Hi everyone , i know it seems to be a rediculous question but i started to study electrical engineering and i have some problems understanding some Basics and i need your help ....

- i studied a circuit analysis course (where i heared about ground) and my instructor said "the ground in a circuit is nothing but a refrence point and it can be any node in the circuit since it is virtual ".... i got it and it was ok until i knew about a real world (not virtual) Ground , i googled it and read some topics but i still see the fog .

first of all in my countrey we have 220V outlet with only two prongs (unlike the rest of the world i guess) so we don't have that Ground thing and i need answers from those who have it ...

1- it is common that somebody touches the hot wire accidently and gets shocked , but why ? where is the circuits ? current flows from the soruce to the wire to someone's body to what ? i asked this question before and the answer was simply " because that one was standing on the ground " but i didn't get it .. we have two wires : hot and neutral so the ground is not even in the circuits .. can you explain why current flow through someone's body (the image i attached illusrates my visualization, help me correcting it)

2- i heared that if you want to discharge yourself just stand with bare foots on the ground , why ? does the ground absorbs electricity ? is that the same reason why electricity flows through my body to ground (because ground absorbs electricity??!!)

3- my last question .... ground in real world is the planet earth , isn't it ? considering my weird visualization (about ground absorbs elctricty) , an apartment in the fifth floor, my two prongs outlet and me touching the hot wire the current will flow from the soruce to the wire to my body and then nothing , now why am i still being shocked ? i am five floors away from the ground ? what is the connection between planet earth and the fifth floor ground that causes the current flow ??

thank you all i know it is some sort of stupidity but i need some answers to clear the fog

 

To answer your question, you have to know something about how the power-distribution-grid in your country is set-up. In the USA or CAN, if you are standing on moist earth in bare feet and you touch the narrow prong in a standard wall outlet, you will get a nasty shock or be dead. If you touch the wider prong, nothing happens, because of how the power grid is wired.

How is it wired in your country? Since you didn't put in a country when you registered for this web site, we have not a clue!

 

http://www.allaboutcircuits.com/textbook/direct-current/chpt-3/shock-current-path/

 

first of all in my countrey we have 220V outlet with only two prongs (unlike the rest of the world i guess) so we don't have that Ground thing and i need answers from those who have it ...

A country where you do not use a third, protective earth, connection is probably not a developed country but you can still add this protection in your own installation. Most countries have transitioned over several decades. In my building I installed my own protective ground years before it was installed in the whole building.

At any rate, even if this protective ground connection is still optional in your country, the generators and transformers are grounded and that is why you complete the circuit with your bare feet.

 

To answer your question, you have to know something about how the power-distribution-grid in your country is set-up. In the USA or CAN, if you are standing on moist earth in bare feet and you touch the narrow prong in a standard wall outlet, you will get a nasty shock or be dead. If you touch the wider prong, nothing happens, because of how the power grid is wired.

How is it wired in your country? Since you didn't put in a country when you registered for this web site, we have not a clue!

my country is Egypt , and you are right i don't know how the grid is wired

 

A country where you do not use a third, protective earth, connection is probably not a developed country but you can still add this protection in your own installation. Most countries have transitioned over several decades. In my building I installed my own protective ground years before it was installed in the whole building.

At any rate, even if this protective ground connection is still optional in your country, the generators and transformers are grounded and that is why you complete the circuit with your bare feet.

ok grounding generators will close the circuit and get me shocked , but why grounding generators in the first place ?? is there any need to do this ?

 

http://www.allaboutcircuits.com/textbook/direct-current/chpt-3/shock-current-path/

thank you i will take a look

 

Also take a look here from U of Penn.
It also covers the misuse of the Earth ground symbol.
http://www.ese.upenn.edu/detkin/instruments/misctutorials/Ground/grd.html
The practice of electrical grounding is a safety measure.
In N.A. a piece of equipment can also be double insulated so is not fitted with a ground, but a GFI outlet is advisable in some conditions.
Max.

 

Egypt uses type C and F sockets, rated at 220V 50Hz, type C is Ungrounded and rated at 2.5 amps max, and is being phased out in Europe, replaced by types E,F J,K upto 16amps grounded.

The generator at the power station will be at ground potential and Earthed, and connected to Neutral, this cable is also brought out to the supply with Phase called TNS or TNCS (PME.)

http://www.worldstandards.eu/electricity/plugs-and-sockets/

 

ok grounding generators will close the circuit and get me shocked , but why grounding generators in the first place ?? is there any need to do this ?

If you don't connect a generator to a known ground, it can accumulate static electricity or a tiny internal leakage can cause the machine to be hundreds of volts (in either polarity) compared to planetary ground. This voltage can arc across delicate parts or it can go through a person. Better to hard wire it to a ground you know than to let it find its own equilibrium voltage and send that through a person.

