current returning to a different source

[mull982]

What happens when current originating from from one source (transformer) returns on a nuetral to a different source (different transformer)?

Say I have a 120V single phase transformer 1 which is sending current out via the hot leg of transformer 1 to a device, however the the nuetral coming off of the device does not return to the nuetral of transformer 1, but rather the nuetral of a different transformer I'll call transformer 2. Will the load or device still see the correct current and voltage it needs or will no current circulate because there is no path back to its origonal source?

 

[roger]

Unless there is a conductive path somehow tying both transformers together, the circuit will see no current flow.

Roger

 

[jghrist]

What happens when current originating from from one source (transformer) returns on a nuetral to a different source (different transformer)?

Say I have a 120V single phase transformer 1 which is sending current out via the hot leg of transformer 1 to a device, however the the nuetral coming off of the device does not return to the nuetral of transformer 1, but rather the nuetral of a different transformer I'll call transformer 2. Will the load or device still see the correct current and voltage it needs or will no current circulate because there is no path back to its origonal source?

If each transformer secondary neutral is bonded to a common grounding electrode or separate, interconnected electrodes, then the return current will flow through the ground system; not a good situation. If the neutrals are bonded to separate unconnected grounding electrodes, the return current will flow through the earth; a worse situation.

 

[steve66]

If each transformer secondary neutral is bonded to a common grounding electrode or separate, interconnected electrodes, then the return current will flow through the ground system; not a good situation. If the neutrals are bonded to separate unconnected grounding electrodes, the return current will flow through the earth; a worse situation.

Sorry, but thats not correct. There will only be return current through the ground system if there are more than one neutral-ground bond on one of the systems.

Steve

 

[jghrist]

Sorry, but thats not correct. There will only be return current through the ground system if there are more than one neutral-ground bond on one of the systems.

Steve

There is more than one neutral-ground bond on the described system. The neutral wire is bonded to ground at transformer 2. The transformer neutral is bonded to ground at transformer 1.

Current will flow from the phase of transformer 1, through the circuit phase wire, through the load, through the circuit neutral (grounded) conductor, to the neutral bond of transformer 2, then through the grounding system to the neutral bond of transformer 1.

 

[dereckbc]

Its against the law, Kirchoff's Law to be exact. Some of the return current maybe taking an unexpected path such as two transformers sharing a common ground electrode, but physical laws dictate all currents returns to its source.

My guess is yo have nuetrals cross-wired from the transformers

 

[steve66]

There is more than one neutral-ground bond on the described system. The neutral wire is bonded to ground at transformer 2. The transformer neutral is bonded to ground at transformer 1.

Current will flow from the phase of transformer 1, through the circuit phase wire, through the load, through the circuit neutral (grounded) conductor, to the neutral bond of transformer 2, then through the grounding system to the neutral bond of transformer 1.

If we have two separate transfomers, we should have two separate neutrals. Sure, the neutrals are both tied to the same ground, but as long as each neutral is only bonded to ground in one place, there are no parallel paths for the current to flow on.

(Parallel conductors are tied together in two places. If we tie a neutral to ground in only one place, there is no way for any of the current to flow through the ground. It's when you get a second connection between neutral and ground that you start to get current flow on the ground.)

Here is what I am thinking of:

http://s49.photobucket.com/albums/f252/Sragan/?action=view&current=Transformers.jpg
STeve

 

[Rick Christopherson]

This is probably going to raise a few hackles, but any time you have a difference in voltage, you will have current flowing. It does not matter if there is a completed circuit or not. The monkey wrench in this statement is that in order to have a difference in voltage, there will generally need to be a common reference point, and in most cases, this will end up being a return current path.

I once got into this discussion a long time ago on a different forum, but the participants were the same as this forum. Frankly, it is too complex of a discussion to get into, and I don't want to try to defend it again. I just put this out there as "food for thought". It is possible, but I don't want to get into the drawn out discussion of defending it.

I registered for the forum because I wanted to ask a question, but this topic caught my eye. Sorry.

 

[jghrist]

If we have two separate transfomers, we should have two separate neutrals. Sure, the neutrals are both tied to the same ground, but as long as each neutral is only bonded to ground in one place, there are no parallel paths for the current to flow on.

What you say is normally true, but the original post says that the neutral from the device goes to a different transformer than the source transformer. So, in effect, the neutral for this device is partly transformer 1's neutral and partly the wire that is connected to it which goes to transformer 2.

 

[roger]

Rick, just to get this straight, if I have a car sitting in front of my house and connect a lamp to the positive terminal of this battery and then take a jumper to the negative terminal of another cars battery 1/4 mile down the street, I'll be able to light the lamp.

Roger

 

[steve66]

This is probably going to raise a few hackles, but any time you have a difference in voltage, you will have current flowing.

That's absoultely true if you shuffle across the carpet and then touch the door knob.

However, with electric circuits, we normally talk about a sustained current that keeps flowing as time goes on. Not just a short zap.

