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Can a neon sign transformer with an output of 12000V and 30mA kill you?
calexanian:
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)
uncle_bob:
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
Cubdriver:
--- Quote from: calexanian 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)
--- End quote ---
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
CatalinaWOW:
--- Quote from: Cubdriver on February 02, 2016, 06:58:53 pm ---
--- Quote from: calexanian 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)
--- End quote ---
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
--- End quote ---
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.
Cubdriver:
--- Quote from: CatalinaWOW on February 02, 2016, 08:33:12 pm ---
--- Quote from: Cubdriver on February 02, 2016, 06:58:53 pm ---
--- Quote from: calexanian 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)
--- End quote ---
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
--- End quote ---
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.
--- End quote ---
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
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