight (or similar) DVM's, use an industrially rated meter if working on high power/energy circuits that may be live. Also if you have to replace the meter fuse, replace it with the EXACT replacement, they are usually designed with higher then normal interrupting and voltage clearing rating (AFAIK Fluke uses 17kA / 1kV ceramic cartridge fuse in ammeter circuit as an example).
  5. Circuit breakers should be mechanically exercised ONCE A YEAR. This was a revelation to me, but with our TC's of various flavors pounding our house panels, please take heed. The CB mechanism can be uncalibrated by extended time running at 90-95% of breaker ampacity by internal heating. This may preclude the breaker from operating at all. If you operate the breaker and it does not "feel" right, or sounds "mushy" when the contacts open and close; REPLACE THE CB. It is cheaper then replacing your house!
  6. Fuses are a much more reliable high energy interrupting means then CB's. They are commercially available with interrupting ratings to 300kA, and low-peak fuses will clear a high energy fault in less then 1/4 cycle 60Hz (4 millisecs). Low peak fuses also dramatically limit arc/flash exposure.
  7. Use GFI's, they are lifesavers.
  8. Wear cotton clothing rather then synthetics when working around HV or high energy circuits, the synthetics when exposed to arc/flash can melt into the skin and cause severe 2nd and 3rd degree burns.
  9. Avoid working on HV circuits alone, use the "buddy" system.

Be safe out there...

Dave Sharpe TCBOR/HEAS, Chesterfield, VA. USA

What happens if you discharge a high voltage high energy storage capacitor charged to 9kJ through a watermelon in the form of a 9kV, half million ampere discharge?
Here is the answer:
 +  +  =  
Image (© by Kelly Drews Photography)
taken with permission from the website of Sam Barrows

Ok, that was the amusing part.

Now please think about the difference (electrical wise) between a watermelon and a human hand, arm, leg or whatever. Yes, there is no big difference.
That means if you would touch a charged high energy high voltage capacitor, the result will be the same: there will remain only a big mess of bloody flesh... 

Please treat every charged HV-cap with the respect it deserves!  

PS.: Keep a fire extinguisher in the coiling room at all times. Make sure you get the type that is safe for use on electrical fires. Water is bad here for obvious reasons (though the professionals use it in form of millions of small droplets - but don't try this on your own!). Powder also is only for use below 1000V, makes a LOT of mess and, even more important, when used inside a room, you can't see if the fire is really stopped because of all the powder hanging around in the air and makes you leave the room quickly (you can't see any more!). So what will I use in future? Well, I decided to use a CO2 fire extinguisher. But you have to be aware that 6% of CO2 in the air is deadly! And 1kg of CO2 makes more than 550 liters of CO2 gas. So please be careful in small rooms. Fire extinguishers are known for the fact that they can't be stopped sometimes and spew all the things out they have inside (be it water, powder or CO2). A typical CO2 fire extinguisher therefore is deadly in a room with only 10m2! Fire will stop burning if it gets less than 15% oxygen. You will stop living if you'll get less than 17% oxygen! A CO2 fire extinguisher will only stop the flames, not the glowing materials. So it is possible that the fire will re-ignite when the oxygen comes back (and you are not longer in the room). Therefore CO is only good for a fire which just started (but you are standing beside your running coil and will act quickly). Smoke and all the hot toxic gasses will hang below the ceiling, so you should crawl to the door. Call the fire department immediately!

[home]   Famous last words: Oh, a Tesla coil - I heard you can touch it without getting hurt --> Zzzzzapp ...
... and who gets his high voltage supply?