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Electric Shock

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Nick'

New Member
I am just wondering what actually is used to determine the electric shock. We have current, voltage and watt. For example, I have these:

cableA = 1A, 240V, 240watts

cableB = 240A, 1V, 240watts

Which one will shock a person?

Does it depend on voltage, current or watts?
 

BrownOut

Banned
Are you familiar with ohm's law? Shock is a result of current through your body. However, from an electrical standpoint, your body is a resistor. So, in order to analyze the whole "circtuit", you need to know the voltage and output resistance of the shocking source. 1V will not produce enough current to shock you. 240 might, depending on the source resistance.
 
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JimB

Super Moderator
Most Helpful Member
There is an old saying:

"Its the volts that jolts, but the mills that kills".

A high voltage is needed to drive current through the body.
To do you any harm needs a certaing level of current, from memory 100mA is very likely to kill you.

Electrostatic charges, such as those you get from walking on a nylon carpet can easily build up to 20,000 volts, but when you touch something which is earthed and the current flows from your body it can give you an unpleasant nip but will not hurt you. The current is low, less than 1mA, the source resistance is high.

However, if you touch something with 20,000 volts and the source resistance is low (such as the overhead power wire for an electric train), and there is a low resistance path through your body to earth then several amps will flow and you will be dead, money back guaranteed.

On the internet is a video clip of a guy in India, he his standing on the top of a train, he reaches up and touches the live wire and he is toast.

So, in your example cable A is obviously dangerous because of the voltage, it can kill you.

Cable B has other dangers, there will be strong magnetic field which could attrach metal objects. If the wires are bare, be carefull not to drop anything metalic onto the conductors, there will be one hell of a flash and a bang from the short circuit.

JimB
 

Boncuk

New Member
To do you any harm needs a certaing level of current, from memory 100mA is very likely to kill you.JimB
100mA is already 3.3 times overkill.

Safety circuit breakers (detecting current between live and protective earth) are set to the safe side of 15mA.

30mA will kill for sure.

The Indian was well done and crispy.

Boncuk
 
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BrownOut

Banned
I refer you again to ohm's law. A 9-volt battery would only push 9mA into a 1k ohm load. A solar panel only 12mA, if it's output is 12V. What if the panel outputs 25V with 1.5KOhms of output resistance. What would the resultant current be into a 1KOhm load?
 

giftiger_wunsch

New Member
But i think 30mA is very small. A 9V battery would produce more. My solar panel produces 0.5A.
A 9V battery would not produce a 30mA current through your body. A 9V would very likely produce a 30mA current if you were to shortcircuit it with a piece of wire, but fortunately for us we have much higher electrical resistance than that of copper.

As a very approximate estimate, try gripping the terminals of an ohmmeter in each hand and check your hand-to-hand resistance; I usually get 100-400kΩ (though since the human body also isn't an 'ohmic' resistor, this figure shouldn't be considered reliable). By ohm's law, to reach 30mA at 100kΩ, the supply voltage would need to be 3kV (to reiterate, 100kΩ is not reliable. 3kV would be mega overkill; don't even think about it).

A current as low as 1mA can be felt as a tingling sensation; 10mA produces quite a painful shock; 20mA can start to cause burns; 30mA is often deadly. This is only an approximate guide though.

As for the actual dangers of a shock, the most important factor is the energy of the shock. For example, 3kV @ 10mA is 30W, and if it's sustained for 10ms (0.01 seconds) then the total energy is 300mJ, which is comparatively little energy and is unlikely to cause serious injury, though it might be quite painful. This is comparable to a static shock.

On the other hand, 230V @ 50mA sustained for 10 seconds is 115J and is likely to cause serious burns (among other problems). This is comparable to being shocked by a mains supply.

I hope this has helped rather than confusing you further. :D
 
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bountyhunter

Well-Known Member
I am just wondering what actually is used to determine the electric shock. We have current, voltage and watt. For example, I have these:

cableA = 1A, 240V, 240watts

cableB = 240A, 1V, 240watts

Which one will shock a person?

Does it depend on voltage, current or watts?
The standard threshold for dangerous voltage is about 60V. Below that, no worries.
 

kinarfi

Well-Known Member
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Pommie

Well-Known Member
Most Helpful Member
100mA is already 3.3 times overkill.

Safety circuit breakers (detecting current between live and protective earth) are set to the safe side of 15mA.

30mA will kill for sure.

The Indian was well done and crispy.

Boncuk
I thought (residential) RCD were set at upto 35mA and 50mA was considered the lethal level.

