Author Topic: Can a neon sign transformer with an output of 12000V and 30mA kill you?  (Read 28755 times)

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Offline StuUK

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #25 on: February 02, 2016, 09:55:59 am »
If you grabbed one lead in each hand while it was running it could very well kill you, if it can actually achieve 30 mA in that situation.  Some people say that it "should" take more current to kill you, but there are a lot of variables including your own medical condition.

Yes, there's a risk of death and serious injury such as burns and damage to the heart and nervous system.

An RCD my trip at 30mA but the current doesn't flow for long.

Surely that depends on the type, if it's isolated then how would the RCD trip?
 

Offline FlorinTopic starter

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #26 on: February 02, 2016, 10:34:27 am »
I really want to thank you for all your answers  :-+, it looks like high voltage it's really dangerous even if the current is low
 

Offline Srbel

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #27 on: February 02, 2016, 10:35:14 am »
30 mA is NOT low!
 

Offline Kilrah

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #28 on: February 02, 2016, 10:58:12 am »
it looks like high voltage it's really dangerous even if the current is low
NO! You obviously didn't read much of the answers you got.

Again it IS that current that is dangerous, the voltage only makes sure that amount of current will flow even through a high resistance (body).
As explained in posts above the problem is that 30mA is NOT low when it's going through a human, and is well into the "can cause heart failure" range.
 

Offline CatalinaWOW

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #29 on: February 02, 2016, 05:22:17 pm »
Let's err on the side of caution on this one. 'Tasers' output ~1200VDC upon contact (unsure of the amperage). They have been known to kill people who have major heart defects, on drugs etc... etc... They call it a "less than lethal" option for a reason. A more politically correct description could be "It might kill you... just depends".

This may be one of the best answers.  The anecdotal evidance of survival indicates that a neon transformer is not be a reliable way to kill you.  But unless you are suicidal you don't want to rely on this lack of reliability.  Some previous responses to my previous answer indicate that some didn't understand the spirit of my answer.  I don't think anyone knows the odds or understands all of the variables involved, but there is a very real chance of death from improper contact with these things, a very real chance of permanent injury and a 100% chance of an extremely unpleasant experience with improper contact with one of these transformers.  That all adds up to treating them with respect and the appropriate safety measures.  Based on my own experience that includes making absolutely certain that there are no unintended (sneak path) connections back to you or anyone else.  At these voltages that can be an involved process.
 

Offline calexanian

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #30 on: February 02, 2016, 06:32:39 pm »
The main problem that many of the people here do not understand is the nature of Neon transformers. They can produce currents many times their rated output under relative shorted conditions. The human body at those voltages would represent a very low impedance path and the impedance of the secondary would defiantly reduce the voltage across the load, in this case you, but would allow a current of many times the rated value. That rated value is assuming a very long neon tube of a relatively high breakdown voltage of the neon. Not the pure resistive load of a slushy bag of electrolytic salt water (The human body)
Charles Alexanian
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Offline uncle_bob

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #31 on: February 02, 2016, 06:34:10 pm »
Hi

There actually *is* data on how much it takes to be *sure* you kill somebody. It was at the core of a debate between Edison (a DC power guy) and the AC power world. There is an enormous gap between what *might* kill you and what is *sure* to kill you.

One of the biggest hazards is a lack of feedback about this sort of stuff. Long ago, it was pretty much impossible to do any circuit work without dealing with high voltage. Inevitably part of the learning process was "getting bit" by the circuit. Early on you learned techniques to avoid this happening. In the era of low voltage circuits, there is no feedback and no learning process. You simply do not develop the skills for high voltage work. If you are going to be working on high voltage stuff and only have a normal (low voltage) background - take the safety lecture to heart....

Is it current or voltage? Safety specs are written in terms of DC (or low AC) current over a significant fraction of a second. Walk across the room in the winter and grab a door knob. Notice the spark? Play a bit more and you can get a nice big spark. That's probably > 10KV running around and you are still alive. The current involved is a VERY short burst. How short is a "that depends" sort of thing. If it's a microsecond, it might be up in some pretty high numbers for that entire period. Averaged over a tenth of a second, it comes out to nothing (current wise).

Want to build an electric chair? Ok, well let's hook things up and see what happens. Hook up wires to two fingers on the same hand and you turn the hand to mush. No more hand, but nobody is dead (at lest not immediately). Run the same power from hand to hand (through the heart) and you get a different result. Even for a specific current, there are qualifiers. Grabbing a pipe in one hand and reaching into a high voltage circuit with the other ... not a real good idea.