 

I don't think anyone has mentioned yet that mains ground is connected to the Neutral line either at your junction box or at the power plant. You're still making a circuit.

 

Maybe this vid will help (start at 9:30)

 

- i studied a circuit analysis course (where i heared about ground) and my instructor said "the ground in a circuit is nothing but a refrence point and it can be any node in the circuit since it is virtual ".... i got it and it was ok until i knew about a real world (not virtual) Ground , i googled it and read some topics but i still see the fog .

first of all in my countrey we have 220V outlet with only two prongs (unlike the rest of the world i guess) so we don't have that Ground thing and i need answers from those who have it ...

What you could do as an exercise to find out if the service provider uses a (Grounded) neutral conductor is to drive a (6ft) ground rod and measure the voltage from your two supply conductors and see what kind of voltage you get, if one is very low or close to zero, then use a incandescent lamp from the low conductor to the rod and again measure the voltage, it would be close to zero if a neutral is used..
The U of PENN article give a very good definition of what earth ground exactly is.
Max.

 

May I say, as a the most basic conclusion, that in any circuit the only thing that a schematic cannot lack is "common" (properly denoted by the triangle shown below)?

 

Hear Hear !


Max.

 

May I say, as a the most basic conclusion, that in any circuit the only thing that a schematic cannot lack is "common" (properly denoted by the triangle shown below)?

View attachment 93390

Lots of schematics don't show a common. Consider the schematic for something like a flashlight or just about any other battery powered device. A common symbol can be a handy convenience, but it is certainly not something that absolutely has to be indicated, particularly for trivially simple circuits.

 

Mohamed, Your drawing is missing a connection at the power generator. There is usually a connection from the NOT-HOT(neutral) side to ground at the power source(generator, transformer, etc), From that you will see that touching the HOT side will complete a circuit through YOU(or any load).
As for being in a five story building and getting a shock, the same will apply but it depends on what you are wearing(rubber soled shoes or Nikies, etc) and the floor covering. Concrete is not regarded as a good insulator(steel reinforcing bars) but wood carpet(dry) can be ok.
Also if you contact the HOT side and any metal pipes (or any appliance which has the metal case connected to ground) which go to ground somewhere you will be shocked.
The purpose of having a separate "earth" conductor connected to any metal appliance is to allow any current which occurs as a result of a fault in the "appliance" to flow directly to "ground". This will cause a large current and trip a breaker or blow a fuse to protect the wiring.
Many places now install "Residual current detection" circuit breakers which have the HOT and "NOT-HOT" wire wired to them and can detect very small(30mA) differences between the wires feeding the load. If the difference exceeds the fixed value then the breaker trips.
Basically this means that if you contact the HOT side of the load, current will flow through you to "ground" instead of the load. This will cause the RCD to "see" an imbalance and trip, protecting you from serious harm.

 

Lots of schematics don't show a common. Consider the schematic for something like a flashlight or just about any other battery powered device. A common symbol can be a handy convenience, but it is certainly not something that absolutely has to be indicated, particularly for trivially simple circuits.

I knew that a smart guy would find a flaw in my proposal. What if we set for a minimum of 4 component not all of them in series?

And, for the nitpicking sake, battery powered micro-based circuits do exist. Lots of them. Some of them should use the "common" symbol at many places in the schematic.

And that is how the war started....

 

I knew that a smart guy would find a flaw in my proposal. What if we set for a minimum of 4 component not all of them in series?

Then it would be pretty easy to offer up a circuit that had five components, not all of them in series, that you would almost certainly agree gained little or nothing from the presence of a common symbol.

There's little point in trying to define some arbitrary number of components after which the only thing that the schematic cannot lack is a common symbol.

And, for the nitpicking sake, battery powered micro-based circuits do exist. Lots of them. Some of them should use the "common" symbol at many places in the schematic.

And your point?

Of course battery powered micro-based circuit exist. What on earth could possibly have led you to believe that I was claiming they didn't. My point was merely that most battery-operated devices could get by just fine without including a common symbol. But note that I also stated that such a symbol can be a handy convenience, but that it does not absolutely have to be there, particularly for trivial circuits.

I never said that it couldn't, or even shouldn't, be used in such circuits. Your claim was that the conclusion of the discussion is that the one thing that any schematic absolutely cannot lack is a common symbol. It only takes a single counter-example to prove such a claim false. Establishing that it is reasonable to draw the schematic for a flashlight without using a common symbol proves the claim false, but in no way makes a counter claim that all schematics for battery-powered devices can't, or even shouldn't, use a common symbol.

 

Dear William,

A sentence starting with "May I say..." is not a claim.

Too the OP, sorry for digressing.