Communities

Writing
Writing
Codidact Meta
Codidact Meta
The Great Outdoors
The Great Outdoors
Photography & Video
Photography & Video
Scientific Speculation
Scientific Speculation
Cooking
Cooking
Electrical Engineering
Electrical Engineering
Judaism
Judaism
Languages & Linguistics
Languages & Linguistics
Software Development
Software Development
Mathematics
Mathematics
Christianity
Christianity
Code Golf
Code Golf
Music
Music
Physics
Physics

Dashboard
Notifications
Mark all as read
Q&A

Why isn't voltage of electric chair higher?

+2
−2

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?

Why does this post require moderator attention?
You might want to add some details to your flag.
Why should this post be closed?

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 2 days 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 1 day 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 1 day 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 1 day 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 1 day ago

Show 4 more comments

3 answers

+2
−0

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.

Why does this post require moderator attention?
You might want to add some details to your flag.

0 comments

+2
−0

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.

Why does this post require moderator attention?
You might want to add some details to your flag.

0 comments

+0
−2

it seems intuitive to use much higher voltage to achieve higher current - Actually, no. Voltage and current are independent. Increase one and you can keep the other steady or up or down. The thing that is true is that increasing voltage (or current) while keeping current (or voltage) steady will increase power. But that really isn't the issue when it comes to an electric chair.

I don't know why particular voltages have been picked for the "electric chair" (not sure I want to know...). But I can explain a bit about voltage vs. current vs. power, and the deadly combinations thereof.

There is voltage (think 120V or 240V in most homes). There is current (think 2A for a phone charger output, 12A for a hair dryer, 30A for a clothes dryer, etc.) Then there is power which is, essentially, voltage times current.

  • 2A output of a phone charger at 5V DC (DC vs. AC is relevant, but after this line, I'll ignore it as it makes little difference in the grand scheme of calculations here) = 10W (output, a little more on the input side due to conversion losses)
  • 2A of electric lighting (e.g., 4 "60W incandescent bulbs") at 120V = 480W.

So the power produced at higher voltages is higher than at lower voltages. But the current is not necessarily higher. For example:

  • 12A at 120V = 1,440W of power - that's the most you'll get on a standard 15A circuit for continuous usage. (More or less, sometimes calculated based on 125V = 1,500W).
  • 6A at 240V = 1,440W of power. 1/2 the current to get the same result (in terms of heating or lighting or motors or whatever)
  • 12A at 240V = 2,880W of power. Same current, double the voltage = double the usable power.

All of this matters a lot in design of appliances. The reason (in the US) that dryers, water heaters, heat pumps, etc. use 240V is to get more power without using a lot of current so that wire size can stay small (among other reasons).

Now back to the "electric chair". It really only takes a very little bit of current through the heart to kill someone. That's why Ground Fault Circuit Interrupters work at incredibly low current - typically 6ma - 8ma. The same current at low voltage (e.g., 9V battery) won't normally do anything except a slight tingle. But mains voltage (even 120V, but it gets more dangerous with higher voltage) can more easily make its way through the skin, especially if wet, to complete a circuit through a human body.

The "electric chair" is a big contraption, designed, I suspect, both to intimidate and also designed before a lot of the details of how electricity works (and how it kills) were understood. Wet both hands of a death-row inmate, attach one hand to neutral, the other to hot and flip the switch on a standard 120V circuit and I suspect the effect would be as immediate and deadly as thousands of volts through a big contraption.

Remember this when your kitchen or bathroom GFCI trips and you complain "why'd this stupid thing stop working again, maybe I should just plug it into a different, non-GFCI, receptacle and stop these annoying trips". Water + electricity kills.

Why does this post require moderator attention?
You might want to add some details to your flag.

5 comments

The effect is not immediate, it takes up to a minute, hence the question. And if you have to start the answer with 'I don't know', consider not posting anything Kranulis‭ 2 days ago

I seriously considered just leaving a short comment. And then I started thinking about the ramifications of this particular issue. I may make some changes, and if someone comes up with a better "real" answer I may delete mine. manassehkatz‭ 2 days ago

"Increase one and you can keep the other steady or up or down." Not unless you also control the load, which in this case you don't. For a resistive load, for example, the current will be proportional to the voltage. If I give you a specific resistor, you can choose the voltage you put across it, but you don't get another degree of freedom to choose the current. The resistance sets that relationship. A body isn't a resistor, but you still only have one degree of freedom. Olin Lathrop‭ 2 days ago

"... 6ma - 8ma. The same current at low voltage (e.g., 9V battery) won't normally do anything except a slight tingle." Completely wrong! Again, you only get one degree of freedom. If you specify 8 mA, then the voltage will be whatever it needs to be to result in 8 mA. That's going to hurt, a lot, cause real damage, and easily kill you if it flows near the heart. It doesn't matter what voltage it took to make 8 mA. It's the current that kills you. Olin Lathrop‭ 2 days ago

@Olin I do realize that with a static load (e.g., a simple resistor), raising/lowering voltage will have a definite effect on the current (and vice/versa). My point is that "much higher voltage to achieve higher current" doesn't work that simply when designing a device. manassehkatz‭ 2 days ago

Sign up to answer this question »