Why use ground wire. Isn't neutral the same?

[skyline77]

a normal breaker will not trip if the hot wire is tied to an electrode as an electrode @ 25 ohms would generate an approx 4 amp load. the Nuetral/grounded conductor that returns back to transformer is where the fault will trip. We do connect the EGC to the GC at 1 point only. I stand corrected as my comments did refer to the electrode system's purpose.

@ 25 ohms is the resistance to the ground, but, if the transformer is far injecting a current in the electrode won't be 4 Amps it would be less because at distance the earth potential is different.

 

[Carultch]

Hi,

Since neutral wire is grounded i.e. has the same potential as the ground. Why then we run three wires and not only line neutral and bond the receptacle ground with the neutral?
As in the attached photo, a guy did this an it's working with no problems.

I told him it's wrong but he said why?

You want to keep current on the live and neutral conductors, during normal operation.

You want to prevent the metal parts that don't intentionally carry current, from carrying current during normal operation. Examples would be equipment housings, enclosures, metal conduit, building steel, concrete structures. The EGC's purpose is to bond all metal/conductive parts that do not intentionally carry current, and provide an opportunity for the return path of fault current in the event of a short circuit where a live wire unintentionally contacts non-current-carrying metal.

If you were to share the ground and neutral, you would create a parallel path through the non-current-carrying metal. Current doesn't just take the "path of least resistance". It takes ALL paths, inversely proportional to resistance. It would inevitably energize the equipment housing, if you didn't have a separate ground and neutral.

 

[GoldDigger]

 

[Electricmo]

In the event of a fault the current will flow through your ground instead of you. That’s why you should use the ground . If your neutral connection is lost their is still a parallel path back to the panel that doesn’t include you in the circuit. It’s their to keep you alive when things go wrong.

 

[jap]

In the event of a fault the current will flow through your ground instead of you. That’s why you should use the ground . If your neutral connection is lost their is still a parallel path back to the panel that doesn’t include you in the circuit. It’s their to keep you alive when things go wrong.

If you're in contact with a piece of equipment and grounded when it faults, the current will flow through your EGC "and" you until the fault clears.



JAP>

 

[Electricmo]

If you're in contact with a piece of equipment and grounded when it faults, the current will flow through your EGC "and" you until the fault clears.



JAP>

Most likely you are correct. I sure would want that ground wire though.

 

[charlie b]

If you're in contact with a piece of equipment and grounded when it faults, the current will flow through your EGC "and" you until the fault clears.

That is absolutely true. And the amount of current flowing through you (i.e., a fraction of an amp) will be enough to kill you, if it is allowed to flow for a long enough time. What the EGC does is cause enough current to flow (i.e., from the breaker to the fault point, to the point at which the EGC connects to the load, back to the panel via the EGC, and finally back to the "source" via the N-G bond at the main panel) to result in a breaker trip so fast that you might not even feel the shock.

 

[charlie b]

Since neutral wire is grounded i.e. has the same potential as the ground.

Let's not let "language" get in the way of "communication." The word "ground" is used in this thread in more than one context.

Yes, the neutral bar at the main panel is connected by a wire to planet Earth. So at the main panel, the neutral bar (and any wire connected at that bar) is at the same potential as planet Earth. But the farther to get from the main panel, the less true this statement becomes. And yes, the neutral bar and the ground bar are connected to each other at the main panel. So they have the same potential at that location. Here again, the farther to get from the main panel, the less true this statement becomes. We connect the EGC to the external metal parts of the load so that, if there is a short circuit from hot conductor to the case, for the reason I describe in my post immediately above this one.

We don't connect neutral to EGC anywhere downstream of the main panel (specifically meaning we don't allow it at receptacles) because making that connection will cause the neutral wire and the EGC wire to be in parallel with each other. Therefore, all current that would normally flow only in the neutral will now flow through both the neutral and the EGC. That means that every metal conduit and every electrical component's metal enclosure throughout the building will be energized.

 

[charlie b]

As in the attached photo, a guy did this an it's working with no problems.

No it isn't. It may be working, but it is not working "with no problems." It is an accident (or even tragedy) waiting to happen. And as some famous guy once said, an accident waiting for a place to happen will, given time, find that place.