Safety FAQ is here -- draft, asking for comments.
I finally got the safety FAQ/info sheet done. This is a first draft and
needs peoples comments. Therefore, could you read it and send me (or the
list) comments? I marked the areas that I really need comments and
scrutiny with >>>. Thanks in advance.
>From chip-at-grendel.objinc-dot-comSat Jul 27 20:50:20 1996
Date: Thu, 25 Jul 1996 15:50:58 +0700
From: Chip Atkinson <chip-at-grendel.objinc-dot-com>
Tesla coil safety info sheet.
(Not an FAQ, since there doesn't seem to be any set of FAQ's regarding
1) Electrical Hazards
1.1 General electrical hazards by Mark S. Rzeszotarski, Ph.D.
1.2 Tesla Coil specific electrical hazards
>>> I would like some scrutiny and comments on this paragraph.
1) Electrical Hazards
1.1) General Electrical Hazards
>From Mark S. Rzeszotarski, Ph.D.
Lightning kills about 300 people each year in the United States, and
injures an additional three to four times this number. (Sorry, I have no
data for the rest of the planet.) Over 1000 people are killed each year in
the U.S. due to generated electric current, and several thousand more are
injured. (This would include potential tesla coilers.)
In the case of lightning, the voltage and current are extremely
high, but the duration is short. The current tends to flow on the outside
of the body and may cause burns, respiratory arrest and/or cardiac arrest.
Many die from lightning due to respiratory arrest rather than cardiac
arrest. (The portion of the brain controlling breathing is often severely
affected in a lightning strike.)
Power line deaths usually involve lower voltages and currents, but
the duration may be significant. Often the current flows inside the body,
causing deep burns and cardiac arrest. Frequently, the individual cannot
let go of the power source due to involuntary muscle contraction.
The brain and heart are the most sensitive organs. The dose
response for animal and human data suggest the following: for less than 10
mA hand to foot of 50-60 cycle line current, the person merely feels a
"funny" sensation; for currents above 10 mA, the person freezes to the
circuit and is unable to let go; For currents of 100 mA to 1 ampere, the
likelihood of sudden death is greatest. Above 1 ampere, the heart is thrown
into a single contraction, and internal heating becomes significant. The
individual may be thrown free of the power source, but may go into
respiratory and/or cardiac arrest.
Six factors determine the outcome of human contact with electrical
current: voltage, amperage, resistance, frequency, duration and pathway. I
will discuss each individually.
Low voltages generally do not cause sudden death unless the external
resistance is low (so don't fire up your coil in wet areas). As the voltage
is increased, more and more current passes through the body, possibly
causing damage to the brain, heart, or causing involuntary muscle
contractions. Perhaps 100-250 volts A. C. is the most lethal voltage,
because it is high enough to cause significant current flow through the the
body, and may cause muscles to contract tightly, rendering the victim
incapable of letting go. Lower voltages often are insufficient to cause
enough current flow, and higher voltages may cause the victim to be thrown
clear of the hazard due to the particularly fierce involuntary muscle
contractions. Arcing may occur with high voltages, however. Naturally,
burns become more severe as the voltage is increased.
Greater amperage means greater damage, especially due to heating
within tissues. As little as 10 microamps of current passing directly
through the heart can cause ventricular fibrillation (heart muscle fibers
beat out of sync, so no blood is pumped) and cardiac arrest. Because of the
air filled lungs, much of the current passing through the chest may
potentially pass through the heart (pun intended). The spinal cord may also
be affected, altering respiration control. 100-1000 millamperes is
sufficient to induce respiratory arrest and/or cardiac arrest. Thermal
heating of tissues increases with the square of the current (I^2 x R), so
high current levels can cause severe burns, which may be internal.
A heavily callused dry palm may have a resistance of 1 megohm. A
thin, wet palm may register 100 ohms of resistance. Resistance is lower in
children. Different body tissues exhibit a range of resistances. Nerves,
arteries and muscle are low in resistance. Bone, fat and tendon are
relatively high in resistance. Across the chest of an average adult, the
resistance is about 70-100 ohms. Thermal burns due to I^2 x R losses in the
body can be significant, resulting in the loss of life or limb long after
the initial incident. Limb diameter determines the approximate "cross
section" which the current will flow through, (for moderate voltages and low
frequencies). As a result, a current passing through the arm generates more
temperature rise and causes more thermal damage than when passing through
The "skin effect" also applies to a human conductor, and as the
frequency gets above about 500 kHz or so, little energy passes through the
internal organs. (I unfortunately have little data in the 50-250 kHz range,
where we operate most tesla coils. I'll check another reference I have at
home.) At a given voltage, 50-60 A.C. current has a much greater ability to
cause ventricular fibrillation than D.C. current. In addition, at 50-60 Hz,
involuntary muscle contractions may be so severe that the individual cannot
let go of the power source. Higher frequencies are less able to cause these
Obviously, the longer the duration, the more severe the internal
heating of tissues. Duration is particularly a problem when working with
110-240 volts A.C., which can render the individual incapable of letting go.
