Quizzes & Puzzles9 mins ago
AC/DC shocks
16 Answers
Can you get an electric shock from a DC voltage ?
What is the lowest voltage that can kill a human ?
Not that I'm planning to kill anyone I'm just curious !
What is the lowest voltage that can kill a human ?
Not that I'm planning to kill anyone I'm just curious !
Answers
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1) yes
2) Its isn't the voltage that kills the human - it's the current (amps). Which is why birds (or humans) can sit on a high-voltage power lines and suffer nothing - there is no current flowing because the resistance down to ground is very high. The worst case scenario is wet bare feet touching the ground. In this situation the resistance to ground is much lower, so it takes a much lower voltage to be touched for the current (that kills you) to be large enough as it flows through the body. I hope that makes sense. There is a concept known as Safe Extra Low Voltage (SELV) which is about 28V. This is regarded as the maximum voltage that a human could touch under worst case conditions and no damage to tissues occurs. So your answer is something above 28V.
2) Its isn't the voltage that kills the human - it's the current (amps). Which is why birds (or humans) can sit on a high-voltage power lines and suffer nothing - there is no current flowing because the resistance down to ground is very high. The worst case scenario is wet bare feet touching the ground. In this situation the resistance to ground is much lower, so it takes a much lower voltage to be touched for the current (that kills you) to be large enough as it flows through the body. I hope that makes sense. There is a concept known as Safe Extra Low Voltage (SELV) which is about 28V. This is regarded as the maximum voltage that a human could touch under worst case conditions and no damage to tissues occurs. So your answer is something above 28V.
50mA or 1/20 th of an amp can cause ventricular fibrilation and thus be fatal, whether by direct or indirect contact
protection mostly is by earthing or reducing the voltage below 50v by transformers, like in a bathroom where the risk of shock is increased, this type of supply is known as separated extra low voltage (SELV) and this system is electrically separate from the earth
outside the home R,C.D.s are used to cut out in 30mS if they are working correctly, and shortly the 17th edition of the regs will apply and R.C.D.s will be used more inside the home in areas such as bathrooms
protection mostly is by earthing or reducing the voltage below 50v by transformers, like in a bathroom where the risk of shock is increased, this type of supply is known as separated extra low voltage (SELV) and this system is electrically separate from the earth
outside the home R,C.D.s are used to cut out in 30mS if they are working correctly, and shortly the 17th edition of the regs will apply and R.C.D.s will be used more inside the home in areas such as bathrooms
As others have stated, it's the current that kills, not the voltage. (Although, once again as others have said, there's a voltage below which safety from electrocution can normally be assumed).
When I was teaching physics, it was standard practice to use a Van de Graff generator to produce static electricity and then discharge it by getting a pupil to touch the metal sphere and point at an earthed object. This produced a large blue spark which flashed between the pupil's finger and the earth point. Doing so, passed electricity through the teenager's body, with a potential difference of up to 100,000 volts between his two hands. It's a perfectly safe thing to do because the current is so low.
However, anyone who accidentally touches both terminals of a 12V car battery simultaneously will experience a very painful jolt. That's because, despite the low voltage, there's a very high current.
It's actually quite difficult to kill someone with an electric current. As Terence has indicated, the greatest risk is when there's minimal resistance on the path to earth because of the presence of water. The risk is also much higher if the path of the electricity passes through the heart muscles. However, I've worked on live electrical circuits and managed to connect myself to the mains on lots of occasions. It hurts like hell (and can leave a limb without much muscle function for a short while) but I still seem to be here!
Chris
When I was teaching physics, it was standard practice to use a Van de Graff generator to produce static electricity and then discharge it by getting a pupil to touch the metal sphere and point at an earthed object. This produced a large blue spark which flashed between the pupil's finger and the earth point. Doing so, passed electricity through the teenager's body, with a potential difference of up to 100,000 volts between his two hands. It's a perfectly safe thing to do because the current is so low.
However, anyone who accidentally touches both terminals of a 12V car battery simultaneously will experience a very painful jolt. That's because, despite the low voltage, there's a very high current.
It's actually quite difficult to kill someone with an electric current. As Terence has indicated, the greatest risk is when there's minimal resistance on the path to earth because of the presence of water. The risk is also much higher if the path of the electricity passes through the heart muscles. However, I've worked on live electrical circuits and managed to connect myself to the mains on lots of occasions. It hurts like hell (and can leave a limb without much muscle function for a short while) but I still seem to be here!
Chris
Current, the flow of electricity, is what in sufficient quantity can do harm or be lethal.
Voltage, the force which pushes current through a conductor, determines how much current will flow through a given conductor.
