AC current and neutral

[Ropeadope]

In alternating current, is the alternating just between phases, or is neutral alternating as well ? I know neutral is for the imbalances.

 

[Smart $]

In alternating current, is the alternating just between phases, or is neutral alternating as well ? I know neutral is for the imbalances.

Fact: All alternating-current circuits have alternating current.

If a neutral conductor of an alternating-current system carries current, then it is:

a. alternating
b. not alternating​

 

[gar]

110425-2127 EDT

Current is something you view or measure at a point. Voltage is something you measure between points.

Consider a wire and pick any point you choose and instrument that point to measure current. If the current at that point always flows in one direction then this is described as a DC current. It might have a fluctation on it and then it might be described as a DC current with an AC component.

If at the measurement point the current flows in one direction for a while and then changes to the opposite direction for another while and repeatedly does this such that the average DC current is zero, then it is called an AC current. If there is alternation of the current but the average DC current is not zero, then it might be described as an AC current with a DC component.

Now to your three phase Y system with a neutral conductor that is part of the load circuit. If there is no DC component in the system and current flows in the neutral, then the current in the neutral is an AC current.

.

 

[Little Bill]

Fact: All alternating-current circuits have alternating current.

If a neutral conductor of an alternating-current system carries current, then it is:

a. alternating
b. not alternating​

c. neutrally alternating:grin:

 

[Ropeadope]

110425-2127 EDT

Current is something you view or measure at a point. Voltage is something you measure between points.

Consider a wire and pick any point you choose and instrument that point to measure current. If the current at that point always flows in one direction then this is described as a DC current. It might have a fluctation on it and then it might be described as a DC current with an AC component.

If at the measurement point the current flows in one direction for a while and then changes to the opposite direction for another while and repeatedly does this such that the average DC current is zero, then it is called an AC current. If there is alternation of the current but the average DC current is not zero, then it might be described as an AC current with a DC component.

Now to your three phase Y system with a neutral conductor that is part of the load circuit. If there is no DC component in the system and current flows in the neutral, then the current in the neutral is an AC current.

.

Thank you for taking the time.
Ok, so all current is alternating. Then why do textbooks say, the neutral wire is the return wire ? It is alternating as well. Although it does take the imbalance between phases.

 

[Ropeadope]

Fact: All alternating-current circuits have alternating current.

If a neutral conductor of an alternating-current system carries current, then it is:

a. alternating
b. not alternating
​

Thank you

 

[gar]

110425-2233 EDT

Ropeadope:

For a current to flow you generally need a closed loop.

If you have a conductor leaving a voltage source, then you need another conductor going back to that source. At any instant of time if current flows into the first conductor, thru the load, and back thru the second conductor to the voltage source, then you have a closed loop and can call one of the conductors the return path. That the current changes to another direction later doesn't change the convention that one of the conductors is assigned the name of return path.

Return path just means there is some part of a path for current to follow in a closed path, and get home again. It is arbitrary to define the neutral as the return path, but it logically makes some sense.

.

 

[Ropeadope]

110425-2233 EDT

Ropeadope:

For a current to flow you generally need a closed loop.

If you have a conductor leaving a voltage source, then you need another conductor going back to that source. At any instant of time if current flows into the first conductor, thru the load, and back thru the second conductor to the voltage source, then you have a closed loop and can call one of the conductors the return path. That the current changes to another direction later doesn't change the convention that one of the conductors is assigned the name of return path.

Return path just means there is some part of a path for current to follow in a closed path, and get home again. It is arbitrary to define the neutral as the return path, but it logically makes some sense.

.

Got it ! Thx

 

[infinity]

Then why do textbooks say, the neutral wire is the return wire ? It is alternating as well. Although it does take the imbalance between phases.

IMO saying that it's the return wire is misleading and not really true.

 

[Besoeker]

IMO saying that it's the return wire is misleading and not really true.

Maybe it's a hangover from the old days of DC.

 

[LarryFine]

In alternating current, is the alternating just between phases, or is neutral alternating as well ? I know neutral is for the imbalances.

It alternates in every circuit conductor. The relative direction of that current in the neutral at any given instant depends on the relative line currents. But, it's always alternating.

 

[Smart $]

Fact: All alternating-current circuits have alternating current.

It alternates in every circuit conductor. The relative direction of that current in the neutral at any given instant depends on the relative line currents. But, it's always alternating.

Always is technically not true... all the time. In some instances where a half-wave rectifier is used, the current would not alternate. So, technically we should say typically rather than always.

 

[LarryFine]

Always is technically not true... all the time. In some instances where a half-wave rectifier is used, the current would not alternate. So, technically we should say typically rather than always.

Whatever! :roll: grin