No current flow on a balanced neutral?

[LarryFine]

For there to be absolutely no current flow (which the math predicts) the impedance both of the L-N circuits must be 100% equal.

We are talking in theory here, right? That let's us use 100% equal loads, impedances, and currents for our discussion.

 

[realolman]

If you mean a 3-wire circuit (two hots and a neutral) from a 3-phase supply, there would be neutral current, which is why the neutral counts as a CCC in such an installation.

That is what I meant. From my perspective, the discussion at hand is whether there is no neutral current flow in a balanced MWBC, or whether the opposite current flows cancel each other out, similar to the situation of having a Clamp on ampmeter around both conductors of an AC circuit, as some folks have used to explain the operation of a GFCI.

Although there is current flow, the clamp on reads nothing, because..... well, you know why.:smile:

My thoughts were that it might be useful to consider current flows in unbalanced MWBC 's on both single and three phase supplies.

Maybe not.

I think this whole thing is over my head... I think I'll just stand by in case you need some sort of inane input.

Let me know.:smile:

 

[ronaldrc]

For there to be absolutely no current flow (which the math predicts) the impedance both of the L-N circuits must be 100% equal. This first step in your measurements would be all but impossible to obtain, so what tolerances or adjustments are you willing to accept?

If the circuit or whatever was showing rounded out amperes and the result showed only a few 100 ma. I would be willing to say that there is no current flow.


Realman

This is simple and basic stuff. Like Larry said this is theory, no one can see
the working or whats going on inside of this conductor. I'm sure you understand basic circuits and that qualifies you to know as much about it as any of us.

Thanks

 

[gar]

080917-2042 EST

ronaldrc:

What size load do you want to use? Is 12 A ok (10 ohm resistor)?

.

 

[ronaldrc]

Gar

Yes thats fine.

Ronald

 

[gar]

080918-1000 EST

ronaldrc:

I have run the experiment for you to see what problems you might encounter.

I used two heaters. One rated at 1500 W, my test 10.6 ohms resistor when heated. The other rated 1320 W. Both are basically Nichrome heating elements. I first tried two similar ceramic heaters but their resistance was not very stable. To provide adjustment of resistance and balance the heaters I use a 7.5 A Powerstat (Variac) with a 250 W bulb in parallel with the 1320 W heater.

The instrumentation was a Fluke 27 and Fluke Y8100 Hall type current probe. This probe's calibration is 2 V for 20 A input. With no current the residual reading is 0.002 V or translated 0.020 A. Note the Powerstat adds a reactive component that is not compensated. Adjusting for a minimum current I got 0.006 V or 0.060A or 60 MA. Better than your required criteria. If I had used a variable resistor for balancing, then the null point would have probably been the 0.002 reading. Later I will do this. Also if I eliminated the Hall current probe and used a normal ammeter, then I should get the null point lower.

So try your own experiment.

.

 

[Besoeker]

Application of Kirchhoff's first law, anyone?

 

[gar]

080918-1042 EST

ronaldrc wants a non-mathematical way to answer his question.

I do not know if he has the tools to run the experiment.

.

 

[ronaldrc]

Thanks Gar


The best meters I have are a SD LCD Electronic multitester and a
couple clamp on amp meters.

I didn't even know they had a field effect type ammeter.

Would that be more sensitive that a low noise Fet type tester?





I said if it where within a few 100 ma I would except that.
I will take your word for it that no current would flow in the neutral with a perfectly balance neutral.

Thanks: Ronald

 

[ronaldrc]

Thanks Gar


The best meters I have are a SD LCD Electronic multitester and a
couple clamp on amp meters.

I didn't even know they had a field effect type ammeter.

Would that be more sensitive that a low noise Fet type tester?





I said if it where within a few 100 ma I would except that.
I will take your word for it that no current would flow in the neutral with a perfectly balance neutral.

Thanks: Ronald

Gar sorry I meant to say Hall effect instead field effect above,I was in a hurry.

 

[rattus]

Some one said Threads where very cheap so I thought I'd better start another one for this question.

On a circuit like single phase 240/120 volt center tapped secondary where everything is exactly equal on both sides of the Neutral.

How could you prove that there is no current flowing on the neutral?

In other words if I take two magnetic fields that are identical and equal and
of opposite polarity and put them in the core of a CT then the CT. coil is going to generate no voltage although there are two currents flowing in two
different directions that create these magnetic fields.

