electric shock felt by homan body

[u04f061]

when human body comes in touch with live wire coming from the suply source when his body is also touching the ground(earth) he feels electric shock.it means that some amount of current ~50mA is passing through his body which may cause death.this means that a circuit is complete for current to flow.

but when a voltmeter is connected with one lead connected to live wire and other connected to ground(our earth) then voltmeter gives zero volts reading.if no voltage is present between these two points then why humans feel shock?

 

[tamerakshar]

I think the voltmeter cicuitary acts as a high resistance path for the current while the human body acts as a low resistance path.
TeE ThE EdE

 

[vsgiri]

In a three pin socket (Phase,Neutral,Ground), if you connect voltmeter b/w phase and ground you'll find that it's live! This clearly proves that there is a potential difference b/w phase and ground.
(If you don't find any live voltage, then your ground line is open - potentially dangerous! Fix it quickly!)

Giri

 

[Sal]

Hi

I agree with vsgiri, you may have measured with the wrong terminal, employing the above notation you can measure between phase and any ground metal such as the water supply pipes, you will find a latent voltage.

Sal

 

[u04f061]

i am not talking about that the voltage does not exist b/w live and ground.i am talkig about this
we (friends) measured voltage by connecting red lead with live wire black with our earth (a planet on which we are living not a wire ).it gave us no reading .but if a person standing on earth touches the live wire he feels shock.if voltmeter does not give voltage b/w live and earth it means voltage does ot exist.if this is the case why we feel shock?

 

[tamerakshar]

Have you read the first post.
Grrrrrrrrr.
TeE ThE EdE

 

[XNOX_Rambo]

Is the voltmeter digital (high impedance input) or analogue?

 

[vicky]

hi
dear read this
The primary variable for determining the severity of electric shock is the electric current which passes through the body. This current is of course dependent upon the voltage and the resistance of the path it follows through the body. An approximate general framework for shock effects is as follows:

Electric Current
(1 second contact) Physiological Effect
1 mA Threshold of feeling, tingling sensation.
10-20 mA
"Can't let go!" current - onset of sustained
muscular contraction.
100-300 mA Ventricular fibrillation, fatal if continued.

One instructive example of the nature of voltage is the fact that a bird can sit on a high-voltage wire without harm, since both of its feet are at the same voltage. You can also see that the bird is not "grounded" -- you will not be shocked by touching a high voltage if there is no path for the current to reach the Earth or a different voltage point. Typically if you touch a 120 volt circuit with one hand, you can escape serious shock if you have insulating shoes which prevent a low-resistance path to ground. This fact has led to the common "hand-in-the-pocket" practice for engineers and electrical workers. If you keep one hand in your pocket when touching a circuit which might provide a shock, you are less likely to have the kind of path to ground which will result in a serious shock.

 

[Eric Best]

i am not talking about that the voltage does not exist b/w live and ground.i am talkig about this
we (friends) measured voltage by connecting red lead with live wire black with our earth (a planet on which we are living not a wire ).it gave us no reading .but if a person standing on earth touches the live wire he feels shock.if voltmeter does not give voltage b/w live and earth it means voltage does ot exist.if this is the case why we feel shock?

In my opinion, if the voltmeter really doesn't show any voltage, then you have selected most likely the dc range. Another possibility is a very poor contact between the probe and the earth - if the earth is dry (sandy or so), it can have quite high resistance - although even in this case the (ac) voltmeter should display a voltage different from zero!
Note: As to the human body, it can "feel" a very low ac electric current passing through it (in case when the earth resistance is high).

Eric

 

[vicky29]

is there some circuit which trips off whole power supply when someone comes in contact with live(is getting a shock)

 

[roy mathew]

Hi u04f061,

Our planet earth is considered as an electron bank. How ever a good electric connection required proper contact if you just connected earth by just touching a terminal to the soil the contact may not be that good. When you stand on ground your naked foot is establishing contact to earth with a force corresponds to body weight this helps conductive substance in the soils to come more closely to your foot and helps conduction... The amount of electric shock or conduction depends on the soil composition and the amount of moisture present in the soil as well as on your skin.

 

[XNOX_Rambo]

Most likely you are feeling a capacitive current.
You can tell the difference by the sensation in your body. A capacitive current
will only manifest itself at the point of contact with the conductor, i.e. you will
feel a local tingling in your skin. A "real" current through the body will be felt
throughout the entire current path - I have taken 110 VAC from hand to hand so I
know the feeling... :?

When measuring a capacitively coupled voltage in a floating conductor a digital
voltmeter will show a value - maybe 50 VAC - due to its high input impedance, but
an analogue voltmeter with a lower input impedance, say 100 kΩ, will "bleed" the
minute capacitive current to ground and show 0 V.
This is a common measuring misstake due to the popularity of DMM:s.

 

[u04f061]

hi
dear read this
The primary variable for determining the severity of electric shock is the electric current which passes through the body. This current is of course dependent upon the voltage and the resistance of the path it follows through the body. An approximate general framework for shock effects is as follows:

Electric Current
(1 second contact) Physiological Effect
1 mA Threshold of feeling, tingling sensation.
10-20 mA
"Can't let go!" current - onset of sustained
muscular contraction.
100-300 mA Ventricular fibrillation, fatal if continued.

