Why do we get electric shocks when there is no potential difference?

[asad1111]

so i have learned that potential difference always occurs between points which have some common node that is if you have two circuits which don't have anything in common there will not exist any potential difference between any two points my question is why do we get electric shock when we touch live wire because there is nothing common between distributed live wire and Earth and even if i check potential difference between live wire and Earth using dmm i get 0 volts so why do we get electric shock when there is no potential difference

 

[Bassalisk]

We went through this so many times. It depends. Depends on a lot of things. Does null and Earth have same connection, where are u standing, how isolated you are... Use search forum.

 

[asad1111]

okay let me explain if you touch live wire bare foot by standing on floor you will get electric shock right but when i measure potential difference between live wire and floor iam standing on using dmm it comes out to be "zero" now simply question is how can current flow through me when there is no potential difference
regarding your question about is Earth and neutral common iam using wires commming right out of electric meter if neutral coming from electric meter is earthed somewhere in the distribution or transmissin station i don't know about that.

 

[Bassalisk]

okay let me explain if you touch live wire bare foot by standing on floor you will get electric shock right but when i measure potential difference between live wire and floor iam standing on using dmm it comes out to be "zero" now simply question is how can current flow through me when there is no potential difference
regarding your question about is Earth and neutral common iam using wires commming right out of electric meter if neutral coming from electric meter is earthed somewhere in the distribution or transmissin station i don't know about that.

How do you know you will get electric shock? You tried this?

 

[I_am_learning]

How do you know you will get electric shock? You tried this?

What are you asking? Are you insisting him to try it before believing its true. Please don't try it.
It can be Fatal.

 

[Zryn]

Question:

my question is why do we get electric shock when we touch live wire because there is nothing common between distributed live wire and earth

Answer:

potential difference always occurs between points which have some common node

if you have two circuits which don't have anything in common there will not exist any potential difference between any two points

So there must be something in common otherwise you wouldn't get shocked, no?

if i check potential difference between live wire and Earth using dmm i get 0 volts so why do we get electric shock when there is no potential difference

If you touch a live wire and Earth and get shocked, and then measure that same live wire and Earth connection and get 0V, then its possible that protection (CB/RCD) somewhere has tripped out the live wire due to fault detection.

Have you ever played around with a 9V battery on your tongue and a DMM?

 

[asad1111]

How do you know you will get electric shock? You tried this?

well yeas i accidently touched bare part of live wire while looking at electric meter now can ypu give some resonable answer to question

 

[asad1111]

Question:



Answer:





So there must be something in common otherwise you wouldn't get shocked, no?



If you touch a live wire and Earth and get shocked, and then measure that same live wire and Earth connection and get 0V, then its possible that protection (CB/RCD) somewhere has tripped out the live wire due to fault detection.

Have you ever played around with a 9V battery on your tongue and a DMM?

i don't think that protection has tripped but mot only in my home in every home when you touch live wire bare footed by standing on Earth current will flow though us and i highly doubt that in every home protection is tripped so can u explain how this current flow without any potential difference and without protection damge the only thing that i think of is some where in transmission or distribution center neutral is connected to Earth and thus when we touch live wire it we complete the circuit and current flows through us because without Earth connected to neutral circuit should never be complete when we touch live wire
regarding have i played with battery yes i have

 

[Zryn]

...i don't think that protection has tripped...

So go check the circuit breaker on your house or see if other appliances still work.

...but mot only in my home in every home when you touch live wire bare footed by standing on Earth current will flow though us and i highly doubt that in every home protection is tripped so can u explain how this current flow without any potential difference and without protection damge

There had to be a potential difference when the current was flowing, otherwise it wouldn't flow. This is one of those laws that you can't get around. That there isn't a voltage now, doesn't mean there wasnt a voltage then.

the only thing that i think of is some where in transmission or distribution center neutral is connected to Earth and thus when we touch live wire it we complete the circuit and current flows through us because without Earth connected to neutral circuit should never be complete when we touch live wire

The neutral wire in a house (depending on where you live) is connected to an Earth stake, in a system known as Multiple Earthed Neutral (MEN). When you touch an Active wire and the Earth you have an Earth Leakage fault occur, and the house protection known as a Residual Current Device (RCD) is set to detect any discrepency between the Active and Neutral wire greater than 30mA, so with the Eearth Leakage fault shocking you, the current is traveling through the Earth as its return path and not the Neutral, and a discrepency is registered, which opens a contact (switch in a relay) and shuts off power to that part of the house.

Also, just about every transformer between the power station and your house will be earthed, both step up and step down, wherever the neutral on the Star/Wye is.

And in some odd cases the power companies use 11kV:11kV transformers where they can ground the neutral on one side and put a resister in series (10R to 150R) to control any fault currents (called a Neutral Earthed Resister or NER).

 

[asad1111]

"zryn" thanks for your thorough reply this was the part i needed to know
"Also, just about every transformer between the power station and your house will be earthed, both step up and step down, wherever the neutral on the Star/Wye is.
"
so if i understand correctly the neutral of the star connection coming out of transformer is connected to Earth that's why when we touch live wire we actually complete circuit between live wire and neutral and thus get electric shock is this right?

 

[Bassalisk]

What are you asking? Are you insisting him to try it before believing its true. Please don't try it.
It can be Fatal.

I wasn't encouraging him to do that. I simply asked how could he know he will get shocked if he didn't actually get shocked this way. But like he said in the post after, he did.

It didn't make sense to me, that DMM is measuring 0 V and he gets shocked. He had to complete the circuit somehow. Anyway Zryn gave him the most probable situation.

 

[Zryn]

so if i understand correctly the neutral of the star connection coming out of transformer is connected to Earth that's why when we touch live wire we actually complete circuit between live wire and neutral and thus get electric shock is this right?

Close.

Your house also has a connection where the neutral wire is connected to an Earth stake (copper rod driven a few feet into the ground), so technically you would be completing the circuit up your houses earth, not up the distribution transformers neutral connected earth.

 

[siri.satyam]

If, by chance, outside electrical energy enters our bodies, now conductors, we will be shocked when the voltage encounters, and interferes with, the internal electrical energy our nervous systems produce. The shocks to our bodies, and the amount of damage the electricity does to them, depends upon the voltage our bodies are subjected to, upon its level of energy, and upon how much our bodies resist the flow of the electrical energy.

Ref:-http://www.coolquiz.com/trivia/explain/docs/electric.asp
http://www.allaboutcircuits.com/vol_1/chpt_3/3.html