Mike.
 

things

New Member
I was taught that at 70 ma you are in pain and can't let go because you muscles are contracting, at 80 to 90 you get burnt, at 100 to 200 ma your heart goes into ventricular fibrillation and it takes paddles to save your life, CPR won't help, over 200 ma and your heart clamps, once the power is removed, CPR may save your life.
Kinarfi Googled it - Liked these
OSHA Construction eTool: Electrical Incidents - How Electrical Current Affects the Human Body
Electric Current Needed to Kill a Human
Nope, I would say at 200ma you would be totally fried! Infact, even 30ma is extremely painful, even lethal ... (In my case, it was extremely painful, luckily it only got me through the hand (15kV 30ma neon sign transformer))

6ma across the heart is enough to kill ...
 
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giftiger_wunsch

New Member
Nope, I would say at 200ma you would be totally fried! Infact, even 30ma is extremely painful, even lethal ... (In my case, it was extremely painful, luckily it only got me through the hand (15kV 30ma neon sign transformer))

6ma across the heart is enough to kill ...
We've heard many different versions in the past few posts, which only goes to prove that it can vary significantly. But things is correct, 6mA is the accepted figure for causing defibrillation when it flows through the heart, and 30mA hand-to-hand is also a good estimate (you could expect approximately 6mA of this current to flow through the heart rather than taking other paths). It's difficult to provide concrete figures because it depends greatly on the individual physiology and other factors.

As already mentioned though, 200mA, or even 100mA, is enough to turn you pretty crispy :eek:
 

Pommie

Well-Known Member
Most Helpful Member
Well, as nobody has questioned it, I'm going to reiterate my belief. That is, 35mA is what RCD can be set at and above 50mA is considered lethal.

Mike.
 

Nick'

New Member
Wow, deadly electricity. Can i touch a 240v/240W/1A wire with a plastic(3 cm squared) which i am holding? If yes, why? Since the plastic is a resistor.
 

Boncuk

New Member
Wow, deadly electricity. Can i touch a 240v/240W/1A wire with a plastic(3 cm squared) which i am holding? If yes, why? Since the plastic is a resistor.
Plastic is generally an isolator.
 

mneary

New Member
Wow, deadly electricity. Can i touch a 240v/240W/1A wire with a plastic(3 cm squared) which i am holding? If yes, why? Since the plastic is a resistor.
It depends on the substance being called plastic.

More importantly, it depends on the care, understanding, and experience of the person. Not intending to insult, I would recommend for you considerably more than 3cm safety clearance from uninsulated 240V. If it's an undamaged product, use the normal care expected of any consumer.

As stated earlier, you can survive an accidental 240V shock most of the time, but there are other ways to learn about insulation, what is deadly, and such.
 

giftiger_wunsch

New Member
With a plastic.... what? You haven't said what or where the plastic is. The plastic is an insulator, not a resistor. As such, if it is in series with your body such that all current which flows through you must also flow through the plastic, it should protect you, depending on the thickness of the plastic. e.g. if the wire is insulated and you touch the insulation rather than the bare wire, of course you should be fine.
 

flat5

Member
What nobody has mentioned is the path through the body.
Hand to foot is one thing. Most of the current may not reach the nerves near the heart.
Hand to hand, most of the current may indeed affect nerves near the heart. I've always read the path through the body is important. At 100ma all bets are off :)
 

giftiger_wunsch

New Member
What nobody has mentioned is the path through the body.
Hand to foot is one thing. Most of the current may not reach the nerves near the heart.
Hand to hand, most of the current may indeed affect nerves near the heart. I've always read the path through the body is important. At 100ma all bets are off :)
It's current flowing through the cardiac muscle which is dangerous rather than through "the nerves near the heart". Also, I did mention earlier that I was talking about hand-to-hand current, and that the biggest danger will be a proportion of the current passing through the heart.

You are of course correct that hand-to-hand contact is usually much more dangerous than, for example, hand-to-foot contact as there's a good chance that most current from hand to foot on the same side of the body will flow through that side of the body and not through the heart or other particularly electrically-sensitive organs. (Really just the heart and brain mainly: the only other organ which is likely to produce a life-threatening effect would be the lungs, and they'd need to be paralysed by the current for about 5 minutes to cause death. By that time you'll probably be quite badly cooked).

Of course, another very important factor is health though. Heart or lung conditions, epilepsy, many disorders of the nervous system, pacemakers, and metal plates or rods as a result of surgery, may all have a significant contribution towards making any electric shock more dangerous for the individual. Don't forget that a significant electric shock will disrupt a decent portion of the body's own electrical activity, and electrical signals are used throughout the entire body for a wide variety of purposes.
 
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