One instructive example of the nature of voltage is the fact that a bird can sit on a high-voltage wire without harm, since both of its feet are at the same voltage. You can also see that the bird is not "grounded" -- you will not be shocked by touching a high voltage if there is no path for the current to reach the Earth or a different voltage point. Typically if you touch a 120 volt circuit with one hand, you can escape serious shock if you have insulating shoes which prevent a low-resistance path to ground. This fact has led to the common "hand-in-the-pocket" practice for engineers and electrical workers. If you keep one hand in your pocket when touching a circuit which might provide a shock, you are less likely to have the kind of path to ground which will result in a serious shock.

i think if one lead connected to hot wire and other connected to mother earth are at different voltage levels.are not?
i think u tried to answer my question well but i can't see what i am looking for.however i am thankful to u for this and request u to have a look at the problem once again and help me.one of my friend says
"I can now see what you are trying to do. I think the main reason you aren't seeing a voltage is the conductivity of the ground you are probing. The very small tip of the probe is only contacing a very small part of the ground and if that small part of the ground is not conductive you won't see any voltage. When a human stands on the ground his feet are in contact with more surface and hence a greater possibility of conducting electricity. If you were to drive a metal rod into the ground then you would probably be able to measure a voltage. Also if you were to hose water over the ground this may also help. "

this is similar in some fashion to fact u pointed out.but voltage does not depend upon conductivity level.it should exist if cct is open

 

[u04f061]

Have you read the first post.
Grrrrrrrrr.
TeE ThE EdE

yes but u are talking about high resistance which should be considered if i would have been measuring current.but this is not the case.i am talking about the voltage which must exist even if the circuit is open

Added after 6 minutes:

Is the voltmeter digital (high impedance input) or analogue?

we tried for both analogue and digital and got same results

Added after 15 minutes:

i am not talking about that the voltage does not exist b/w live and ground.i am talkig about this
we (friends) measured voltage by connecting red lead with live wire black with our earth (a planet on which we are living not a wire ).it gave us no reading .but if a person standing on earth touches the live wire he feels shock.if voltmeter does not give voltage b/w live and earth it means voltage does ot exist.if this is the case why we feel shock?

In my opinion, if the voltmeter really doesn't show any voltage, then you have selected most likely the dc range. Another possibility is a very poor contact between the probe and the earth - if the earth is dry (sandy or so), it can have quite high resistance - although even in this case the (ac) voltmeter should display a voltage different from zero!
Note: As to the human body, it can "feel" a very low ac electric current passing through it (in case when the earth resistance is high).

Eric

we took care of this factor that whether the voltmeter is in ac or dc.we measured voltage on ac scale.i am not understanding the context of poor contact.we just dipped one probe into earth.we also repeated this by pressing probe hardly against wall.it means contact was proper.

more over the concept of resistance is irrelavent to measuring voltage.

your last note is quite reasonable.if u want to extend this more,then i think may i be able to get solution to my problem

Added after 11 minutes:

is there some circuit which trips off whole power supply when someone comes in contact with live(is getting a shock)

there was no such circuit

 

[lmtalsoul]

One instructive example of the nature of voltage is the fact that a bird can sit on a high-voltage wire without harm, since both of its feet are at the same voltage. You can also see that the bird is not "grounded" -- you will not be shocked by touching a high voltage if there is no path for the current to reach the Earth or a different voltage point.

So you mean to say that if say, by misfortune, the bird puts just one leg in the beginning and then in a split second, the other, it'll still die because it suffered potential difference? I'm sorry, if the question is vague but I didn't quite get your explanation.

 

[u04f061]

Hi u04f061,

Our planet earth is considered as an electron bank. How ever a good electric connection required proper contact if you just connected earth by just touching a terminal to the soil the contact may not be that good. When you stand on ground your naked foot is establishing contact to earth with a force corresponds to body weight this helps conductive substance in the soils to come more closely to your foot and helps conduction... The amount of electric shock or conduction depends on the soil composition and the amount of moisture present in the soil as well as on your skin.

it means by pressing hardly the lead of voltmeter against earth will make the connection proper and voltmeter should give the reading

Added after 8 minutes:

Most likely you are feeling a capacitive current.
You can tell the difference by the sensation in your body. A capacitive current
will only manifest itself at the point of contact with the conductor, i.e. you will
feel a local tingling in your skin. A "real" current through the body will be felt
throughout the entire current path - I have taken 110 VAC from hand to hand so I
know the feeling... :?

When measuring a capacitively coupled voltage in a floating conductor a digital
voltmeter will show a value - maybe 50 VAC - due to its high input impedance, but
an analogue voltmeter with a lower input impedance, say 100 kΩ, will "bleed" the
minute capacitive current to ground and show 0 V.
This is a common measuring misstake due to the popularity of DMM:s.

i have never read about capacitive current .plz will u guide me what it realyy mean ?more over u are confusing voltage with curren
"When measuring a capacitively coupled voltage in a floating conductor a digital
voltmeter will show a value - maybe 50 VAC "unit of v with i.moreover what is floating in this problem.

 

[XNOX_Rambo]

u are confusing voltage with curren

No, I'm not - but I understand your confusion. Here is a link that deals with
different types of coupling: http://www.cda.org.uk/megab2/elecapps/earthing/sec101.htm

You can make an experiment to verify the effect. Take two lengths of insulated
wire - 2 meters should be enough. Twist them together throughout the entire length.
It needn't be at tight twist, just so they are next to each other. Connect one
of the wires to a hot live AC wire.
If you now touch the end of the other, floating wire you should feel the capacitive current.

The picture below has been taken from here: **broken link removed**

 

[roy mathew]

is there some circuit which trips off whole power supply when someone comes in contact with live(is getting a shock)

Hi, Earth leakage circuit breakers are available. ELCB