Bob
 

Offline Cubdriver

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #32 on: February 02, 2016, 06:58:53 pm »
The main problem that many of the people here do not understand is the nature of Neon transformers. They can produce currents many times their rated output under relative shorted conditions. The human body at those voltages would represent a very low impedance path and the impedance of the secondary would defiantly reduce the voltage across the load, in this case you, but would allow a current of many times the rated value. That rated value is assuming a very long neon tube of a relatively high breakdown voltage of the neon. Not the pure resistive load of a slushy bag of electrolytic salt water (The human body)

No - they can't.  They're specifically designed to limit at their rated current.  The nature of the beast (neon tube) is that it requires a high voltage to initiate the discharge.  Once that discharge begins, the tube becomes a very low impedance load.  The transformers are designed with shunts to limit the current.  Once the tube ignites, the current goes up to the nameplate rating and the voltage drops to the appropriate value to maintain that current in the load presented by the tube.

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline CatalinaWOW

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #33 on: February 02, 2016, 08:33:12 pm »
The main problem that many of the people here do not understand is the nature of Neon transformers. They can produce currents many times their rated output under relative shorted conditions. The human body at those voltages would represent a very low impedance path and the impedance of the secondary would defiantly reduce the voltage across the load, in this case you, but would allow a current of many times the rated value. That rated value is assuming a very long neon tube of a relatively high breakdown voltage of the neon. Not the pure resistive load of a slushy bag of electrolytic salt water (The human body)

No - they can't.  They're specifically designed to limit at their rated current.  The nature of the beast (neon tube) is that it requires a high voltage to initiate the discharge.  Once that discharge begins, the tube becomes a very low impedance load.  The transformers are designed with shunts to limit the current.  Once the tube ignites, the current goes up to the nameplate rating and the voltage drops to the appropriate value to maintain that current in the load presented by the tube.

-Pat

You are absolutely right.  But it doesn't change the fact that these things can hurt you, and there are at least a few documented cases of them killing.  Argueing over whether it is voltage or the current, or some combination, or whether it depends on the person and the relative humidity or whatever factor might be important doesn't change those facts.  Should you run in terror when you see one.  No.  Should you be cautious, keep clear when applying power and observe a range of other safety precautions.  Absolutely.
 

Offline Cubdriver

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #34 on: February 02, 2016, 08:40:56 pm »
The main problem that many of the people here do not understand is the nature of Neon transformers. They can produce currents many times their rated output under relative shorted conditions. The human body at those voltages would represent a very low impedance path and the impedance of the secondary would defiantly reduce the voltage across the load, in this case you, but would allow a current of many times the rated value. That rated value is assuming a very long neon tube of a relatively high breakdown voltage of the neon. Not the pure resistive load of a slushy bag of electrolytic salt water (The human body)

No - they can't.  They're specifically designed to limit at their rated current.  The nature of the beast (neon tube) is that it requires a high voltage to initiate the discharge.  Once that discharge begins, the tube becomes a very low impedance load.  The transformers are designed with shunts to limit the current.  Once the tube ignites, the current goes up to the nameplate rating and the voltage drops to the appropriate value to maintain that current in the load presented by the tube.

-Pat

You are absolutely right.  But it doesn't change the fact that these things can hurt you, and there are at least a few documented cases of them killing.  Argueing over whether it is voltage or the current, or some combination, or whether it depends on the person and the relative humidity or whatever factor might be important doesn't change those facts.  Should you run in terror when you see one.  No.  Should you be cautious, keep clear when applying power and observe a range of other safety precautions.  Absolutely.

Oh, no disagreement whatsoever - an NST can absolutely light you up and potentially kill you - no question.  I just wanted to clarify that fact that it CAN'T put out several times its nameplate current rating into a short, because it is designed specifically to be a current limited device.  I spoke only to the operational nature of the transformer, which was mischaracterized in at least two places in this thread.  Energized NSTs certainly deserve a great deal of respect, and I have no desire whatsoever to become a load for one.

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline LaserSteve

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #35 on: February 02, 2016, 08:42:03 pm »
One of the worse cases is if a short stub or sharp barb of the wire penetrates the skin.   Once a current is subcutaneous, the danger level really climbs.
We were given serious training on avoiding sharps attached to even low voltage in a medical products plant...

Steve
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Offline calexanian

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #36 on: February 03, 2016, 02:31:57 am »
Traditionally the only "Limiting" going on is a capacitor in series with the primary winding. I will grab one from storage next time I am in Oceanside and set up a little demonstration.
Charles Alexanian
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Offline KE5FX

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #37 on: February 03, 2016, 03:24:40 am »
Traditionally the only "Limiting" going on is a capacitor in series with the primary winding. I will grab one from storage next time I am in Oceanside and set up a little demonstration.

