Grounding

W

whatever

Member
Location
Florida
Occupation
Switchgear technician
I've been told that electricity always wants to get to ground and then I've been told that electricity always wants to get back to the source. With that being said, when something becomes grounded it trying to get back to its source through ground is that correct? And why exactly would a voltage want to flow into ground since earth is considered 0v it is just becuase it has a it has higher potential then earth?
 
It flows on all paths back to the source. With a grounded system, the earth is one path, but it will have an impedance 100s to 1000s of times higher than the code required effective fault clearing path. n
 
whatever said:
And why exactly would a voltage want to flow into ground since earth is considered 0v it is just becuase it has a it has higher potential then earth?
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Voltage from the utility is trying to get back to the source through the earth because the system is physically connected to the earth.

The voltage from your car battery isn't trying to get back to the source through the earth. Connecting one terminal of the car battery isn't going to do anything either. Push a screwdriver into your lawn and run a jumper wire from the positive battery terminal on your car to the screwdriver. Nothing is going to happen.
 
ActionDave said:
Voltage from the utility is trying to get back to the source through the earth because the system is physically connected to the earth.

The voltage from your car battery isn't trying to get back to the source through the earth. Connecting one terminal of the car battery isn't going to do anything either. Push a screwdriver into your lawn and run a jumper wire from the positive battery terminal on your car to the screwdriver. Nothing is going to happen.
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Ok, understandable. Just an available path, so if the negative of the battery was connected to earth too, it would connect the loop. Thanks
 
don_resqcapt19 said:
It flows on all paths back to the source. With a grounded system, the earth is one path, but it will have an impedance 100s to 1000s of times higher than the code required effective fault clearing path. n
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Ok pretty much if it was a ungrounded system its less likely to take ground as a path compared to a grounded system. Becuase its not as accessible thanks
 
whatever said:
Ok pretty much if it was a ungrounded system its less likely to take ground as a path compared to a grounded system. Becuase its not as accessible thanks
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That's more or less correct. But if one circuit conductor becomes connected to earth accidentally now you have a voltage between earth and the other conductor that no one is expecting. And you don't know which conductor it might be. That's the basic reason people ground systems: so that the 'hot' conductor(s) have a predictable voltage to earth and the grounded conductor has a predictable voltage to earth that's close to zero. It generally makes it simpler to detect a second fault and open a protective device to turn off the circuit.
 
jaggedben said:
That's more or less correct. But if one circuit conductor becomes connected to earth accidentally now you have a voltage between earth and the other conductor that no one is expecting. And you don't know which conductor it might be. That's the basic reason people ground systems: so that the 'hot' conductor(s) have a predictable voltage to earth and the grounded conductor has a predictable voltage to earth that's close to zero. It generally makes it simpler to detect a second fault and open a protective device to turn off the circuit.
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There was a post on here that I've never been able to find again where the guy describes what you are talking about happening in Norway where they tried to go ungrounded throughout the whole country.
 
jaggedben said:
That's more or less correct. But if one circuit conductor becomes connected to earth accidentally now you have a voltage between earth and the other conductor that no one is expecting. And you don't know which conductor it might be. That's the basic reason people ground systems: so that the 'hot' conductor(s) have a predictable voltage to earth and the grounded conductor has a predictable voltage to earth that's close to zero. It generally makes it simpler to detect a second fault and open a protective device to turn off the circuit.
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I'm kind of having hard time visualizing this.
Ok so say the hot has a 120v to earth and ground close to zero. You have 120v of potential on ground during a fault. So it makes it predictable? Is this what you mean? Thanks
 
whatever said:
I'm kind of having hard time visualizing this.
Ok so say the hot has a 120v to earth and ground close to zero. You have 120v of potential on ground during a fault. So it makes it predictable? Is this what you mean? Thanks
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Suppose you are standing on damp ground with your bare feet in front of a main service panel...

If there is a ground rod at your feet, and a copper wire to the neutral bar, and a metal jumper between the neutral bar and the panel enclosure, then it is predictable that touching the box will not give you a shock, because almost all the current that might flow through you to the ground is already flowing on that wire. Touching the ungrounded conductor, by comparison, is likely to shock you. Similarly, say the ungrounded conductor's insulation is damaged by a tree somewhere. Any current that might flow through the tree to the earth to the spot your standing will flow through the rod and wire back to the neutral, and the amount that flows through you will likely be negligible.

Now remove the wire to the ground rod and the jumper to the box, but keep the damaged insulation in the tree. One conductor is connected to the damp ground beneath your feet through the tree. If you touch a terminal for the other conductor of the circuit, you are now the only and best path to complete the circuit through the tree. But you don't know which conductor is safe to touch and which will kill you.

It's a bit of an exaggerated scenario but it gives you the general theory.
 
jaggedben said:
Suppose you are standing on damp ground with your bare feet in front of a main service panel...

If there is a ground rod at your feet, and a copper wire to the neutral bar, and a metal jumper between the neutral bar and the panel enclosure, then it is predictable that touching the box will not give you a shock, because almost all the current that might flow through you to the ground is already flowing on that wire. Touching the ungrounded conductor, by comparison, is likely to shock you. Similarly, say the ungrounded conductor's insulation is damaged by a tree somewhere. Any current that might flow through the tree to the earth to the spot your standing will flow through the rod and wire back to the neutral, and the amount that flows through you will likely be negligible.

Now remove the wire to the ground rod and the jumper to the box, but keep the damaged insulation in the tree. One conductor is connected to the damp ground beneath your feet through the tree. If you touch a terminal for the other conductor of the circuit, you are now the only and best path to complete the circuit through the tree. But you don't know which conductor is safe to touch and which will kill you.

It's a bit of an exaggerated scenario but it gives you the general theory.
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Makes perfect sense thanks man
 
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