Could it be that there are two 120 volt series circuits and each half flowing through the neutral in two different directions beside each other. Or do your
think they actually oppose each other and there is no current flow in the neutral?

I not sure myself.

The outcome is the same no matter which way, I just thought I would get some other opinions.

Ronald, on paper you can define opposing currents, but in reality you will measure the difference in these currents because that is what is really happening. If they are equal and opposite, they cancel each other and the neutral current is zero.

 

[ronaldrc]

Please if you are a new comer to the Electrical field please don't get involved in this discussion untill you understand basic Electrical circuits
and the theory behind a Edison balanced neutral. Although it is fairly simple it can be confusing and this will add to that confusion.Thanks

Hello Rattus

I'm looking for a experiment that can show physically that there is zero electrical flow in the neutral conductor with a balance circuit.

I know practically it doesn't make a hill of beans rather it does or not but wouldn't you like to know for sure?

Most not all electrical theories say that electricity operates at the speed of light.We can see the results and effects but we can't see electrical flow and aren't really sure exactly what its makeup is.

I know and you know that some on here will claim they know for sure there is no current flow.But they don't.They have the same tools and mentality that the rest of us do they are limited to their 20-20 vision and have the same sense of touch we do. I don't know of any body that has claimed they have seen current electricity flow in a wire or copper conductor if you know of such occurrence please point me in that direction.


Can you tell me for certain that in the 120/240 volt center tapped balance circuit that the current does not flow in two different directions in the neutral conductor in two 120 volt circuits and at the speed of light changes two a series circuit the instant the neutral is cut? You need to show me with a practical experiment and it would be very courteous of you if you or anyone could even show it with math and I'm not just talking about posting the results of the math for a null circuit.

I want be able to make heads or tails of that math but maybe the other Engineers can share there opinions.

Thank: Ronald

 

[LarryFine]

Ron, just build a sample circuit, with an AC ammeter in place of the neutral.

 

[ronaldrc]

Ronald, on paper you can define opposing currents, but in reality you will measure the difference in these currents because that is what is really happening. If they are equal and opposite, they cancel each other and the neutral current is zero

Rattus did the bold text statement mean that you think it can't be shown
in a simple experiment?

 

[ronaldrc]

Larry

Even with a shunt series ammeter you would still have a equal negative and positive at each ammeter terminal. And it would read zero.

If there is actual current flowing in the neutral it appears as if it is not
with our testing equipment.

Am I wrong with that theory?

 

[LarryFine]

Even with a shunt series ammeter you would still have a equal negative and positive at each ammeter terminal. And it would read zero.

If there is actual current flowing in the neutral it appears as if it is not with our testing equipment.

Am I wrong with that theory?

Maybe.

What instrument measures what you're looking to detect?

 

[ronaldrc]

Larry

None that want give me a false reading. Larry I did come up with a circuit I think will work though.

Please give me your opinion and check the flow for me.

 

[LarryFine]

That seems to work. You gonna build it?

I still say you'll get no reading on the neutral, because the same theory works with both AC and DC.

 

[rattus]

Hello Rattus

I'm looking for a experiment that can show physically that there is zero electrical flow in the neutral conductor with a balance circuit.

I know practically it doesn't make a hill of beans rather it does or not but wouldn't you like to know for sure?

Can you tell me for certain that in the 120/240 volt center tapped balance circuit that the current does not flow in two different directions in the neutral conductor in two 120 volt circuits and at the speed of light changes two a series circuit the instant the neutral is cut? You need to show me with a practical experiment and it would be very courteous of you if you or anyone could even show it with math and I'm not just talking about posting the results of the math for a null circuit.

I want be able to make heads or tails of that math but maybe the other Engineers can share there opinions.

Thank: Ronald

Ronald, the math is quite simple; just apply Kirchoff's Current Law:

|In| = |I1| - |I2|

or, algebraically,

In = I1 + I2

If the loads are balanced,

In = 0

Trust me, the practice of defining opposing currents in a wire is just a trick of circuit analysis.

If you insist on an experiment, set up a balanced circuit with two identical light bulbs with a third bulb in the neutral and see if it glows. No meters required.

 

[ronaldrc]

Rattus

The bulb circuit wouldn't work you have a equal neg and pos at both terminals it will null or they will buck against each other.And it would not burn
Physically just like having two cars front to front and equal forces behind them pushing them they would not move.

I think the circuit I just drew will work.

Thanks : Ronald