If the current passes through the brain or heart, the likelihood of
a lethal dose increases significantly. For example, hand to hand current
flow carries a 60% mortality, whereas hand to foot current flow results in
20% overall mortality. Be aware that foot to foot conduction can also
occur, if a high voltage lead is inadvertantly stepped on or if grounding is
Obviously, the A.C. line voltage, the high voltage transformer and
the high voltage R.F. generated by a tesla coil are all potentially lethal
in their own unique way. One must always respect this extreme danger and
use high voltage shielding, contactors, safety interlocks, careful R.F. and
A.C. grounding, and safe operating procedures when working with coils. A
safety key to prevent inexperienced operators from energizing a coil is
essential. High voltage capacitors can also retain lethal energies
(especially in the "equidrive" configuration) and should always be grounded
before adjusting a primary.
Whenever possible, have a buddy around to assist you. Place one
hand in your pocket when near electrical components so the current won't
pass through your chest, and use the back of your hand to touch any
electrical components so you can let go if it happens to bite you. Remember
that most deaths are caused by regular 110 A.C. power! Never perform
coiling when overtired or under the influence of one or more mind altering
drugs. Watch a tesla video instead!
1.2) Tesla coils have their own dangers associated with them. The
previous article mentioned some of them in a general electrical hazard
context, while this article will attempt to discuss the dangers from a
tesla coil point of view.
Exposed wiring on transformers
Neons have exposed lugs
Most all of the neon sign transformers that I have seen used for
tesla coil usage have exposed lugs. A 15000 volt transformer has
a turn ratio of 125:1 (assuming 120 volts in). If you haven't
disconnected your input power from the source (unplugged your
variac), you may be in for a surprise. A variac that is putting
out two volts will give you a 250 volt shock if you touch the
high voltage outputs of the neon sign
Pole pigs have the same dangers as mentioned above, as well as
having much more current available. At the output voltage of a pole
pig, the current that can go through you is not really limited by
anything other than the current regulation that you attached to the
Once I shocked myself with one end (7500 volts) of a 60ma. neon
transformer. I just brushed against an exposed end, so I wasn't
gripping anything. It was quite painful, much more so than touching a
sparkplug wire. I felt the path of the current follow my arm, and
go down my leg.
Equidrive will almost always have charge The "equidrive" system uses
two capacitors in series with the gap and the primary between
them. The gap is on one side and the primary is on the other.
>>> NOTE: I am unclear as to where the HV input from the
>>> transformer goes in this circuit. If it goes across the gaps,
>>> then won't the charge dissipate through the HV transformer?
Capacitors can build up charge from electrostatic
sources Capacitors have been known to
accumulate a charge from various sources such
as static electricity and electric fields. IF
YOU STORE A CAPACITOR, STORE IT WITH A WIRE
ACROSS THE TERMINALS. (MAKE SURE YOU DISCHARGE
THE CAPACITOR BEFORE PUTTING THE WIRE ON!!!)
Capacitors can "regain" charge from dielectric "memory"
The dielectric in a capacitor is put under
electrical stress during use. During
operation, this stress may cause the molecules
in the dielectric to orient themselves in such
a manner that they store this charge in their
structure. The charge remains after the
capacitor has been discharged. Later the
molecules return to their original states and
the charge that they "captured" ends up on the
plates of the capacitor. This charge is then
available to shock you.
>>> Comments on correctness are requested.
Other sources of danger
Jump from primary to secondary when drawing sparks:
(Contributed by R.W. Stephens)
You are literally playing Russian Roulette when you stick a
hand held metal rod into the output streamer of your coil
running at 3kvA, while standing on a concrete
When you start running these kind of power levels (or
even less) some coils have a tendancy to form a corona
or even send a streamer down to their own primaries
every once in a while. A grounded strike ring is often
added around the primary to try to prevent this self
striking streamer from hitting the primary coil and
thus introducing a high voltage pulse into the 'bottom
end electrics' where it could do damage to components.