I'm not sure what you're thinking of, but it doesn't bear any resemblance to any neon sign transformer I've worked with.  Any good pointers for further reading on this?
 

Offline Cubdriver

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #38 on: February 03, 2016, 03:39:16 am »
Traditionally the only "Limiting" going on is a capacitor in series with the primary winding. I will grab one from storage next time I am in Oceanside and set up a little demonstration.

If that's the case, then everything that I've learned from using and reading about neon sign transformers over the past 30+ years is wrong, as is Wayne Strattman in his description of one in the book "Neon Techniques", where he explains that it is purposely designed with poor regulation and that the nameplate current is in fact the short circuit current.

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline calexanian

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #39 on: February 03, 2016, 04:13:57 am »
Oh. I forgot gapped transformer types. Those would be the most used types lately, apart from switching types that work on a completely different principal. The gapped type works on the principal of reducing the saturation point of the core, but less than the inductance forming a self limiting transformer. Its similar to how inherently limited U.L. transformers are made. Those types can defiantly produce more peak current than rated. I have used them in X ray tube test setups. 
Charles Alexanian
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Online Someone

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Re: Can a neon sign transformer with an output of 12000V and 30mA kill you?
« Reply #40 on: February 03, 2016, 04:51:09 am »
If you grabbed one lead in each hand while it was running it could very well kill you, if it can actually achieve 30 mA in that situation.  Some people say that it "should" take more current to kill you, but there are a lot of variables including your own medical condition.

Yes, there's a risk of death and serious injury such as burns and damage to the heart and nervous system.

An RCD my trip at 30mA but the current doesn't flow for long.
The wikipedia article has some of the current vs time relationships:
https://commons.wikimedia.org/wiki/File:IEC_TS_60479-1_electric_shock_graph.svg
But that is only for hand to foot conduction of AC, the limits are higher for DC.
 

Offline filter4ever

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I know this is an old post but I was curious about the same thing and there's something important I needed to share

I have a Franceformer 15kV 35mA NST. On the secondary I figured it was isolated from ground but it is actually CENTER TAPPED to ground. This means you could get a 7.5kV shock on each side of the secondary on this particular transformer (with respect to ground).

I've seen Tesla coils made out of "pole pigs" which are always center tapped when installed (I don't have one unfortunately). Multiple kV that amount of current available - I don't think you'd get a second chance.

I've heard the most dangerous voltage is between 2kV and 4kV - the electric chair is 2kV for example. A MOT (microwave oven transformer) is usually 2 kV 500mA

I know any current over 5 mA should be considered lethal this is what GFCIs are usually set at. Everyone says "it's the current not the voltage that kills you" but since I = V/R a higher voltage with a current source greater than 5mA is more dangerous than a lower one.

Alternating current sources are usually given in RMS instead of Peak - to - Peak as well. A 120v sine wave current source would actually have a maximum voltage of 120/(0.707) = 170V (about) so this actually would be [15000 / (.707)] / R

At my previous job my boss saw someone fatally shocked wiring up a 240v dryer circuit while standing water. In the US, 240v circuits are actually 2 120v circuits (with respect to ground) it really shook me up. UK, Europe and other places in the world are mostly 230V with respect to ground

You can never choose which way the current will go through you accidentally. I also heard that as your skin is burnt from current R goes down which is not a good thing...

Have fun and stay safe 👍
« Last Edit: May 26, 2023, 07:21:26 am by filter4ever »
 

Offline AVGresponding

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It's a bit more complicated than just "it's the current that kills you". I thoroughly recommend watching this video, and just as thoroughly recommend you do not try anything you see in it:
Code: [Select]
https://www.youtube.com/watch?v=BGD-oSwJv3E&t=10s
« Last Edit: May 26, 2023, 12:32:20 pm by AVGresponding »
nuqDaq yuch Dapol?
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Offline jonpaul

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NST, MOT, and magnetic (arc lamp) ballasts  are magnetic shunt laminated transformers.

They are current limiting with an open ckt voltage, running voltage under a specified load current and a short ckt currtn.

j
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Offline ejeffrey

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But, for example, if a transformer will be limited to, let's say, 1 - 10 mA or even lower it will be safe regardless of the output voltage?

1 milliamp AC should be relatively safe even if the open circuit voltage is high.  10 mA is still enough to cause a painful shock but unlikely to kill a person unless they have a underlying heart condition.  I still would treat it as dangerous, and who wants to find out that they have an underlying heart condition when an HV transformer shocks them?

With HVDC supplies you also have to worry that it might have a large output capacitor that can store significant energy.
 

