Hi, I've got a question about Earthing.
First, according to the law of conservation of energy which states that: Energy can be neither created nor be destroyed, but it transforms from one form to another.
here is my question:
Where does the leakage current go to after it goes to the earth? and why doesn't the earth shock us due to the current it gets from Earthing?
Thanks.

 

See the 'Concept of earth ground'
Here.
http://www.ese.upenn.edu/detkin/instruments/misctutorials/Ground/grd.html
The earth return current requires a source reference.
Earth is considered an electrically neutral body.
Max.

 

Well, that means that there are 2 electrodes dug in the ground for each building?
one for the source and the other for the leakage current?

 

Answer to question 2 first : No there is one earth electrode, although it may have multiple prongs.

Question1 about conservation of energy :

Current is not energy, it is electric charge. I don't know how much physics you have done but the energy involved depends on the other electrical parameters as well as charge such as voltage, resistance and time.
This all adds up to the leakage energy being very low (hopefully).

If the leakage is not low then yes you can get a shock from a defective piece of equipment that produces that excessive leakage, but not from the earth itself.

The earth is defined as a special connection that does not change its voltage potential regardless of how much current you put into it.

This is has its limits since nothing is a perfect earth, but it needs somethig very powerful such as a near miss from lightning to raise the earth potential sufficiently to shock.

 

Don't all buildings have an "earth electrode" (usually the incoming gas main and/or mains water supply pipes) and the mains neutral connected to earth at the nearest substation making two?

 

The earth just acts as a very large conductor that carries any leakage current to the source ground point (such as the power pole transformer ground). Remember all current flow requires a complete circuit.

The earth also acts as a large capacitor which can absorb charge, such as from a lightning strike, but that's balanced out from the opposite charge carried to the ground by the rain drops.

To be shocked requires a voltage difference, so even if the earth is charged, what is that with respect to? A bird can be sitting on a 100kV power line and not be shocked since it's not touching anything at a different voltage.

 

nice information
thanks all

 

Well, that means that there are 2 electrodes dug in the ground for each building?
one for the source and the other for the leakage current?

For purposelessly earth grounded systems, the, often remote, source of supply is directly referenced to ground, at the end service point, the supply may or may not be re-referenced to ground, but in either case a service point ground conductor is created or set up in the manner of ground rod or metallic water supply pipe etc.
Max.

 

Utility company sized electricity isn't one of my things, but I used to sail with a guy who made a career out of it. As I recall, for a standard 3-prong AC plug, leakage current returns to the power company's generator. That the conductor also is connected to another conductor that is buried in the ground does not mean that leakage current is somehow flowing into the dirt. Earth ground is a reference potential, not a power conductor.

ak

 

Don't all buildings have an "earth electrode" (usually the incoming gas main and/or mains water supply pipes) and the mains neutral connected to earth at the nearest substation making two?

It all depends on the geographic area among other things. Where I live, an earth connection is established for Neutral at the distribution transformer. A ground at the building is optional.

By the way, I have read more than once that it is poor form to use a gas pipe for a ground connection. It probably hasn't happened very many times if ever, but imagine what a spark in close proximity to a gas leak might do. Water pipes (if metal) ok, gas pipes -probably not.

 

In N.A. the earth ground is not only supplied by the service supplier, but is also re-referenced to ground and the neutral at the service entry.
I know at one time in the UK, not only was a earth conductor not supplied by the service Co. it was a no-no to connect the earth and neutral at the panel.
A local qualified earth ground had to be established either via metallic water supply or a ground rod.
Max.

 

It all depends on the geographic area among other things. Where I live, an earth connection is established for Neutral at the distribution transformer. A ground at the building is optional.

By the way, I have read more than once that it is poor form to use a gas pipe for a ground connection. It probably hasn't happened very many times if ever, but imagine what a spark in close proximity to a gas leak might do. Water pipes (if metal) ok, gas pipes -probably not.

Please have a look at this.

 

Hello, paulktreg.

I hope you are not under the impression that the pictures in your rerference in post#12 are (edit 'not' deleted) examples of using the gas pipe as a protective earth for the mains electrical system as you suggested in post#5 ?

Your pictures show 'cross bonding' (it's stated in there somewhere) between the gas service pipes and the earth connection probably supplied by the electricity board.
This is an entirely different proposition.

No supply these days should rely on connection to another incoming service, which probably arrives in a plastic pipe.

 

... why doesn't the earth shock us due to the current it gets from Earthing?
Thanks.

The voltage between earth and a point above it can be measured. It changes with the seasons and the time of day and increases as the point goes up. The voltage is not very high though, as the charge has a huge amount of space to spread over, the entire earth. There would be sparks if it was not for the fact that appliances are earth grounded.

 

As a point of info, it is no longer permissible by the National Electrical Code to use gas or water pipes for electrical grounding.

If a plumber disconnects the pipe and there's a ground fault on an appliance, the current path is now through the person!!!

If a pipe is still used as a ground, all power to the entire building must be shut off prior to working on the pipes.

 

Wow, I don't want any of you guys wiring my next house. (I have built and wired two houses by the way.)

You may not use metal water pipe or metal gas pipe as a grounding electrode, but water and gas lines must be bonded (connected) to the local ground. I have not seen any building code that does not indicate that.