Understanding Electrical Ground & How It Works

In summary, the electrical ground works by creating a potential difference between the plus and minus terminals of a battery. This potential difference causes electrons to flow from the plus terminal of the battery to the minus terminal.
  • #36
chroot said:
The Earth is a very poor conductor of electricity when compared to, for example, a copper wire. Your statements later in your post regarding differences in ground voltage are a good example of how poor a conductor it is.

- Warren

You need to clarify your statement. If you are talking about a cubic meter of “earth” as compared to a cubic meter of copper then certainly the copper is a much better conductor. However, when the term “earth” is used in reference to the Earth itself, it is the best possible conductor of electricity because of the cross sectional area, as I pointed out. It is necessary to establish a proper connection to this earth, however. Sometimes that requires driving electrodes deeply into the ground, or possibly treating the ground with chemicals or water. But once a good gound is established it is very possible to transmit electricity from one place to another without the need for a separate ground or neutral wire. As I have already mentioned, that was the practice in the early days of power transmission but because the ground references at the various distribution points were not all properly done and verified it soon became apparent that a separate neutral wire must be provided. I suggest you do some research on this.
 
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  • #37
schroder said:
You need to clarify your statement. If you are talking about a cubic meter of “earth” as compared to a cubic meter of copper then certainly the copper is a much better conductor. However, when the term “earth” is used in reference to the Earth itself, it is the best possible conductor of electricity because of the cross sectional area, as I pointed out.

The resistance of the ground rod to the Earth is also a function of the soil's resistivity as well as the length and radius of the ground rod.

schroder said:
But once a good gound is established it is very possible to transmit electricity from one place to another without the need for a separate ground or neutral wire.

Although this is quite true, it is not how electrical distribution systems are really intended to work under normal conditions. The Earth ground is mainly used when fault conditions occur. Utility companies don't depend on fault current to transmit power.

There is also a slight benefit to the grounds although it is not really an intended design per se. The repeated grounding points throughout the electrical distribution system (power transmission lines for example) help reduce power line losses by essentially creating a parallel network with the transmission line.

CS
 
  • #38
stewartcs said:
Although this is quite true, it is not how electrical distribution systems are really intended to work under normal conditions. The Earth ground is mainly used when fault conditions occur. Utility companies don't depend on fault current to transmit power.

There is also a slight benefit to the grounds although it is not really an intended design per se. The repeated grounding points throughout the electrical distribution system (power transmission lines for example) help reduce power line losses by essentially creating a parallel network with the transmission line.

CS


Yes, I agree with this. I did not mean to imply that today’s power transmission systems use Earth ground to transmit power. I mentioned it in an historical context as well as a physics context to establish that it is possible. Besides the indirect benefits you mentioned, the main advantage today of proper grounding is the safety function, which I would like to point out by a specific example.
Suppose you are supplying three-phase 4000 Volt ac supply to a machine and the source and feeder resistance is 15 ohms. Now one of the phase wires in this machine touches to the motor frame which has a 10 ohm resistance to Earth ground. This will place about 2,300 volts on the frame of the machine with reference to ground, resulting in a flow of 92 amperes between the machine frame and ground. Now if a technician should happen to come along with his test cart, which is itself grounded, and touch the frame of this machine he will be subjected to roughly 920 Volts, which is more than sufficient to kill him instantly.
But if the machine was better grounded, say with a resistance to Earth of only one ohm, the voltage shock would be reduced to about 92 Volts and he will most probably live to correct the fault. There are also in place ground fault circuit breakers, but I am not taking those into consideration in this discussion. Proper grounding is one of the least appreciated and most misunderstood disciplines in electrical engineering and a thorough discussion of this would involve many more posts by myself and others.
 
  • #39
schroder said:
Yes, I agree with this. I did not mean to imply that today’s power transmission systems use Earth ground to transmit power. I mentioned it in an historical context as well as a physics context to establish that it is possible. Besides the indirect benefits you mentioned, the main advantage today of proper grounding is the safety function, which I would like to point out by a specific example.
Suppose you are supplying three-phase 4000 Volt ac supply to a machine and the source and feeder resistance is 15 ohms. Now one of the phase wires in this machine touches to the motor frame which has a 10 ohm resistance to Earth ground. This will place about 2,300 volts on the frame of the machine with reference to ground, resulting in a flow of 92 amperes between the machine frame and ground. Now if a technician should happen to come along with his test cart, which is itself grounded, and touch the frame of this machine he will be subjected to roughly 920 Volts, which is more than sufficient to kill him instantly.
But if the machine was better grounded, say with a resistance to Earth of only one ohm, the voltage shock would be reduced to about 92 Volts and he will most probably live to correct the fault. There are also in place ground fault circuit breakers, but I am not taking those into consideration in this discussion. Proper grounding is one of the least appreciated and most misunderstood disciplines in electrical engineering and a thorough discussion of this would involve many more posts by myself and others.

I agree that grounding (not to mention bonding) is not very well discussed in Electrical Engineering courses - most unfortunate.

CS
 
  • #40
we were told in our starting course of EE
that electrisity as we see it at home
has nothing to do with EE

further more we were told that
todays electrical engeneer doesn't have to know what's triple faze current
 
  • #41
transgalactic said:
we were told in our starting course of EE
that electrisity as we see it at home
has nothing to do with EE

further more we were told that
todays electrical engeneer doesn't have to know what's triple faze current

That's most unfortunate that you were told that because it is not true. Two of the EE's that work with me specialize in power systems. If they didn't know anything about three-phase systems they wouldn't be employed.

CS
 
  • #42

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