Return path?

[Minnow]

What is meant by the term return path?

They talk about it in school with respect to the neutral (grounded conductor) providing a return path for unbalanced current on a single-phase 120V system.

A single-phase 240V system that has no neutral (grounded conductor) provides a return path through one of the hot (ungrounded) conductors because the two legs are in phase but of opposite polarity.

Similarly in ground-fault situations, stray currents are "trying to get back to the source" (i.e., transformer)

Then we learn that in an AC (alternating current system) electrons (current) are (is) changing directions 120 times/s (at 60Hz), so how is there a return path if there is really no net movement of electrons (i.e., they don't return anywhere)?

Is there a better way to think of this?

Thanks for listening,

 

[iwire]

Welcome to the forum. :smile:

Now I suggest you fasten you seat belt as this could get mighty long around here.

the two legs are in phase but of opposite polarity.

I agree with you, but that statement above has resulted in 400 post threads. :grin:

 

[charlie b]

Is there a better way to think of this?

Let's talk about a single phase, 120 volt circuit. On one half cycle, current flows from the source to the load along the ungrounded conductor, flows through the load, and returns to the source along the grounded conductor. On the other half cycle, current flows from the source to the load along the grounded conductor, flows through the load, and returns to the source along the ungrounded conductor.

On a single phase 240 volt circuit, the description above still works, if you change the names of the two conductors to "ungrounded conductor #1" and "ungrounded conductor #2."

 

[charlie b]

. . . that statement above has resulted in 400 post threads. :grin:

I have chosen to not attempt to read "that thread." But I strongly suspect it is a classic case of an argument that I like to describe in the following terms:
(Person 1): "The grass is green."
(Person 2): "No. You are wrong. The sky is blue."

 

[iwire]

(Person 1): "The grass is green."
(Person 2): "No. You are wrong. The sky is blue."

I think you nailed it.

 

[Pierre C Belarge]

Charlie
Since when has the sky been blue, I always thought the grass was green...

 

[crossman]

(Person 1): "The grass is green."
(Person 2): "No. You are wrong. The sky is blue."

LOL! :grin:

But I must inform you that those participating in the thread have gotten some entertainment value, and perhaps have even learned something.

 

[crossman]

What is meant by the term return path?

When speaking of "return path" with AC circuits, it is simply a throw-back to DC circuits, where current is always flowing the same direction. Don't get hung up on the term, just accept it.

Much of job-site "electrishun" theory talk is more based on DC theory than AC. That is okay. It may be simplistic, but it still gets the point across.

So, the neutral can be thought of as a return. Most electricians will view the situation as having current flowing out of the breaker, through the load, and then to the neutral, thereby returning to the source.

But: If I am standing barefooted in a puddle of water at my house, and I grab ahold of a bare hot wire, half the time current is flowing from the hot wire through my body and to the puddle of water, and half the time the current is flowing from the puddle of water through my body then to the hot wire. (Of course, there is a completed path involving the earth and other components).

Another use of the term "return" around my neck of the woods is for a switch leg. Hot to the switch, return to the light. This comes about when the hot and neutral are at the light j-box, and we run a hot down to the switch and then return back to the light with a switch leg.

 

[rattus]

What is meant by the term return path?

They talk about it in school with respect to the neutral (grounded conductor) providing a return path for unbalanced current on a single-phase 120V system.

A single-phase 240V system that has no neutral (grounded conductor) provides a return path through one of the hot (ungrounded) conductors because the two legs are in phase but of opposite polarity.

Similarly in ground-fault situations, stray currents are "trying to get back to the source" (i.e., transformer)

Then we learn that in an AC (alternating current system) electrons (current) are (is) changing directions 120 times/s (at 60Hz), so how is there a return path if there is really no net movement of electrons (i.e., they don't return anywhere)?

Is there a better way to think of this?

Thanks for listening,

Think "closed circuit, complete path, complete loop".

And, BTW, if two sinusoidal waves are in phase, they cannot be inverses of each other, and of course they must be of the same frequency.

 

[dbuckley]

Is there a better way to think of this?

Yes; forget about electrons and things, they are toys for physicists, not electricians

 

[iaov]

Charlie
Since when has the sky been blue, I always thought the grass was green...

The sky is always grey here in Wisconsin and What the heck is grass?:grin:

 

[peter52]

I think electrical theory is an attempt to explain the effects of something we really don't understand. If you removed an electron from an atom of copper it isn't copper any more. Current is explained as the movement of electrons frome hole to hole. Bla, Bla, Bla. The math is fun though.

 

[charlie b]

If you removed an electron from an atom of copper it isn't copper any more.

Yes it is. It might be more properly called a "copper ion" than a "copper atom," but copper it remains. The difference between one element and any other is in the number of protons in the nucleus, not the number of electrons or neutrons.