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How Exactly Does Earthing Work?

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RCinFLA

Well-Known Member
Are you refering to G.F.I.'s (ground fault interrupter)?

If so, they don't really need a ground wire.

G.F.I.'s take the two power leads and run them in opposite turns direction on to a toroid core. A sense winding feeds an amplifer/detector determines if an output exists on the sense winding.

If the power leads currents are exactly equal (goes in exactly equals goes out) their fields will cancel in the toroid core and there will be zero output from sense winding.

A slight imbalance due to leakage to ground on one of the two power leads will result in non-cancelling fields in the sense transformer and therefore and output in the sense winding that is used to trip open the relay on the power leads.

They can detect 30-50 microamps of leakage with 5-10 amps on a hair drier.
 
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Nigel Goodwin

Super Moderator
Most Helpful Member
No basic Earthing that prevents electric shocks:D
That's not what it does - the use of earthing is often mis-understood, even by many members here. It can help under certain specific circumstances, but is far more dangerous under just as many other specific circumstances.

Wont the leaking current always be passing through ground?
Hence wastage of enormous current?
No, there is no leaking current.
 

transistor495

Member
Forum Supporter
Actually all metal parts of appliances that may come direct contact with our body normally earthed. Imagine there's a leakage of current to these metal parts by accidental contacts. the grounding system provides a cool less resistive auxiliary path for the current to flow to the ground than your body. Thus you are escaped.

This is my concept :)
 

colin55

Well-Known Member
Let me explain. The alternating current that comes to your house from a supplier consists of two wires. One wire is connected to ground at the supplier-end and this wire is called neutral. The other wire is called “live” and it actually goes 150v higher than ground then 150v lower than ground at a rate of 60 times per second. If you touch the neutral wire, nothing will happen. You will not get a shock. But if you touch the live wire you will get a tingle.
Now we come to a toaster.
The heating element inside the toaster is insulated (isolated) from the metal case at both ends and if the metal case is not connected to any other wire, you will not get a tingle if you touch it.
But suppose a paper clip falls into the toaster and it touches the element where the neutral wire is connected. Again, if you touch the case you will not get a tingle. But if the paper clip touches the live wire and the case, you will get a tingle.
If we connect the case to a wire that goes to the ground or earth, when the paper clip touches the active wire and case, the 150v positive/negative will cause a current to flow and if this current is large enough, it will trip the circuit breaker or blow the fuse.
Both the neutral and earth wires are at zero potential and you would think you could simply connect the neutral to the case. But if we did this, we would have a problem.
Suppose someone wired the toaster so that the neutral and active were reversed.
Anyone touching the outside of the toaster and also touching a metal item such as the sink, would get a tingle, even though the toaster did not have a “fault.”
That’s why the earth is a separate wire and in most houses it is generated at the front of the house – such as connecting to a water pipe or a pipe buried in the ground. It does not come from the street.
This is mainly done because the neutral wire develops a voltage when long runs are encountered and high currents are flowing.
Earthing at the house just pulls everything to absolute zero volts.
 

HATHA

New Member
hi friends
That's not what it does - the use of earthing is often mis-understood, even by many members here. It can help under certain specific circumstances, but is far more dangerous under just as many other specific circumstances.



No, there is no leaking current.
like what?
can you explain little bit more(if you don't mind)? under what circumstances will earthing be dangerous?
for example when lightning happen is it lead to make any closed path with the device being earthed?:confused:
 

Nigel Goodwin

Super Moderator
Most Helpful Member
hi friends


like what?
can you explain little bit more(if you don't mind)? under what circumstances will earthing be dangerous?
Hand on earthed scope, other hand on live wire - BANG.

To get a shock you need two connections, earthed appliances give you one of those instantly. Most items these days are type II, double-insulated, with no earth, which are probably the safest?.
 

colin mac

New Member
It doesn't let me link directly. Click Electricity > Household Wiring
Look at the links as well, there is one called Ground Wire
 
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HATHA

New Member
Hand on earthed scope, other hand on live wire - BANG.

To get a shock you need two connections, earthed appliances give you one of those instantly. Most items these days are type II, double-insulated, with no earth, which are probably the safest?.
aha!! I forgot that. simple way to make grilled chicken:D
 

crutschow

Well-Known Member
Most Helpful Member
Another Ques about Earthing:
Why not all appliances have 3 pin plug (included earth pin)?
It depends upon the insulation technique used for the device. It it has double insulation between the power and and any metal exposed parts, or the device has an all plastic case, then it doesn't need to be grounded.
 
It depends upon the insulation technique used for the device. It it has double insulation between the power and and any metal exposed parts, or the device has an all plastic case, then it doesn't need to be grounded.
Ok, then why can't the Comp monitor be done in the same way(double insulation)?(So that it doesn't cause tingle; jus like TV)
If thats done to all devices, then there is no requirement of earthing line!!!???
 

mneary

New Member
It's difficult to make a computer monitor with no exposed metal parts because of the video cable.
 
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