[manny0124]

Tnx and regards

[ebaines]

Earth (called "ground" in the US, or "earth" elsewhere) is essentially a huge sink for electrons. It's primary roles in elecronics are (a) to provide a constant reference potential, which is important to get ICs and other components in electronics to work together properly, and also to assist in minimizing EMI through the use of shielding between circuits, or (b) for safety considerations, as a way to minimize excessive voltages by carrying away fault currents - for example, grounding the chassis of an appliance ensures that if there is a frayed power wire inside the machine you won't have lethal voltages present on the chassis.

[stanfortyman]

, or (b) for safety considerations, as a way to minimize excessive voltages by carrying away fault currents - for example, grounding the chassis of an appliance ensures that if there is a frayed power wire inside the machine you won't have lethal voltages present on the chassis.

This is not accurate.
The reason you will not have voltage present in this example is because the grounding conductor is bonded to the service neutral, not merely connected to a spike in the ground. THIS is why breakers trip. The earth itself has no bearing on this function.

The earth is never supposed to be a path for fault current. Dirt is a very poor conductor, even when wet.
If you have a ground fault to a grounding conductor that is simply "earthed", and not bonded to the service neutral, then all you will do is bring up worms.

[stanfortyman]

what is the use of earth in electricity...
tnx and regards

Why not try again and ask your question with some detail?

Is this some sort of homework or test question?

[ebaines]

Stan - I was responing in a general way regarding the use of earth in electronics, not as advice on how to wire the neutral and/or ground in the house, or how they are connected at the electric panel. But the point is still valid - the potential of the appliance chassis is kept essentailly equivalent to ground, to minimize chances for large (and potentially lethal) voltage differences between the chassis and other things in the room (like a water pipe). That's why you have a ground rod.

[stanfortyman]

Stan - I was responing in a general way regarding the use of earth in electronics, not as advice on how to wire the neutral and/or ground in the house, or how they are connected at the electric panel.

Funny, the question was "what is the use of earth in electricity", not "electronics".
I am sure you are well aware that electricity and electronics are not nearly the same thing.

But the point is still valid - the potential of the appliance chassis is kept essentailly equivalent to ground, to minimize chances for large (and potentially lethal) voltage differences between the chassis and other things in the room (like a water pipe). That's why you have a ground rod.

Sorry. Still wrong.
The chassis is kept at the same potential as other "grounded" metal parts of the system. This potential ALL stems from the neutral to ground bond at the main service disconnect.
A grounding electrode is just along for the ride in case of lightning or HIGH voltage surges such as from primary utility (as in thousands) voltages.

[ebaines]

I am talking here about potential differences (voltages) and the danger of having metal surfaces at different potentials - not whether there's current flow through the ground rod.
You seem to be saying that all the neutrals of the electrical outlets in the house would be at the same potential as all other metal surfaces even if there was no ground rod connection at the service entrance. But there are many metal surfaces that are not part of the electrical system but that are grounded locally (things like handrails, swing sets, lamp posts). If you did not have a ground rod at your service entrance then you are relying on the utility's neutral to be at the same potential as your local ground, but it's not - you could have significant voltage differences between the hot/neutral of an outlet and these surfaces, which could indeed be dangerous.

[stanfortyman]

You seem to be saying that all the neutrals of the electrical outlets in the house would be at the same potential as all other metal surfaces even if there was no ground rod connection at the service entrance.

No. I specifically did not say that. I said: "The chassis is kept at the same potential as other "grounded" metal parts of the system."

But there are many metal surfaces that are not part of the electrical system but that are grounded locally (things like handrails, swing sets, lamp posts). If you did not have a ground rod at your service entrance then you are relying on the utility's neutral to be at the same potential as your local ground, but it's not - you could have significant voltage differences between the hot/neutral of an outlet and these surfaces, which could indeed be dangerous.

So you are saying that a ground rod stuck in the ground on one side of the house would cause a breaker to trip if a hand rail or swing set out in the yard became energized??
This is completely false. The earth simply does not have enough impedance to carry that current. The earth is a poor conductor. The swing set would HAVE to be bonded to the house's electrical system in order for a breaker to trip.
A lamp post would/should already be bonded so that is a non-issue. The equipment ground run with the circuit to the light bonds the post and fixture. This equipment ground eventually goes back to the main panel. The neutral to ground bond at the main panel IS what would cause a breaker to trip in the case of a fault.

If not for the fear of someone actually trying it I would suggest you test your theory in real time. You could stick a live wire in the ground right near your service's grounding electrode and the breaker would NOT trip.