The human body has a fairly low resistance to current flow, so depending on the path provided, the amount and duration of current flowing through the heart is often the most lethal consideration.
Direct current (current that flows continuously in one direction) is often considered to be more dangerous than alternating current, the reason given that it can cause muscles to clamp down on the source of current making it difficult to release oneself from it before significant damage results. However, higher voltage AC current is typically a much more prevalent and therefore more frequently occasioned hazard.
Very high frequency alternating current tends to flow along the surface of a conductor however the low frequency of mains alternating current does not demonstrate this characteristic.
Chris, I too have been thrown violently by muscle spasms due to redirected current flow. Fortunately we both have (so far) landed in a place where we lived to relate the unpleasantness of being a live conductor of electricity.
Even disconnecting a lowly 1.5V AA battery from an inductive circuit can under the �right� conditions knock you off your perch. There is (at a minimum) one good reason to keep one hand in your pocket when working with 'live' curcuits.
Voltage, the force which pushes current through a conductor, determines how much current will flow through a given conductor.
The human body has a fairly low resistance to current flow, so depending on the path provided, the amount and duration of current flowing through the heart is often the most lethal consideration.
Direct current (current that flows continuously in one direction) is often considered to be more dangerous than alternating current, the reason given that it can cause muscles to clamp down on the source of current making it difficult to release oneself from it before significant damage results. However, higher voltage AC current is typically a much more prevalent and therefore more frequently occasioned hazard.
Very high frequency alternating current tends to flow along the surface of a conductor however the low frequency of mains alternating current does not demonstrate this characteristic.
Chris, I too have been thrown violently by muscle spasms due to redirected current flow. Fortunately we both have (so far) landed in a place where we lived to relate the unpleasantness of being a live conductor of electricity.
Even disconnecting a lowly 1.5V AA battery from an inductive circuit can under the �right� conditions knock you off your perch. There is (at a minimum) one good reason to keep one hand in your pocket when working with 'live' curcuits.
Almost without fail, Buenchico�s posts are very accurate/correct, however he is wrong to suggest touching both terminals of a 12V car battery will result in a very painful jolt.
Although a car battery has the capability to deliver over 100 amps for short periods, the factor limiting the amount of current that will flow is the resistance of the human body, and so very little current will flow, and no jolt felt. This will be the case whether touching of the battery terminals is accidental or deliberate.
All you car mechanics can relax, knowing that you are not in imminent danger of electrocution.
Although a car battery has the capability to deliver over 100 amps for short periods, the factor limiting the amount of current that will flow is the resistance of the human body, and so very little current will flow, and no jolt felt. This will be the case whether touching of the battery terminals is accidental or deliberate.
All you car mechanics can relax, knowing that you are not in imminent danger of electrocution.
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The inside of the body is salty and quite conductive. However dry skin is a reasonable insulator and this stops you getting a shock from a car battery.
Sweaty skin is much more conductive and you can get an unpleasant shock from 30 volts DC.
Electrocution has happened from as little as three volts. The case involved two workers cleaning out an electroplating bath. These baths contain highly conductive ionic solutions and no doubt they were also sweaty. Lots of current flowed.
An AC shock is worse than DC because it continually reverses. The body tends to polarise against the DC voltages so after a while the current tapers off.
However given enough voltage DC can be horrific. The EHT supplied to the old CRT colour television is 25 to 30 kilovolts. Technicians squating behind the set and coming into contact with the EHT can be stimulated to jump extraordinary heights and hit the ceiling. This happens because the muscles are much stronger than the brain ever tells them to be.
Sweaty skin is much more conductive and you can get an unpleasant shock from 30 volts DC.
Electrocution has happened from as little as three volts. The case involved two workers cleaning out an electroplating bath. These baths contain highly conductive ionic solutions and no doubt they were also sweaty. Lots of current flowed.
An AC shock is worse than DC because it continually reverses. The body tends to polarise against the DC voltages so after a while the current tapers off.
However given enough voltage DC can be horrific. The EHT supplied to the old CRT colour television is 25 to 30 kilovolts. Technicians squating behind the set and coming into contact with the EHT can be stimulated to jump extraordinary heights and hit the ceiling. This happens because the muscles are much stronger than the brain ever tells them to be.
hi figs, I get that a lot as well. It seems to happen especially if I have synthetic soles on or synthetic jumpers, and often occurs in department stores and shopping centres. I was taking a sandwich off the (metal) shelf in Boots recently when what felt like 2000 Volts popped out of my finger, I yelped and the shop assistant smiled, casually pointing out that 'Och we get that all the time in here', which obv made me feel much better :-)
I don't know why some people get it more than others. It's maybe cos we're cool people. lol
I don't know why some people get it more than others. It's maybe cos we're cool people. lol
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