No current flow on a balanced neutral?
- Thread starter ronaldrc
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gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
080917-1125 EST
charlie b:
Modeling the circuit as a pair of physically opposing currents for purposes of calculation is not what I believe ronaldrc is asking. I believe he wants to know if there is any current flowing in the neutral.
That is why I believe the 0 voltage approach gets closest to describing what is physically occurring.
ronaldrc:
Try it this way. If you have zero volts across any resistor, then is there any current flowing in that resistor?
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charlie b:
Modeling the circuit as a pair of physically opposing currents for purposes of calculation is not what I believe ronaldrc is asking. I believe he wants to know if there is any current flowing in the neutral.
That is why I believe the 0 voltage approach gets closest to describing what is physically occurring.
ronaldrc:
Try it this way. If you have zero volts across any resistor, then is there any current flowing in that resistor?
.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
I believe Kirchoff's Law says there actually is zero current on the neutral. If the currents I1 and I2 cancel at the load, there is no current available to flow on the neutral.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
In reality, there is no current. The mathematical balancing means that the physical event never occurs. All of the current flows through the lines and the loads, none through the neutral.ronaldrc said:
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Again, metering.winnie said:
winnie said:
My feelings exactly Winnie
If the circuit was large enough and with enough voltage drop on the neutral
do you think maybe fine steel filings sprinkled around the neutral would show anything?
I believe your idea of heat would be the best way to tell.
ronaldrc said:Larry
I don't agree that metering would prove it unless you can prove there is no opposing magnetic flux there.
How about using three meters?
Meter#1 around leg#1 and neutral, Meter#2 around leg#2 and neutral, and Meter#3 around leg#1 and leg#2
If our loads were 10 amps, Meter #1 and Meter #2 would read 10 amps whereas Meter #3 would read zero.
Roger
Hello Roger
We already know that the neutral is going to show zero if it is balanced.
I would just like to know for certain that no current is not flowing in the neutral, so far the heat on the neutral that Winnie spoke of sounds like the best bet.
I hope this has not really flipped some out that don't understand the theory of the neutral.
We know for sure the net result will be the same as no current flowing.
Reguardless of rather it does or not.
We already know that the neutral is going to show zero if it is balanced.
I would just like to know for certain that no current is not flowing in the neutral, so far the heat on the neutral that Winnie spoke of sounds like the best bet.
I hope this has not really flipped some out that don't understand the theory of the neutral.
We know for sure the net result will be the same as no current flowing.
Reguardless of rather it does or not.
pbeasley
Senior Member
- Location
- Orange County, CA (for now)
It has occurred to me to wonder... did these same discussions take place many years ago, and the center-tap tranformer is the result?
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
080917-1451 EST
ronaldrc:
You can experimentally use any means you want and you will not measure any current flow in the neutral. Measure voltage drop, directly measure current with an microamp meter, measure the wire temperature rise, measure magnetic flux around the wire, or any other possible measuring means and the result will be zero.
Try this: put a 1 megohm resistor in series with the neutral and a microvolt meter across the resistance. The voltage will read zero, and the current will be less than 1/(1,000,000*1,000,000) amps.
Fundamentally the result is self-evident if you understand electrical circuit theory. Otherwise you may never develop an understanding.
Another example to think about. Two 1.5 V batteries. These two batteries are exactly 1.5 V. Connect the two negative ends together. Put a voltmeter between the two positive ends. What does the meter read? Next wire the two positive terminals together with a 1000 ohm resistor. How much current flows in the resistor?
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ronaldrc:
You can experimentally use any means you want and you will not measure any current flow in the neutral. Measure voltage drop, directly measure current with an microamp meter, measure the wire temperature rise, measure magnetic flux around the wire, or any other possible measuring means and the result will be zero.
Try this: put a 1 megohm resistor in series with the neutral and a microvolt meter across the resistance. The voltage will read zero, and the current will be less than 1/(1,000,000*1,000,000) amps.
Fundamentally the result is self-evident if you understand electrical circuit theory. Otherwise you may never develop an understanding.
Another example to think about. Two 1.5 V batteries. These two batteries are exactly 1.5 V. Connect the two negative ends together. Put a voltmeter between the two positive ends. What does the meter read? Next wire the two positive terminals together with a 1000 ohm resistor. How much current flows in the resistor?
.
Probably about anything I think of has been thought of through the years and mill over time after time, but I still like to think about it.
Could a man go to his garage or shop tap a run of 14/3 and load it down with say 100 watt bulbs untill it starts running a little hot and then hook and unhook the neutral and check the heat and prove or disproof this.
I've been thinking about it but I'm to lazy.
I know I'm crazy but what the heck!
Could a man go to his garage or shop tap a run of 14/3 and load it down with say 100 watt bulbs untill it starts running a little hot and then hook and unhook the neutral and check the heat and prove or disproof this.
I've been thinking about it but I'm to lazy.
I know I'm crazy but what the heck!
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
ronaldrc said:
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?
I wonder if there would be any point in considering where the current goes in an unbalanced circuit.
A MWBC that has two loads each hooked to a "hot" phase and a common neutral. one draws 6 a and the other 12.
They would each draw that amount hooked to two wire circuits, and yet the magnitude of the neutral current in a MWBC using two poles of a single phase supply would be 6.
The current has to be going somewhere.
Am I correct in saying that the magnitude of the neutral current would be 9.5 on the same two pole MWBC fed from a 3 ph supply?
Current flows added as complex numbers?
When the load is balanced on the single phase supply, it would work just as well on the two phases with or without or the neutral.
On a three phase system , I'm not so sure.
Seems to me the same principles would have to apply, three phase or single phase, balanced or unbalanced.
What those principles are??? beats the heck outta me
Here's a good one I know is useful. The current on a MWBC neutral will be less than all the loads added up together. A person can actually use that one.:smile:
A MWBC that has two loads each hooked to a "hot" phase and a common neutral. one draws 6 a and the other 12.
They would each draw that amount hooked to two wire circuits, and yet the magnitude of the neutral current in a MWBC using two poles of a single phase supply would be 6.
The current has to be going somewhere.
Am I correct in saying that the magnitude of the neutral current would be 9.5 on the same two pole MWBC fed from a 3 ph supply?
Current flows added as complex numbers?
When the load is balanced on the single phase supply, it would work just as well on the two phases with or without or the neutral.
On a three phase system , I'm not so sure.
Seems to me the same principles would have to apply, three phase or single phase, balanced or unbalanced.
What those principles are??? beats the heck outta me
Here's a good one I know is useful. The current on a MWBC neutral will be less than all the loads added up together. A person can actually use that one.:smile:
grantcool
Member
- Location
- Atlantic Beach, Florida
hey, do i get some kind of points for starting a hot discussion? i did the same thing a couple months back with my question about why 2 different phases in house power is called single phase. (i now understand that one)
- Location
- Massachusetts
jim dungar said:
I was thinking along the same lines. My thought was you would need to place some sort of variable impedance on one side of the circuit and adjust it while the current reading was being taken on the neutral.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
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.realolman said:
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