Offline BrianHG

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Styropyro has thoroughly described the situation here:


 

Online Someone

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Styropyro has thoroughly described the situation here:
Except its not thorough or complete:
https://www.eevblog.com/forum/chat/is-it-the-volts-or-amps-that-kill-(video-from-styropyro)/
and that "information" is in the most infuriating format of an advertisement supported video so people cant easily skim/quote/refer to specifics. There is much more to electrical safety or human responses to electrical current. We already had a comment covering most of that in this thread:
https://www.eevblog.com/forum/chat/can-a-neon-sign-transformer-with-an-output-of-12000v-and-30ma-kill-you/msg857194/#msg857194

But, for example, if a transformer will be limited to, let's say, 1 - 10 mA or even lower it will be safe regardless of the output voltage?
1 milliamp AC should be relatively safe even if the open circuit voltage is high.  10 mA is still enough to cause a painful shock but unlikely to kill a person unless they have a underlying heart condition.  I still would treat it as dangerous, and who wants to find out that they have an underlying heart condition when an HV transformer shocks them?

With HVDC supplies you also have to worry that it might have a large output capacitor that can store significant energy.
Again, in this thread there are several examples of outcomes that will kill you well below the currents that can cause a heart to stop so its not the best measure of potential lethality. As you expand upon with capacitances, that does not seem to reach people on this forum who just carry on regardless:
https://www.eevblog.com/forum/reviews/completely-non-sketchy-mini-high-voltage-transistor-tester-(emeco)/
Small, handheld, "limited" output current, already dangerous, but then turned up to 11.
 

Offline CatalinaWOW

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So to directly answer the OPs question.  YES!  It can.  It may not.  In fact you may survive several exposures.

Perhaps an analogy would make things clearer.  Can you define a speed at which a motorcar is absolutely safe?  Not really.  Imagine something trapped between a wall and a motorcar going 0.1 miles/hour towards the wall.  Even at this speed a fatality in this case is not unlikely.  As the speed increases the special conditions required to cause a fatality become less and less special.  But people have survived operating motorcars at speeds over 400 mph.  And even survived wrecks.  But the percentage of people who have been killed while driving at speeds over 400 mph becomes pretty substantial.

It is well worthwhile exercising extreme caution when operating the transformer identified by the OP.  There are a number of minor mistakes which can be made which would result in a very painful session and possibly even death. 
 

Online Psi

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It definitely could kill yes.

Due to the much higher voltage it's a lot more likely to pump the full 30mA through your body than sticking your finger in a 230V power point where your body may or may not have a good path to ground. 

On the other hand, 30mA is much less than the 20A available to flow from sticking your finger in a power point if your body has a good connection to ground.
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline David Hess

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The output of a neon sign transformer can definitely kill you, but maybe I got lucky.

When I was in high school, I accidentally picked up my 15 kilovolt 30 milliamp neon sign transformer by the terminals and insulators while it was plugged in.  I got as far as lifting it before I consciously set it down and released it rather than dropping or throwing it.  The total time was a couple seconds.  After that I sat against the wall for a couple minutes sweating.

I have experienced 120 volt AC line voltage a couple of times and I would say that it was worse, but of course then the impedance is lower and the current is higher.

Another time I was working with a 1000 volt DC power supply that I had built for a strobe and managed to short the output out from my finger tip to my elbow while standing on an aluminum ladder.  That knocked me off the ladder and across the concrete floor.  I had a pair of burn marks on the tip of my finger and my elbow, and my whole arm hurt for days.  In this case the power supply had 10s of microfarads of capacitance which was way too much, lesson learned.

safe? i would not call it safe by any means, even a few mA at 12kv will burn you at least

I was not burned but there was no sustained arc.

30 ma at a couple of KV (DC or low freq AC) will knock you across the room from the muscle contraction.(no it does not knock you, your muscles knock you, the result is the same and it hurts). Yes I have empirical data ...

No, I have experienced both and the current limited AC will not.  Even 1000 volts of DC can knock you across the room, and off of a ladder in my case, if it has a moderate amount of capacitance or low enough impedance.

By the way, if a transformer is marked "30mA", this is a continuous rating. In the case of a short circuit, (for example through the "low" resistance of an human), it will happily supply 10-50x more -> 300mA to 1,5A.

To these lethal effects of electric current, at that high voltages and high current, the heat of the arc will burn flesh.

The output current of a neon sign transformers is deliberately limited by the transformer's impedance.  They could certainly burn flesh if an arc is present, however inadvertent contact will likely result in either immediate recoil or intimate contact.  In either case an arc is not present for long enough to burn.
« Last Edit: May 27, 2023, 10:47:46 am by David Hess »
 


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