For any sustained current, you need a complete loop for the current to flow around. In the diagram I posted, there is no way to make a loop that includes the ground wire between the transformers, so no current will flow through that path.

Steve

 

[steve66]

What you say is normally true, but the original post says that the neutral from the device goes to a different transformer than the source transformer. So, in effect, the neutral for this device is partly transformer 1's neutral and partly the wire that is connected to it which goes to transformer 2.

I see what you are saying now. And after reading the original post a few times, it does seem to say we are connecting the neutral from one transfomer to the load on another. So I have to agree with you if there is a grounding system, and Roger if there isn't any interconnection.

Steve

 

[rattus]

Heresy!

Heresy!

Rick,

What you speak is heresy!

? A steady current can exist only in a closed circuit?????.?

[Sears, ?Electricity and Magnetism?, Addison-Wesley, 1954]

Furthermore, examples abound of voltages existing with no current.

 

[Rick Christopherson]

Rick, just to get this straight, if I have a car sitting in front of my house and connect a lamp to the positive terminal of this battery and then take a jumper to the negative terminal of another cars battery 1/4 mile down the street, I'll be able to light the lamp.

Roger

He...He..No. :smile: Doing this will cause the two references to have the same voltage, and no current will flow. That is the complicated part of this discussion. On the other hand, if there was something that anchored each battery to a specific source, then, yes, current would flow.

As I said in my original posting, I know that this will raise a few hackles, and it will be hard to swallow. That's because we automatically view current flow as requiring a circular loop. While not really feasible, just for example, if you connected a wire between the Earth and the Moon, you would have a monstrous current flowing in that wire, even though there was no return circuit. The reason is because of the innate voltage difference between these two bodies.

We do see this every day in real life, but normally the charge between the two bodies is low enough that they equalize too rapidly to account for the difference. If the voltage difference was sustainable, then the current would remain indefinitely, regardless of a return path.

 

[roger]

On the other hand, if there was something that anchored each battery to a specific source, then, yes, current would flow.

Rick, the batteries would be the sources, individual sources, tying them together with a common connection changes it to one source.

Roger

 

[Rick Christopherson]

Rick,

What you speak is heresy!

:grin: :grin: :grin: :grin: This is funny, and is the response I expected from the outset. If you carefully review Ohm's Law, it refers solely to voltage differences, and not to completed circuits. What I stated is not heresy, but is actually founded in electrical laws.

As I said in my first posting, I did not throw this up with the intention of trying to defend it. The defense of this requires far too much mathematics and discussion, and I am not willing to go through this exercise. It is interesting to see the responses, but I will leave it to the other Electrical Engineers here to argue the fine minutia. Nevertheless, I do enjoy throwing the curveball out there! :grin:

 

[roger]

Rick, don't be a wimp, stick around and defend yourself, the members here are not scared of a long discussion.


Roger

 

[iwire]

I once got into this discussion a long time ago on a different forum, but the participants were the same as this forum. Frankly, it is too complex of a discussion to get into, and I don't want to try to defend it again.

So basically what your saying is 'It's over all your heads'.

Nice. :roll:

 

[rattus]

More of a beanball!

More of a beanball!

:grin: :grin: :grin: :grin: This is funny, and is the response I expected from the outset. If you carefully review Ohm's Law, it refers solely to voltage differences, and not to completed circuits. What I stated is not heresy, but is actually founded in electrical laws.

As I said in my first posting, I did not throw this up with the intention of trying to defend it. The defense of this requires far too much mathematics and discussion, and I am not willing to go through this exercise. It is interesting to see the responses, but I will leave it to the other Electrical Engineers here to argue the fine minutia. Nevertheless, I do enjoy throwing the curveball out there! :grin:

Rick,

First, I can't see that Ohm's Law in any way supports your argument.

Second, One has to be pretty full of himself to argue with a professor of physics from MIT!

Third, I for one would like to see a defense of your argument. You said it, you defend it. The rest of us already know the outcome.

 

[Rick Christopherson]

Rick, don't be a wimp...

Hey, when it comes to being a wimp, I have no equal. I can run and hide with the best of them!! :grin: :grin:

If I am not mistaken, the raw definition of Ohm's law states that current will flow between any two points with a voltage difference, and the rate of current flow will be proportional to the resistance between these two points. There is nothing in Ohm's Law that says current has to return to the source before it can flow. It is simply a relationship between voltage, resistance, and current.

If you can maintain a voltage difference between these two points, then you will have a current flow (assuming a conductor exists).

What makes this concept so hard to understand is that in 99% of the situations of a voltage difference in the "REAL WORLD" is that we also have a return path by the mere existence of the reference voltage.

In reality, it is possible to have a voltage difference without having a return path. Lightning is one example, and a conductor between the Earth and upper atmosphere is another example. In both of these cases, current will flow, even though there is no return path. The later is an example of recent investigation of power sources.

If you cannot maintain a voltage difference, then it is a moot point--no current will flow.