These strike rails are not 100% effective. The
streamer can still, and sometimes does strike a point
downstairs that is part of the LETHAL 60 Hz circuitry.
When such a contact is made, any person also connected
to a corona/streamer link to the secondary at the same
time will, via the ionized air path, become connected
to lethal 60 Hz mains current. You could try the trick
you described standing on the cement floor in your
tennis shoes half a dozen times and live, or be killed
the very next time you try it. The fact that the
bottom of your secondary is tied to ground will not
If you isolate your own body well away from the floor and any
other potentially conductive objects in the vicinity, such as
sitting or standing on an elevated insulated platform (I would
NOT consider a plastic milk crate adequate!), then you will
survive if 60 Hz is introduced into the streamer you are in
contact with by the mechanism described above. However, in
setting up this insulated platform you must consider the path
that may be taken from streamers that will re-emerge from your
body and head off looking for other targets.
In a safety warning I have about the potential hazards of
Tesla coils mention is made of a stage lecturer while
demonstrating how he could cause long sparks to come out of
his fingers (by standing on a specially constructed coil),
was electrocuted when the discharge created an ionized path
to grounded overhead pipes supporting stage back drops, and
the lower voltage but far more deadly 60 cycle current passed
through his body along that path. The name of this lecturer
is believed to be Transtrom.
I was dinking around once with a vacuum tube coil
drawing 15 inch streamers to a hand-held, 10 megohm
metal film porcelain resistor about a foot long while
standing on a carpeted, elevated wooden floor in
composition rubber soled dry shoes. I inadvertently
got the resistor too close to the primary tank coil
(the top end directly connected to the 3 kilovolt
output of the plate supply transformer) and the high
voltage RF closed a path to the primary. I felt an
uncomfortable 60 Hz shock through my entire body. Had
that resistor been a solid metal rod I would have
experienced a very painful jolt or worse, and had I
been standing on a cement floor, I'd probably be 'worm
I think the danger of electrocution is just as real
by making contact with a hand held florescent lamp
tube, as any solid conducting metal object.
I cringe when I hear of some body contact stunts
proposed by people on this list! The potential (no
pun intended) for death is very real. Be careful!
During the operation of the tesla coil, significant static
charges can build up on the secondary. If you need to move
the secondary (say you are adjusting the coupling), you will
get a nasty zap right across your chest when you pick it up
with both hands. Before you touch the secondary, wipe it
lightly with a grounded wire. You can sometimes hear the
crackling as you do so.
Besides the shock hazard, there is the physical hazard caused
by the shock. You will likely drop the secondary or jump into
something that isn't soft.
Fire starting from sparks to flammable points
The sparks from a tesla coil are hot. Depending on where they
strike, these sparks can cause a fire. Richard Hull has
captured fires caused by sparks from his coils on video tape.
>>> Richard Hull, correct me if I'm wrong
Be sure that when you run your coil, that there are no
flammable substances around. For example, gas cans
(e.g. for a lawnmower), ammunition, sawdust, fireworks, etc.
Fire from other induced currents.
Tesla coils are good at inducing currents. Beware of metal
things that are connected to the same ground as a tesla coil.
For example, I run my coil in my garage, which has a wooden
door on metal tracks. The tracks are against the concrete
floor, and near the strap that serves as a ground for my
coil. When the coil operates, it causes sparks to jump
between the running hardware of the door and the tracks.
Hazards to electronics:
Strikes to house electrical ground -- also goes to power(?)
A tesla coil must be connected to a ground that is separate
from the house ground or water pipes. Connecting your coil
to either of these grounds is a recipe for disaster. Notice
that your stereo, computer, vcr, etc., have three prong
plugs. Also, note where your telephone box is grounded. It
is likely grounded to the water pipes.
Consider what happens when your coil strikes the
grounded strike rail, or an unexpectedly long spark that hits
an electrical receptical. That enormous voltage at high
frequency will now be connected to the grounds of all your
electronic goodies or your telephone. Furthermore, a spark
is a conducting path in the atmosphere. By creating this
path, you open your electrical system up to connections
between the 120/220v house system and ground.
Strikes to garage door opener rails
Since many people do their coiling in the garage, this topic
deserves individual consideration. If you have a garage door
opener, or are installing one, you should put in a mechanism,
such as a switch or plug and socket, that allows you to
disconnect the opener from the house power.
My garage door got zapped by my coil. The door is connected
to the opener track so the opener got zapped too. The strike
caused the opener to attempt to open the already open door.
