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Q&A

Why isn't voltage of electric chair higher?

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I recall vividly a story told by my grandfather who worked with high voltage power lines. A worker drove heavy machinery into 700kV line and then jumped out of the truck, instantly combusting upon touching the ground.

I recently read about executions by electric chair, and got curious as to what voltage is used, since the described process seemed to last upwards to a minute, which seems incredibly unnecessary. Various sources indicate that voltage ranging from 1400V-2300V is used, most often figuring around 2000V. If we know that it is current that kills, it seems intuitive to use much higher voltage to achieve higher current, in effect speeding up the process.

Are there any considerations from electrical perspective, such as safety regulations, fuse ratings etc. that could be a reason for using this particular voltage and not going higher?

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9 comments

Why the downvotes? Somebody has to design these things, and the voltage they run at must be a consideration. Asking about the design tradeoffs is totally legitimate. Olin Lathrop‭ 3 months ago

@Olin Lathrop Well... nobody has to design them. Engineers with some sort of moral code might refuse to do so. But I agree that questions regarding why a certain voltage is used by certain electrical equipment are on-topic here. Lundin‭ 3 months ago

As for why a certain voltage is used... the aim of an electric chair isn't to burn someone to crisp by making their whole body a conductor for high current, that would be extremely unethical and similar to burning someone alive. Lundin‭ 3 months ago

As for your grandfather's story, it sounds like hogwash. For something to actually catch fire, you would need several Ampere running through it. The resistance of the human body + clothes, shoes (likely rubber) etc + the ground itself, is many Megaohms. So even if someone manages to charge their body to a potential that is 700kV higher than ground, they would never realistically discharge that voltage with high enough current to make something catch fire. Lundin‭ 3 months ago

Are there any considerations from electrical perspective, such as safety regulations - I don't think safety is a consideration if the object of the exercise is to shuffle off someone's mortal coil. Andy aka‭ 3 months ago

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2 answers

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After some research I found some reasoning behind the voltage range:

1500V is sufficient to destroy the somatic nervous system, which is responsible for consciousness and feeling of pain. After applying the voltage, within 4ms the subject becomes unconscious faster than the nervous system can register pain. The autonomic nervous system (which is responsible for basic functions such as breathing and heartbeat) requires >2000 volts to stop the heart. Allegedly, 20% is added to "be sure". Furthermore, after voltage is applied and the body saturates, there is a 10% voltage drop that varies based on the electrode resistance and the body resistance. It was also noted that the current should be below 6A to prevent burning, since that is not the goal.

Fred A. Leuchter Associates, Inc., which made these devices seems to be the only company in US, however, the owner had no formal engineering experience and was dropped as a manufacturer, so it is unclear whether these numbers are accurate and make sense at all.

If this is accurate, it seems that properties of the human body are the primary drivers of design choices, and not safety concerns.

If anyone has any more information regarding the accuracy of this, please do share.

I feel that I also have to say that my interest in this is purely out of curiosity, and I do not plan to build one or sit in one. From the perspective the question is asked, this is an electrical appliance that has specs, and the reasoning behind these specs needs clarification.

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2 comments

(Disclaimer: I don't know much about medicine save for a CPR class.) To stop the heart you just need to make the (I think they are called) beta receptors freak out, which only takes a relatively small current. These control the heart rhythm and if they stop acting reliable you get a heart failure. The defibrillator heart starters aim to "reset" these beta receptors with a similar current, so they start acting normally again. A defibrillator uses some 300-500V pulse. Lundin‭ 3 months ago

The 6A current limit sounds like hogwash. The human body has too high resistance to ever get close to currents like that. And the currents are what matter here, not the voltages. Lundin‭ 3 months ago

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I think your grandfathers story is, shall we say, apocryphal.

You should know that electrocution kills by stopping the heart (or causing fibrillation), and the heart must be kept from beating long enough for the person to die. It only takes a few mA to accomplish this and there is no benefit...no speedup...in using drastically higher voltages or currents.

Some people have been struck (or nearly struck) by lightning and survived. The high voltage stopped their heart but the heart started beating again without intervention.

On the other hand, using higher voltages requires more expensive equipment and presents a greater risk to bystanders.

Please don't interpret anything I have said here as support for capital punishment.

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2 comments

I don't want to promote anything like "snuff movies" or the like, and the video I refer to below is not for those easily distressed, but I recalled a video of a man dying pretty much instantly in similar circumstances to the grandfathers story. It shows a man being urged down from a train in India, but instead he grabs hold of the live catenary cable. You have been warned, but you can Google search for "man died on train by current in india" and it probably be the top result. narnian99‭ 3 months ago

I do see what you mean. And the train line seems to be "only" 25kV. Since 700kV is 28 times more, I also think that the story could be true. Kranulis‭ 3 months ago

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