Path Of Electricity

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mikoal

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Hi everyone.
I got a pretty long post, but if someone can dissect my problems that would be great! i'm eager to learn!

I've read in another forum
"All neutral (or fault) current from the main panel back to the transformer takes all paths. The least resistance one is the neutral wire to the transformer. A code target for ground electrode systems is 25 ohms. But they can be much higher or much lower. However, nothing is going to compare to the less than 1 ohm of the service neutral (unless it breaks!)."

So basically when neutral current goes to a point of ground or back to system, it would choose system due to low resistance, but i have many questions with this statement.


So here are my questions:

(I know this statement below is wrong, but would like someone to make it easier for me to understand)
I dont generally see ground wires running from load to ground. There is usually hots and neutrals in conduits, and sometimes bonding wires which are connected to the ground. Usually ground rods are connected ground wires then to busses is what I've seen.

1) Is this true? (no is my answer, but it seems like i dont see a lot of ground wires running with the other conductors, is it because it's usually taking a different physical path? IE bonding equipment and not in all conduits? IE receptacles circuit i dont see ground wires......)

2) So i guess another question would be, when to include ground wires, and when its not needed?

3) The reason why I ask because I found some electrical drawings showing 4 wires (3 hots and neutral) plus Ground. So I would assume that is the grounding conductor (earth ground)? Electrical drawings always have +6G or whatever size the ground needs to be. Yet looking at receptacles the ground wire is just bonded to the metal box, which I assume is connected to the neutral bus bar which is grounded. I have trouble visualizing the ground wire and where it goes.

4)
So in that case looking at a receptacle there are 3 wires, hot, neutral, ground.
Hot will be source
Ground will be bonded to the metal box which is all bonded back to the bus bar then to the rod.
a) Are all the grounded bus bars bonded? Why or why not? (I believe they are)

Neutral will carry neutral current going back to the source then will hit a point (I think its a few points, not just 1 point) where either it should choose the ground rod path or the source/transformer/neutral path. (the least resistant path is the source/transformer/neutral path. )

b) So the neutral current will be going back to the source, but at every ground rod point, it "chooses" the neutral path. is that correct? That is the reason why the neutral conductor carries current and under normal condition a grounding conductor should not.
 
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realolman

Senior Member
The conduit itself would often be the Equipment Grounding Conductor

If it is a sub feed, the neutral and the grounding buss are NOT connected, because you want the neutral current to flow through the neutral, and NOT through the grounding conductor. You do not want current flowing through the ground and causing a voltage drop, and raising the voltage of the grounded parts... which could cause a bit of the current to flow through you.

there was a real good thread a year or so ago where a guy drove a bunch of ground rods and demonstrated that the earth (the planet) has Zero resistance...

the thing to keep in mind is that current does not take just the path of least resistance... it takes all paths, in inverse proportion to the resistance.
 
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erickench

erickench

Senior Member
Location
Brooklyn, NY
The neutral should only be bonded to ground at the service. It's called a main bonding jumper or system bonding jumper if the system is separately derived as with a generator or a transformer.
Additional ground wires are used for isolated ground systems such as would be found in hospitals. Though the metal raceway would be an equipment ground the isolated ground wire runs all the way back to the service where it is connected to the neutral.
 
charlie b

charlie b

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Staff member
Location
Lockport, IL
Occupation
Retired Electrical Engineer
You are mis-applying several of your terms. You seem to speaking of fault current flowing back to the source via the neutral. That will not be a low resistance path, unless the fault takes place from the hot to the neutral BEFORE current has passed through any load. Otherwise, the total resistance of the fault path will include the resistance of the load.

Secondly, the earth will not be a significant player in the fault current path, unless you are dealing with voltages of 4000 and higher.

The Equipment Grounding Conductor (EGC), the green insulated or bare copper one, is attached to the outer case of the load, and normally carries no current. If there is a short circuit from a hot wire inside the equipment to the outer case, then the EGC will complete a very low resistance path back to the source. This creates a large amount of fault current, and will force the breaker to trip, thus terminating the event before anyone can get hurt.
 
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