Since the door couldn't go any further, the opener started
binding. I was able to unplug the opener and keep the thing
More than one person on the list has replaced their opener as
a result of their coiling activity. Be warned of the
dangers to the equipment. An untested suggestion is to put a
grounded wire underneath the rail and opener to draw the
sparks to the wire.
Electric fields inducing currents and killing sensitive meters.
Oddly enough sensitive meters and measuring equipment is just
that -- sensitive. Solid state instruments are much more
susceptible to damage from being near tesla coils than are
vacuum tube items.
>>> Perhaps someone can elaborate on these problems.
Good electrical practice
Place your coil in a location that will prevent the strikes
from hitting electrical outlets, people, animals, and
sensitive electrical equipment.
Turn off and unplug computers in your house.
Keep one hand in your pocket when working near or with
charged items. (Capacitors, secondary coils, etc.)
Disconnect the power to the variacs before touching any of
the HV circuitry.
Quaff the ales later during bragging hour, not when you are
As any professional arc welder will tell you "Don't Look At The
Arc!" Spark gaps produce a large amount of UV and visible
light. The visible light is extremely bright and will damage
your eyes. UV will sunburn your eyes. The arc is so bright
that you couldn't make out any detail anyway, so why bother?
It is not too difficult to rig up a piece of plastic, cardboard,
etc. that will shield yourself and others.
>>> Does anyone know about the coil arcs?
One type of spark gap, the air blast gap, produces loud noise.
Buy and use a set of ear muffs or ear plugs. There is a wide
variety of types of ear plugs and muffs, so you will likely find
one that works well and is comfortable. I prefer the roll up
foam type myself. If you are on a tight budget (blew all the
$$$'s on the pig), you can wash the foam ear plugs. Just put
them in a pants pocket (one that closes is best) and run the
pants through the wash. Works great.
When a coil is in tune, you will notice a dramatic increase in
the noise level as it sparks. This noise is loud enough that it
can damage hearing. See the warnings in the previous paragraph.
Hearing is important -- how will you tell if your teenager is
mocking you behind your back without it?
During operation, rotary gaps spin at high speeds. The
spinning rotor or disk is subjected to tremendous force
At a modest 3600 RPM, the periphery of a 10" disk is
subjected to a force of
>>> Math check
1835 Gs. A 5 gram (0.011 lb) 1/4-20 brass acorn nut used
as an electrode will exert a force of over 20
pounds. The peripheral speed of the 10" disk is 107 MPH.
At 10000 RPM, the edge of the disk is running at about
All these numbers translate into one thing: Danger.
The best way to guard against this danger is to shield the
rotor and build the entire system carefully and take pains
to balance it.
The shielding must be nearly bullet proof (literally). Lexan
(polycarbonate) is an excellent plastic for shielding. It is
non-conductive, strong, and tough. Consult with your plastics
dealer to determine what thickness you need.
Capacitors are great at releasing energy very quickly. The
explosion danger in a capacitor occurs when it shorts out and
suddenly produces a large volume of hot vaporized capacitor guts.
Since capacitors are usually in an air-tight container, the
volume of gas will cause the container to explode. Sending
pieces of solid cap guts all over.
One recommended method of shielding capacitors is in an HDPE
(High Density PolyEthelene) pipe. These pipes are used in the
pyrotechnics industry as mortars because of their strength and
the fact that they don't create shrapnel as steel or PVC pipes
Gasoline on premises (mowers, etc.)
Without a spark, what's a tesla coil? What's it take to ignite
gasoline? Consider the location of gas cans, lawnmowers, etc.
when operating your coil. Remember that when you operate your
coil, it's usually in the dark with plenty of exposed high
voltage wires. Not a good combination for fighting a fire in
FCC: No modulation
When I first got interested in tesla coils, I called the FCC to ask
about the legal aspects of coiling. While the man that I talked
to wasn't too sure about the potential interference, he did say that
modulation of the output is definitely illegal. Of course, if you
shield your coil from emitting RF to the outside world, you can do
anything you like.
Coils are noisy. Please consider your neighbor's sleep habits.
-- For new parents, sleep is the most precious commodity that they have.
-- Not everyone works 8am to 5pm.
-- Not everyone is tolerant or nice.
Try to be aware that your coil may cause various interference
problems. If you know about any, take care to eliminate them if
possible before they figure out who caused it.
Kids are quite curious, innocent, and ignorant. Their judgment
isn't the greatest either. If you have children and they have
access to your coil, install some sort of key lock on your power
cabinet, variac, or whatever. Killing or injuring a child, be it
yours or neighbors, will most likely be the worst thing that will
happen to you in your life.
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